Melling M561

[DAVe3283]

I'm rebuilding the LB7 in my utility bed, and need to replace the oil pump.

It looks like about 6 months ago Melling released the M561 as an upgrade to the M316. From what I can see it switches from the stock spur gear design to a gerotor.

Has anyone tried one of these? Can't find much information about it beyond that mostly useless announcement.

 

[1FastBrick]

They have a video that shows the internal difference. Personally I have not heard of the cavitation erosion issue that they mentioned. Also not sure whom they are referring to as the top builder that did the independent testing. I went with an OE replacement, pined it and shimmed it myself.

Source: https://www.youtube.com/watch?v=TYXAn-3yQNY&t=105s&ab_channel=MellingEngineParts

 

[Chevy1925]

A georotor pump is a much better pump imho. I’ve not used one yet but we have one ordered for an engine rebuild we are doing

 

[DAVe3283]

I prefer gerotor pumps too, so I might also order one and try it out. Going to be a nearly stock rebuild (LBZ rods, race cast pistons, SAC45 injectors) but a better oil pump can't hurt.

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[1FastBrick]

I am curious to see how they perform. No doubt the Gerotor is a better design.

 

[bimmer95]

I installed one in my lb7 last week just to try it out. Same pressure at idle as the oem I took out but at 2k rpm looks like picked up 5-7ish psi. Apparently due to being a bit more efficient. It is a bit of a pain to torque the gear nut since there is no second shaft in pump to keep it from turning.

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[1FastBrick]

You have to hold the center of the shaft with an 8mm and use a torque extension per there video...

Source: https://youtu.be/7S1-GCvHke4?si=1rOonjVvYPyjvAk3

 

[bimmer95]

Ya that's what I did

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[1FastBrick]

I would like to see the data they collected on it during testing Vs. OEM pump.

 

[Bdsankey]

Certainly interesting and could very well be a nice change!

I'm hoping they don't have the same inconsistency issues that they had with the M316 pump seems to have.

 

[DAVe3283]

Pump showed up. To an untrained eye, it looks pretty nice.


Not a big fan of phillips-head screws. They were hand-of-God tight, had to use an impact screwdriver to break them loose.


No threadlocker or lubrication on the threads, so just torqued like mad. Will probably just put them back in with some threadlocker and go less stupid on the torque.


Yep, it's a gerotor!


The inner rotor is keyed to the shaft, nice! But no keyway on the outer shaft. Might have my machine shop key the gear and shaft while they are doing the cam.


Surface finish on everything looks... decent? Again, untrained eye.


Looks like they intentionally bleed a little high-pressure oil to lubricate the shaft.




Any measurements or photos anyone wants? Any idea how to check the relief pressure? Or not worth touching the regulator?

 

[1FastBrick]

You have to pull the valve out, Measure the depth where the spring is and test the spring on a spring compressor. I recently did this on a new OEM pump.

 

[1FastBrick]

Here is an old one I took apart from my LBZ to play with. But I verified the spring on the new one was the same.

.200 worth of shim was the 30 lbs showing on the spring tester.

 

[1FastBrick]

On the oil pump shaft you may want to pin it. I prefer the DHD method.

I am not sure you can really put a key way in it.

 

[DAVe3283]

OK, that's not the best thing to see. A bit of flashing is jammed in the pressure relief, and I wouldn't be surprised if that eventually got pushed out and circulated through the pump into the engine.


This weekend I will take the regulator apart, clean out the flashing, and do my best to measure the spring (don't have a fancy spring gauge).

Based on this, if you do get one of these pumps, it might be worth your time to take it apart fully before running it.

 

[TheBac]

....or send your findings back to Melling so THEY can do a better job of quality control.
Heaven knows they would never cover an engine that blows bc of their pump build negligence....

I noticed the OEM pump also uses phillips-head fasteners, too......

 

[Chevy1925]

....or send your findings back to Melling so THEY can do a better job of quality control.
Heaven knows they would never cover an engine that blows bc of their pump build negligence....

I noticed the OEM pump also uses phillips-head fasteners, too......

It don’t matter. I buy my pumps through Amazon and take them all apart and pick the best of them, then send the other back.

 

[1FastBrick]

Not good to see... Obviously needs to come apart to verify the relief valve even moves properly.