Farmall super m correct compression

Hey all, I live in upstate ny. I tested the compression on my farmall super m and all cylinders are showing around 80-85 psi. Does anyone know if this is a good compression or is it low? There is wheaping by the valve cover gasket, along with the head gasket. (Tractor has been sitting for a while so it has that hardened on grease around all the baskets so kind of hard to tell how much it?s seeping). Was just curious if anyone knew where I should be running compression wise. Thanks
 
That is way low. Shoot even a flat head Ford 8N will have 125psi on a good engine and a poor engine that still run 90 in min on that ford. A super M should have 125psi plus
 
How are you checking compression? It should be done with all spark plugs out and throttle wide open. Also if the tractor has been sitting a while the rings could be stuck. Years ago I was told to shoot a little oil into the cylinders and recheck compression, if it comes up it is probably a ring problem. If not more apt to be valves. It might not hurt to run the tractor a while, work it a bit and then recheck.
 
did you check the compression after engine was warmed up?? did you give it 5 puff's per cyl.? plus it depends what pistons are in there. i would say it should be closer to 90-100 psi. with the low compression pistons. but if it runs good and smooth all is well. also depends on your guage too, because you dont have much variance which is good.
 
So the tractor was cold, throttle was at idle, I took one spark plug out at a time and cranked the engine over until the gauge stopped going up.
 
Engine should be warm throttle wide open and even better if the plugs are out so it spin faster. I do not think they made a dual fuel Super M and that being the compression should be on a good to fair engine 125psi
 
Run the engine until it's fully warmed up. Then remove all plugs the plugs and set the throttle wide open. Finally crank at least a dozen revolutions, or until the gage stops rising.

Depending on which pistons and head your SM has, a "good" compression reading should be somewhere between about 110 and 140 psi.
 
Another mistake most make when checking compression is to not clear carbon flakes from the combustion chamber. Loosen all 4 spark plugs about a full turn, replace the plug wires on the plugs, restart the engine, let it idle a minute, rev the engine wide open several times, let it run another minute, then return to low idle, shut it off, remove plugs and test compression.

All the carbon bits around the base of the plugs break loose and can get caught in the closing exhaust valve holding it open a few thousandths of an inch, enough to lower the compression on the gauge.

Back in the 1960's Hot Rod Magazine used to have great technical articles in every issue, C.J. Baker, and several others, Gordon Jennings wrote facinating technical articles for Cycle Magazine. Articles about pistons and piston rings, Why Bearings Work, And why they fail. Anyhow, I got this tip from HRM about 50 years ago!
 
Great point about the accuracy of the gauge. The only real test is to compare it to a known to be good gauge while using both of them. errors happen in the fittings as well. Jim
 

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