Mk.lll crank venting and primary leaks

Hi,

I imagine it could in extreme cases, but look elsewhere first. Incorrect assembly of the primary drive would be my guess of why it leaks. Then loose gearbox and / or engine mounting bolts that would allow the gearbox to move in relation to the primary drive, allowing oil to get past the clutch seal.

chris

check your primary oil level it should only be 200cc or 7fl.oz well below the height of the alternator grommet, I've had a blown crankshaft seal caused I'm sure by starting the bike with a sump full of oil.the piece of wire fitted as a circlip was not man enough to retain the seal also there was no spring or plunger in the timing cover both problems now sorted ,If you have too much oil and its not from an overfill and as you are going into the primary to change the grommet it may be an idea to take the extra hour or two to check that the crankshaft seal is in place

steve

Hi Chris,

As Steve says check the contents of the primary case, if its mysteriously over 200cc then you may have a problem. A quick method to check if the main seal has blown is; remove either of the primary inspection caps, and start the engine.(No oil will blow out ) then hold a piece of tissue or cloth over that hole. If the cloth/tissue puffs and blows then the seal is most likely gone. You can also hear it going chuff chuff !!

I hope for your sake its not, because its a bugger of a job, on a Mk111 anyway.

CheersHans

Hi Hans

You say replacing a priamary side crank oil seal is a bit of a bugger, which I will not dispute!

I think that almost certainly mine has gone as it appears to be leaking oil from the crank tunnel past the seal.

I have put a lot of work into fixiing primary side problems. Replaced sprag clutch, crank end gear, alternator, primary chain, rebuilt anti-backfire mechanism, rebuilt clutch, welded up and machined the the inner primary chain case bosses that the primary chain had eaten (fantastic job too, good to know an excellent engineer), new primary chain auto-tensioners, seals, refurbished starter motor etc.

To say that I am vaguely heartbroken to have to take it all apart yet again is a huge understatement.

I will now have had the primary apart 3 times if I have to take it all apart again. Worth noting that I was supplied incorrectly machined crank end gear, machined undersize; it's a known problem down in Andover (and they were very helpful)...and is why your new sprag clutch may only last three starts, like mine did...

Anyway, less of my moaning, do you know if it is possible to replace the primary side crank oil seal with the primary drive/alternator removed, failing that with the primary inner cover removed, without stripping the whole engine?

BTW Chris: if you have a MK3 electric start, the gear box alignment is adjustable. There is an adjuster on the timing side, to allow you to get the gearbox output shaft aligned with the inner primary case seal etc. It is just above the cases hidden away on the frame. I adjusted mine, it appeared to have dropped over time so the gearbox output shaft oil seal was never going to...seal that is. Anyway it adjusted pretty well to be honest, be aware that it is a four handed job though.

I used good ol' silicon sealant on very clean cases to fix the alternator cable leak, and for the first time I had a dry primary side!!

Previously hans_taylor wrote:

Hi Chris,

As Steve says check the contents of the primary case, if its mysteriously over 200cc then you may have a problem. A quick method to check if the main seal has blown is; remove either of the primary inspection caps, and start the engine.(No oil will blow out ) then hold a piece of tissue or cloth over that hole. If the cloth/tissue puffs and blows then the seal is most likely gone. You can also hear it going chuff chuff !!

I hope for your sake its not, because its a bugger of a job, on a Mk111 anyway.

CheersHans

Previously jack_blakemore wrote:

BTW Chris: if you have a MK3 electric start, the gear box alignment is adjustable. There is an adjuster on the timing side, to allow you to get the gearbox output shaft aligned with the inner primary case seal etc. It is just above the cases hidden away on the frame. I adjusted mine, it appeared to have dropped over time so the gearbox output shaft oil seal was never going to...seal that is. Anyway it adjusted pretty well to be honest, be aware that it is a four handed job though.

Jack, never heard of this and I'm 100% positive my bike dosen't have this feature. Are you sure somebody hasn't modified your bike, as standard, the Mk3 'boxes are in a fixed position to the cradle as primary chain tension is taken care of by the hydraulic adjuster.

Can you post any pictures or more info?

Hi,

I also do not have an adjuster for the gearbox, nor saw anything like it during the gearbox rebuild.

The crank seal maybe able to be replaced with the primary drive removed, but you need to fabricate or modifiy a scriber with 90 degree bend in one end so you can get the end of the wire circlip out of the groove. It you can do this the rest should be straight forward, though I have never tried it. It may not have a wirecirclip fitted, as it may have been omitted if the seal was repalced in the past. Maney racing does a silicon seal that is supposed to be better than original, but again I have not used it. It would be nice if there was a proper circlip that was known as a suitable repalcement.

Hope this helps.

Certainly can, I hope!

Previously simon_ratcliff wrote:

Previously jack_blakemore wrote:

BTW Chris: if you have a MK3 electric start, the gear box alignment is adjustable. There is an adjuster on the timing side, to allow you to get the gearbox output shaft aligned with the inner primary case seal etc. It is just above the cases hidden away on the frame. I adjusted mine, it appeared to have dropped over time so the gearbox output shaft oil seal was never going to...seal that is. Anyway it adjusted pretty well to be honest, be aware that it is a four handed job though.

Jack, never heard of this and I'm 100% positive my bike dosen't have this feature. Are you sure somebody hasn't modified your bike, as standard, the Mk3 'boxes are in a fixed position to the cradle as primary chain tension is taken care of by the hydraulic adjuster.

Can you post any pictures or more info?

As requested

Your bike has been modified from standard. If it helps to get the gearbox mainshaft in line with the crank drive shaft then all well and good.

Errr, no it hasn't, it's actually in the maual old lad...how do you think I found out?!

But I woudln't take it too hard, the lads at Andover didn't know either...

Previously simon_ratcliff wrote:

Your bike has been modified from standard. If it helps to get the gearbox mainshaft in line with the crank drive shaft then all well and good.

It's not in my genuine workshop manual, and dosen't feature on my bike (I'm the second owner bought at 17,000 miles) Are you sure you've got a Mk3?

The 850MkIII does NOT have an adjuster as standard. I have had mine from new.

I agree with Simon, are you sure your bike is a real MkIII ?

Simon: To be fair, it is the Haynes manual that this is covered in, and it's an old one at that! In fact after reading it, the Norton workshop manual says it shouldn't have one so that the gear selector shaft can't be misaligned, if I understand it correctly. So you are probably right, but it does work, if you are careful. Maybe it's a clever mod?!

Tony: "is it a real MKIII"; nope it's an ice sculpture, how silly of me...

It is a 1975, numbers matching, 850 MKIII ES, with an adjustable gear box. You have seen the photograph.