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Discussion Starter #1
Was getting ready to prime a fresh 406 for initial startup and notice my priming tool, which is an old stock dist. would not engage the oil pump shaft. Measeured to the top of the intake flange from the top of the oil pump shaft and it was 7 5/8, dist is 7 3/4 in length.. based on rought cam gear measurement itwould mesh properly if i could lower the dist, however it bottoms out. i can go with an adjustable collar msd. im just concerned why it was doing this? dont want to overlook something and go with the adj collar dist if there is something else wrong. I did mic another intake and it was the same so i have no idea why it would be off. also tried another dist and it did the same thing. i also measured the bottom of the cam gear to the top of the oil pump shaft, it was aboutg 7/8 of an inch and appears to be in range. Any help would be appreciated. thanks
 

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The distributor gear fits over the top of the oil pump shaft so it will be slightly longer then the distance from the top of the shaft to the manifold.400's use the same oil pump shaft as all other smallblocks.
 

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A 400 uses a cut down oil pump shaft due to the larger main bearings.
 

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Discussion Starter #4
when you say "cut down" are you refering to diameter or length? the shaft spins free and is engaged with the oil pump, i just cant reach it with the dist.
 

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Discussion Starter #6
i thought that might be the case, since that is the only 2 shafts that are normally used/offered. I didnt build the bottom end, the shaft spins smooth in the block and is engaged to the pump. If it is the big block pump/shaft, i would think the adjustable collar dist would be the properly application. can you think of any problems that would arise?
 

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Check that shaft with another one, back in the day A friend picked up a fresh big block with a small block shaft,dist wouldnt reach, the engine was allready in the car... so ,, we put a MOPAR type - "tang" on the shaft, and it reached fine,, no runout no problem engines fine after almost 10 years,,,:yes:
 

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The length is the same, but it needs a narrower diameter shaft than 350 main blocks, and then you still need to check for clearance through the main cap and back of the block wall. It should have a little free wiggle to it to ensure it is not hitting/ rubbing.
 

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Discussion Starter #10
is the shaft diameter smaller at the top of the shaft or just where it goes through the main? it does have some wiggle and free play in it, i tried a slip collar dist today, when it went in, it meshed with the cam gear and then stopped, i did not touch the intake and measured 7 3/4 to the mark. i tried to hand turn the engine while putting light pressure on the dist, no luck, so could the shaft be too close to the cam gear?
 

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It needs to be thinnest as it goes through the cap. what happened to me is I installed it in the cap and it felt nice and free, but when I turned the block rightside up and it sat down on the end of the oil pump shaft, it cocked in the cap and also hit the back of the block wall. I cut the diameter of the drive shaft down a little more and then all was well. This was in a Dart block with 400 mains, though.
 
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