Crank Oil seal failure and roller bearing mod

[morini_tom]

My 501 ate a crank oil seal at Cadwell. Anyone seen this before? some details:

Engine rebuilt in 2007/8, new seals throughout (obviously)around 4000km covered since.

Engine is a late 501 with the alternator side roller bearing modification.

The crank oil seal face is completely detached from the rest of the seal.

There are radial cracks inward from what I think is the seal lip edge (a bit hard to tell on the mangled strip which is left) which look like the rubber has perished and cracked, but the rubber feels supple still so this could be secondary damage I suppose

I cant feel any play in the crank bearings.

I had a look at my spare 501 motor (also with roller bearing conversion) to get the oil seal code, and discovered that this seal also shows signs of damage. There is a clear witness mark around the seal face, and has split all the way through around 1/3 of the way around (see photo below- this is the seal from my spare motor, but the failure mode I suspect is the same as happened at Cadwell).

Maybe the dished washer behind the timing belt could have been rubbing on the seal, but how? Crank axial expansion in the roller bearing pushing the seal against the lower pulley/dished washer?

I'm reluctant to replace the seal blindly if this is going to keep happening- it's not the sort of job I want to add to 'service items' Has anyone else experienced this, particularly on engines which have had the timing side roller bearing modification?

And while we're at it, can someone tell me the correct code for the crank oil seal, as both of mine are damaged beyond reading. In fact, I might replace all of the external seals just in case- if anyone has a complete list of the codes that'd be handy!

[Steve Brown]

Hi Tom, surprised no-one else has responded to this. I can't comment on the modified bearing issue as I've never done it or seen one done, but for the seal can you not measure the relevant dimensions when the engine is in bits? I took a look at the 350 parts list (as I don't have one for any 500/501's) as it might well be the same size seal used??? The dimensions given there are 30x40x7 mm.
Ref the seal damage, I would guess as you suggest it was secondary-can you post pics of the damaged cranks? In my manual it also mentions the positioning of the seal in the casing, the most of them being placed 2mm back from the outer faces.
Another thought, that seal in your pic above looks like a double edge seal? Hard to be sure with my eyes but they are often a bit thicker at least where the extra lip is and when I have tried them in a couple of cases they foul something else or are just a pain to fit over their shafts.
Good luck with finding the cure and letting us all learn from it!

Talking of learning, I just re-read your post properly and see that the seals are the only casualty now... so now I'm thinking more along the lines of wrong seal or wrong positioning of the seal. Still like to read what you find though!

[MickeyMoto]

That would be my suggestion, that the oil seal ios the wrong size, but as this appears a common mod why hasn't anybody else seen the problem?

[morini_tom]

Thanks for the replies-

The oil seal is a 30 40 7. There's certainly not 2mm clearance between the seal and the dished washer, and I'm convinced that these contacting has been the cause.

I've not extracted the damaged seal yet but the edge is more or less flush with the outside of the crankcase. From memory the 40mm bore in the crankcase is all the way through so I don't want to push the oil seal 'home' to find out if its been moved outwards.

The roller bearing sliding inner race is about 38mm diameter so this moving on the crank (or large crank end float) could cause this to push the oil seal, but no evidence of it having moved on my spare crank and the end float feels fine. The original plain bearing journal of course is larger so even with massive crank end float it couldn't touch the seal (it'd hit the crankcase first!)

I'm going to try a 30 40 5 oil seal and see how that copes...

[morini_tom]

Okay so I've now had a better look and I'm afraid it's terminal. Engine rebuild for me this autumn!!

The oil seal itself was more or less completely destroyed, the metal inner was stripped of all rubber and what rubber was left was very brittle. The crank has blued beneath the oil seal, and the oil seal impacted upon the back of the dished belt guide washer:



all that's left of the seal:


Now the telltale sign that means I have to pull the cases- The inner race of the roller bearing has moved ~4mm outwards on the crank, squeezing the gap for the oil seal down from 7mm + clearance to 4.5mm. You can see in the next photo the blued taper on the crank, then the diameter which the seal runs on, and then only a few mm further back the inner bearing race which is as I say a good 4mm out of place:



I'm keeping my fingers crossed that the plugs I put into the crank oil gallery where the bearing journal was are still in place, otherwise I'll have oil starved bigends too...