Help! Rear main seal mystery

[marathon26]

I took my '89 in to have the have the rear main seal replaced. They replaced it, but it was still leaking. They took it back apart and found that the seal does not seal on the top of the crank shaft. I went to the dealership and had a look. The solution is to take out the guide dowels and put it back together and see if it will make a better seal. My question is - after all this time how could the block be out-of-round so that the seal will not form properly to the crank or do they have a bad seal?

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[vetteoz]

My question is
after all this time how could the block be out-of-round so that the seal will not form properly to the crank or do they have a bad seal?

I would be checking seal 1st

Seal is not in the block.
Seal is in the alum housing bolted to rear of block
Seal ( grey ) can be seen in pic between crank and alum housing

 

[marathon26]

Installing new seal today looking at some other options. I'm still puzzled as to how this could have been OK for all these years and now be out-of-round.

 

[Curious George]

Installing new seal today looking at some other options. I'm still puzzled as to how this could have been OK for all these years and now be out-of-round.

Nothing is "out of round". The crankshaft may have developed a "wear notch" due to age and other variables. This is not uncommon in high mileage engines. If this is the case, you can buy a rear crankshaft sleeve that goes over the end of the rear crankshaft and provides a perfectly flat surface for the new seal to mate with. They are cheap and work great.

Chevy / GM 4.3 5.0 5.7 Rear Crank Seal Repair Sleeve EXCEPT LS1 LS6 346 engines

Also, there are two different types of rear main seal material - Teflon and good old rubber. The Teflon seal is a hard(er) type seal and seems to be OK when used from the factory. I prefer the rubber type seal because it is more forgiving when being put on. The Teflon one requires great care when assembling the "rear seal appliance" or it could be damaged.

 

[marathon26]

The second seal seems to be working

The second seal seems to be holding. Now just need to get a few other mistakes that they made fixed. Thanks to all for the help.