C-85 Top Overhaul 0-200 STC

Mooney Fan

Mooney Fan

Cleared for Takeoff
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Mooney Fan
It’s only $$

So took my C-140 in for first annual. I flew it about 30 hours since buying it in Dec 20 Compression on #1 cylinder was 42psi. 2 and 3 low 60’s. #4 solid mid 70’s. I went ahead and changed all 4 to new Superior cylinders. Engine is at 500 smoh.

What surprised me was when ordering the cylinders I had to accept them with C-85 pistons. Had to buy the 0-200 pistons for my existing STC separate. Watching the install and #1 cylinder had marginal valve clearance. Only one with an issue. They were working that when I left.

I plan to sell my new C-85 pistons and old jugs. Pic of new

241C882D-D17A-40B0-A9A8-D1A927083855.jpeg
 
MBDiagMan said:
C85 pistons have a different pin to crown distance to compensate for the different stroke. They won’t work in an O-200. If it were myself freshening up the top, I also would have used new pistons.
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A already had 0-200 pistons as it was part of the STC. I just opted to replace them.
 
Update- With 6 hours on the new top I'm chasing an engine roughness issue at low idle and power settings. I have checked the intake hose connections, added new plugs and there is still a slight miss. Applying carb heat makes it worse, but leaning smooths it out, Mechanic wants to check the low speed idle on the Stromberg. Also we will verify the timing since the mags had the internal timing adjusted. These are times I wish we had a wrench on our field.

Would like to hear what you experienced folks think
 
Mooney Fan said:
Update- With 6 hours on the new top I'm chasing an engine roughness issue at low idle and power settings. I have checked the intake hose connections, added new plugs and there is still a slight miss. Applying carb heat makes it worse, but leaning smooths it out, Mechanic wants to check the low speed idle on the Stromberg. Also we will verify the timing since the mags had the internal timing adjusted. These are times I wish we had a wrench on our field.

Would like to hear what you experienced folks think
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My first thought is that there’s a cylinder or two running rich (or the carburetor idle setting is too rich) which would make sense if carb heat makes it worse, but leaning smooths it out. How do the intake and exhaust gaskets look?
 
RyanB said:
My first thought is that there’s a cylinder or two running rich (or the carburetor idle setting is too rich) which would make sense if carb heat makes it worse, but leaning smooths it out. How do the intake and exhaust gaskets look?
Click to expand...
Thx. They should be new. I thought about induction leak and made sure things were snug. Can an exhaust leak cause roughness / stumble? I see no evidence of a leak. Will double check.
 
Mooney Fan said:
Thx. They should be new. I thought about induction leak and made sure things were snug. Can an exhaust leak cause roughness / stumble? I see no evidence of a leak. Will double check.
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If there’s a broken or worn gasket, it will definitely cause roughness at idle and low power settings, but generally won’t be noticeable at higher power settings. Without leaning it, does the roughness improve as you advance the throttle to higher power? Also, does it idle at a higher than normal RPM?
 
Have you been running it hard since the new cylinders?
 
RyanB said:
If there’s a broken or worn gasket, it will definitely cause roughness at idle and low power settings, but generally won’t be noticeable at higher power settings. Without leaning it, does the roughness improve as you advance the throttle to higher power? Also, does it idle at a higher than normal RPM?
Click to expand...
Yes. It runs smoother as RPM’s increase. I’ll have to check on the idle RPM.
 
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