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2JZ CRANK SEAL
Lance M Wolrab
December 29th '04

BACKGROUND
All oil pumps build increasing flow with increasing rpm. It is inherent in the design. The Supra oil pump has (as most OEM oil pumps do) a piston type valve with a spring behind the piston. When the pump pressurizes, the piston compresses in its bore against the spring. The spring determines the ultimate pressure the pump will create, because the piston's bore has a hole drilled in the side of it to relieve the pressure once the piston compresses enough. In the Supra's case, the hole that is bored in the side of the piston's bore isn't large enough to flow the amount of oil necessary to control pressure at higher than stock rpm, so the pressure just keeps rising. Eventually something has to give, and it is usually the oil pump seal (which is technically what members are calling the crankcase seal).

The oil pump is concentric with the crank, so there are only four seals for the engine: the two cam seals, the oil pump seal, and the rear main seal. When the oil pump seal goes, the other seals have also been stressed, but not as hard, and the oil pump seal is right at the heart of the problem, so it sees a higher pressure than any other part of the engine. It fails, and typically dumps a LOT of oil very quickly.

SOLUTION
Forget the oil being "dirty", at 1400 miles it has hardly had a chance to suffer any damage at all. What needs to happen to resolve the problem, is the oil pump needs to have the pressure relief valve return hole enlarged to flow enough oil to keep the pressure under control. A superior seal will only cause one of the other seals to fail, and you will end up chasing your tail until all the seals are super tight (not good for seal life, very bad for horsepower, and pressurizing the oil excessively only leads to even more power loss. You shouldn't see more than 80 psi ever, and I would set it up to run 75 psi.

I would also run a temperature sensor on the oil sump to know when the oil is up to temperature. Cold oil makes a LOT more pressure than hot oil, so even properly modified, it is possible to make too much pressure and blow a seal if you run an engine with cold oil up to redline. The BMW M5 has a variable redline for just this reason. As the engine warms up, the redline goes up. The same is true for 2JZs that have altered the stock redline (even a stock engine with heavy oil jeopardizes the oil pump seal when revved hard while cold). As I recall, Jason Chien blew his oil pump seal on a basically stock TT Supra while racing a bike on the freeway, so this isn't unique to high power Supras, but it is certainly a LOT more common.

Lance

The above article is copyright Lance Wolrab and TO4R.com and cannot be reproduced in any way without written permission from the author.

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