Following a recent customer’s oil leakage problem, I have, with great cooperation from that customer, done some investigating in the area of the crankshaft oil seal.

It seems that there are two problems. Firstly, the oil seal is an imperial sized item with a 2” bore and it is designed to run on a 2” shaft - the shaft protruding from the Centa rotor, on which the seal runs, is only 50mm. therefore, 0.8mm undersize or 0.032” if you prefer. SKF, who produce this type of oil seal, recommend a much tighter tolerance in the region of plus 0 minus 0.01mm. The second problem is the surface finish of the shaft - as already pointed out on these pages - the finish is much too rough and in some cases badly damaged due to clumsy manufacture.

I have identified a cure for the problem for those wishing to use a standard Centa component. SKF produce a repair sleeve which can be pushed over a damaged shaft to bring the surface back to a useable state. Luckily for us it also increases the shaft diameter by 0.56mm bringing it much closer to the required 2 inches. The sleeves also have a surface finish designed specifically to promote good sealing and also good seal life. For reference, if you are fitting one, the seal lip and therefore the middle of the sleeve should be 15mm from the flywheel end of the shaft. The sleeve can be fitted complete after the alternator is bolted to the Centa rotor or, if you prefer, the flange can easily be removed from the sleeve and the alternator rotor fitted afterwards but be careful not to scratch the sleeve.

The old seals which I have examined after being used on the standard Centa shaft are all worn flat and need to be replaced at the same time as the sleeve is installed - not expensive so no point in not replacing it.

A stunning virtual bevel box which demonstrates all this and also the very simple method of fitting using the tool supplied with he sleeve, can be seen here :- https://www.youtube.com/watch?v=wsIklI3xtME

SKF spec :-
Part Number: 99196
Type: Speedi-Sleeve And Tool Kit
Part Information:
• Flange Diameter: 2.2440 in
• Shaft: 1.9690 in
• Shaft From: 1.965 in
• Shaft To: 1.971 in
•

I hope this helps sort the problem for people. I have posted it as a new post and on the end of the thread about the problem

Good luck,
Phil

Awesome post Phil. Thanks for doing proper research on the subject.

Just another little tip - if you decide to fit one of these sleeves over a shaft which has the chuck jaw marks present then make sure you file them down before fitting the sleeve. The sleeves are thin and any bumps underneath will show up as ripples in the surface of the sleeve.

Good info Phil, thanks. That will help explain the frequent crankshaft oil leaks, along with the chuck jaw damage to the shaft. Can I have a sleeve fitted when I bring my engine and Centa to you next month for mods please? It sounds like a sensible thing to do when it's all apart.

I took a couple of photos while Phil wasn't looking.

This is the sleeve along with the metal container which is used to tap it into position.


And, here is the sleeve fitted to one of Phil's super shafts.


Note, this photo also shows Phil's modified, turned-down socket-headed bolts which allow a decent size allen key to be used compared to the somewhat fragile originals. Also note the rebate in the end of the shaft to take an o-ring.

No problem but in future all of my Centa spline upgrades will be the right size and finish!

Oh, and thanks Bunny - I never remember to take pictures, or is it that greasy hands and cameras don't mix? Anyway, maybe I should make you my official photographer?

The right size and finish sounds just right, I will go with that then please