The Cessna 120-140 Association Forum

Hi,
I know that there is an STC for putting an O-200 crank, rods and pistons in a C-85 engine. Is there any performance to be gained by doing this, or is it just a matter of having better accessibility to the parts? I am disassembling the engine, and have given thought to this "upgrade" Any thoughts?

Thanks,
Dave
1946 C-140

6054 wrote: ↑Sat Nov 10, 2018 8:58 amIs there any performance to be gained by doing this, or is it just a matter of having better accessibility to the parts?

Yes. You're increasing the displacement to 201 CI from 188 and also upping the compression from 6.3:1 to 7.0:1.

From personal experience and the "feel" after the "upgrade" @ overhaul, there's definitely a difference in climb performance. While it isn't pin-to-the-seatback acceleration, it's perceptible. From memory, at least part of the reason for the original STC being sought was the growing scarcity of C85 cranks...and, the additional performance potential was a bit of a "bonus" that came along with it(?). One part of related discussion that I don't recall is the reason for the "new" engine label specifying timing revised to +/- 27 & +/-29 (28 & 30 previously)...admittedly a minor change, but interesting (John?). In any event, it's an upgrade I'd suggest as almost a no-brainer. However, factoring in the BIG bucks for 0200 cranks these days compared to a "good" C85 crank already in hand & the cost difference certainly could reverse that "brainer" .


Mac

I installed this mod on the C-85 in my Aeronca Champ several years ago. There was a definite increase in power. The girl at Aircraft Specialties that did the paperwork told me I wouldn’t find it in print anywhere in the STC but the engine would make 96.3 HP at 2700 RPM. There definitely was an improvement. The STC said I had to send the case off to someone and have it machined to make room for the rod bolts to clear at a certain point. I don’t remember the particulars very well but when the case was returned from Divco I could see what they had accomplished. I could have done the work in about two minutes with my air powered die grinder and a steel burr. If I do it again, I will. When I did it in about 2009 the cost, as I remember, was about $5000 for the kit.
Steve

Jhopefully weather permitting a week from monday im flying one home with set up as you describe. I wont be able to give you comparisons but i can let you know our general performance

8322 wrote: ↑Sat Nov 10, 2018 10:05 pm Jhopefully weather permitting a week from monday im flying one home with set up as you describe. I wont be able to give you comparisons but i can let you know our general performance

Yes, indeed, keep us posted on the progress with your "new" 140! ...hope you get some good CAVU for the trip. Mac

Its a worthwile upgrade but If I recall the red line of the modded engine is unchanged making the 96hp at 2700 spec. pretty irrelevant.


Joe

Just got mine home, I thought it performed well, but honestly forget to make specific notes on climb rates and such, but it didn't seemed to do the job well. We definitely were at gross, though I'm sure the cold temps helped as well. I don't believe it jumped off the runway as well as my friend's with the true 0-200, but I also think there may be some weight difference there as well...



I will be up in her again soon, and will try to make mental note for you of specific climb performance and such...

Ray

Thanks for the replies, and I am also thinking about just finding an O-200, and putting that in the plane. Problem with that is that there are two parties listed with the STC. One, a Pipeline patrol company must be out of business, and I cannot find a phone number. The other, in California (Randy Thompson) had phone disconnected. Any ideas on the O-200 route? I am going to post a new thread about the O-200. Hopefully someone out there has more information.

Dave

Randy hangs out here. I'm sure he'll pipe up soon, unless his phone is disconnected because the forest fire burned the lines... (He's in Northern California.)