1970 Water pump pulley installation

[Kenneth H.]

I'm having my mechanic install a correct 608 replacement rebuilt water pump (however the date code is from late 1966) on my LT1. The pump that's being replaced wasn't correct and was leaking badly. Once the pump was installed he attempted to attach the water pump pulley (correct 3848904) but the pulley is rubbing against the pump. Any ideas what the problem might be? Should there be some kind of spacer between the pump and the pulley? Help!!

Thanks.

[Joe L.]

Re: 1970 Water pump pulley installation

I'm having my mechanic install a correct 608 replacement rebuilt water pump (however the date code is from late 1966) on my LT1. The pump that's being replaced wasn't correct and was leaking badly. Once the pump was installed he attempted to attach the water pump pulley (correct 3848904) but the pulley is rubbing against the pump. Any ideas what the problem might be? Should there be some kind of spacer between the pump and the pulley? Help!!

Thanks.

Ken------

This is a fairly common problem. Pulley-to-waterpump clearance on 55-70 short leg waterpumps was often minimal. In fact, if you look at 608 waterpump castings you will often note a slight "groove" on the casting where a pulley made contact until the pulley sufficiently established its own clearance.

I don't recall if the 3848904 pulley had a welded-in reinforcement on the rear of the hub-mating surface. In any event, no separate reinforcement was originally used. You could add one but then your other pullies might not line up. The GM part number for the reinforcement/spacer is 3720616.

The first thing I'd do, though, is to make sure the hub spacing is correct on the waterpump you have. Measured from the block mating surface to the waterpump hub pulley mating surface the dimension should be 5-9/16".

[Kenneth H.]

Re: 1970 Water pump pulley installation

Joe, thanks for the info. It was exactly what I was looking for. I called the mechanic and he said that the pulley needs about a 1/4" spacer in order to clear the pump. I gave him the info regarding hub spacing and pulley alignment and he's going to check it out and get back to me. We can then figure out what to do.

Thanks.

[Tom W.]

Re: 1970 Water pump pulley installation

I had a similar problem with my 71.
The advice given on this forum was perfect.
I soaked the water pump pulley flange with WD-40 then used a small gear puller to move the flange forward just enough to clear the pump housing yet still line-up with the other pulleys. Been fine for over a year now.