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Flywheel or "Rear Main" Seal Story

All seals are equal, but some seals are more equal than others.

The "rear main seal" on VW flat four engines (all of them) does not actually seal against the crankshaft. Instead, the flywheel bolts to the back of the crankshaft with an O-ring in between, and the lip seal (pictured) seals against a polished surface on the flywheel. The flywheel seal on all 72-79 Buses and all years of the Vanagon air and water cooled flat four engines (not diesel, which is just a Rabbit/Jetta diesel engine) all have the same outside diameter (OD) and inside diameter (ID). All the seals we measured had the same OD and ID. However, the thickness (front to back, or width) were different on two of them, and on one (the dealer part, which was, of course, the most expensive by a factor of about 10) had a substantially larger diameter spring wire diameter (22%). Why are we talking about this?

An Aftermarket seal on the left, OEM seal on the right.

Well the most common problem we have to address on the waterboxer engines we build are flywheel seal leaks.  This has been a reoccurring problem for years.  There are probably some of our engine customers reading this that know what I am talking about.  I had to replace the one on my own 2.5 a couple of weeks ago.  We have gone out of our way to make sure every flywheel we install not only gets the thrust surface ground perfectly smooth and square, but everyone gets the sealing surface polished to practically a mirror finish.  Even still, one in twenty of our engines, or so, would LEAK!  I just figured there must me something up with the seal.

So, I decided to buy one of every seal we could get our hands on.  In the process of my investigation, I heard all sorts of theories, like "You gotta use this super gee-whiz goop" or "You gotta put it in with a golden hammer" or "You gotta use the factory VW, OEM seal only available at the dealer for ten time the cost."  I had no trouble believing everything I was told, except the last one.  I KNEW that was BS...

Well, good thing I did not bet any money. Sure as $#%@, the damn VW dealer-only seal is the bomb! It was actually one of our shop techs that pointed out the difference to me. I wasn't sure if the guy was BSing me or not, so I had to go through this exercise. I should've just listened to him in the first place! 

Anyway, what we found was that the common seal that comes in ALL the gasket kits has two problems. The first is that they are too narrow (width) front to back. So, when you install them in a water-boxer, you can put them in too far, not far enough, or catty-wompus (that's technical jargon for eccentrically misaligned). We found one seal that was the correct thickness, a Victor-Reinz part that was all orange, and sold separately
—in its own box and everything. Interestingly, it is NOT the same seal that is included in the Victor-Reinz full engine gasket set. Go figure. So we thought, viola! We don't have to buy the stupid expensive seal at VW. WRONG. What our tech correctly pointed out is that the OE VW seal comes designed with a considerably heavier spring. None of the other seals have a spring nearly as heavy. Kudos to our shop tech, right? 

What is even more interesting about this VW dealer-only seal is that it is all black and it is made in Brazil (SABO brand). These two traits are typically what we refer to in the industry as... well... CRAP. But, you can't argue with success, right?

So, we bought every seal VW had in the United States. Starting about five engines ago, we have switched to the VW dealer-only seal exclusively. We are keeping track of which engines have them with an extra "dot" next to the engine displacement stamp we put on each GoWesty engine. Let's see if the seal is worth it. If it turns out to be the fix, I may have a trip to Rio de Janeiro in my future...

For now, if you need a flywheel seal for your water-boxer (029-105-245), we've got them! In fact, last I checked with VW, we got ALL of them! Get yours below!


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