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compression testing

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Rob in NH
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compression testing

Postby Rob in NH » Sun Aug 28, 2016 4:02 pm

I checked the compression in the cub today, varied from 95 to 80. i did it with all 4 plugs out and the choke pulled. Is this the right way to do it? Thanks
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tst
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Re: compression testing

Postby tst » Sun Aug 28, 2016 4:43 pm

Hi Rob, compression should be checked with all plugs out, throttle open, check it cold then hot, note the difference if any, after a dry test give it a squirt of oil in the cylinders, then retest, if there is a large difference in readings wet and dry it shows the rings worn
Tim

Rob in NH
10+ Years
10+ Years
Posts: 2729
Joined: Sun Oct 03, 2004 7:11 am
Zip Code: 03848
eBay ID: panelbeata
Tractors Owned: 1947 circle cub
1950 cub demonstrator
1957 cub
1967 cub
Circle of Safety: Y
Location: NH, Kingston
Contact:

Re: compression testing

Postby Rob in NH » Sun Aug 28, 2016 4:46 pm

thanks Tim
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Rob in NH
10+ Years
10+ Years
Posts: 2729
Joined: Sun Oct 03, 2004 7:11 am
Zip Code: 03848
eBay ID: panelbeata
Tractors Owned: 1947 circle cub
1950 cub demonstrator
1957 cub
1967 cub
Circle of Safety: Y
Location: NH, Kingston
Contact:

Re: compression testing

Postby Rob in NH » Sun Aug 28, 2016 5:35 pm

Forgot to ask, what is a good number for compression
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tst
10+ Years
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Posts: 5184
Joined: Tue Jan 12, 2010 2:08 pm
Zip Code: 12514
Circle of Safety: Y

Re: compression testing

Postby tst » Sun Aug 28, 2016 5:47 pm

cylinders should all read within 10% of each other,if it is over 90 it is probably ok, nice and tight around 125 lbs, they will run on less, I have seen them with 50 lbs and run but not much power

Eugene
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Re: compression testing

Postby Eugene » Sun Aug 28, 2016 5:50 pm

Anything within 10% difference between high an low is considered acceptable. 70 to 80 psi is getting on the low side.

I'm more concerned with cold engine psi, dry test. Looking for the 10% difference.

I would do the dry test again with a dead cold engine, then a wet test on the dead cold engine.

The tractor with 80 to 95 psi per cylinder will still pull a plow or mow. I used my Cub after initial purchase with slightly lower psi numbers for two years - until I rebuilt the engine.
I have an excuse. CRS.


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