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Compression

D

d282

Member
I checked the compression in my tractor the other day:
126/127/127/126. After I let the engine warm up for 10 minutes I checked again and had 100/100/96/90.

Is it normal for the compression to drop after the engine has warmed up, or is this a sign that I have weak rings?

I am red to the core, but acquired the above tractor (AC D-17). Don't worry, my plans are to get it running good, and trade it for another red one.

Thanks for the help.
 
I would not be sure it had the throttle in the same place on the second try. If the throttle is closed, it will be sucking a partial vacuum and not read accurately on the gauge. Run the tractor, it will be fine (opinion) JimN
 
I would not be sure it had the throttle in the same place on the second try. If the throttle is closed, it will be sucking a partial vacuum and not read accurately on the gauge. Run the tractor, it will be fine (opinion) JimN
 
If the tappets were too tight it may lose compression but I don't think 10 minuetes of running would warm it up enough to hold them open. The cold oil on the first test would seal better than the warm oil on the second. Does it smoke blue? Like Jim said, was the throttle open for both tests?
 
Thanks guys. Honestly I can't tell you if the throttle was at the same place or not. I will try it again with the throttle half open. I have not noticed any blue smoke. Perhaps I should give it a good tune up, rebuild the carb and take it from there.

Thanks for the help!
 
Compression should always be checked with the throttle wide open so the maximum amount of air can enter and be compressed.
Even 1/2 throttle will offer some restriction to air intake and give a lesser compression number.
 
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