Mopar Performance P3690715 Shaft Diameter

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Cal Tonsley

Cal Tonsley

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Just wondering what the maximum lower (above the hex) shaft diameter is meant to be on the Mopar Performance P3690715 oil pump drive shaft? The new one I have measures .449” versus .407” for the original / std 360 shaft. The std one spins perfectly in the block but the MP one binds and is hard to turn. Just in case you’re wondering, the issue is where it passes through the block below the bronze bush (I have reamed this and both shafts are exactly the same size there and turn nicely through the bronze bush) At the moment I can only run the std shaft due to binding but would be happy to turn the MP shaft down to a smaller diameter so a target size would be helpful. Thanks in advance.

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Mmmmm... so the shafts are the same size where they run in the bushing? And I see the binding just above the hex on the new shaft. Some thoughts:
  • The bushing is not reamed straight with the axis of where the shaft needs to run in-line with the pump hex.
  • The new shaft's hex is off-center
  • The pump's hex is off-center
I would think that spinning the new shaft in a drill press and some light sanding will not do anything of any significance to its strength there. But I'd double check the 2 hexes' centering
 
You need to use the bigger shaft and correctly burnish the bushing.


Edit: where you are showing the measurement you are taking has no affect on the size of the bushing. You need to measure the shaft under the gear, and the bushing is ~ an inch long so from the hear down 1 inch is where you need to measure.
 
Some bushings allow for a drop in, others need the burnishing like Yellow rose said.

Durabond sells a hardware kit through summit for 19 bucks, has the bushing and drip plate , cam bolts, plate bolts, keys..
I pressed it in and the shaft dropped right in perfectly.
 
MOPAROFFICIAL said:
Some bushings allow for a drop in, others need the burnishing like Yellow rose said.

Durabond sells a hardware kit through summit for 19 bucks, has the bushing and drip plate , cam bolts, plate bolts, keys..
I pressed it in and the shaft dropped right in perfectly.
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Thanks, just to be clear I have already burnished the bronze bushing, this isn’t where the issue is, (both shafts are the same diameter through the bushing) if you look closely at the MP part on the lower shaft you can see where it’s binding. nm9stheham raised some good points that I’ll look into but I’m still interested in what the diameter should be on the lower shaft.

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You may be able to get away with sanding and polishing that portion of the shaft with emery cloth. It may only a little time to get the clearance you need.
 
Rocket said:
You may be able to get away with sanding and polishing that portion of the shaft with emery cloth. It may only a little time to get the clearance you need.
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That’s what I’m thinking it’s close but binds enough for me to be concerned
 
Are the scoring marks even all around, or are they deeper/more concentrated on one side? If more on one side, that probably says something is not concentric on the shaft or hex. If even scoring all around, then it is either the bushing off-center or just a tight fit in that lower hole in the block.

How is the mesh of the gear with the cam gear?
 
nm9stheham said:
Are the scoring marks even all around, or are they deeper/more concentrated on one side? If more on one side, that probably says something is not concentric on the shaft or hex. If even scoring all around, then it is either the bushing off-center or just a tight fit in that lower hole in the block.

How is the mesh of the gear with the cam gear?
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Thanks, I did have a look at this yesterday, the scoring is fairly even and the mesh with the cam gear is good. Regardless, I’ll have a look at the shaft on some v blocks this week to check straightness. The shaft is tough to install and remove even with no oil pump or cam in place so I’m still thinking it’s just a tight fit in that lower hole, appreciate your help.
 
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I have used this part number in a couple 360 engines and it always had plenty of clearance in that area, which should never touch the block itself.
Check your block carefully. Maybe Chrysler had different machining specs for blocks in Australia, or something is damaged in the block around that part of the shaft.
The shaft itself is not the problem here, if it has contact all the way around.
 
Yep, just could be a tight hole there. Or some casting flash... Again, spinning and sanding down that .010" in diameter will have negligible effect on strength.
 
Cal Tonsley said:
Thanks, I did have a look at this yesterday, the scoring is fairly even and the mesh with the cam gear is good. Regardless, I’ll have a look at the shaft on some v blocks this week to check straightness. The shaft is tough to install and remove even with no oil pump or cam in place so I’m still thinking it’s just a tight fit in that lower hole, appreciate your help.
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So then it If I’m remembering it right it is binding in the main cap. Did u have the rear cap off. R u sure it’s installed properly? Kim
 
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Well, I thought I’d buck the normal trend around here by providing a conclusion to the original issue posed!
Checked the shaft on v blocks - was straight.
Determined that bind witness marks were fairly uniformly distributed around the shaft.
Cleaned up lower shaft on lathe by turning it down .009” - lower shaft is now .440”
Shaft now looks good & turns perfectly - no bind!

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I have never seen this happen, ever. Were you able to verify there is nothing else wrong that would have caused this, like a burr or casting flash, or some other form of debris that may come loose and cause problems later?
I hope there is nothing else wrong.
 
Bobzilla said:
I have never seen this happen, ever. Were you able to verify there is nothing else wrong that would have caused this, like a burr or casting flash, or some other form of debris that may come loose and cause problems later?
I hope there is nothing else wrong.
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No nothing, I checked with a bore scope again after I read your comment, may be just an Aus machining thing given that there is plenty of clearance with the stock shaft. I guess that the only other thing that was never really cleared up was the answer to my original question-what is the diameter of the lower shaft meant to be?
 
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I have had Chrysler parts that were tight and aftermarket bushings that were not.
I dont do this for a living so havent done as many as some of you .... maybe just a coincidence.
 
Without a part drawing, we can't solidly answer the diameter question. We can only measure similar parts and compare numbers.
 
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