The Cessna 120-140 Association Forum

My C85 crank failed inspection at Aircraft Specialties for a cracked flange. I've found a recently overhauled 0-200 crank that will require the STC to use in my C85. I'm working with an A&P with engine overhaul experience.

For anyone who has done this, is there anything I should be aware of before spending the big bucks to acquire this crankshaft? Anything specific to the Aircraft Specialties STC? Are there limitations on which part number is applicable? (this is the old 530182)

Gary Prost
Stockton, CA

Aircraft Specialties should be able to answer those questions. Congrats on finding a good crank. I'm on the waiting list with them to get a new one...

You will need O-200 Rods and Pistons with the O-200 crankshaft. There is a quarter inch more stroke and the C-85 rods won’t fit the O-200 crank.

The STC costs money, but in the end it will be worth it.

A replacement crank, (Aircraft Specialties can answer questions, as I recall it's their STC)
You will need the case worked for the changed front bearing as I recall. And the parts mentioned above.

You will gain about 5-10HP.

Did my engine with the O-200 crank in 2011 including 4 new ECI nickel carbide cylinders. It was a great investment and I’m glad I did it.

Definite HP increase. Judging by before and after static run up RPM, I estimate 14 HP total increase using the power curves for the C-85 with some of that (guessing 4 or 5?) from having new cylinders, the rest from higher compression and increased displacement with the O-200 pistons and crank.

Over 1,000 hours since the overhaul and I’m climbing at 2425 RPM, fully loaded at 70 MPH.

I have the STC on my engine and just put a new Top on it. The downside was when ordering the new Millennium cylinder kits from ASS they came with the C-85 pistons. I could not substitute and had to purchase the 0-200 pistons separately. Sold the C-85 pistons so that helps.

Also note in the STC text about the different timing settings for each magneto.

6930 wrote: ↑Tue Aug 30, 2022 9:30 amI’m climbing at 2425 RPM, fully loaded at 70 MPH.

For a minute there I thought it said "2425 FPM"

Well, you’ve heard of Super Cubs…..mine is a Super 140

tdragger wrote: ↑Tue Aug 30, 2022 12:36 pm Also note in the STC text about the different timing settings for each magneto.

Very true....however the standard timing for the C85 is 28R/30L BTC. The timing for the Aircraft Specialties STC 0-200 upgrade is 27+/-1 R and 29 +/-1 L.

I have my mechanic set the timing to the original 28/30 which is within the STC tolerance. The advanced timing makes my airplane climb like an Atlas V rocket unless I've had too much pizza the day before

6930 wrote: ↑Tue Aug 30, 2022 8:47 pm

tdragger wrote: ↑Tue Aug 30, 2022 12:36 pm Also note in the STC text about the different timing settings for each magneto.

Very true....however the standard timing for the C85 is 28R/30L BTC. The timing for the Aircraft Specialties STC 0-200 upgrade is 27+/-1 R and 29 +/-1 L.

I have my mechanic set the timing to the original 28/30 which is within the STC tolerance. The advanced timing makes my airplane climb like an Atlas V rocket unless I've had too much pizza the day before

Does anyone know if the STC timing is consistently 27 ± 1 R and 29 ± 1 L across the various holders of the STC?