M38 Oil Pump drive

dfb · Post by **dfb** » Sun Apr 30, 2017 2:11 pm

I will be working on an M38 soon that seems to have an oil pump drive shaft installed a tooth off. Earlier I have worked on it and found that the distributor can not be rotated far enough to get the timing correct before the body of the distributor hits the block. What I have read so far, is that the oil pump needs to come out to re align it properly with the cam. Any advice or tips on performing this job correctly are greatly appreciated. The motor is installed in the chassis and my intention was to do this in frame.

Post by **wesk** » Sun Apr 30, 2017 8:53 pm

The entire procedure is covered in adequate detail in your TM 9-8012 and TM 9-1804A. Just make sure you use the photos I have on the subject in my album.
http://www.willysmjeeps.com/v2/modules. ... _album.php

The oil pump must be installed with the cam at TDC#1 dead nuts on. This can only be guaranteed with the use of a dial indicator or by removing the front timing cover and aligning the cam timing marks on the crank & cam gears. Holding your finger over #1 hole till the air blows your finger off the hole and assures you are within about 5 degrees BTDC to 5 deg ATDC. The pump is difficult to pull in the chassis but not impossible. If it's been on a while then the gasket will probably tear and there are teo different styles of gaskets/pumps. Also you haven't told us if you have a stock M38 gear driven cam engine or an earlier chain driven cam engine.

dfb · Post by **dfb** » Sun Apr 30, 2017 9:30 pm

OK, is it possible to use the TDC mark on the balancer? As for the chain vs. gear drive, I don't know. It is not my Jeep and I did not assemble the motor. Once the pan is down I should be able to tell which drive it has. I don't have the Jeep yet for the job and will be doing it on a lift. Are there specific issues removing the pump you suggest? Does the motor stay on it's mounts or will I need to raise and support it to get the pump out? Thanks for the info.

Post by **wesk** » Sun Apr 30, 2017 10:43 pm

Why are you removing the oil pan?

The existing timing marks either on the flywheel or the front timing cover/balancer are only as reliable as the installer made them. These jeeps are way to old to assume any parts are matched properly. The flywheel timing marks can be 180 off if the installer failed to verify #1 cylinder piston position before installing it. There are three different combinations of front cover timing marks so unless you saw the cam gear and crank gears aligned before they were installed it is only guesswork. You may have a balancer installed that originally went with a different cover timing mark.

here's a few examples:

Notch or hole in pulley and two raised bumps on cover.

Here the cover marks are stamped.

Here's the later type bolt on tab.

Your biggest enemy when extracting the oil pump with the engine installed is the steering gear box and sometimes the exhaust.

dfb · Post by **dfb** » Sun Apr 30, 2017 11:37 pm

Great news there, thanks. I assumed oil pump was in pan, and was only going by what I remembered from last year when i saw it last. Manifolds and exhaust will be off for other work also making oil pump removal that much clearer. Moving steering gear or jacking motor should be no problem at that point if necessary. I will use the indicator to confirm TDC. Thanks for the Great, detailed info and speedy replies. It is very much appreciated.