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I need to replace my oil pump out of my m38. I received one in the mail to find the driven gear is in opposite direction as the one i took out. Does anyone know where i can sent this to switch out the driven gears? i have removed the pin and they wont budge on either one.

Matt R

OK. Stupid question on my part. How do I tell if my oil pump isn't working properly? They are mechanical, gear driven pumps so I wondered about the likelihood of their failing, given our infrequent use.

How do I tell if my oil pump isn't working properly?

The oil pressure gauge. They rarely fail catastrophically. They usually only wear to the point they are unable to maintain adequate oil pressure or they start to leak externally. The TM's 9-1804A for the M38 and 9-8015-1 for the M38A1 and M170 cover the complete inspection and rebuild of oil pumps.

Does anyone know where i can sent this to switch out the driven gears? i have removed the pin and they wont budge on either one.

If you don't have a split bearing puller then take it to your local auto machine shop and they will have the tools to remove the gear.

No local auto machine shop around here. Were in the toolies. Can you buy just that drive gear?

Matt R

Yes. Just pull the gear PN from the ORD 9 and order it. If your old gear is serviceable then pull it and swap them. Beg, borrow, buy or steal a split type bearing puller and swap the gears.



Or just mail that chain drive cam engine oil pump back and have them send you the correct gear drive cam oil pump.

Found a shop thats pulling it now. Will be done by 3pm. Had to drive out of town to find one.

Matt R

See if they can provide a new pin.

Funny you say that. I took the pin out and for got to send it with it. They said they will put a new one in it.

Matt R

OK this is what i have found on the oil pumps.
MB, GPW, CJ2A up to SN 44417 uses the same oil pump due to it being chain driven

CJ2A SN 44418 uses the same oil pump through the M38a1. (Cj2a, CJ3A, CJ3B, CJ5, M38, M38a1)The way to tell what you have is hold the main body (housing) with the shaft facing away from you, the driven gears on the oil pump go to the left on the later pump and the driven gears on the earlier pump go to the right. You have to pay attention to the serial # on the engine. Because you could have a earlier motor mounted on a later jeep frame. So the engine # is the key on the CJ2A.

Matt R

Nice work Matt.

Having been into these engines since the 70's I can say with certainty the real key is the cam. The chain cam engines can be converted to gear cam engines and vice versa quite easily and the serial number of the engine won't help you. Always confirm which type cam you have by removal of the timing cover before you order an oil pump. Yes, I know the timing covers are different but a chain drive timing cover will fit on a gear drive cam engine.

More good info.

Matt R