Oily Roadster....

Alright Paul,

on the left hand side it's either going to be primary chaincase or gearbox oil. Gasket between inner chaincase and crankcase can blow, I've binned this gasket and use a light smear of Loctite 5699 flange sealant (grey colour). On a 750 there's only the felt(?) seal arrangement on the gearbox mainshaft and as you say the sleeve gear spacer seal, which should be replaceable as you suggest. Don't know about any mods for the felt seal arrangement as I've got a Mk3,

Simon.

Previously paul_smith wrote:

Hi all,

I'm getting a lot of oil over the back left hand side of the bike - I think the seal behind the front sprocket has failed - can I replace this from the sprocket end, by removing the clutch, then the sprocket?

Any other ideas for the source of the nile?

Bike is a '72 Roadster, Combat.

Regards - Paul.

Hello Paul,

Just had a similar problem with my 1974 850. Got back from a ride and found it had used even more engine oil than usual. Oillevelin chaincase had risen. Found a lot of engine oil on left leg of centre stand etc.. Cannot see any obvious source. I think that it is blowing oil mist through main bearing into chaincase and from there going out rear of clutch onto gearbox sprocket/chain and being flung onto surrounding area.

Thought there could be a piston/ring/barrel problem causing excess crankcase pressure, but a check shows good cylinder compression and same result for both sides.

Considering replacing main bearing oil seal, looking at manuals it looks as if it should be possible to pull the sealout once the engine sprocket has been removed.

Decided to have another run or two first, preferably in cooler weather when the engine and oil will not get as hot, and see if problem continues. Clutching at straws, but have stripped and rebuilt primary so often recently that I am getting fed up doing it!

Let me know how you get on. Best of luck,

Richard

Hi Richard,

I have had the same experience with two Commandos, and can suggest the following.

Be very careful how much oil you put in the tank. Best to check it when engine is hot, ie after a journey ( not that you go out with no oil ! ) Too much causes the pressure to build in the crankcase and is forced out into the chaincase. A simple test is to take out the timing plug or clutch access plug in the chaincase and start the engine. If you hear a chuffing noise and can feel puffs of air with your hand, then the seal has blown.

It is possible to replace it from the outside, after removing clutch, alternator etc etc, It may well just fall out or you can drill a 2mm hole in the outer and pull it out with a self tapper. Replacement is straight forward but dont push it too far or it may go through, and according to some Norton engineers you should Araldite it in !! Dont forget to re-align the primary chain sprockets.

Good luck.

HT

I must disagree with Hans diagnosis that too much oil will cause excess pressure. The pressure is a function of the speed and efficiency of the oil pump. If however your engine oil has drained down into the crankcases (wetsumping) then when the engine is next started it will try and blow it out of whatever orifices are available, the LH main bearing oil seal is one of them. If you have not used your bike for a couple of weeks, and lets face it, not many Norton owners put their bikes to frequent use, then it is well worth dropping the contents of the crankcases into a jug and tipping it back in the oil tank before starting. be prepared for the whole lot to be in there if it's stood for any more than a couple of weeks. ie make sure your container is big enough.

When re fitting the primary drive, tighten the clutch nut and the front sprocket nut, adjust the primary chain tension, then remove the clutch drum, chain and front sprocket then centralise the discs holding the crappy felt seal in the back of the primary chaincase on the gearbox main shaft, then replace the whole lot again. Deep joy!

Problems on my Mk 3 850 with oil discharge at rear of bikebehind oil tank was solved by never filling oil more thanhalf way between high and low marks on dipstick (with level checked onlyafter a good run) - read in aspecialist Norton restoration book that high level dipstick mark as supplied by Nortonwas wrong. Oil mist was being forced from pipe connectionat rear of tank when level right up to high mark.

Wet sumping after weeks of standing was completely cured bythe easy to fit Mick Hemmings anti-drain valve.

Hans,

Thanks for that, I had checked at an inspection cover and felt no air escape, and I had also held a piece of tissue paper next to it and it wasn't either blown away from or sucked towards the hole. However I am still suspicious of the seal!

Richard

My 750 Commando was oil tight until one of my pistons partially siezed on a very long ride back from Germany. I ended up with oil blowing out of every possible gasket joint. Rockers, timing cover.....you name it.

I did the decent thing of new pistons, cylinder honing, replacing all gaskets and oil seals but still had a pool of oil under my bike aftersubsequent long runs.

I then did the suggested trick of cleaning all the potential external leak sites, dusting with talcum powder and riding until staining was noticed. The main culprit turned out to be the crankcase joint. The only solution to this being a bottom end strip and rebuild. B*******r!!!

The message here being that the cause of oil drips is not always the most obvious one.

Left hand crankcase seal on the MK3 may be located with a wire style reatining circlip. It is not easily removed with the crank in-situ due to the gap between the circlip and crankshaft and the fact it has no 'eyes' on it to insert circlip pliers. Steve maney does a seal that is supposed be very good for sealing this area.

As others have mentioned, ensure that oil level is between max and min, and always check after it has been run.

That's about the best use I can think of for two concentrics, I hope the rest of the bits were scrap.

Have now replaced drive-side crankshaft oil seal and been out for a ride of about 180 miles. There has been no noticable increase in oil level in primary chaincase; this time itstill contains ATF without engine oil mixed in with it. Nevertheless I am fitting a valve on the breather just to be on the safe side!

Old, probably original, oil sealhad only about 1mm larger internal diameter than the new one, but had got much harder. Also was rather a loose fit in the crankcase.

Previously david_evans wrote:

That's about the best use I can think of for two concentrics, I hope the rest of the bits were scrap.

I disagree Dave,

was having problems with mine recently. Strip revealed one float was bent down, possibly due to ethanol. Replaced with Amal stay-up float kit inc. aluminium float needles. Slow running through town traffic is now fine as is pick-up coming out of hairpins and roundabouts. Bit cheaper than your Keihin flatslides!

Previously paul_smith wrote:

All - just to complete this thread and return to the main subject!

The route cause was a split at the top of the oil tank just behind the small bracket top left hand corner that attaches to the frame via the rubber threaded post.

I submerged the oil tank in the full bath (plugged all holes and attached a hose and blew down it) and saw the bubbles from the small hole - cut off the bracket, got my mate to weld up the hole, tested again in the bath and then welded back the bracket.

Much better now - Regards - Paul.

Is the oil tank still out? Might want to reinforce the bottom mounting while you are at it. Cheers, Bennie

Also it is better to braze rather than weld the bracket. Problems come when the rubbers fail and that is usually because oil spills on them.

Yes, good idea to check the bottom mountingbecause if a top mounting breaks the bottom mounting is usually not far behind.

My Mk 3 has been right since 1990 after brazing the same bracket.. Wipe the oil off those rubbers.