Experienced Vette mechanics going nuts!!
Thread Starter
Pro
Joined: Apr 2005
Posts: 590
Likes: 0
From: Boynton Beach, FL
Experienced Vette mechanics going nuts!!
1990 one piece rear seal L-98 race motor runs all day on dyno, no rear seal oil leaks, runs on race track and rear seal leaks like sieve. Inside of bell housing soaked. WHAT COULD CAUSE THIS??? Pro built race L-98 ran at least half a dozen track events before developing a slight rear seal leak, small drop on floor after sitting in garage between races for a few weeks. Big problem developed overnight, went from small leak to soaker in one race weekend. Since then have replaced rear seal several times, including a crank sleeve and an off set seal. Replaced oil pan with race pan. After sleeve and new seal ran on dyno all day, no leaks, went to track, soaks bell housing again!! Crank never turned, good oil pressure. Its not the transmission either, confirmed by changing transmissons. This problem has more than a few Pro mechanics scratching their heads. Leaks on track, not on dyno???
Any thoughts??
Any thoughts??
Le Mans Master
Joined: Feb 2005
Posts: 5,146
Likes: 3
From: The Motor City
Originally Posted by Pete K
Excessive crankcase pressure? Low tension oil rings and no vacuum pump could cause this. Improperly seated rings could also contribute if it is a leakdown issue.
Race Director
Joined: Feb 2004
Posts: 12,518
Likes: 19
I have also seen the rear plug behind the cam leak. They have a skinny sealing lip and are the most difficult soft plug to install. I use blue locktite, and smear epoxy around the sealing edge of the plug after I install it.
Race Director
Joined: Feb 2004
Posts: 12,518
Likes: 19
Originally Posted by Corvette Kid NC
Are you 100% sure it's the seal leaking? Have you checked crank end play lately?
Thread Starter
Pro
Joined: Apr 2005
Posts: 590
Likes: 0
From: Boynton Beach, FL
Good suggestions guys
Thanks for the suggestions. Because engine has AFR heads with poor oil drain back, engine has two baffled breathers on each valve cover plumbed via large diameter hoses to a single over flow can. I'd be surprised if it was crank case pressure. If it was, I would think it would leak at the pan gasket and front cover before the rear seal. Crank is stock standard size journal Chevrolet mated to original factory block, not line honed. Crank end play is a possibility. How can you check on an assembled engine in car?
BIGGER QUESTION? Why can engine run on dyno under full load, in gear and not leak, yet run on track and leak.
Keep throwing out ideas guys. This one is a stumper.
BIGGER QUESTION? Why can engine run on dyno under full load, in gear and not leak, yet run on track and leak.
Keep throwing out ideas guys. This one is a stumper.
Last edited by Vetracr; Dec 8, 2005 at 08:30 AM.
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Melting Slicks
Joined: Nov 2004
Posts: 2,799
Likes: 2
From: Cape Coral FL
Stickshift or auto?
In the case of manual transmissions, the constant "in and out" of the clutch will cause the crankshaft to walk back and forth, especially in the case of hard use (track racing, etc.), which takes a heavy toll on the thrust bearing. This is very prevalent on higher mileage engines. Check the endplay of the crankshaft and if it's excessive..the engine has to come out. To check the endplay, you'll need a dial indicator and some means of prying the flywheel or damper (be VERY careful) back and forth.
Good luck!
In the case of manual transmissions, the constant "in and out" of the clutch will cause the crankshaft to walk back and forth, especially in the case of hard use (track racing, etc.), which takes a heavy toll on the thrust bearing. This is very prevalent on higher mileage engines. Check the endplay of the crankshaft and if it's excessive..the engine has to come out. To check the endplay, you'll need a dial indicator and some means of prying the flywheel or damper (be VERY careful) back and forth.
Good luck!
Last edited by RacerX70CC; Dec 8, 2005 at 08:57 AM.
Intermediate
Joined: Nov 2005
Posts: 31
Likes: 0
From: Bradenton Fla,
I see by your picture you are road racing. It doesn`t leak on the dyno when everything is stationary it only leaks when the car has side to side movement and is sloshing oil around in the pan ,leaking into the bellhousing and then after the car becomes stationary Shows up on the ground. I would look at the pan gasket or the piece that holds the rear main seal.