What is an acceptable range for gear-to-housing clearance? Not end clearance, but the sidewall of the housing to the gear tips. My used Melling M22F measures at least .0035 there. I don't see a spec for it in the factory service manual, and online sources vary (Hot Rod article says .0025" max, enginebuildermag says .003 max). FWIW each of the two gears have several teeth that show nail-catching scratches at the contact area.

https://www.hotrod.com/features/hear...-982-1637-54-1

https://www.enginebuildermag.com/201...e-proposition/

 

I have a couple of new ones on the shelf at work. Ill try to remember and look at one in the morning. Not sure if you will find an actual spec for allowable wear.

 

Melling pumps are junk anymore, and have been for awhile. I take em apart and send the gears and housings off the be coated. U.S. made crap.

 

Yeah, the newer Melling pumps are very notchy when you spin them. Mark had trouble sending me one, had them failing on the dyno. I have a NOS US made Sealed Power high volume oil pump that is much smoother.

 

One of the "side" stories I have not really mentioned from our dyno testing is oil pumps. Each time we take the engine apart I try some different "stuff". Things like side clearance, as mentioned in this post. Put a gasket between the cover and the body. Probably 3-4 different things we've tried so far, all with interesting results. Eventually I will summarize them.....

jerry

 

Jerry, very interested in what you've seen.

 

I'm thinking of picking up a pump from the local parts store to measure myself and see if there is a significant difference in side-clearance. I found an M22G pump for a diesel application...anybody know what the difference is between M22F and M22G?

 

Sorry I have been swamped at the shop and forgot to measure the pumps I have. Promise to do it Monday The difference between the M22 and the M22G is the M22G has a gasket between the cover and the body. It is done that way because GM specified it for those engines. There is a Big Block Chevy pump that is the same way. As far as i know the gasket is the only difference.

 

I just checked a M22F and a M22FHV. I can just barely get a .003" feeler gauge in between the gear and the housing on both of them. I also checked a M77 Big Block Chevy pump and got the same results.

So I would say your .0035" is just fine.

Theoretically the tips of the gears should not wear at all because they never touch anything

 

So were you having a problem ? Just curious. You can get a rebuild kit for it if the body is ok. Its about 1/2 the price of a new pump. Melling K22F

 

Not that I know of, but the engine had a slight rod knock, multiple bearings showed damage, etc... so I wanted to make sure the pump was OK before reusing it. I've only got the rally pack gauges so no way to know what pressures it was a putting out prior to being pulled. Thanks for measuring your pumps, every bit of info helps.

 

Other engines that I work on indicate wear limits in their manuals on gear type pumps, the following; end play 0-.004, gear backlash .002-.003 wear limit of .006. My stock Olds pump w/140k was well past those values so I replaced it, drive shaft/housing was worn quite a bit also, .003-.004 on the dia. new Melling was much better, also shaft fit well, about .001 clearance.