Question for Duke Williams

[Terry R. Payton]

Your post re: oil leaks, rear main vs. pan gaskets/leaky valve covers etc. has really helped me. Also, you stated that the old rope seal type usually does not leak from the start...well, my 283(rebuild) has leaked from the start(now 1400 miles later still leaks-has the rope) Am I totally hearing you correctly that my problem may not infact be the rear main?Just need a little confirmation here and thankyou for your expertise.

[Duke W.]

Re: Question for Duke Williams

Take off the inspection cover on the bottom front of the bell housing and check the front of the flywheel. If it is dry, then the leak is probably something other than the rear main.

The rope seals usually work, but often start to seep slightly at about 50-75K miles, but I think they are blamed for a lot of leaks that originate at other sources. In particular, very slight leaks may not lose enough oil to drip below the source, but, as was the case with my Cosworth Vega, the oil may migrate along the pan rail to drip at the lowest spot of the engine, which is at the back of the pan.

Isolating a leak begins with getting the engine completely clean and free of any petroleum residue. I use Gunk. Treating suspect areas with talcum powder, as John H. recommended is a good idea. You can also buy indicators to put in the oil that will show up to a "black light".

The tricky part of diagnosing the leak on my CV was that in order to see the source, the cam drive, covers, and camshaft sprockets had to be removed. Once I did this the evidence, although slight, was there - a very thin film of oil and just a bit of dirt right below the cam seal behind the inlet sprocket. The area behind the exhaust cam sprocket was bone dry and squeaky clean.

The message here is that just because the leak is at the rear, it's not necessarily the rear main - particularly if the leak is very minor. If could be that oil is just slowly migrating down to the lowest part of the engine from another source.

Duke

[Joe L.]

Re: Question for Duke Williams

Terry-----

A few comments:

1) A replacement neoprene or fluroelastomer seal is available for Chevrolet small block engines originally using rope seals. It's not available from GM but is available through aftermarket sources.

2) Usually, a rear main seal leak will be seen as a drip (with the drip rate varying depending upon the severity of the problem) with the engine running.