I have a 66 445 stroker, completely machined and built by a reputable shop here in Mass that does a lot of FE stuff, scat crank, roller cam, Rubber main seal, Tuned and initially run on their dyno. No leaks or issues, Finished and installed around 2024, running original C6.
Shortly, like maybe 50 miles, a small leak starts showing at the transmission inspection cover. We spend weeks checking everything to make sure it is not something else, after confirming it has to be the rear main, the builder comes to my garage and replaces the rear main in the car, Nothing changed.
Pulled the motor in 2025, and sent back to builder, he disassembled it and checked everything, does not find anything out of the ordinary. Puts a new rubber seal in, puts it back together and on the Dyno for testing, after a couple pulls the rear main burnt and started leaking.
Builder Disassembled the motor again and rechecked everything, this time it is reassembled with a graphite rope seal, put back on the Dyno and tested with 12-15 pulls over 2 days with no leaks.
We installed the motor this weekend, and after less then five miles of shakedown in the neighborhood, i put it back on the lift and it’s leaking at the rear inspection cover again, this time the oil is black, I assume it’s the graphite and oil from the rear main.
Any helps and thoughts would be appreciated.
A couple things I wonder:
Could it be crankcase pressure? On the Dyno i noticed valve covers are open, no breathers or PCV, on the car I run it with a breather in one cover and PCV in the other.
Could the rope seal take time to fully absorb oil and seal better.
Should I try running without PCV, and just 2 open breathers?
