Rear Main seal failure and case pressure issues
A lot of people have trouble with premature rear seal failure . I have seen some of these types of issues through the year, But it is almost ever due to a bad seal . I would say there are commonly 3 things that lead to premature rear seal failure. Most often is case is case pressure, when we increase engine displacement and compression we are now making a higher percent of case pressure even if our leak down/ blow by is acceptable. An engine is basically one big air pump. We don’t want the compressed air to get in to the engine case. Yet, no matter what the instance some air will because no engine is 100 percent efficient. Even my personal engine that was showing less then 3% leak down per cylinder will build pressure. Again, this is and effect of us increasing the displacement and compression. There for we need to also increase the amount of crank ventilation. I personally like like the tower breathers, they are very clean looking and effective. The idea taken from the early Porsche idea.Both the empi and CB Performance box’s work equally with the berg box’s being superior. Yet, the berg box’s come at a high price point. I enjoy using the tower breathers because if done correctly you do not need vented valve covers. I personally don’t like all the hoses running every where and the hassle of valve adjustments with vented covers. It is not that big of a deal and some engines they are a must but I try to avoid them on my builds. Some thing I think a lot of builders miss is opening up the case internal baffling. After market cases do not have the same insides. When building a larger engine it is important to open up the walls that section off the case internally to that air/ case pressure and move through the engine instead of get trapped in one part of the case and trying to find its way out through the weakest link aka (rear main, front pulley, fuel pump, valve cover. ect) In the factory Bentley it shows when up grading from a 1500 to a 1600 you must increase the internal baffling hole from 13 to 15mm. So how much is necessary for a 2110? We also want to add some grooves for oil drain back, so the oil does not build up in places that it can leak out. Most after market cases do this decently well with add grooves by the front and rear of the engine.A front sand seal is a great improvement to Vw engine as it seals both extra air from entering the engine and oil from exiting the engine. The factory pulley had left hand grooves to help pull oil back into the case and make some what of an air lock. This has be found to suck in air and add to case pressure issues.
Another is very simple way for rear seal leaks is the end play. If the crank and flywheel is moving back and forth it is very easy for the seal lip to get flipped and leak past or tear the seal. Some times the seal can flip out the wrong way and flip back in. When inspected it looks fine but in fact it is weakened and must be replaced. Check your end play I really prefer .0035-.004 the spec Is .003-.006. PULL THE BELT OFF the alternator to check end play. People all the time try to so me the end play is tight with the belt on. The belt hold tension on the crank and will give you a false measurement. I only run .006 on race engines, I know a builder that runs .010 and I am always hearing about leaks from his clients.
The final killer we will cover is heat, once the seal is overheated it loses its elasticity and no longer will hold in oil. Always check or engine temps, external oil cooler and fan set ups are cheap insurance on any good engine even a 1600. Signs your engine is getting hot, hard starting, hard hut offs, engine dieseling or run on after the ignition is off, dark black oil on oil changes. The list goes on and on. The best thing we can do as owner is check our spark plug colors to see that the jetting is correct. Make sure our timing is in spec and our engine is not pinging or knocking with hard loads(climbing hills or long grades) or hard acceleration. Checking the head temps and case temps can also be another good indicator simply using an Infer Red gun.
While this is not ever issue that can cause rear main leaks it is what we see 9 out of 10 times.