C85 Stroker (SE00979AT)

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matthewhinmann120cm
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C85 Stroker (SE00979AT)

Post by matthewhinmann120cm »

Wanting to hear anyones input on the Continental C85 STC SE00979AT, allowing the O-200 crankshaft and pistons. I hear it converts the C85 into a “O-200” , allowing you to get the benefits of the O-200, but in a C85. Ive heard them called “strokers”. I’ve read that it basically allows the C85 to have more lower end torque.

What’s your input?

Thanks!
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Re: C85 Stroker (SE00979AT)

Post by 8224 »

I had an Aeronca 7AC I restored about ten years ago that included an engine overhaul. The crank had been turned .001” under and I was a little suspicious of it so ordered the 0-200 STC kit from Aircraft Specialties in Tulsa. The young lady there told me I would not find it written anywhere in the STC paperwork but the engine would produce 96.4 horsepower at rated rpm. I am an A&P with IA and have restored about 25 planes including the engine work and the increase in performance was dramatic! Didn’t go any faster but boy would it jump off the ground! I am restoring a 47 C-140 and wish I had installed the 0-200 STC when I rebuilt the engine.
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Re: C85 Stroker (SE00979AT)

Post by 8362 »

I have one in my 120 with a 7148 prop.
No hard and fast improvement numbers but I’d say the plane gets off the ground faster.
I do have to throttle back so I don’t over rev in cruse. Never had to do that with the old engine.
So basically it turned a standard prop into a climb prop.
My understanding is if you need a crank it’s the only option.
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Re: C85 Stroker (SE00979AT)

Post by 6930 »

My engine was overhauled in 2011. I needed a new camshaft and while I was at it, decided to add four new ECI Nickle carbide cylinders along with the O-200 upgrade. I have been very pleased with the results and highly recommend it.

I believe I ended up with about 14 more HP than I had before the O/H. I could tell by the difference in static runup RPM. Prior to the O/H, with a 7148 prop, I was getting about 2375 static runup RPM. After the O/H, about 2425 RPM. Looking at the engine curve for the C-85 that translated into about 14 HP gain. How much of that was because of the stroker upgrade is not certain....but I think most of the increase was because of that.

I did a bunch of time to climb tests after install, and discovered that my Vy went from the book value of 82 MPH to 70 MPH. Also, when I level out with full power the engine speed will climb right up to (and beyond?) redline at 2575 RPM which is another clue that the delivered HP had increased. There is no useable increase in straight and level airspeed as the operating speed limitations remain the same. The big difference is in climb performance which is what I think is more important.

The stroker upgrade give you a hybrid engine. Displacement and stroke is increased, but the cam dwell is the same as the stock C-85 which is not the same as the O-200 or C-90. At my annuals, I have my mechanic set the mag timing to the stock C-85 values which is within the stroker timing tolerance. I think that give a slight performance improvement as well.

If you have to O/H your engine it is a no brainer in my opinion. Good luck!
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Re: C85 Stroker (SE00

Post by a64pilot »

Neighbor has a140 with a stroker, she also says 14 HP increase, so I asked her how much pitch did she have to add to the prop. her answer was none. same prop. So I asked if she could hold level flight without over speeding and she said yes.

So,I’m at a loss, increase HP by a large amount but don’t have to increase prop pitch to keep it from over revving, How does that work?

Personally I’d rather have a C-85 than an O-200, so if the day comes to me having to have anew crank, I’ll do the Stroker kit, but I think I’ll add an inch to the prop pitch.
It’s been years ago but when I got my seaplane rating at Jack Brown’s, all the Cubs had Stroker kits.
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Re: C85 Stroker (SE00979AT)

Post by edidin »

Just flew a 120 w/stroker about 1400 nm. Fuel burn seems to be about 5.6-5.9 gph at 2450 rpm, indicating around 107 mph at 4500'. How do these values compare to others with a stroker? The aircraft has no mixture cable, just has the carb mixture wired full rich. Believe this is the carb that even if one does add a mixture cable, it still won't kill engine at ICO, but may save 1 gph by having some ability to lean in flight. Any info on that?

Just based on the longer stroke, my math seems to suggest the hp is in the 91-92 range, but if others know it's closer to 96, great! Have flown other 120s with O-200 conversions and did not feel they got off the ground any better than the C-85 with stroker conversion. This aircraft will climb 400-50 fpm at gross in summer, and does an easy 700+ fpm in the cold on most recent flight at probably 150# under gross. Like others have noted, Vy seems to be in the 75-80 mph range down low, but it was so cold could do a cruise climb at 80 and still see 500 fpm.

Aircraft has what believe is "standard" 7148 prop. And needs quick throttle reduction as level off to keep rpms in range. Seems to burn about 1 qt. every 8 hours or so.
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Re: C85 Stroker (SE00979AT)

Post by 6643 »

edidin wrote: Sun Nov 28, 2021 9:38 amit still won't kill engine at ICO,
The Stromberg mixture control works on an entirely different principle from the Marvel carbs. It works off of the pressure drop in the venturi, and at idle there is no pressure drop in the venturi, hence no leaning effect. It's called a "back suction mixture control".

Try this: pull the mixture all the way to full lean, then move the throttle "smartly" to full throttle. If the mixture control is working correctly the engine will die.
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Re: C85 Stroker (SE00979AT)

Post by phil123 »

My C-140 with an O-200 at 2500ft with throttle full fwd will maintain about 120 indicated in the yellow arc ( GPS about the same) and is turning about 2750 on the rpm with a 50 pitch McCauley 1A101, I doubt any stroker will do that. Theirs a lot of marketing hype on the stroker vs an original rebuild or 0200 swap.

Stroker benefits:

1) You can replace a rare C85 crank with it.

2) The original C85 prop can be used although limited on rpm.

3) There is no engine mount modification.

O-200 benefits:

1) Higher rpm allowed do to through studs in case for better strength.

2) Vacuum pump mount pad.

3) Increased value

4) You can honestly say you have an O-200. lol
edidin
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Re: C85 Stroker (SE00979AT)

Post by edidin »

phil123 wrote: Sun Nov 28, 2021 6:55 pm My C-140 with an O-200 at 2500ft with throttle full fwd will maintain about 120 indicated in the yellow arc ( GPS about the same) and is turning about 2750 on the rpm with a 50 pitch McCauley 1A101, I doubt any stroker will do that. Theirs a lot of marketing hype on the stroker vs an original rebuild or 0200 swap.
FWIW, during one hour (only one flown at lower altitude that is) of my recent long cross country, the C120 with stroker was indicating just under 120 mph at 2500 MSL at around 2450-2500 rpm. Note that this is relatively light example based on useful loads once posted to the board, and the OAT was about 10 F.
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Re: C85 Stroker (SE00979AT)

Post by edidin »

6643 wrote: Sun Nov 28, 2021 4:28 pm
edidin wrote: Sun Nov 28, 2021 9:38 amit still won't kill engine at ICO,
The Stromberg mixture control works on an entirely different principle from the Marvel carbs. It works off of the pressure drop in the venturi, and at idle there is no pressure drop in the venturi, hence no leaning effect. It's called a "back suction mixture control".

Try this: pull the mixture all the way to full lean, then move the throttle "smartly" to full throttle. If the mixture control is working correctly the engine will die.
Thanks for the info. In any case, don't have a mixture cable so for now anyhow.

The difference you describe sounds somewhat analogous to how Continental vs. Bendix fuel injections systems meter fuel in their large bore injected engines (speed vs. pressure drop).
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