Making mainseals seal

Lots of flywheel seals get replaced and still leak. The primary reason is that the f/w has a groove worn in the seal race, this being much more of a problem with wbx’s than it was with older VW boxers because they tend to be left in the vehicle for two or three times the typical rebuild interval of aircooleds. When you do this job you must be sure to inspect the f/w hub surface or you may be doing the job over.

.

Repositioning the seal at a different depth by using a 10mm deep seal will not help, 2mm isn’t far enough to put both seal lips on smooth race, instead it will probably wear the new seal quickly, not that longevity matters when it’s also still leaking, so in you go again.

.

My standard is if the groove on the sealing race is deep enough to catch your fingernail in, it’s too deep to fix up by simple means. Shallower than that, and you can make the seal race like new again, by spinning it and using progressively finer abrasives to rework the surface to a bright polish.

.

Backing up a bit: when you have a flywheel in hand you should take the opportunity to have the clutch friction surface reground if it isn’t smooth or is deeply and unevenly blued, especially if you are replacing the clutch disc. This is one of the most routine jobs automotive machine shops do so any one you can find should be able to help you. However, I’ve asked a few machinists if they would regrind the sealing hub for me and the answer has always been no.

.

It is possible to install a redi-sleeve, a very thin tube that can be driven onto a hub like this and trimmed to fit. That’s a reasonable alternative to replacing the f/w if the groove is deeper than can be hand-ground out. A redi-sleeve will cost almost as much as a f/w resurface, they’re not cheap, but added together it’s less than a new f/w.

.

To me a sleeve is a last-ditch and less desirable fix, though, when for a half-hour of work you can grind (sand) out a shallow groove and ensure the seal seals.

.

The FW can be set up in a lathe or other device to turn it steadily (I did my first one by hand bolted to a crankshaft and that laid in V-blocks, but when that worked I made an adapter for my lathe). It could be a rod laid across two tables or crates brought close together, some peope have jigged it up to a power drill (careful, f/w’s are heavy!).

.

The groove is abraded out and polished by using successively finer grades of abrasive paper or cloth (emery is preferred for steel), lubricate generously with WD40 or something light. Start with a 40-grit until you can’t feel the groove, then work with progessively finer grits up to 1200 or 2000. Take your time and get it to as smooth and bright a finish as possible. Rinse with WD40 and wipe with a clean rag a few times when you’re done to lift any abrasive.

.

Extra points: buffing after that with a cotton buff and compound suitable for steel (green) can bring it to almost a mirror finish. Your seal will be skatin’!

.

This will remove surprisingly little material and have a negligible reduction of the hub diameter, so there’s no worry about making the hub too small for the seal. A seal has a specified fit range of at least .006-.008″, in real life it’s much greater, while this grinding job typically removes no more than .002-.003″

Submit a Comment

Your email address will not be published. Required fields are marked *