Compression

Two Banger · Jul 4, 2010

I have a farmall H. Right now it only has 75lbs of compression. What is it supposed to have?

Brian Jasper co. Ia · Jul 4, 2010

I would expect a healthy engine to be in the 125 psi range.

old · Jul 4, 2010

Rule of thumb on most tractor is 90PSI or better but you have to check it the correct way if you do not you can get a bad reading from doing it wrong. Throttle has to be wide open and engine warm and even then you do a wet and dry test

daman · Jul 4, 2010

(quoted from post at 20:13:59 07/04/10) I have a farmall H. Right now it only has 75lbs of compression. What is it supposed to have?

Did you check it at operating temp throttle wide open?

try a different gage.

Bob Bancroft · Jul 4, 2010

Lots of good advice. I also hook up the battery charger so that by the time I'm on the last cylinder the cranking speed hasn't diminished.

Jerry/MT · Jul 4, 2010

It depends on what the compression ratio is supposed to be. A lot of the gas tractors of this era had a 6:1 or 6.5 :1 compression ratio. That would mean that a new engine would be in the range of 125-140 psi and a the lower limit is on the order 0f 90 psi. really low compression pressures indicate valve problems. You have to run a compression test corrctly to get good numbers. the engine should be at operating temperature and the throttle plate should be wide open and the air cleaner disconnected. It"s easier on the starter if all the spark plugs are removed. Affter checking the compression dry on all cylinders, add a couple of ounces of motor oil to each cylinder and repeat. Record both sets of numbers. then get back here with the results.

Bob · Jul 4, 2010

Is this a tractor that has been working all along or one that's been sitting idle for a while?

If it's NOT a working tractor, run it and WORK it and warm it up and after a few hours of that, THEN check the compression.

That will be a whole lot more meaningful.

The other thing is that your numbers are apparently consistent across all the cylinders.

I would rather see an engine with low, but consistent compression numbers than one with one or two cylinders WAY out of the range of the others.

Two Banger · Jul 4, 2010

Thanks for all the advice, I didn't have the throttle all the way open, next time I will. I just bought it from a guy that left it sitting for a while, I wil run it for a while and then check it.

old · Jul 4, 2010

If it has been sitting like as in a year or more pour some ATF in the cylinders and let it sit a few days then run it. sounds like it may have rings that are sticking and ATF will free them up

Compression

Two Banger

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Brian Jasper co. Ia

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old

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daman

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Bob Bancroft

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Jerry/MT

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Bob

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Two Banger

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old

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