So, this is a 20k mile 12A Mazda reman, that's used in an IT7 racecar.



Last season worked great, ran strong. No changes to the setup, this year first track day, it leaks alot of oil out of the rear main, it seeps past the inspection covers significantly, and it drips on the ground significantly after each 20 minute session.



The crankcase is vented to a non sealed catch can. No change from last year.





Is this a common sign that something's wrong internal to the motor? Like a broken side seal or something pressurizing the oil system and blowing oil past the seal?



I still need to do a comp. test and pull the motor to look at the seal. Just wondering if I need to be worried about something more than a bad seal.



Thanks,

Neil

 

It sounds like there's a tear or rip on the main engine oil seal. TO get at the rear main oil seal, you got to drop the tranny. Remove the flywheel and you will see a big rubber seal. It's most likely orange if it's been rebuilt recently. You need to replace that. When you do replace it... make sure you apply a liberal amount of oil to coat the thing so you don't nick or tear it when you push the new one in.

 

Most likely rear main seal but while you have the tranny down and flywheel off go ahead and pull the rear stat gear out and change the internal o-ring that seals the stat gear to the rear iron. They can leak as well and gush massive amounts of oil when they do. Hate have you drop the tranny twice to fix the problem.

 

id look closely at the flywheel where it seals against the seal.



usually dont see rear main leakage, maybe it got pinched a little on installation

 

Long ago there was no money and stock pans and pumps. There would be this problem when old seals would not. And excess oil would be thrown about. The tiny breather tube in the oil filler is way too small.



A piece of 1/2 electrical conduit brazed into the filler neck is just right. Then a hose run downhill to an open catch tank. The new seal can be perked up by removing the spring. The small end is screwed into the big end. Unscrew it and shorten the big end about 3/8". Screw it back together winding it backwards first, so it stays screwed together. Replace the spring. Install the seal. A bit of hand cleaner on the outer surface lets it glide right in with little fuss and no damage. Add some grease between the lips (stop it you savage) so that the seal will not start up dry.



Now you can crack a corner seal or side seal and not fill the catch tank. You can race a very tired engine and not fill the tank. You can reuse that stationary gear in several engines and never change the seal.





Lynn E. Hanover

 

Thanks for the info.



I'm not 100% sure what you mean about shortening the spring, but I'm going to see if I can figure it out this weekend.



On another note, it sounds as if you are saying that a tired engine, or one with a broken side or corner seal can pressurize the oil system and cause leaks?



Thanks,

Neil

 

The inner seal lip is loaded with a small diameter spring, to help apply pressure to the seal lip. Another lip faces outboard to keep dirt out. It has no spring. The grease (between the lips) makes for very long lived seals.



Regular amounts of blowby gasses get past the seals, even when they are fresh. As the engine seals wear out that blowby gas volume goes up. The increase in gas going through the same breather hole size makes for a higher velocity (Bournulli) and thus carries away more oil vapor with it into the catch tank. One way to slow the velocity and reduce the amount of oil blown out of the engine, is to increase the diameter of the breather tube. Larger tube diameter with the same gas volume= lower velocity, = less oil in the catch tank.

Larger breather tube diameter= less pressure in the crankcase, = less oil passsed the rear main seal.



I grind out the oil return hole in the rear stationary gear for better oil return and less of a pile of oil jammed up against the rear main. On hard accelleration, the oil gets real deep back there.





Lynn E. Hanover

 

Please Archive this important thread

 

ok

 

Neil,

Also take a look at your rear stationary gear "O-Ring" They will crack and you may think its a rear seal. Look for leakage between the stationary gear and the rear iron.