Water Pump Pulley Wobbles

[Ian H.]

I have installed a 3782608 water pump, rebuilt by Bill Mock on my 1967 327/300. My pulley has the number 3890419 CT stamped on it. The fit between water pump shaft and the pulley was tight during assembly and now the pulley has a wobble while the engine is running.

What should I do to correct this? I'm afraid to put too much torque on the bolts.

How much slop is OK between water pump shaft and the pulley? Is it OK to enlarge the center hole in the pulley by drilling or filing? Using a standard drill or a tapered reamer? Or should the pulley hole be machined in a lathe?

[Jack H.]

Re: Water Pump Pulley Wobbles

The 3890419 pulley is what's called out for a '67 SB with C60, air conditioning. You didn't supply the configuration specifics of your car...

The AIM doesn't call out a pulley reinforcing plate (3720516) for SB engines with C60, but it does call out the plate for base engine cars AND shows its presense on BB engines with C60. The reinforcing plate will absorb some space on the water pump hub resulting in the fan clutch NOT being sucked down as far onto the pump's shaft as an installation without the reinforcing plate. Do you have the plate?

Last, it IS a tight fit between the water pump's forward shaft and the ID of the fan clutch. But, that's normal....

[Ian H.]

Re: Water Pump Pulley Wobbles

Yes, my car has C60 - air conditioning and I do not have the plate mentioned.

[Jack H.]

Re: Water Pump Pulley Wobbles

I suspect the C60 drawing that fails to disclose the presence of the reinforcment plate is a drafting oversight. The plate went onto the base engine car and was there to 'beef up' the center of the pulley w.r.t. stress cracking...

The fact that the equivalent BB C60 drawing has a cut-away of its pulley showing the presence of the reinforcement plate that's originally called out on base SB engines indicates it WAS used on engine configurations beyond just the base car.

If memory serves, this part (PN cited above) is still available from Chevy. It should absorb some stack-up space from the hub of the water pump up to/through the fan clutch AND move your pulley outward ever so slightly to thwart side-loading of the v-belt...

[Timothy B.]

Re: Water Pump Pulley Wobbles

I installed the reinforcing plate on the outside when I put the correct water pump on my 67. I was not aware it goes on the inside, is this correct?

[Jack H.]

Re: Water Pump Pulley Wobbles

Well, from a tolerance stack-up view, it doesn't matter where the reinforcing plate goes. But, to get the benefit designers intended, the reinforcing plate won't be reinforcing the center hub of the pulley unless it's placed beneath the pulley where the pulley makes contact with the water pump hub...

[Joe L.]

Re: Water Pump Pulley Wobbles

I have installed a 3782608 water pump, rebuilt by Bill Mock on my 1967 327/300. My pulley has the number 3890419 CT stamped on it. The fit between water pump shaft and the pulley was tight during assembly and now the pulley has a wobble while the engine is running.

What should I do to correct this? I'm afraid to put too much torque on the bolts.

How much slop is OK between water pump shaft and the pulley? Is it OK to enlarge the center hole in the pulley by drilling or filing? Using a standard drill or a tapered reamer? Or should the pulley hole be machined in a lathe?

Ian-----


Do NOT enlarge the pulley pilot hole. If the water pump pilot shaft will fit the hole, that's fine. You WANT this to be as tight as possible-----this is what ensures that the pulley is centered. The 4 bolts (or studs) WILL NOT ensure the centering of the pulley (or, the fan clutch). If the paint on the pulley is especially thick in the area of the pilot hole and this is what's causing interference, you can remove the paint.

I would check to be sure that there's nothing that's interfering with the seating of the pulley on the water pump flange. The rear of the pulley must be completely flat against the flange. Otherwise, the pulley will "wobble".

If, after you've checked all of the above and you still have "wobble", then you might want to check the runout on the water pump flange with a dial indicator.

There's also the possibility of a bent pulley.

[Ian H.]

Re: Water Pump Pulley Wobbles

Thanks Jack and Joe. I will look into that pulley reinforcing plate #3720516 and check the mating surfaces again.