pulley alignment - Pontiac GTO Forum
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post #1 of 5 (permalink) Old 08-19-2018, 07:29 PM Thread Starter
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pulley alignment

'72 400 engine pulleys on crank and water pump appear to be off by about 1/16". The crank pulley sits in farther to the engine. I have the spacer ring on the outside face of crank pulley as someone suggested. But, it seems if it was installed behind the crank pulley it would be spaced correct. I also have a '73 400 engine and it is installed the same way and has the same misalignment. It actually threw a belt while I ran it on a run stand. What causes the alignment issue?
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post #2 of 5 (permalink) Old 08-19-2018, 10:49 PM
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First thing is the ring is correct, it is absolutely designed to be on the outside of the pulley. Its purpose is not as a spacer but to go beneath the bolt heads as a big washer to distribute the bolt loads and to prevent wobble in the pulley. I've included an excerpt from Jim Hand's book.

The Second thing comes to mind is if the motor has been recently rebuilt and if the crank thrust bearings were not installed in the correct journals the crank can move axially quite a bit and put a side load on the rods, big problems if this is the case, ask me how I know. In high school 1981 had a buddy who assured me he knew what he was doing rebuild a Pontiac 400 for me and lucky we didn't throw any rods. The motor ran ok but on throttle up the crank would visibly move about 3/16" forward, then pull back on throttle release. Tore down the motor, replaced the crank bearings and all was well. Watch for the crank movement .

Otherwise I don't know what would cause your problem. Timing cover/Water Pump gaskets too thick? Just throwing it out there.
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post #3 of 5 (permalink) Old 08-20-2018, 12:39 PM
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Getting pulleys aligned properly on a Pontiac is the stuff of nightmares. For some odd reason there were a significant number of factory variations from Pontiac - why, I have no idea. Example: In 1969 alone there were three different water pump pulleys, all with different back-spacing, just for A-body (Tempest, LeMans, GTO) cars.

Your starting point should be making dead-nuts positive that all of your accessory mounting brackets and pulleys are from both the same model year AND the same body style - and that's just to start. If you've added any aftermarket parts into the mix, then get ready for a bumpy ride.


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post #4 of 5 (permalink) Old 08-20-2018, 01:34 PM
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we need your pulley numbers

they should all start with 48 _ _ _ _

sounds like you have a 9790842 on the crank

stock balancer ?

water pump and power steering line up nice ?

did you have these pulleys on an other motor and they lined up ?

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post #5 of 5 (permalink) Old 08-20-2018, 07:56 PM Thread Starter
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This motor was in pieces when I bought the car. I also had another 400 from a '73 GTO with 60k on it thrown in on the purchase. In the parts pile were two pulleys for the water pump that looked alike. I needed one to put on the '73 motor to fire up on a run stand to verify condition. The other pulley I put on my '72. They both seem to be off the same. I'll try to get part numbers tomorrow and report back.
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