Ford 641 compression - what is too low?

tysmobiletractor · Apr 18, 2018

I have this project tractor I am working at.
It does run but has numerous issues. And as I am
found repairs on it I did a compression test and I
have about #115 per cylinder.
I know that is not great.
So my question is....at what compression rate are
you typically looking at the need to rebuild?

Obviously there is horsepower loss at 115.
I guess my question is about light duty use.
How low could this compression typically be, and a
engine similar to this still be of some use.
I know there are many variables.

I would appreciate opinions and especially
experience in this matter.

Thanks Ty

Fordfarmer · Apr 18, 2018

As long as it starts, has enough power for your use, and doesn't smoke you off the seat... run it. Those Red Tiger engines are usually ok down to 100# or so.

Ultradog MN · Apr 18, 2018

I would say that engine will do some useful work for a while yet.
My I&T manual says compression on a 601 should be 130-140 psi. But that seems like a very tight range to me.
For comparison, I looked at compression specs for a 3000 gasser and they say it should be 115-150 psi. Much wider range.
I kind of wonder if that 130-140 # is correct.
Anyway, I agree with Fordfarmer; if it doesn't smoke too bad I wouldn't worry about it.
Add oil as needed and keep working it.

tysmobiletractor · Apr 19, 2018

Thanks for the response.
Helpful info.

Texasmark1 · Apr 20, 2018

I have a 1963 2000D (yours with blue paint) just now rolling 3800 original hours, working OEM Proofmeter. It smokes a little when you goose it but starts fast and runs smooth. I ran some snake oil through the crankcase last year and keep it in the fuel (Power Services products) and it cleaned up the smoking almost completely, except on fast acceleration and a lot of that is fuel. Change oil once a year (dino 15w-40 on my old tractors) and usually don't add between changes.

I guess I'm part of the "it it ain't broke don't fix it" crowd and leave well enough alone. Never know what you are up against when you decide to fix something that really doesn't need "fixin". Omen? Don't know but it works for me.

tysmobiletractor · Aug 20, 2018

Just an update. I’ve done numerous little things to this to date. It starts easily and runs well. Haven’t really worked it much hard at anything,but doing fine.

Craig 59 641 · Aug 21, 2018

I have a 641 110 psi each cyl . Run tractor with front end loader. Back blade,York rake,4disk or brush hog. 3 to 4 times a wk with one or the other attachments. No smoke pulls all good.. Useing no oil between changes. I say your ok as is.

Hobo,NC · Aug 21, 2018

Anything less than 20% of the original spec things start to go down hill fast... When you see a minimum compression spec its based on 20% leakage...

New engines can have 10% leakage add another 10 you have 20% in theory you are at 30% you are not gonna get much work out of it... Its time to call in the family... I dunno what your minimum spec is use the original new spec and go from there...
..

Ford 641 compression - what is too low?

tysmobiletractor

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Fordfarmer

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Ultradog MN

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tysmobiletractor

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Texasmark1

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tysmobiletractor

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Craig 59 641

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Hobo,NC

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