Page Created 2/14/99
The 150 and 165 HP Franklin aircraft engines that came in our Stinson 108's have been out of production for many years. Some major parts for these engines (crankshafts, cases, pistons, valves) have become difficult, if not impossible, to find. As a result, many Stinson owners are interested in alternatives. Here is an attempt to gather in one place a summary of known engine alternatives for these aircraft. The options are summarized below in alphabetical order - Continental, Franklin, Lycoming. Obviously, some of this information, first gathered in 1999, has changed. I have tried to update the page as new information comes to me, but that task is challenging. Also, I have retained some outdated informatin for historical perspective. Additional information or corrections are welcome - contact me by clicking here.
But first, an update on Franklin engines.... After going out of production in the United States in the 70's, PZL began producing Frankin engines in Poland during the 80's. This provided a source of 220 HP Franklins for those wishing to make the STC'd upgrade. With corporate changes during 2002-2003, and the purchase of PZL by Pratt & Whitney of Canada, production ceased and it looked like Franklin would go out of production forever. But like a Phoenix rising, a new Polish company formed around 2006 and promised engines and support. They purchased all of the tooling from PZL. The new company, Franklin Aircraft Engines, had a booth at Oshkosh 2007. The company completed the long process required to receive the production certificate and had begun producing parts. On hand at Oshkosh 2007 were new magneto gears and pistons. The company was NOT at Sun 'N' Fun in 2009 or at Oshkosh Airventure in 2009. Nor did they appear at these events in 2010. Many in the Stinson community have become discouraged about the prospects of the new company succeeding. The global economic downturn is likely to be a factor contributing to the lack of progress. As of January, 2011 signs of progress were not good. The company website had not been updated for many months and there were reports (rumors?) of a possible sale if investors could be found. However... in late 2014 and early 2015, there have been rumors that the company is still alive and even intends to make parts for the 150-65 engines. We'll see...
The company website is: www.frankin-engines.com The company is:
Aircraft Engines Sp. z o.o.
Maciej Smolinski and Roman Sadowski at the Franklin Aircraft Engines booth, Oshkosh 2007
The saga seems to continue with a new player on the field...
In May of 2013, George Gillespie announced on the Yahoo Stinson discussion forum the formation of Franklin Aerospace, LLC. The new company purchased Franklin parts and engine inventories from several sources, including the "Baker Inventory," the Fort Collins inventory from the former PZL importer, and several other smaller companies. The inventories are substantial and will allow limited production of the 4 cylinder 4A-235 engine and the 210 HP helicopter engine. The new company has the goal of making parts available for a range of Franklin powered aircraft, including Stinsons. They have warehouse space in Thomasville, North Carolina and had a display at Sun 'N' Fun 2013. Photos on their website show a pretty Aeronca Champ with the Franklin 4A-235 and a number of enignes. Mr. Gillepspie said they would be at Oshkosh, 2013. Contact information is as follows: Kelly Bartlett, President, owner, firstname.lastname@example.org, phone 704-968-3730; George Gillespie, Vice President, email@example.com, phone 704-451-9807.
What follows is more or less "archival" and is retained for historic perspective.
Franklin expert Greg Lucas had this to report to the Stinson community in August, 2006:
"The [new] owner of Franklin
Engines had a booth [that] Bruce Kown and I manned at Oshkosh . They are building
the 6-350-C1R (220 hp) and they are building the 6A-335-B1 (180 hp) , that is
the proper engine for a Stinson if you are turning it into a 108-5. They are
also going to produce the 4A-235 (125 HP) four cylinder. They already have many
replacement parts for the 150 and 165 engines nearly ready to certify. These
parts include bronze valve guides and exhaust valves with the chrome flash on
the stem so they won't stick in the guides. I was informed the new rings
are in house and they are currently doing some testing to make sure they are the
best quality. The last engines from PZL were costing about $15,400 with no
accessories. The new Franklin 180 and 220 are going to sell for just under
$20,000 with carb, mags, starter and alternator. [Consider the value of the
accessories] and the price figures about the same as the old PZL prices. The
main difference with this company is they will offer factory support in the
states by reputable shops they chose to use. We never had that with PZL.........
I received the following note by e-mail on February 5, 2007:
I just wanted to let you know that Iíll be at Sun 'n' Fun [in April 2007] with Bruce [Kown]and Greg [Lucas]at their booth. Since Sun 'n' Fun did not want to give us a spot inside one of the hangers, Roman [Sadowski] is not coming. Instead he will be at the Friedrichshafen show in Germany. Unfortunately I do not have any new information yet because weíre still closing the certification process. We will explain what was taking so long at a later time. If youíre going to be at Sun n Fun please stop by and visit us at Bruceís and Gregís booth. I think itís going to be under the Franklin Connection, but Iím not sure.
Maciej Smolinski, Franklin Engines Manager, firstname.lastname@example.org, +48 667-677-327"
Spring 2008 Update
Susan Prall of Franklin
Engine Company USA (
I'm sorry that we've been so quiet for such a long time, but we're still kicking. We understand everyone's frustrations because so far all we've been doing are promises without actual results. Roman understands the desperate situation that people are starting to loss their confidence with us and the Franklin Engines. We are also frustrated our selves because we didn't realize it was going to be this difficult and take so much time. Roman is currently out of the country keeping an eye on production issues which are keeping him from attending Sun n Fun this year. He asked me to come to Sun n Fun with Bruce and Greg, and try to ask all of our dedicated Franklin lovers to be patient with us for a few more months. We realize that our web site hasn't been updated for at least a year, but this is because of production frustrations. The web page is under construction and will be updated shortly as soon as Roman gets back into the country. It's very important for us to keep everyone informed through our website. I talked with Bruce who let me know the three most important items right now to keep the engines flying Camshafts, Flywheels, and Front seal retainers. Roman has assured me that he will have at least these three items at Oshkosh and maybe more. Once again Roman would like me to apologize for everyone's frustrations, disappointments, and ask everyone not to give up on us. The Franklin Engine is Roman's life long dream so he doesn't want to fail. I'm attaching a letter below that Roman wrote and I translated.
Maciej Smolinski, Franklin Engines Manager
Hello guys. I'm sorry that I haven't been responding to your e-mails and that we've been so quiet for such a long time. We are still alive; I know that you need engines and parts. Unfortunately I wasn't expecting there would be so many difficulties in starting the production of the Franklin Engine. Even though we had so many difficulties we are still moving forward. I promise to keep you informed about every new step I take from this point. Crankshafts and camshafts are under control if they pass our tests we will come with them to Oshkosh. Currently I'm fighting with the production of the cylinders; unfortunately they weren't able to cast the cylinders in Poland. I'm out of the country right now, but hopefully I will have the first castings in May. If they pass through the tests then we will have a set of parts at Oshkosh. Franklin is my life long calling and I'm convinced that I'll solve all of the engine problems this year. Your ongoing support is very important to me, and I hope that this year we will honor the start up or our engines together. I just want to ask everyone to be patient for a few more months and we will celebrate Franklins success together.
Continental IO-360 210 HP
This Continental is reported to be similar in weight, size, and power to the Franklin 220 HP conversion, and offers the advantage of a readily available, US built engine. Ken Huxham of Tyee Aero in British Columbia developed the following STC. Details as listed by the FAA are:
STC Number: SA00904NY
Ken flies his 108-2, C-FJEE, serial # 108-2219 behind a Continental IO-360D. Ken can be reached by e-mail at email@example.com. Tyee Aero Conversions has a new mailing address: Box 72, Black Creek B.C. Canada, V9J 1K8. Phone: 250-337-8717. Ken reports that Tyee Aero Conversions Ltd. has AMO 96-01. This is the Canadian equivalent of a PMA number. It is unclear if this STC is actively supported currentl (2015)..
Dave Miller in British Columbia installed the Tyee Aero conversion in his 108-2, CF-GYF. You can find details of his experience (and lots of other good Stinson stuff) at his web site called Flight Lines. Dave had some problems with support for the Tyee conversion. Ken Huxham acknowledges those problems, though stresses that they were unintentional. In an e-mail to me dated June 12, 2002, Ken states: "We remain committed to producing a trouble free engine conversion [for] the Stinson 108's. The increase in performance alone is worth the effort." In another update in June of 2010, Ken indicated that while the STC was still current, the PMA needed some work. "There hasnít been a production run of the Tyee Stinson Kit since 1997, so would need several interested parties to start the process again. One at a time runs make the kit too expensive." Dave has since sold his Stinson.
Another STC for the Continental IO-360 is (or was) held by Robert H. Klein, 6918 South 120th Place, Seattle, Washington. STC 9817SA714NW (NM-S) provided for the installation of a Continental IO-360C engine and a McCauley 2A34C203/90DCA-8 propeller in the Stinson 108. The STC was reissued on 6/19/92 but the current status is unknown. The Stinson with this conversion, N6216M, once owned by Robert Klein, was exported to Scotland and is now registered as G-WAGN.
Steve Reese is the former owner of a 108-3, N912C, with an IO-360-H conversion. This conversion was done by former owner Robert Diehl, with help from Robert Klein. According to Steven, plans were for a multiple STC, but they "got tangled up with the FAA and ended up getting a single for just this plane." The one-time STC was issued 5/13/97. Steven offered this information: "The engine came off the back of a C-337, and the engine mount was a modified Seneca II mount. The plane had the Lycoming 190 previously so the battery was already behind the baggage compartment. Bigger fuel lines, header tank, and an extra fuel shutoff were some of the changes. No air filter on the lower cowl either."
Way back in October of 1987, Gary Murdock provided this report: "For those of you looking for bigger engines for your 108's, here's one for you. Steve Knopp (306-629-4812) of P. Ponk Aviation, Camano Island, WA, has done several Continental IO-360 conversions for Stinsons. The latest was for Tom Founts ..., Camano Island, WA [this plane has been sold]. Some of the pertinent figures are 2000 ft/minute rate of climb after takeoff with a 1000 ft/min average to 8000 feet. Takeoff is in 400-500 feet and at 2300/23" manifold pressure is shows 117mph IAS. Empty weight of Tom's converted 108-2 is 1366 lbs! Burns 8 gph at 110 mph cruise."
Another Stinson, a 108-1, N8462K, has a 210 HP Continental IO-360-C. According to a report by Gary Murdock in 1992, the engine for this one-time STC conversion was removed from a Piper Seneca. The rear of the Seneca engine mount was modified to fit the Stinson. A Cessna 182 prop was used and the exhaust came from an M-4 Maule.
A few of the Stinsons with the IO-360 conversion include:
Continental O-470 230 HP
Stan Bearup has an O-470-S installed in his 108-3. In a posting to the Stinson Yahoo group, he answered a question about the suitability of an O-470-U in a 108-3:
"I think that the O-470-U would be an excellent engine for the -3. I looked at that engine as an alternative myself before a friend offered to sell me his engine and prop from his 1976 Cessna 182 when he decided to install an O-520 Texas Skyways conversion on his bird.
Since the O-470-U did not exist when this multiple STC was awarded, that engine was not listed on it. You should go to your local FSDO and have them pre-approve that engine using a 337. You can then install the O-470-U rather than an O-470-A, -J, -K or -R. You would then submit the 337 after the installation of the STCd' engine installation. I did just that when I installed an O-470 -S model on my 108-3. My local FSDO did not have a problem with it at all. I worded the back of the 337 something like this:
"Removed Franklin 6A4-165-B3 S/N ......., and propeller..........
Installed Continental O-470-S S/N...... and McCauley propeller 2A34C203, S/N ....... All work was done in accordance with STC ....... with the following alteration: Installed Continental O-470-S in place of an O-470R.........."
Other well known Stinsons flying with the Continental O-470 include the late Ken Brock's 108-3, 984C, Tom Zedaker's colorful 108-2, N400 CL, and Sam Valdez's 108-3, N6470M. Due to weight considerations, the O-470 engine is located closer to the firewall than the Franklin engines and the rear of the engine cowling is shortened to accommodate the change. This engine is reported to be on the heavy side at about 435 pounds. Bill Bailey reports 135 kts@2350 rpm & 12 gph, 250' t/o over 50' obstacle.
I have heard of more than 30 planes with the O-470 conversion. Here is a sampling:
I've been asked about the Continental IO-520. I'm pretty sure there are no STC's for this installation, but Byron Miller reports that he once owned a 108-3 that had an IO-520 installed, at least temporarily. Here are Byron's comments:
"I used to have a 108-3 that had been converted to an IO-520. I purchased it without the engine and 3 blade prop, as no one could come up with the paperwork for the installation. They removed the engine and prop while I waited for it. When I got the plane home I found all the documentation for the installation although it wasn't quite complete. The paperwork was all wet lying in the belly of the plane. I made copies of everything and kept a copy even after I sold the plane years later. I didn't fly in it with the IO 520, but talked to a guy that had. Performance was INCREDIBLE!! Weight and balance was a whole different story however. The plane had been put in the experimental category. At Oklahoma City they told me it couldn't be brought back to the standard category, however the local guys did allow that once I put everything back original. I could share that info if anyone wants to go that route. I have drawings of the engine mount also. Weight and balance was so bad you couldn't put anyone in the other front seat until you first had someone in the rear seat. I probably even have a photo or two around with the IO-520 and three blade prop installed.
Regards, Byron Miller"
Stinson 108-3 with Continental 300 HP IO-520 and three bladed prop. Photos courtesy of Byron Miller.
Franklin 180 HP
Noted Stinson restorer, the late Butch Walsh of Arrington, Virginia flew his beautiful 108-2 with a 180 HP Franklin and constant speed prop for many years. He felt the 180 is the perfect match for the 108-2 or 108-3. Butch also installed the F-180 in his 1998 restoration of NC6233M, shown above. Unfortunately, the 180 Franklin is a relatively rare engine. Let's hope that it does go back into production at www.frankin-engines.com.
Mark Meiggs is extremely pleased with the
6A-335-B1 installation in his Stinson 108-3. He says there isn't a flight
where "the engine doesn't justify itself through performance and economics."
That, combined with the fact that the conversion "from the 165 B3 to the 335
was, in the parlayence of engine changes, effortless..
Mark provided additional performance information in a post to the Yahoo Stinson discussion group on December 2, 2006:
"Above 5000' we cruise the 6A335 in our 108-3 at 2500 rpm with the max manifold pressure attainable. In our case, we look to lean to about 1375 degrees on the EGT's. (If we use max manifold pressure below 5000' in level flight, the IAS is too far in the yellow for comfort.) Cruise speeds at normal weights range from 121 kts at 5000' to 113 kts at 12,500'. I haven't had it above 13,000' for anything other than terrain or cloud clearance so TAS figures for our airframe haven't been accurately recorded above 12,500'. Fuel burns average in the 9 to 9.5 gph range, depending on trip length. The first hour burn is upwords of 12 GPH when heavy and climbing to altitude on a hot day.
"Our empty weight was 1383 lbs. prior to the engine change. The new reweigh put us at 1415 lbs. We worked very hard in eliminating the ounces/pounds to keep the increase to a minimum however going to a constant prop has it's limitations."
The type certificate, A-767, as amended in 1964, includes the option of the 180 HP 6A-335-B1 engine in aircraft serial numbers 108-3501 and up (108-3) when installed in accordance with Univair Stinson Service Bulletin 269, dated June 11, 1964. This converts the plane to a 108-5 model. Required equipment with this engine includes a McCauley 2A31C21/84S constant speed prop, Woodward governor P/N 210453, and Cessna Spinner P/N 0752004. The battery is relocated and an oil cooler is also required.
Frank Bales sent an unofficial copy of Service Bulletin 269, which he hand-typed from a very poor photo copy. It is offered here for information purposes only for those considering this upgrade. Frank also provided an unofficial copy of the Flight Manual Appendix for the Franklin 180 upgrade. Those who plan to make the conversion should obtain the official documentation from Univair.
While conversion in accordance with Service Bulletin 269 can be accomplished without STC on the 108-3, another option is the STC listed below. This STC, SA1666NM, also permits conversion to the 180 Franklin on the 108-2.
STC SA1666NM for the 108-2
and 108-3 permits the installation of a Franklin 6A-335-B or 6A-335-B1
engine, McCauley 2A31C/84S-4 to -8 propeller, spinner and associated systems.
Modification includes installation of a 40 amp alternator, Model SFA 5582.
The STC for the 180 Franklin is now held by:
Those who talked with the new Polish owner of Franklin Engines (www.frankin-engines.com) at Oshkosh 2006 report that the 180 Franklin will go back into production, though that goal had not been achieved as of the end of 2008.. Note that the Polish manufacturer has a (slightly) different URL than the Colorado company. This can be a bit confusing... The new company is:
Franklin Aircraft Engines Sp. z o.o.
There are several Stinsons with the 180 HP Franklin conversion. These include:
Franklin 220 and PZL-Franklin 220 HP
The Franklin 6A-350-C1 or C2 has been a popular option that offers an impressive performance boost. The STC for this conversion was originated by Seaplane Flying, Inc. in 1976 but has passed through several hands since then. Interest in this conversion increased when the PZL-Franklin engine went into production in Poland and was available at attractive prices in the US.
Recent corporate changes (as of July 2003) have put future production of the PZL 220 Franklin engine into question. The July 2003 issue of Stinson Plane News, the newsletter of the International Stinson Club, reported "With the apparent demise of the PZL-220 ... our options for continuing with the Franklin line look fuzzy at best." Gregg Horrell, of Ryan Aero Services in Tuscon, Arizona (which closed in July, 2006) is familiar with PZL 220 installations in Stinson and Cessna 170's. In a posting on the Fearless Aeronca Aviators mailing list on August 28, 2003, Gregg had this to report: "The Franklin engines are currently out of production after P&W of Canada bought PZL and shut down the small engine division. Plans are in the works to sell that division to interested companies (rumor has it ECI is one of the bidders)". As of September, 2004, I have seen no evidence that P&W has sold the division or the type certificate, nor is there any evidence that P&W ever intends to produce Franklin engines. My understanding is that P&W purchased PZL to increase production capability for its line of turbine engines.
On February 27, 2005, Marc Cook wrote an column for Avweb titled "Motor Head #5: Is Franklin Gone For Good?" The lead-in to the article stated "It isn't always true that the 'best' products are the ones that succeed. Franklin engines are still loved by many, but it looks like there won't be any new ones." Cook went on to write:
"The short version is this: United Technologies -- Pratt & Whitney's parent company -- purchased Polish company PZL, which has been a subcontractor for Pratt & Whitney Canada. PZL owned the rights to the Franklin line since 1975, and had been happily producing mildly updated versions of the Franklin engines since. P&W doesn't much care about piston engines and so shut down the old Franklin line. What had been a trickle of new engines into the U.S. has dried up to nothing. Not that this is particularly news -- it happened in 2002 -- but the rumor mill was producing content up to the roofline describing savvy benefactors and/or engine-parts manufacturers interested in buying the rights and tooling to at least some of the engines and returning them to production. With every month that passes since the shutdown, the likelihood of Franklin rising, Phoenix-like, pares itself down to zero."
However..... In April, 2006, it appeared that a Phoenix-like rising might be possible. One International Club Member noted that a new website, www.franklin-engines.com, was up and running and was promoting the engines once again. The website stated: "Franklin Engines are Back - New - Certified - Better." The contact info for the company was listed as follows:
Franklin Aircraft Engines Sp. z o.o.
Also mentioned on the website were scheduled appearances at Sun 'N' Fun in April, 2006 and Oshkosh AirVenture in July, 2006. ISC member Logan Boles was at Sun 'N'Fun 2006 and reported the following on April 12, 2006:
am just back from Sun 'n Fun...had a great time but am a little tired.
There are some new developments regarding the Franklin Engine. I don't have the
full story but got some "tidbits" of information. The latest story is that the
Franklin Engine never left Poland...and must not have gone to Pratt & Whitney.
On April 19, 2006, I received this message
Dear, John Thank you for
posting our information on your website. All of the information you have is
correct except the phone number. It should be +48 56/46-54-313 instead of 316 at
the end. [I've made the correction.]
At this time I do not have any new information but we will
keep everyone updated on our website. If you have any questions please feel free
to contact me. Thanks, Maciej Smolinski,
Franklin Engines Manager,
firstname.lastname@example.org, +48 667-677-327 In a posting on the Yahoo Stinson discussion group on May
24, 2006, Stan Bearup had this information: "I
spent quite a bit of time with the Franklin engine guys while at SNF. Roman, the
new owner of the Franklin engine type certificates and tooling says he will have
parts available for existing 6A-350 engines this coming winter and hopes to be
shipping new 6A-350 and 4A-235 engines by early 2007. Bruce Kown of Classic Aire
in Cartersville, GA will be one of the known importers of the engines and
Thank you for posting our information on your website. All of the information you have is correct except the phone number. It should be +48 56/46-54-313 instead of 316 at the end. [I've made the correction.] At this time I do not have any new information but we will keep everyone updated on our website. If you have any questions please feel free to contact me. Thanks,
Maciej Smolinski, Franklin Engines Manager, email@example.com, +48 667-677-327
In a posting on the Yahoo Stinson discussion group on May 24, 2006, Stan Bearup had this information: "I spent quite a bit of time with the Franklin engine guys while at SNF. Roman, the new owner of the Franklin engine type certificates and tooling says he will have parts available for existing 6A-350 engines this coming winter and hopes to be shipping new 6A-350 and 4A-235 engines by early 2007. Bruce Kown of Classic Aire in Cartersville, GA will be one of the known importers of the engines and parts."
More than 30 Stinsons are flying with either the original 220 HP Franklin produced in Syracuse, New York, or the PZL-Franklin 6A-350-C1R produced in Poland. PZL also produced the 6A-350-C1L which you will want to avoid - the prop turns the wrong way for our Stinsons!
At one point, these engines were imported by Atlas Motors of Winchester, Virginia. Atlas stopped importing the engines in the 90's. A new importer, John Askeland of Franklin Aircraft Engines, Inc. in Fort Collins, Colorado purchased the STC for this conversion several years ago (STC#313NW) and offered firewall forward packages available for the 108-1, 108-2 and 108-3. The company was still promoting the conversion on its web site in April, 2006.
In an e-mail to me in January, 2002, Gregg Horrell of Ryan Aero Services in Tucson wrote, "I am VERY impressed with this engine and agree with others that a 6 cylinder engine monitor is a MUST HAVE on the 10.5:1 compression ration 6A-350-C1R ....as essential as an oil pressure gauge in my opinion. Mags are set at 28 degrees BTDC for this installation and the engine is started by engaging the starter, getting it up to speed and then switching on the mags...EASY to start, hot or cold. BTW, Matt Haag, owner of the 1952 C170B I just finished, gained 30 knots airspeed and doubled his rate of climb...fuel burn @ 10gph. At a little over 2000 lbs, 2500' elevation at 65 degrees, 20 degrees of flaps and a 5mph headwind he was airborn in 186' .....installing this engine in either airplane presents the new owner with a subtle problem....they'll be able to take off from fields they could never land in...HAH! Gregg Horrell, Ryan Aero Service" (Gregg no longer operates Ryan Aero Services in Tucson. In 2006 he moved to Alaska and is working for the FAA.)
Joe Dexter, Technical Section editor for the International Stinson Club (N604C, e-mail: firstname.lastname@example.org) and Dennis Dow, former President of the International Stinson Club (N6209M, e-mail: email@example.com), both have 220 Franklins in their 108-3's.
There has been some confusion concerning this conversion for the 108-1. The original STC covered the 108-2 and 108-3 only, but was amended in 1985 to cover the 108-1. The STC does not cover the straight 108. The late Dick Ward ofChenango Forks, NY, installed the 220 PZL/Franklin in his 108-1, N8547K. First flight with the PZL was on November 15, 2000. On the 108-1, the fuel system must be brought up to 108-2 standards (1/2" fuel lines, finger strainers in the tanks, fuel selector, and gascolator). The 108-1 will also require the incorporation of the 108-2 rudder trim system. Dick Ward's installation was based on "Installation Instructions" from Atlas Motors and was begun before firewall forward packages were available from Franklin Aircraft Engines in Colorado. His installation involved an alternate engine mount and two oil coolers.
Some who have completed this installation have made some deviations from the STC#313NW, for example, relocation of the oil cooler. Any deviation from the appropriate STC Installation Instructions may require a Field Approval.
Rich Tweedie ran an original (not PZL) F-220 in his 108-2, N175C, for many years. For photos of his engine installation and his notes about installing and operating the F-220 in Stinsons, check out the 220 Franklin Notes page. Rich also discusses the oil cooler options he faced with that original installation. Note that Rich's original installation was completed many years ago before firewall forward packages were available from from Franklin Aircrafr Engines. Rich died of cancer in March of 2000, and 175 Charlie was sold to Charlie Miller in early 2001.
Urs Meyer of Switzerland has a Franklin 6A-350 in his HI27 Acrostar, a European aerobatic aircraft. Urs sent me an email regarding his Franklin in June, 2010. While hard aerobatic use has required more frequent maintenance, Urs says that "If used in normal flight, the Franklin engine is really fine. Exchange the intake manifold gaskets to the cylinder with Viton gaskets and forget a lot of complex problems due to air leakage and loose bolts."
Lycoming O-320, 150-160 HP
This may be an option for those with a Stinson 108 or 108-1 who need a new engine and seek the economy of a 150 or 160 HP engine. Word about this conversion first appeared at Oshkosh '98. At least one Stinson, a 108-1, N97886, is flying with this conversion. The STC was held by Abel Hera in Miami, Florida. The STC is # SA01365AT for Lycoming 0-320 150-160HP. Includes Exhaust mufflers, cross over pipe, R&L hot air, Carb air box, Conical engine mount and paper work. In April 2011 I learned that the STC had been purchased by a new owner, Mark Julicher in Bulverde, TX, who hoped to be marketing the STC in 2012 after the paperwork is back in order. This STC has been dormant for a while, but I received an email in October of 2015 from Bobby May, Maviation Aircraft Services, 210-618-5834, indicating that he is working with Mark Julicher on an "aggressive plan" to "move this STC from a 'dormant' state to active." Stay tuned...
Lycoming O-360, 180-200 HP
Univair Aircraft, the holder of the Type Certificate for the Stinson 108 series, offers two Lycoming conversions for the 108 series. For the 108, 108-1 and 108-2, the 180 HP O-360 with a fixed pitch prop is available. For the 108-3, Univair offers the 180HP fixed pitch prop and the 200HP O-360 with constant speed prop. For both conversions, Univair offers the "Minimum Conversion Kit", sold as a complete package only and also the "Detail Kit" with miscellaneous items needed to complete the conversion. For more information contact Univair Aircraft Corp., 2500 Himalaya Road, Aurora, CO 80011, telephone 303-375-8882. Their web site is at http://www.univair.com.
Univair 180 HP
SA2718NM for the entire 108 series involves the installation of Lycoming O-360 (180 HP) engine and a Sensenich fixed pitch propeller, model 76EM8. The STC was amended 11/13/85. The 3/8" fuel lines in 108 and 108 aircraft will need to be replaced with 1/2" fuel lines. Also, the 108 and 108-1 aircraft that do not already have a rudder bungee kit will be required to have one installed. The conversion will allow the use of existing cowling, with modifications to the lower cowl and nose cowl. The existing mufflers may be modified or replaced. Engines approved for this STC are the O-360-A1A, -A1D. -A1F, -A1F6, -A2A, -A2D, -A1AD, -A2E, -A2F, -A3A, -A3AD, -A4AD, -A5AD, and -A4M. There are two kits, one for newer "wide deck" engines, and one for older "narrow deck" engines. Lycoming switched over to the wide deck in the 60's or 70's. According to Univair, the narrow deck kit comes with the alternator bracket and adjusting arm. The wide deck doesn't come with this bracket. The two cases use a different mount for the alternator. Everything else the same. Univair's cost for the 180 HP "minimum kit" for the wide deck engine in July of 05 was $8,515.19, not including the engine or prop. The cost for the minimum kit for the narrow deck engine was $8742.32. The "detail kit" for the 180 HP conversion listed at $2944.82.
Dagley Reeves (firstname.lastname@example.org) completed a 180 HP Lycoming Univair conversion on his 108-1, N8871K,in March of 1999. He reports a dramatic improvement in climb performance and airspeeds comparable to the F-165. Cost for the conversion was about $26,000, including a new prop, used engine, conversion kit, and installation by his A&P. Dagley reports only one major hangup on the conversion. There has been a modification to the case of some O-360's since Univair did the STC years ago. The alternator bracket they sent would not allow the alternator to be attached without rubbing the nose bowl. This was finally rectified by by using a bracket from a Piper Seneca and "bumping" the nose bowl slightly. Other problems with the conversion kit were minimal.
Charlie Shaw used the Univair 180 HP conversion for his 108-3, N671C. He sent this complete report to me on 11/17/99:
My Stinson was flying well and the Franklin was running great (80 hrs STOH).....but the engine had been majored too many years ago and the crankshaft was over 50 years old. I flew with my kids and family and was just not completely comfortable with the Franklin. I looked at the different alternatives (including majoring Ol' Frank) and decided that I would remove the Franklin and sell it while it was running well and change over to the Univair Lycoming 0-360 STC.
The conversion to the Lycoming was more time consuming and more expensive than was originally anticipated. That being said, I am very pleased with the changeover and the performance of my Stinson.
At takeoff (from CMA at sea level) the airplane now will climb at 1500 fpm at a speed of 75 mph. I've seen 1000 fpm all the way up to 8000 ft. The STC'd Sensenich prop seems to be aimed at this climb performance as the airplane is about 5 mph slower in cruise at most all altitudes and will exceed redline at full throttle in level flight. I don't mind the tradeoff. One of my desires was to have an airplane that would perform better at smaller airstrips without having to worry as much about density altitude.
The 0-360 starts easily, runs smoothly and uses 3 gph less fuel at cruise speeds. The engine seems to have a bit more vibration at some power settings than the Franklin used to have. The amount of room under the cowl with the smaller physical size of the Lycoming makes maintenance and visual inspections a breeze.
The Univair conversion kits have some very good points and some very mediocre points. The engine mount is a thing of beauty. The dual oil coolers keep the oil temp at 182 degrees in the toughest long climbouts. The sheet metal parts provided needed a lot of fitting and reworking. The plans and instructions are fair at best. Despite buying both the basic conversion kit and the detail kit, there were still many assorted items that needed to be purchased. The kits are not a 100% complete-bolt everything in-and go flying right away proposition!!!
This conversion is not cheap. The 0-360 was a factory reman with 1200 hours out of a wind damaged Cessna conversion. It was $11,500. The Univair kits and STC ran about $9000. A new B&C lightweight starter was $500. I had to buy a new alternator (the Cessna wasn't a 12 volt system......my error!) and many assorted electrical components that set me back another $1000 or so. The Sensenich prop was $2000. There was the inevitable new plugs, painting, bracket fabrication, etc. that all contributed to running up the final cost. I participated in helping with the conversion, but my A&P stopped keeping track of his time at 120 hours (this included removing and shipping the Franklin, weight and balance, etc.). Needless to say, I have a firm financial grip on my 108-3.
The lower cowling has to be modified to fit the 0-360. The nosebowl has to be modified on top and in front to accommodate the Lycoming. The battery box has to be relocated to the center of the firewall. The tachometer has to be replaced (rotation is opposite the Franklin). There is no provision for engine priming in the conversion, so that has to be engineered and completed.
Halfway through the conversion I was questioning my sanity. Finding the Lycoming was an adventure into itself! The airplane was down 2 1/2 months during the process. As in anything that has to do with airplanes, nothing was simple.
Would I do it again? Absolutely! I can confidently fly anywhere with my family now. I know that there will be parts and factory support for the Lycoming for the long term. An added bonus is that the Cessna 170 guys are jealous! If any Stinson people have any questions just forward their e-mail and I'll be glad to help out.
Here's another report on the 180 HP conversion from Larry Wheelock:
"I have made a test flight in a couple of Stinsons with the conversion. Takeoff performance is somewhat better than the Franklin, and climb is somewhat better. Speed is only slightly increased. This is to be expected since you are only adding 30hp. You have not stated the prop you are using. That will have a great influence on performance. The Univair conversion calls, I think, for a Sensenich 74 in diam by 56 in. pitch. Since the prop for the Franklin is either a 52, 53, or 54 in pitch, you can see that there cannot be much of a speed increase.
The plus side is the ability to use 100LL without destroying the engine, ready availability of parts, and 2000 hr TBO, at no increase in weight or fuel consumption. Of course the 4 cylinder is not as smooth, but the ones I flew were suprisingly smooth."
Larry Wheelock, 12/17/99
Steve Passmore offered the following comment on the Univair conversion (he removed a Lycoming O-435) in June of 2000:
"I installed the 0-360 about 3 years ago using the Univair kit. The kit is well-done and results in a nice clean installation, but it is rather spendy. The airplane performance is improved in all aspects except cruise speed over the O-435 installation. Takeoff distance is slightly improved, climb is significantly better, noise level is much lower, and the most noticeable improvement is fuel economy. I have flown a number of other Stinson's, but never one with the stock Franklin, so I can't offer much comparison there."
Univair 200 HP
SA1552NM for the 108-3 involves the installation of Lycoming IO-360 (200 HP) engine and a Hartzell constant speed propeller model HC-C2YK/7666. The STC was issued 5/13/83. This conversion retains the existing lower cowling, however it must be modified. A new deeper nose cowl and longer side cowling are required. The existing mufflers may be modified or replaced. A new fuel boost pump is required. Because of the installation of the constant speed propeller and related components, the battery box must be relocated behind the baggage compartment. In July of 2005 the "minimum kit went for $8,172.15; the "detail kit" was not listed in their online inventory in 05 but was about $3000 in 1999. The engine or prop are not included. Engines approved for this STC are the IO-360-A1A, -A1B, -A1B6, and -A1C.
Cooper's Landing 180 HP (formerly Alpine Aviation; formerly Bobcat)
An alternate to the Univair STC may be SA963NW (NW) for the 108-1, 108-2, and 108-3. STC specs call for a Lycoming O-360-A1A, Sensenich 76EM8-0-56 propeller, cross over exhaust, and modified carburetor inlet. The STC was issued 7/23/80. Pete Jenny (email@example.com) has this conversion using an O-360-A4A in his 108-3, NC6093M, and reports that this was the "forerunner" of the Univair STC. He says the Lycoming results in more vibration and cabin noise than the Franklin, but performance is good and fuel burn is 8 GPH. At the time of Pete's report, the contact for the Alpine Aviation STC was Thomas H. Bond, Habegger Co., Cincinnati, OH. Around 2005 the STC was sold to Tom and Carol Buce who operated a Bed & Breakfast in Kimberly Oregon called "Land's Inn." Around 2012, the Buce's sold the STC. The new owner is:
Cooper's Landing Stinson LLC - Gerald Cooper purchased the business previously known as Stinson Bobcat from Tom Buce. Cooper now holds the STC for the Lycoming O-360 conversion and the STC for 8:50 tires for the Stinson 108 series. Now located in Washington State. PO Box 2312, Pasco, WA, 99302. You may contact Gerald by either by e-mail (firstname.lastname@example.org) or by phone, 509-586-3467 or 509-947-3168.
Brian Thompson, of Explore Aviation, LLC in Yakima, Washington, completed a Stinson Bobcat conversion on his straight 108 and offered these comments on the Stinson Yahoo discussion group in June, 2008:
Lycoming O-435 190 HP
This was a popular conversion in the 50's and 60s when surplus O-435 Lycomings were available at low cost. Though there are about 95 Stinsons on the FAA register with this conversion, this conversion is no longer supported and is out of favor. One factor is the extraordinary overhaul cost of the Hartzell prop. Here's information on the old STC:
SA4-398 (WE), 108-2, 108-3 (Landplane). Installation of Lycoming O-435-C engine. Amended 7/10/75. This STC was held by Serv-Aero Engineering Inc., Salinas, California. Russell Williams reports that Serv-Aero no longer sells or supports this STC.The O-435 is also listed on the Type Certificate Data Sheet for the Stinson, as item #110, referencing an engine conversion kit by P.E. Page Aircraft of Erie Colorado, installed in accordance with instructions by Page Aircraft. I do not believe the conversion kit or instructions are currently available.
On Christmas day, 1999, Steve Passmore offered this evaluation of the O-435 in response to an inquiry on the International Stinson Club Correspondence page:
"I've had a 190 Lycoming in
my Stinson for 25 years, although I recently converted it to the 0-360
In April, 2006, Vic Steelhammer offered this summary of the Lycoming O-435 in a posting on the ISC message board, in response to an inquiry about the engine:
"I would regard the
Lycoming O-435 as even less desirable an engine than the poor orphaned Franklin.
Lycoming has not supported this engine for decades. the war surplus parts stock
is fast dwindling and are very expensive when you do locate what you need.
although a robust engine, you will eventually need top cylinder parts and they
are difficult to find.
Larry Wheelock, who regularly contributes his
considerable knowledge of Stinsons on the Yahoo Stinson forum, offered this
There are however, a few owners out there who love their O-435 powered Stinsons and are pleased with the power increase, though recognizing the drawbacks of this engine installation.
Lycoming O-540, 235-260 HP
As the hot rodders say, "There's no substitute for cubic inches." The Lycoming O-540 certainly is the winner in the cubic inches contest. A check of the FAA STC listings for the Stinson 108 series indicates there are no "regular" STC's for the O-540 conversion, but there are at least two one-time STC's and several 337's out there to use as Approved Data for a field approval. While field approvals are becoming harder to get through the system, Vic Steelhammer (in February 99) received approval for his conversion on N6252M. Best to work with your IA and his PI before any work is done. Some Stinsons with the O-540 conversion include:
As reported by Vic Steelhammer in the September 1998 Southwest Stinson Club newsletter, Rodney Engeman is making engine mounts, exhaust systems, a carb heat box, and baffles for this conversion. Cost for these items is about $5000. You supply the engine, prop, oil cooler, hoses, etc. Vic says Rodney is easy to work with but does have a "daytime" job besides his "sideline work", so deliveries are not instantaneous. Rodney's correct phone number (the area code has recently changed) is 541-389-4010.
Vic installed a lightweight, low compression version of the O-540, the 235 HP O-540-B4B5 in N6252M. It uses 80 octane fuel and has a 2000 hour TBO. Compression ratio is 7.2:1. At only 360 pounds, this engine is about 75 pounds lighter than the Continental O-470. Reports are that fuel burn with the 235 HP engine is about 10 gallons per hour. Vic is also installing a fixed pitch prop. This engine/prop combination is used in the Piper Cherokee 235. Vic bought an overhauled Cherokee prop for $1250. The relocating of the battery aft of the baggage compartment and the re-wiring of the electrical system is a huge part of the conversion. Vic is done with that and is finishing up on the baffling and instrumentation.
Vic provided this update on 10/20/99: "The install is done except for fabrication of the intake plenum and filter bracketry. I'm doing things a little differently from Sal Fava and Bill Jensen in an effort to get a larger filter in the system. My research leads me to believe that most of our a/c are "starving" for air, ram-pressure effects notwithstanding. The folks at Brackett Air Filter Co. agree and encouraged me to develop as large a panel as possible. Looks like I may be able to get as much as 57 sq in which is about what Brackett recommends for this size engine. When all of this is complete (end of Oct?) we will weigh the aircraft and do the weight & balance calcs and see if my notions on light weight and simplicity are going to pay off. I'm convinced that in order to maintain the nice handling qualities of the Stinson, we must not change the polar moments too much. otherwise, although the static balance will be correct, the inertial moments could be substantially different. This could affect not just the sweet handling but also things like stall/spin entry/recovery. Admittedly, these effects would probably not be large or detrimental in a general sense, but one of the things I've enjoyed about this aircraft all these years is the nice balance of control rates, pressures and response."
Here's another update after first flight on 1/22/00: "Well, today was finally the day!! The feds came and signed off the O-540 installation yesterday and the logs were signed and paid for this morning. At 10:00am this morning, N6252M took to the air after an 18 month "nose job". the results are preliminary, but very promising. In a nutshell the basics are: Lycoming O-540-B4B5, 235 hp @ 2575 rpm, MacCauley 1P235/PFA 8069 (80" dia, 69" pitch) fixed pitch prop, empty wgt 1489#, 1 pilot, full fuel wgt 1975#
forward to seeing everyone at the next fly-in. I'll try to work up an article for the newsletter next month covering all the
weight, performance and general cost figures."
Here's another update from Vic, this one dated Feb 19, 2001:
"Where to start?... well, I completed the conversion exactly one year ago and put 96.2 hrs on it in that time. I feel that all of my design goals were met or exceeded and I'm very pleased with the overall package.
First, what was I after? The 165 Franklin was a fine powerplant in it's day and when new parts were available. unfortunately, new parts are about like hen's teeth nowadays and since I fly at night and IFR, I was getting very uncomfortable with the Franklin even though mine was about as good as one could be. so my first requirement was a reliable powerplant that still has factory support in the U.S.A. 540 cubic inches producing 235 hp seemed like a good idea to me: lots of cubes not working very hard. good recipe for longevity.
Second was weight. I've built too many free-flight models in my life to add uneccessary pounds to any airframe. the O-540B4B5 weighs (395 dry) about 40 lbs less than the O-470 and so wouldn't require as much ballast in the tail. Ultimately, using a fixed pitch prop and light weight starter/alternator, I did not have to add any ballast to the tail. Only moved the battery to aft of the baggage compartment. since I intended to operate the aircraft within it's original design weight and speed, I felt it very important to keep the weight down. In the end I added a total of 112 lbs to the empty weight of the aircraft for a total empty weight of 1490lbs.
Third, I really wanted to keep the lines of the aircraft as stock as possible. the O-470 requires trimming 3" from the top and bottom cowl because they move the engine right up against the firewall in an effort to minimize the effects of the heavy engine. Even so, most O-470 installations require 12 to 15 lbs of lead on the tailpost. Also, the spinner for the constant speed prop looks kinda big on the Stinson; sort of like the Jimmy Durante signature model.
Cost was also part of the whole equation. A constant speed prop would definitely perform better but at a substantially greater initial cost and subsequent maintenance dollars. performance is still very good with my fixed pitch (80 x 69). with 2 guys and full tanks climbout from my home airport (1000') is around 1100-1200 fpm. cruise at 60% to 65% pwr is something like 115-118 kts. this is not too surprising as this is about 155 to 165 hp and the book speed for the Stinson at 165 hp is 135mph (116 kts). I made one calibrated speed run at 8000 msl and full throttle/fully leaned and got 126 kts true. Fuel burn is from 10.5 to 12 gph with the average being about 11 gph. I've essentially got the same range as the Franklin powered airplane, but I do the distance in 30 minutes less time. Handling is still very nice. typical Stinson. The ailerons do seem to stiffen up a little at cruise. perhaps from the higher speed. Otherwise, it flys just like it always did. I have no float experience so I cannot comment but I know there are several -3's operating on floats in the northwest and Canada. I believe Rodney Engeman originally designed this conversion for float use, so it might be a good idea to call him at 541-389-4010 to get the complete story.
Hope this is of some help to you. If you'd like to discuss it further please feel free to call me. I'm always happy to talk airplanes!
Vic had the urge to buy a Bellanca and sold N6253M to Tim Fox in 2001. Sadly, Vic died in an accident in his Bellanca on July 16, 2006, on a flight to the Arcata-Eureka Airport in McKinleyville, California.
Robert Scott completed his own conversion on his 108-3 and his 108-2, using a Rodney Engeman mount. He calls it the "ultimate Stinson." His engine is an 0-540 E4B5, 260HP. The propeller is a Hartzell HC-C2YK-1BF/F8477-4 with an 80" diameter. Robert reports oil temperatures of 210 degrees and cylinder head temperatures of 310 degrees. He says climb rate with pilot and full fuel is in excess of 2000 fpm; with pilot and light fuel in excess of 3600 fpm. With tundra tires and no wind he can take off in 50 feet; with stock tires take-off roll is 200 feet with no wind. Fuel burn varies from 8.8 gph (60mph) to 14 gph (160 mph). Robert used straight exhausts from the previous Lycoming O-435 conversion (they bolted right on!) and weight was calculated to be 35 pounds less than the O-435. Robert is President of SkyAds, Inc., a banner towing company (phone 800 4 SKYADS.) He reports that his 260 HP Stinson is "capable of towing one fifth of a football field!" He has provided the approved "Airplane Flight Manual Supplement" for his conversion. Click here to download the plain text file version of his document.
Dan Larson also used the Rodney Engeman mount, exhaust and baffling on his 108-3. Dan characterized the entire process as quick and painless. The work was done under a 337.
Simon Rose of
Alberta, Canada converted his 108-3 with a 250 HP O-540 and Hatzell constant
speed prop. Details on his conversion can be
found in this MS Word
Document. A photo of his beautiful Stinson, showing the large Hartzell
spinner and modified cowl scoop, can be seen
Simon is working with a Canadian company on an STC, which should be
available, eventually, in the US and Canada. From reports on the Yahoo
Stinson discussion group, it appears the STC will be handled by Dave From
Aviation, Bldg 1 Red Deer Airport, Penhold, AB T0M 1R0 Canada, phone (403)
886-2201. The STC was reported as pending in August of 2008. On
January 31, 2014, I received an email from Matt Machen reporting that he had
found the STC on the Air Canada Database. The STC can be seen
here. The Canadian STC, SA13-47, was issued to
Infinion Certification Engineering, Inc., Box 20040 RPO Kensington, Medicine
Hat, Alberta, Canada T1A 8M4. The STC applies only to the 108-3.
Interestingly, a prerequisite for the STC is the installation of vortex
generators. The STC was approved and issued on September 27, 2013.