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Farmall M No Compression

J

John Lundberg

Member
I have a farmall M that had great compression, 120- 140 pds per cylinder, and now I did a compression check and I have zero on each cylinder. The crack and the fan are turning over, so the crank isn't broke, took the oil pan down, no metal in it. HELP???????
 
take valve cover off. timing gear? old gas will varnish between valve stem and guide and stick valves in open position! if this the case you can spray automatic choke and carb cleaner down guide and stem to release valve without taking off head. just two guesses.
 
Pull the valve cover and see if the rocker arms are moving when cranking over the engine. The camshaft or timing gear may have failed. I think I've read on this forum about the hydraulic pumps on the M's causing timing gear failure. Probably need to do what redih suggested. Still going to involve a good bit of work. Hal
 
Here's the manual procedure for replacing that timing gear. Hal
a46806.jpg
 
If it is the timing gear its a pretty big job. You have to remove the front bolster to get the ft crank pulley off to remove the ft cover on the engine. So if you have any high speed wobble in the front end that would be the time to fix that also.
 
Read that page from my manual. There's a good bit of work just to get to it. You will need to remove the hood,grille, radiator after draining it. The crankshaft pulley needs to be removed so you can pull cover over the timing gear. Once you get the cover off you may need to pull the camshaft if you can't remove the damaged cam gear with a puller. They're probably
a press fit on the camshaft. I would use a cam gear from the Super M since I think they're heavy duty. Take pictures and make notes so you can review them during the reassembly. Hal
 
Something isnt adding up to me, even if the gear is the problem, as mentioned, you are gonna have compression on at least one of the cylinders. I dont think theres a point where NONE of the cylinders will not have compression
 
pulling the valve cover is the primary diagnostic. Putting an assumption on a good tested compression gauge!!!! Jim
 
I would first check compression gauge and see if its right. I wouldn't think it would be a cam gear or broken cam because not all the valves would be stuck open. How long since tractor been used.If it has set for a long time not all the valves would be stuck open you should have compression on a couple of cylinders.
 
Check those push rods to make sure they're not bent and are moving when cranking over the engine. Hal
 
Check your push rods to make sure they're not bent and are moving when you are cranking over the engine. Pull your distributor cap and see if the rotor is turning when cranking the engine. Hal
 
That only works if the compression is LOW, and only brings it up a few points. It will not cure a ZERO compression engine.

Okay, so the pushrods are fine, not bent... Are the valves going up and down?

The only ways you'd suddenly get ZERO compression on all four cylinders:

1. Your compression tester broke.
2. At least one valve on each cylinder is stuck open.
3. Someone spent a lot of time taking your engine apart to steal the piston rings, and put it back together.

If the compression checker is broken, the tractor should run like normal. That begs the question:

Why are you checking compression?
 
If you repaired the intake system, or managed to get sand or rust chips into the engine, the valves will be held open and there will be no compression.
Checking the valve lash (.017" I think) will be an indicator. If the existing adjustment is way loose, like .040" or more, I think there is junk under the valves. Jim
 
(quoted from post at 17:09:45 08/15/11) I have an expensive Snap On screw in compression tester that works fine. I checked it today, and it was maybe up to 10 pds.
Click to expand...

Has the Schrader valve in your compression adapter been replaced with a standard tire valve? The valve for the compression tester and a valve for a tire will interchange but the compression tester needs one without the spring. If you use a valve with a spring your readings will be very low.
 

John,

Did you replace the starter with one that

turns the wrong direction .

Had a local fellow do that , he did 3 valve

grinds before he called me.

george
 
Hi George:
No, I took the original starter off and had mt friend rebuild it. He has has shop and has been doing my staters for 30 years.

John
 
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