Clutch oil seal and sleeve gear bush

[Phil C]

Rupert Ratio (vol 1, p.125) says " For some reason the rubber lip of the seal has a propensity for wearing a groove in the early type bronze sleeve bushes; result, another leak. The only permanent cure for this is to change the one piece bronze item for the later two part steel- backed items."

Would I be able to see any such groove by removing the clutch and the back plate and sprocket? And I guess replacing the bush would mean removing the gear cluster (from the timing side, presumably)?          Phil

[AWJDThumper]

With the chaincase backplate removed, you should be able to see whether the bush is grooved. What slightly confuses me with these bushes is that some of them are split down their length presumably to make insertion easier. The picture shows bush 41-3045. If the bush is split like this, I find it hard to see how this is going to seal properly or prevent unnecessary wear in the clutch seal. Might be worth looking closely to see if your outer bush is split. Unfortunately, you have to take the gearbox apart to replace these bushes.

[Phil C]

Thanks, AWJDThumper. When you say chaincase backplate, do you mean the circular plate behind the clutch - the one that's held in place with BA screws? Phil

[AWJDThumper]

Yep - Looking at the parts book, the official title is cover plate!

[Phil C]

Here is a photo from when I had the clutch off in about June/July 2018 in search of the oil leak. There appears to be a groove. Looking back at what I said on this forum at the time, when I slid the seal over it, although it was a very easy sliding fit, I could feel no play. And I guess it would be a slightly tighter fit once it had been pressed into the circular plate. But I wonder if it would loosen as the bike heated up.

Does the fact that a groove is visible mean it's a likely source of a leak? Should I replace the bush?

Phil

[Blackthou]

I'm not familar with this set up but the split bush is a DU bush. They normally press into a housing and remain static with the shaft in the bore rotating hence the coated lining. A split bush will never seal on its OD and only wear the oil seal out more quickly. The split is there to help distribute the oil along the length of the journal internally.

A plain rotating bush will still wear a flat on a single lip seal, which over a much longer time will leak. They also age harden and leak. Modern seals are more forgiving. Depending on available space it may even be possible to fit a double lip seal which would help no end and counter the wear track from the original single lipped seal. The mark is probably just "polished" unless a distinct groove can be felt. If it is a poish mark a new seal would probably cope with it and seal.

In such an application, usually, the bush if rotating inside the oil seal would be hardened and plunge ground as the oil would track down a conventionally ground bush.

If the bush is a pressed onto the shaft, it should have a smooth outer and be a slight interference fit. 

[Phil C]

Thanks, Rick, but I'm sorry to confess that quite a bit of that I didn't understand. Remember I'm a novice at this. But enthusiastic and keen to learn.
At the time I took the photo, two years ago,  I fitted a new seal, which was a loose slide fit but without any discernible play. Didn't cure the leak.
Should I remove the clutch again and have a close look at the groove/ mark?
Any thoughts, anyone?
Phil

[Blackthou]

No probs Phil. Don't worry about the terminology.

As I said, I'm not familiar with this part of the bike. I assume the oil seal is stationary in the cover plate and the shaft rotates inside it. Is there a bush on the gearbox output shaft? Does it have a longitudinal groove as AWJD said? If there is a bush it can be changed to eliminate the groove. It would also be possible to get a new plain bush manufactured and hardened locally by a local engineering company. Cheaper to measure the outside and inside diameters plus length of it and go to a local bearing supplier. They have catalogues of variations of that diameters in many formats. Very cheap too. We've got to determine too what you need. If the bush is on the shaft it should be a snug fit otherwise oil can track through it internally.

Did you consider the oil level screw? Easiest and cheapest to check.     

[Blackthou]

Also the seal. The size will be written on it in raised letters, for example 11/4" x 7/8" x 1/4" meaning outside diameter, inside diameter and thickness. Again the jolly old bearing supplier will have catalogues of seals. You may be able to find one of the exact dimentions but be double lipped as opposed to single lipped - meaning twice the sealing capabilities, or alternatively be able to accomodate one slightly wider depending on how the seal is retained.

For the amount of work involved could you put up with it until you need to strip it all down? I'd be happy to walk you though the steps when the time came.

[Phil C]

Thanks Rick. I'd feel much happier if I knew for certain exactly where the leak is coming from.  Phil

[AWJDThumper]

I would definitely confirm where the oil is coming from first - as said, use either dye or red coloured ATF oil to do this. My money would still be on a gearbox leak though.

I'm not sure that a small groove in the 4th gear pinion bush would cause the leak provided a new seal was fitted at the time. Sometimes, you find that the outer bush is slightly displaced outwards and it might be possible to tap it further into the pinion moving the groove away from where the seal contacts it. Might be something worth considering before you take the gearbox apart.

[Phil C]

Okay, thanks, well I think I might try again wiping off any oil that's showing at the moment, then draining the pc, and going for a ride with it empty. If there's no leak evident when I get home then that should tell me it's pc oil that's leaking, not gearbox. I've done this once but I guess it won't do any harm to do it again. How far can I ride with an empty pc without causing any damage? Would about, say, three miles be okay?  Phil

[Phil C]

Further to my post of a few minutes ago, I've also just ordered some dye. Phil

[Greenfield]

Hi Phil
The new replacement bush is in two parts. The part nearest the clutch should stick out 3/8". This rotates inside the gearbox sprocket cover oil seal which will wear because of the split. The split should allow a tiny amount of oil to penetrate which should reduce wear. Because the outer shell of the bush is steel there should be little wear in this. The felt washer is quite often missing on these bikes. This will take up some oil and prevent grit getting into the oil seal. Have you checked whether oil could be getting around the layshaft bush (just below and behind the bottom teeth of the gearbox sprocket in the photo. Note the felt washer.) The layshaft bush sits below the oil level of the gearbox.
For some reason the photo has reversed itself so don't let it confuse you.

[AWJDThumper]

Okay, thanks, well I think I might try again wiping off any oil that's showing at the moment, then draining the pc, and going for a ride with it empty. If there's no leak evident when I get home then that should tell me it's pc oil that's leaking, not gearbox. I've done this once but I guess it won't do any harm to do it again. How far can I ride with an empty pc without causing any damage? Would about, say, three miles be okay?  Phil

I don't think a 30 minute ride is going to do any harm with no oil in the chaincase!

From an engineering point of view, it's difficult to see how significant oil can seep out of the chaincase unless there's a gross problem with a seal. It's not as though it is pressurised or there is huge amount of oil in it (140 cc)!

However, this can change if the LH crankshaft seal is not doing its job. If this was the case, it would not only lead to pressurisation of the chaincase but could also let engine oil leak into the chaincase increasing the amount of oil there. I thought I read earlier that you might have found more oil in the chaincase than you expected which might be due to someone putting the wrong amount in but could be due to a leaking crankshaft oil seal. The way to check whether the chaincase is being pressurised is to remove the clutch adjustment plug, run the engine and see whether you can feel any pressure pulses out of the hole.