What would cause the main seal to blowout?

[bigbird]

Rear main seal on my motor keeps blowing out. anyone know what causes a rise in crankcase pressure to cause this?

 

[JoshH]

Blowby or a cracked piston can cause higher than normal crankcase pressure. A blown headgasket could as well. You might want to check to make sure your crankcase vent tube(s) are not plugged.

 

[Turbotug]

Literally blow out, or just leak?

 

[Turbo Buick 6]

I had this prob on my 6.0 PSD, turned out to be from blowby on the rings. The cyls were washed down from running 40 plus timing. This was casued by the roll pin that holds the crank pos ring shearing off and haveing a lot of slop.....drove it for about 5000 miles like that. Was working and had to finish the job and get home to take the injectors and other stuff off

 

[JOHNBOY]

Are you installing with the correct tool?

Look at your PCV also. It is not pluged is it that will blow out the seal.