Oil Pump Questions:1971 LT-1

[Paul C.]

When you have the engine rebuilt should you place the oil pump?

If kept, how hard to rebuild?

What is the part number of the 1971 LT-1 oil pump?

[Duke W.]

Re: Oil Pump Questions:1971 LT-1

There is rarely a need to replace the oil pump but typical "engine builders" will apriori, often with the wrong one. It's easy to disassemble and inspect - just remove the four screws that hold the cover to the housing. Carefully inspect for wear. As long as the pump has not ingested debris it should be okay. Any minor galling on the cover can be removed by dressing it on a flat surface with some solvent wetted 220-400 paper, and deburr the gears if necessary with a small file. It's best to set up end clearance to two to three thou, which might require dressing the end of one gear and the housing as with the end cover. There is no gasket between the cover and housing or between the pump and block. I don't have a service replacement part number handy, but I believe all LT-1s have a 55-60 psi relieve spring rather than the "standard" 40-45 pound spring. Don't let anyone talk you into a "high volume" pump. It's absolutely unnecessarily.

[Paul C.]

Re: Oil Pump Questions:1971 LT-1

Thanks Duke.

[Mark E.]

Re: Oil Pump Questions:1971 LT-1

There is no gasket between the cover and housing or between the pump and block.

Pump to block gaskets are available. Any advantage to adding one? Maybe to ensure all oil goes into the block?

[Duke W.]

Re: Oil Pump Questions:1971 LT-1

The mating surfaces are machined smooth, but with no gasket there is bound to be slight leakage, however this "leak path" is so much smaller than the bearings and valve train that I don't think it would make any difference, which is why Chevrolet didn't install one, however that's not necessarily the case with all engines. Back in the seventies I was rebuilding the engine in the E-production TR3 I owned with a friend. He was not that "hands on" so I had to supervise him carefully. He asked if it was okay to install the oil pump while I was doing something else and I said okay and be sure to install the gasket. Upon startup when it was back in the car, the oil pressure was low, so I took off the pan and pump and found no gasket between the pump and block.

[Joe L.]

Re: Oil Pump Questions:1971 LT-1

When you have the engine rebuilt should you place the oil pump?

If kept, how hard to rebuild?

What is the part number of the 1971 LT-1 oil pump?

Paul------


The original LT-1 oil pump was GM #3848907. The last available oil pump was GM #12555884 but it's now discontinued. The original pump was of GM internal manufacture. I think the 12555884 was, too, but it's possible it was a vendor-supplied part.

[Michael B.]

Re: Oil Pump Questions:1971 LT-1

Paul,

I recently rebuilt a base engine small block and after inspecting the internal gears in the oil pump it was determined it needed to be replaced. I purchased the standard Melling pump for this engine but prior to installation I discovered it had a higher psi relief spring than stock. The original GM pump and the Melling pump looked identical to me so I called Melling and spoke to their "Head Tech Guy" to ask if it was OK to just swap internal gears. He assured me it was, so I was able to keep my original pump with new Melling gears in it.

I would suggest taking your original pump with you to the local parts store and compare it to whatever pump Melling lists for your LT-1. If they look identical then I would bet the internal gears are identical as well.

Good Luck.

Mike

[Joe R.]

Re: Oil Pump Questions:1971 LT-1

Pump to block gaskets are available. Any advantage to adding one? Maybe to ensure all oil goes into the block?

GM did not use a gasket between the pump and the block. The surfaces are milled smooth and should be checked but I would never use a gasket as the high pressure could blow out the gasket and there goes your motor. Also check the service manual for the torque for the mounting bolt.

JR