mcweens

I have an 87 IROC with a rebuilt 406 ci small block. The problem is I do not know which rear seal to use. When i first built the engine, i used a Felpro 2900, and about a minute in to the break-in, it started gushing oil out the back of the engine. When i took it apart, the rear seal had spun and there was about an 1/16" gap between them. We then replaced that seal with the Felpro 2909, the rear seal meant for blocks that have been block aligned bored/honed. Now about 100 miles in, it too is leaking, very severely in my eyes. Obviously, i once again have to pull the motor and replace it. I haven't discovered why the rear seal is failing now, is it the wrong one? To my knowledge, my block has never been align bored, but as i said before, the 2900 gushed oil a minute after running the engine. Which Is the right seal, or is there something i'm missing?

Jorlain

iTrader: (4)

If your block has not been line honed, the 2909 will leak as the bore is smaller than what the seal was designed for.

The best thing I can think of, is imagine going down a Slip 'n' Slide without any water. That's what's happening to that seal on first start if it's not lubed adequately.

2-Piece blocks are a PITA to pin down, because it seems like they always leak. My suggestion would be to try the 2900 again, but lube the seal lip\crank thoroughly to ensure there's no dry time. Preferably with something like assembly lube. This will do two things - ensure there's no dry time on the mating surfaces, and prevent the crank from grabbing the lip and ripping\spinning it.