OK, I'm in need of either some advice or a psychiatric exam or both.
I have replaced the rear main in my GMC 302 motor 4 times in an attempt to stop the
GMC continuous undercoating system and so far all have been unsuccessful.
I have used each of the following seals:
1) FelPro original GMC rear main seal
2) FelPro "new & improved rear main seal with teflon/graphite impregnated rope
3) Tom Langdon's NOS asbestos rope seal
4) Best Gaskets new square rope braid with teflon/graphite impregnation.
All have failed and my rear main leak continues.
Here are my thoughts and tenative plans, but I'm really looking for some solid advice from those of you who have been through rear main hell with a GMC engine before. I've been playing with old GMC's a long time, and I keep telling everyone that I have never seen a rear main that didn't leak; just some leak more than others.
*I'm going to pull the engine and get it on an engine stand (AGAIN!).
*I'm going to use a good dial indicator to measure the runout in the seal surface on the crank. The surface showed a wierd "scrub" mark on it today while replacing rear main seal #4 (Best brand gasket) which almost lead me to think that maybe the crank has some wobble in it. I measured it on the truck with the rear main cap off (obviously) and it showed about 4 thousandths of runout, but the dial indicator setup was less than ideal.
*I'm going to have the seal surface polished as if it were a crank in hopes of maybe finding some runout/play and removing it.
*Is there an oversized seal that is available for these motors?
* I'm going to hang myself in the shower if this doesn't fix it. This is the 4th time in 6 months that I've had this motor apart attempting to seal up the rear main.
Engine runs like a bear and is everything I would ever want in this truck, but this rear main is splashing oil at an impressive rate of about a quart/1000. That's just too much and not to mention what a mess it makes of my undercarriage and canvas top.
Who knows the secret to ending rear main seal hell?
Here's a shot of the rear main cap with the NOS Asbestos Rope seal immediately following removal today:
As you can see, the wear on the bearing surface looks good, the sealed parts look very good, and even the rope gasket is properly seated. So how the H - E - Double hockey sticks is oil slipping by this thing?
Here's the installed Best brand "square rope" seal which I thought was great. In fact, I think it is great, but for whatever reasons, my motor is giving my fits and even this very well designed seal is leaking.
The only plausible explanation I can think of is if the runout in the rear seal surface is out five thousandths or so, it might scrub the seal back on one half of the pass, and then allow oil to slip by on the next half pass. I dunno but I'm about ready to fall on a sword and end this torture!
Help!
