Compression Test

Fatamus · Jan 26, 2015

Finally got a newer compression tester and pulled a compression test on the old TD-9 and I'm going to have to go deeper.
Now it is below zero outside and the engine is cold.
Cyl. #1 75psi dry - 80 wet
Cyl. #2 75psi dry - 80 wet
Cyl. #3 65psi dry - 80 wet
Cyl. #4 75psi Dry - 80 wet

Bob · Jan 27, 2015

I don't think a compression test on a cold engine (especially THAT cold) has ANY validity.

On the other hand, they are GOOD results in that all cylinders are darned near even.

I'm too lazy to look back for the original post, what is the issue causing concern?

Fatamus · Jan 27, 2015

I had it running and starting really nice now I can't get it to fire. Been through the mag; set mag points, new condenser, new plugs, time mag, checked spark (orange spark at 1/4"), checked butterflies, new carb manifold gasket, checked gas level, new gas, burned up a tank heater heating engine.
Think I'll pull out the space heater and tarp tomorrow just the last two days the temp has been low

leon · Jan 27, 2015

Doesn't this old girl have that unique 3-valve per cylinder IH system for starting on gasoline using a spark? If so, I'm not sure what compression to expect. For a conventional spark ignition engine, the results you got wouldn't be bad considering the cold conditions. Find a manual to determine spec, maybe even procedure?

Wayne in MN · Jan 27, 2015

Spark should be bright blue & "snappy". The orange spark will likely be snuffed out under compression.
I would be suspicious of the coil/condenser.

Janicholson · Jan 27, 2015

Those are very correct readings. The compression is fine. The Gas Start engine has low compression to allow crank starting by hand. No issue there, Jim

Fatamus · Jan 27, 2015

(quoted from post at 05:11:45 01/27/15) Doesn't this old girl have that unique 3-valve per cylinder IH system for starting on gasoline using a spark? If so, I'm not sure what compression to expect. For a conventional spark ignition engine, the results you got wouldn't be bad considering the cold conditions. Find a manual to determine spec, maybe even procedure?

Yes it is that 3 valve gas over diesel puppy; when on gas I have read the compression is around 7.5:1 and when on diesel compression is 15.5 to 16:1.
I'm not sure there is a procedure to take compression tests at this temperature but I was surprised to see how close the readings are across the cylinders and really surprised how even the reading were wet. I have never had any engine with readings so close nor so low which makes me wonder about the results.
:shock:
max dry psi = 75
min dry psi = 65
75 x 0.75 = 56.25
min acceptable psi = 56.25psi
all are under 100 psi showing signs of engine wear, however, the fact the engine temp was so cold when the test was preformed I will hold any conclusions until I can worm up the engine and compression tester and preform the test again.

Fatamus · Jan 27, 2015

Thanks Jim
I was expecting way different readings
But I am sure now that the head gasket is fine and rings are better than I expected but when turning over by hand I do hear a hissing valve in the exhaust.
not too bad for 69 years.... 1946 UD-9

David G · Jan 27, 2015

Agree on the spark, clean up points, if still weak spark replace condenser.

Fatamus · Jan 28, 2015

It has a new condenser

Cap and button needs replaced but i have the adjustable button.

Compression Test

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Bob

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leon

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Wayne in MN

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Janicholson

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David G

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