McCormick-Deering Compression PSI

Dave Koenigsfeld · Nov 18, 2008

I have a donor tractor and was wondering what the standard dry compression psi would be? I get zero on #1, 10 psi on #2, 3psi on #3 and 5psi on #4. I was curious if it is even worth trying to drag start it or get it to the motor shop for rings and test if the valves are sticking.

Thanks,
Dave

ScottyHOMeY · Nov 18, 2008

It ain't gonna start with numbers like that! Are ya sure it's got pistons in it? (JK)

Get it opened up and see what you have. Valves would be a real good place to look first.

CNKS · Nov 18, 2008

How are you taking compression? It must be done with the starter, not a crank, with the throttle wide open. Pull all the plugs for faster rpm, if the battery is low. Would also help if your tester screws into the plug hole. Some you just hold in.

Dave Koenigsfeld · Nov 18, 2008

this is a 1926 10-20, no starter. I just unstuck the #1 piston intake value. Compression on that one went to 15. I oiled up the pistons and values to see if I can clean them up a bit without pulling the head.

I know that the compression has to be pretty low or there is no way you could crank the thing.

dave

Dave Koenigsfeld · Nov 18, 2008

I have a compression tester that screws into the piston. There is no fuel in the system and all spark plugs are out.

ScottyHOMeY · Nov 18, 2008

Sounds like you're going about it right. The open throttle is to make sure there's no restriction to incoming air and makes it easier to crank.

That's still quite low (the 113s/123s in my tractors are in the 80-85 range and don't require any special effort to turn) and I doubt it would even fire with compression as low as what you're showing.

Just sittin' in the armchair I'm gonna guess you've got some combination of stuck valves, and badly carboned or eroded valves or seats.

On the rings side, they could be anything from completely worn out to broken and missing.

You don't say (and may not know if you just came into it) what the worst known condition of the motor is. Ever stuck? If so, how did they get it loose? (Towing can do nasty things like bend valves and lifter, break rings . . .)

I don't know that motor at all, but if it has a typical valve cover, I'd start by pulling that and looking things over.

spiffy1 · Nov 19, 2008

No exact numbers handy, but we're not talking in the hundreds on these low compression kerosene burners; maybe 70s?

I'd be surprised if you get it to fire unless you have some numbers up around 50.

I'd agree with double checking those valves. Can you put an air compressor line to your adaptor? You can find out pretty easy if what's going on if it's mostly one problem. Of course, if it has a blown head gasket, and carbon or rust valve seating problems, and worn guids - well you might hear air coming out so many directions you don't know what's what (except the head pretty much needs to come off then).

At least your oil test will tell if it's rings. Good luck!

Edit [as well as multiple grammatical!], maybe you didn't plan an oil test. It's pretty simple, take the reading as normal, then pour a few ounces of engine oil down the sparkplug hole, and take the readings again - no change, rings are either completely shot and you'll have it dripping down the sleeves (a quick peek in the handholes), or, more likely, your primary culprit is in the head, be it valves, gasket, ect.

spiffy1 · Nov 19, 2008

(quoted from post at 16:59:37 11/18/08 )
I don't know that motor at all, but if it has a typical valve cover, I'd start by pulling that and looking things over.

It's really close to the F-20s to paint a quick picture in your mind, and IIRC pretty much is identical to an F-30.

McCormick-Deering Compression PSI

Dave Koenigsfeld

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ScottyHOMeY

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CNKS

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Dave Koenigsfeld

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Dave Koenigsfeld

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ScottyHOMeY

Well-known Member

spiffy1

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spiffy1

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