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Compression on an H

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Andy in Ohio

02-16-2004 19:14:28

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I checked the compression and got 65 psi on all cylinders, is this normal? the tractor starts and runs fine, no smoke. I thought it was supposed to be at least 100psi. Thanks for the replies and suggestions.

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Kurt

02-17-2004 02:21:00

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Re: Compression on an H in reply to Andy in Ohio, 02-16-2004 19:14:28

When I did the compression check on my H. I got 85PSI on all 4 cylinders. I think it is supposed to be 90 or so.

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Wayne Swenson

02-16-2004 20:48:39

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Re: Compression on an H in reply to Andy in Ohio, 02-16-2004 19:14:28

I have been fooled by a faulty tester on occasion; the Schrader valve core from a tire was put in the tester instead of the correct valve core from the tester manufacturer. The tire valve core had a stiffer spring and gave consistant, but low readings.
Next, be sure you have all spark plugs removed, carburetor in the wide open throttle position, fully charged battery, and ignition turned off.
Test all cylinders for readings on the 1st and 4th compression stroke. Now squirt motor oil in all cylinders and re-test. The readings should be a little higher(10# or so). A larger change indicates bad rings(25# or more). All cylinders should read within 10-15% of the highest reading.
The "Cadillac" test proceedure is to do a cylinder leak-down test. It will pinpoint exactly where and how much each cylinder leaks.
Automotive supply stores have that tester available.

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Andy in Ohio

02-18-2004 16:22:19

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Re: Re: Compression on an H in reply to Wayne Swenson, 02-16-2004 20:48:39

Wayne, I think I have one of those type of testers with the tire valve. Why the first and the fourth stroke? The engine was warm and battery was up. throttle not opened, but all plugs out. thanks for the reply, Andy

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George Willer

02-17-2004 08:58:58

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Re: Re: Compression on an H in reply to Wayne Swenson, 02-16-2004 20:48:39

Wayne,

You've mentioned some of the factors that affect the reading. Ambient temperature, engine temperature, oil weight, and altitude are a few others, as well as the condition of the gauge. I consider the absolute readings so subject to outside influences that the only meaningful information is the comparison between cylinders.

To compare Andy's readings to another tractor is meaningful only if the tests are taken at the same time under the same conditions with the same equipment.

A very simple and helpful test is to put low air pressure to the cylinder and listen where the escaping air is heard... Carburetor? Exhaust? Crankcase breather?

YMMV

George Willer

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Joe Evans

02-16-2004 19:38:04

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Re: Compression on an H in reply to Andy in Ohio, 02-16-2004 19:14:28

Andy: excuse me for butting in, but I've seen your posts before, and curiosity begs the question: are you a member of the Land of Legend Antique Tractor Club? My email address is open if you do not want to respond here.

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42FarmallH

02-16-2004 19:29:52

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Re: Compression on an H in reply to Andy in Ohio, 02-16-2004 19:14:28

Agree with CNKS, a rebuilt distillate should have 95 psi and gas head should have 120. Step head/fire crater pistons will change this. I have step heads in my H w/overbore and distillate head and I get 105 psi.

As long as the tractor runs good, doesn't smoke or burn oil excessively I would not worry. I've seen running engines with 40 psi compression with no problems...

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CNKS

02-16-2004 19:24:15

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Re: Compression on an H in reply to Andy in Ohio, 02-16-2004 19:14:28

Assuming standard pistons -- 95 for distillate head, 120 for gasoline.

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riverbend

02-17-2004 16:58:12

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Re: Re: Compression on an H in reply to CNKS, 02-16-2004 19:24:15

Is that what you are measuring ? I have not measured mine, and I'm not sure that it would be accurate until the motor is broken in (only ~15 hours now). My distilate set up calculated out to a 4.3:1 compression ratio, so wouldn't that be about 65 psi ? The gas head and domed pistons came out to about 6.5:1, again, wouldn't that be around 100 psi ?

Greg

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