MP Oil pump drive gear fitment issue

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TurboGLH

TurboGLH

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Went to drop the drive into my new motor and it won't drop all the way.

Motor is freshly machined, new bushing and I verified that it fit the shaft freely after I installed it.

After a bunch of playing around with the old shaft(which fits), the borescope and some sharpie dykem, found what seems to be the issue.

Old shaft the first portion after the key is .405, and the new one is .445. Seems inconsequential, but there's a solid witness mark on the shaft. Its rubbing on the block or the main cap, can't tell which for sure on the camera.

Anyone have any issues, or a hardened shaft they can measure?

Contact point
IMG_20200912_173906.jpg


Left mark is the bushing, middle was nothing and the right is where its in contact

IMG_20200912_174356.jpg
 
Any pic of the original?

I don’t have any SB stuff here to look at, but my recollection is that the SB shafts are undercut from about 1/2 way down???

Edit- found a pic.
Sounds like there’s a reason it’s like that.

720C3233-3F8B-4929-AEFB-49989F161EFD.png
 
Last edited:
It's hard to see, but it's under cut as well. The difference I can find is that on the old shaft the undercut portion is smaller than the new one. That's the .405 vs .445
 
The Mopar HD shafts are also under cut but not as much as the original. I assume this is part of the supposed heavier duty construction aside from the pinned gear. Here is a picture of one I have with the brass gear. There is a little taper mid shaft.

9FBBE4D5-7457-4839-8605-B8618274BCD8.jpeg
 
Mine is a standard gear hardened shaft for small block and is lightly undercut just like the one Rocket posted. In the area yours has contact, mine measures .450” diameter. Can you see what yours is rubbing on? I thought someone else had this question last year but cannot find it now. Here is a picture of mine.
D480C969-D360-49DE-921A-151B92E0C04C.jpeg
 
Just tried mine in one Magnum 360 block and one late LA 360 block. It clears both without rubbing, but it is a damn close fit in there. Photo is the Magnum block because rods are not in the way. Both blocks have new bronze bushings installed and burnished.
6AF63587-E5B1-4993-8ACA-8999CC0A7CA7.jpeg
 
Rocket said:
The Mopar HD shafts are also under cut but not as much as the original. I assume this is part of the supposed heavier duty construction aside from the pinned gear. Here is a picture of one I have with the brass gear. There is a little taper mid shaft.

View attachment 1715594094
Click to expand...

Bobzilla said:
Just tried mine in one Magnum 360 block and one late LA 360 block. It clears both without rubbing, but it is a damn close fit in there. Photo is the Magnum block because rods are not in the way. Both blocks have new bronze bushings installed and burnished.
View attachment 1715594115
Click to expand...

It's a Mopar HD shaft, and I have the same-ish .450 diameter on the first tapered portion.

The photo captures where I think the rub is, on the hole in the block above the cap, but the motor is fully assembled.

Before I took any material off the shaft I wanted to see if anyone else had a similar issue or it there was possibly a mfg issue on the shaft.
 
run it.......Got a lathe? Chuck it in a drill press and run a flap wheel at the interference point.
 
PRH said:
Looks like a little QT on the lathe is in order.
Click to expand...

pishta said:
run it.......Got a lathe? Chuck it in a drill press and run a flap wheel at the interference point.
Click to expand...

It's going in the lathe Monday when I get to work.

Wanted to be sure there wasn't a mfg issue with the shaft before I modified it. Couple of people have verified the dia I got, plus @Cal Tonsley and his fitment issues with the same shaft.
 
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