[sethryder]

Hey guys,
I bought a sled with a burnt piston so i was going to replace the outer crank seals/ oils seals among other things. When i pulled off my clutch and stator, the seals behind them looked ok. There was no obvious cracks, rips, wear marks etc and they seemed to be tight up to the crank shaft. What are the odds that they could still be leaky? Sled is a 91 indy 500 with 6000 miles.

Thanks for your expertise

-Seth

 

[BC_Dan]

With 6000 miles on the engine, I would definitely replace them if you have the engine apart. It's good maintenance. Seals that are bad sometimes don't look bad, about the only way you can test the seal is to spray some starting fluid or carb cleaner on the seal when the engine is idling; a change in idle would indicate a leaking seal.

There are other reasons a piston can burn down besides seals or carb boots. The fuel could have had some debris that clogged the carb or a jet could have iced up, for example. Or varnish build-up could have reduced the diameter of the jet to make it effectivly smaller in size. Sometimes it's never really determined what caused a piston to go. Even bad gas can do it.

 

[kccats]

You'll never see a problem with a seal. Also check the carb boots!

 

[sethryder]

thanks guys, i split the case. As far as replacing the oils seals go... do i just pop out the old seals and slide on new ones? Is there a trick to getting the new seals into the grooves? Also, i believe im suppose to grease the inside of the seals. I have mobile 1 from when i grease my car. Is this ok or should i get a different grease that may be better at lower temps?

thanks!

 

[BC_Dan]

That's pretty much it. Grease with a low-temp grease, Mobile 1 should be fine. Make sure the lip on the seal is oriented correctly, do one half, then the other. Not sure on your crankcase, but some have a locating pin in the crank that goes into a recess in the upper crankcase. Use the right kind of sealant on the case halves, you don't want a material that is too thick. I used to use Threebond 1104 but that product has been superceded by something else, not sure what. Yamabond was another good product, it's probably obsolete too

 

[IRONDOG]

You'll never see a problem with a seal.

Have to respectfully disagree on this statement- seal problems are common.
Jerry

 

[RJ Gleason]

^^^^^^^^^^^^^^
I think he meant that you can not visually see if the seal is bad (usually).

 

[IRONDOG]

^^^^^^^^^^^^^^
I think he meant that you can not visually see if the seal is bad (usually).

OK, I see what he means now. I jumped to the wrong conclusion.
Jerry