LT1 Water Pump Gasket Leaking

[James H.]

I have a newly rebuilt, LT1 and after about an hour of running it successfully, the water-pump gasket that seals the water-pump to the block seemed to blow-out and leak. I pulled the water pump and cleaned all surfaces back to smooth metal. I did notice where there was some paint from the front timing chain cover that stuck to the water-pump, so obviously the back of the pump touches the timing chain cover.

I put it back together, torqued the bolts even a bit tighter than spec. and the thing started leaking again in the same place. I used Hi Tack to stick the new Fel-Pro water-pump gaskets on. The pump is the correct original GM part number, short-style pump that was on the car before I rebuilt the engine.

Has anyone had this problem before? Is the fact that the back of the water-pump contacts the timing chain cover what might be the sealing problem? I have had several small blocks and I have never seen this issue. Any suggestions would be appreciated.

Thanks

Jim

[Mike M.]

Re: LT1 Water Pump Gasket Leaking

straight edge the pumps legs. I'd think that the pump contacting the timing chain cover in no way would prevent the pump from making adequate contact with the block. if anything, the pump displacing the timing chain cover(which it will since the cover is stamped steel and the pump is cast iron),could possible allow the cover to contact the cam assembly, in which case you hear the results.was the water pump rebuilt? good luck, mike

[Mike E.]

[Owen L.]

Re: LT1 Water Pump Gasket Leaking

I'm wondering if you may have a cracked water pump leg.

[Mike M.]

Re: LT1 Water Pump Gasket Leaking

How much of the sealing surface on the pump is eaten away by corrosion? I had to replace a pump that did exactly what yours has done. Couldn’t surface it enough to save it.

I once had a pump that blew hoses due to severe pitting . I silver soldered all the deep pits, then smoothed the silver solder with a piece of crocus. the pump had somewhat of a lip to help in hose retention. I didn't need to form a lip with the silver solder but I suppose it could be done then dressed with crocus. I then lightly glass beaded my silver silver surface, thinking that the blasted surfaces would result in greater frictional surface to inhibit hose separation.
all this being said, if the pump needed is readily available in the aftermarket, best to go that route. mike

[Joe L.]

Re: LT1 Water Pump Gasket Leaking

I have a newly rebuilt, LT1 and after about an hour of running it successfully, the water-pump gasket that seals the water-pump to the block seemed to blow-out and leak. I pulled the water pump and cleaned all surfaces back to smooth metal. I did notice where there was some paint from the front timing chain cover that stuck to the water-pump, so obviously the back of the pump touches the timing chain cover.

I put it back together, torqued the bolts even a bit tighter than spec. and the thing started leaking again in the same place. I used Hi Tack to stick the new Fel-Pro water-pump gaskets on. The pump is the correct original GM part number, short-style pump that was on the car before I rebuilt the engine.

Has anyone had this problem before? Is the fact that the back of the water-pump contacts the timing chain cover what might be the sealing problem? I have had several small blocks and I have never seen this issue. Any suggestions would be appreciated.

Thanks

Jim

Jim------

You didn't say what year LT-1 you have. In this case, it makes a difference.

[David C.]

[Mark E.]

Re: LT1 Water Pump Gasket Leaking

Either the pump has a casting issue or was milled too much. So it's time for another pump; you don't want a crushed timing cover or a pump that won't seat properly. Even if you want a specific PN and date there are lots of cores to choose from.

[James H.]

Re: LT1 Water Pump Gasket Leaking

Thanks Mike.

[James H.]

Re: LT1 Water Pump Gasket Leaking

I bought grade 8 bolts and tightened it a bit more that the torque spec, and for now, it seems to have stopped leaking. I am sure that interference with the timing cover hurt a bit but I figure the extra torque did the trick.. at least for now.

Thanks

Jim

[Mark E.]

Re: LT1 Water Pump Gasket Leaking

I bought grade 8 bolts and tightened it a bit more that the torque spec, and for now, it seems to have stopped leaking. I am sure that interference with the timing cover hurt a bit but I figure the extra torque did the trick.. at least for now.

Thanks

Jim

Be careful. This is a prescription for stripped threads.

[Joe L.]

Re: LT1 Water Pump Gasket Leaking

James-------


Here's the situation:

1955-61 Corvettes used waterpumps with a flat back plate, GM #3704166, and gasket GM #3704168. I believe the latter was a somewhat thicker gasket than used later but I've never been able to come up with an NOS example of it in order to verify this. In any event, with the aforementioned parts there was no problem with interference between the pump back plate and timing cover.

In 1961 things changed. A new rear cover, GM #3782610, and cover gasket, GM #3782611, were introduced. This cover had a raised center which effectively reduced the clearance between the pump back cover and the engine timing cover. In order to help compensate for this, the new gasket was quite thin and, I believe, thinner than its predecessor. In any event, the rear of the pump back cover usually "rests gently" on the timing cover with, essentially no measurable clearance between them. So, under the best of circumstances the situation is "nip-and-tuck" with respect to the ability of the water pump legs to seat on the block.

All of the 1955-70 Corvette waterpumps have a dimension of 1.200" ( + or - some unknown manufacturing tolerance) from the rear plate gasket surface to the plane of the legs block mating surface. If, for any given pump, the dimension is significantly less than the aforementioned, proper seating of the pump legs on the block may be impaired leading to leaks at this point. Even if the 1.200" dimension exists, if a distorted rear plate or significantly thicker-than-original pump rear plate gasket is installed (as is seen on some rebuilt water pumps), the same problem with leg seating may result.

For 1971 and later, Corvette water pumps changed. For 1971-E1972 the pump casting was GM #3991399. However, this pump has the same 1.200" dimension as the earlier pumps. For some reason, though, I have not found these pumps to experience the leg block seating problem as earlier pumps. I don't know why.

[James H.]

Re: LT1 Water Pump Gasket Leaking

Great information. I did have the pump rebuilt so a gasket that is too thick could possible be the problem. It is not leaking for now, but maybe a future project should be for me to buy a new pump and be sure that the gasket is thin enough to not have this happen.

Thanks

Jim