Waiting to drop motor in,need help - Pontiac GTO Forum
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post #1 of 2 (permalink) Old 02-23-2012, 07:35 AM Thread Starter
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Waiting to drop motor in,need help

I am waiting to drop my new motor in b/c I dont know what harmonic balancer to put on the motor,There was not one on the motor when I got it.It's a 1967 400.I been told that any pulley and hb will work as long as it comes off a 400. I also been told it needs to be 65/67 only can someone help me with this?I had a guy tell me to just add a single pully behine the 2 grove pully for the air and that would work, but I dont know if that is right.
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post #2 of 2 (permalink) Old 02-23-2012, 08:11 PM
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Any Pontiac v8 harmonic balancer (326-455) will work for a balancer. For the a/c pulley, it matters which pulley set you already have --- there were many different sets for different years used. It's harder to figure out for a 66 or 67 because at that point in time Pontiac didn't sell any of the crank pulleys as separate items. You had to buy a balancer and the pulleys came with it. The balancer (with 2-groove pulleys) for a non a/c car in 67 was part number 9788194, for an a/c car (with 3 groove pulleys) it was part number 9788193.

However, using the parts book we can do some deductive reasoning here... it turns out that the water pump pulley for both 67 and 68 was the same part number, so therefore the crank pulley set for 68 should work and should line up with your existing 67 pulleys. (Look at your water pump pulley and see if you can find a part number on it that says 9788886. If it does, then you know it's a 67-68 water pump pulley. (If there's no number stamped on it, it still might be). The crank pulley set for a 68 car with a/c would have been part number 9790842 for the 2 groove alt+p/s pulley, 9790843 for the single groove a/c pulley that goes behind it. In fact those same two pulleys were used for 68-70 also. Non-a/c cars would have had a 2-groove pulley only, part number 9790846. The difference between 9790846 (non-a/c) and 9790842 (a/c) is going to be that the a/c pulley will be just a little bit "shallower" than the non a/c pulley, to allow for the space that the a/c pulley takes up with placed behind it - so that when the pair are installed together eveything aligns with the water pump pulley like it's supposed to.

Heres' where things get interesting... all the above applies only if you're using a factory style balancer that has the bevel/chamfer cut into the front edge of the outside ring. This cut is necessary because it makes room for rear edge of the a/c pulley.

If you're running (or plan to run) an aftermarket balancer that doesn't have this chamfer cut, then all bets are off --- nothing's going to fit right. You're going to have to change *all* the pulleys to the later model 71+ versions, plus you're going to have to modify your accessory brackets for a/c, p/s, and alt to move all those components -forward- exactly 1/4" in order to get all the pulleys and belts to line up right.

Why do I know all this? I went through you-know-what solving this problem on my car, with the extra added excitement of the mid-year water pump change Pontiac made in 1969 on top of the fact I'm running an SFI-rated balancer that doesn't have the chamfered edge, and my car has a/c.

I know I rambled a lot on that, so here it is summarized:
For a/c in 67, with the 67 wp pulley, you need:
part number 9790842 (2 groove crank) (or exact aftermarket equivalent)
part number 9790843 (1 groove crank) (or exact aftermarket equivalent)
plus a factory style balancer that has the chamfered edge

If you're running a balancer without the chamfer, or if you don't have the 67-68 wp pulley:
'Safest' route is to convert everything to the 71' pulley set (crank, wp, all accessories) and move accessories forward 1/4"

Ram Air Restorations sells complete pulley sets and also individual pulleys that are very high quality, if you need a source.


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