Cause of intermittent knock in 45 M after it has run a while

Anonymous-0 · Aug 19, 2009

I have a 45 M which runs ok but knocks when it intermittently (misses) usually after it has run for a while. The oil pressure is very good but registers about 20 or so when it starts to knock. Oil level in the pan does not indicate it is low at any time. Any diagnostic hints on this problem or information as to where to start? I was told check the screen on the oil pump first and then bearings and then just as well do a overhaul.

Janicholson · Aug 20, 2009

A knocking sound when an engine misses is not uncommon. Especially if the misfire is a preignition when well warmed up. Several things can cause it. High heat range plugs, Worn plugs, Carbon deposits, Poor gasoline grade (regular unleaded pump gas is just fine), Irratic timing from a cenrtifugal advance mechanism going to the "weeds", or from point bounce from a bad spring, or from a loose bushing in the distributor shaft causing irratic dwell (No feelable play should be in the shaft. Less than .001" radial movement. A stickey valve will also make the same noise. Good luck with this laundry list. JimN

Dick Binfield · Aug 23, 2009

Furher investigating indicates the noise comes from the main shaft in the transmission housing. One can feel the abnormality through the top plate of the gear case at the same time the noise is heard. What is the best remedy? 85 -140 gear lube instead of 80-90 or maybe some Lucas additive to see if it helps. Also oil pressure after 20 min of running drops from the 60 peg to straight up or a little to the left of straight up. Comments on either problem

CenTex Farmall · Aug 24, 2009

Oil pressure sounds ok, especially if it is a well used tractor.

Pull the belt pulley or cover (whichever you have) and look in there for foreign objects, perhaps a ball has gotten loose from a worn bearing and is getting knocked around. That will end badly. A magnet on the end of a heavy piece of wire will work great for fishing around underneath the countershaft along the bottom of the transmission.

You don't say if the noise is under load or at idle or when traveling. An idling tractor in neutral with a weak cylinder and a transmission with some slack will make a rap whenever the weaker cylinder misses and the rotating assembly slows and then speeds up again when the next cylinder hits.

Forget about additives and look for an excessively worn bearing. 85-140 will quiet things down some more at the cost of a little power.

Cause of intermittent knock in 45 M after it has run a while

Anonymous-0

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Janicholson

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Dick Binfield

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CenTex Farmall

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