Comrades,

I am looking at re-powering my Stinson 108-3 With an engine conversion out of a wrecked airplane a 108-2, the STC is no longer supported (so as to my understanding), can STC paper work be moved/ transferred from one aircraft to another? Does anybody reading this currently operate a Lycoming O435 in a Stinson?

Thanks
Brian

STCs are typically aircraft serial number specific. Check the STC paperwork on the wrecked plane and see what it says.

If the STC is indeed an "orphan", you may be able to get the mod approved by the FAA, using that STC as a basis for a field approval. You're going to have to be sure the STC is no longer supported.

But, if it's indeed no longer supported, it shouldn't be a big deal. Find a good mechanic who has good working relationship with the FSDO.

MTV

I know people who've had the O-435 Lyc conversion in a Stinson 108. I think it got popular because it was easy-- as I understand it, it uses the engine mount & engine right out of a Stinson L5 Sentinel. But I've heard it's a dog, understandably-- 435 cubic inches of heavy engine to make only 190hp. IMHO you might be better off sticking with a 165 Frank, or spending the money for a 180 Lyc STC from Univair or a 220 Frank conversion (from ??).

I have some hours in N361C, a 108-2 with the O-435 conversion. It flew like a dump truck drives. Also The only prop that is approved for that conversion is a controllable pitch Hartzell. That thing is a real antique boat anchor. It is not constant speed, but you can control pitch in flight. It uses engine oil pressure against a rubber diaphragm to move the blades. One day the diaphragm let go and all the engine oil promptly followed suit. Within 30 seconds the oil pressure was zero and the windshield was totally covered. That's another story that I might post on zzz's thread about losing the engine oil. I was also flying a 108-3 that was totally original at the same time, with a 165 franklin. The -3 flew much nicer. I don't know if the bigger tail on the -3 would work better with the O-435, but I don't think it would make a big difference.
Changing STC's might be easier if you own the donor aircraft that the STC is coming from.
Tom

Thanks for the input, what I have now is a a turbo 220 Franklin making 250 hp and I am looking at a mogas alternative to this. I am leaning toward putting it back to a stock 165. I have never flown the plane with the 250 and am looking to build some cheap float time. I know more power would be better but everything has a cost, I'm sure it will perform fine with two people. I found a low time O-435 as mentioned above but the added weight to power gain over stock is not there, in addition with the other inherent problems, it just does not make that swap look very good.

Brian

How about just putting an o-470 on it? 225 -230hp and moGas options. And lots of them put there.

TurboStinson wrote:Thanks for the input, what I have now is a a turbo 220 Franklin making 250 hp and I am looking at a mogas alternative to this. I am leaning toward putting it back to a stock 165. I have never flown the plane with the 250 and am looking to build some cheap float time. I know more power would be better but everything has a cost, I'm sure it will perform fine with two people. I found a low time O-435 as mentioned above but the added weight to power gain over stock is not there, in addition with the other inherent problems, it just does not make that swap look very good.

Brian

I've got a friend with the turbo 220 Franklin on his Stinson. Says it's gets up and goes!
John

Look up "Follow on Field Approval" it is exactly for such things, but most FAA have no clue. Good luck whichever way you go.

I'm seconding the suggestion on this older thread to hang an O-470 on there. Lots of J's out there which have been replaced by Ponk 520's.

We are in the process of doing a 470-J conversion on a 108-2 starting next week.... Overhauled the engine a few years back and it has been sitting on the stand due to paperwork issues on the aircraft (import from Canada, long story)

This will be the second 470 conversion we have done in our shop... First was on a metalized 108-3 and that made a real sweet flying machine out of it..

Brian

Brian-StevesAircraft wrote:We are in the process of doing a 470-J conversion on a 108-2 starting next week.... Overhauled the engine a few years back and it has been sitting on the stand due to paperwork issues on the aircraft (import from Canada, long story) This will be the second 470 conversion we have done in our shop... First was on a metalized 108-3 and that made a real sweet flying machine out of it.

I think there are more engine conversions done on the Stinson than anything else, other than maybe the Swift. 165 Frank (into a 108 or 108-1), 180 Frank, 220 Frank, O360 Lyc, IO-360 Lyc, O-435 Lyc, O-540 Lyc, IO-360 Continental, O-470 Continental.
Everything considered, I think the 470 makes the most sense. STC'd, readily available engines & engine parts, proven performance. The 540 Lyc has a lot going for it, but as I understand it even though engine mounts are being produced there isn't an STC, and I think a donor engine is gonna be a lot more money than a 470.

Stinson got moved into the corner of the maintenance shop today... Will be pulling the Franklin in a couple days..

Brian

Brian-StevesAircraft wrote: We are in the process of doing a 470-J conversion on a 108-2 starting next week....

I assume that's an STC'd conversion? Who holds the 470 STC? I've seen one Stinson converted to the 540 Lyc, and know of another with the conversion underway -- fixed pitch prop and presumably out of a Pawnee. Someone in Oregon (?) makes & sells the engine mount but there's no STC.

It's an STC.... Guy that has it lives near Portland OR... I'll have to get into the paperwork for the STC number... Kit has a new engine mount, baffles, exhaust system plus various bits and pieces to install a 0-470-J..

Brian

It's the old PDX conversion STC...I don't remember the guy's name either right now. It's good for a O-470-A, J, K, L or R.
It's a great setup...done a few of them, and at one time contemplated buying the whole STC.
I hold a STC for a set of aux tanks that go in front of the baggage, behind the cabin and hold 13 gallons of fuel that's pumped up into the left main tank. Pretty handy for the 470 conversion.
John

I flew a -2 with the 0-435 for many years and now I have a -2 with the 165 Franklin, The 0--435 with the controllable prop was a substantially better performer on take off and climb. Yes it is heavy for the power, it is a bit of a gas hog though really only about a gallon an hour more than the Franklin. I never really had a serious issue getting parts, I completely overhauled one and did a top on another one.
The Franklin is smoother, has more room under the hood.
I think likely it was the prop more than the engine, with a fixed prop you are stuck in second gear for everything, with the controllable pitch you can have better acceleration and then screw in more pitch as wanted.
The 0-435 was also faster in cruise at a lower RPM setting, again due to the prop.
If I could find a controllable prop for the 165 I would sure like to try it out. It might make for a really nice setup.