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Got A Bit Of A Leak.


shercoman2k8
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Hey there,

Went out, clean bike... come back in, clean bike, one difference... my sump is covered in oil. Definately gearbox oil too. Pinpointed the leak to the crankcase breather, now... This leaks due to pressure, right?

This is what had me stumped, if it purges oil and air under pressure, yet doesnt suck anything in... Where did this pressure come from?

Only happens when bike is hot mind.

Only happens when bike is running.

Gearbox oil not white, so no leaks into here, raising quantity.

Put 430 mL's of g.box oil in, 10.40

No dirt or grit in the oil.

Also cant get the carb to balance properly, it can be running rich, yet still knock... and be running lean, and bog slightly, no happy medium, it seems to change from rich to lean by itself under load. Runs better on choke, then bogs when throttle opened.

Been running the Keihin carby, not got a clue on jetting, although its set perfect as it was running fine the week before. Tried the dellorto. Same problem, this leads me to beleive crank seal, or air leak somewhere... Waved a propane torch, unlit around manifold, and behind flywheel, revs didnt pick up atall.

Although the carb issue isnt important to me at the moment, I can sort that... the gearbox oil leak has me baffled, is this crank seal, then the gearbox oil is coming out of this breather before reaching the cylinder or what? Seems odd to me. Has been running smoky recently, thought the mixture was just really rich, wasn't blue, and wasn't obsessive.

Compressions fine, sparks fine, fuel's fine. May lead to the poor running if these were dodgy, but once again, not the leak.

It isnt a dribble either, in a minute or so I lost maybe 50-75 ml? Work that out to be empty in about 6 or 7 minutes?

Anybody split the cases and got a pic, I have, just cant remember whats on the inside of that breather, crank area or gearbox? Or is it like the water pump weep? Will let out whatevers leaking?

All advice welcome,

Jamie

Edited by shercoman2k8
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Good thing you have a new bike on the way!

This IS starting to sound as something of a Neo bike to me! Except blowing oil out as well?

Ok, lets try this little experiment. Normally I would run the gearbox vent tube up and over the carb fuel inlet, then back down to the skidplate level, making this small hose quite long.

If you were to get your thingie warmed up and spitting, what would happen if you were to take the end of the vent tube and submurse it in water? Does it make bubbles as if the crankcase is pressurizing the gearbox area?

If so, that would suggest a leaking seal on the primary side, or bad center case gasket allowing the crankcase pressure to get to the gearbox side of things. This could also allow oil to travel the other way and create more smoke than normal.

My guess would be that seal, refer to Neo's post for relatively simple replacement, only 40 pages of getting there, skip to the end!

Makes me wonder about seals now! :rolleyes: I am not totally sure if we defined them as being black nitrile or not? ;)

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Seals should be viton.The ones I got last month are a dark grey, sat side by side with a nitrile seal the colour difference is noticeable

Crankcase vent is into a void at the top of the gearbox, would take lots of pressure to get oil up that high & even tipping the bike upside down wouldn't cause it to leak out. Changing the crankseals would be the first & easiest thing to do.

Try Copes test of submerging the breather in water to see if it's a pressure thing, could find your carb problems lessen at the same time

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I have a similar problem

Only occurs when I change the oil

I think the 450 ml quoted by Sherco is for a new build on the engine and when changing the gearbox oil some is retained and consequently a high level is generated in the gearbox and this excess is then pumped out.

I think the low pressure pumping is created by the meshing of the gears and once the level has settled no further oil is lost.

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Cope,

Exactly what I thought, Neo sprung to mind straight away... New bike? New bike? You buying me it? :rolleyes: On hold for a long while possibly.

Anyway, will check to see if its pressurised, there doesnt appear to be much pressure behind it, I removed the hose to see whats going on, and although the rate was excessive, it wasnt that strong of a flow?

Done water pump seals a few weeks back, could this have anything to do with it?

Geebee, as said above, I only change 430 to compensate for those cling on's around the box ;)

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Do you lay your bike right over on it's side when you fill it up, this can fill the camber that the breather enters so as soon as your bike gets warm the expanding air pushes the oil out of that chamber, the same can probably happen if you fall off and the bike goes upside down or it lays on a funny angle on the floor.

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I have a similar problem

Only occurs when I change the oil

I think the 450 ml quoted by Sherco is for a new build on the engine and when changing the gearbox oil some is retained and consequently a high level is generated in the gearbox and this excess is then pumped out.

I think the low pressure pumping is created by the meshing of the gears and once the level has settled no further oil is lost.

I think that the 450ml is fine providing that you get the old oil out. Warming the bike and leaning it over to about 45 deg angle helps. I cannot do it on a stand, oil goes everywhere and makes a mess.

They do seem to naturally expell any excess and find their own level, then fine. :rolleyes:

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Cope,

Exactly what I thought, Neo sprung to mind straight away... New bike? New bike? You buying me it? ;) On hold for a long while possibly.

Anyway, will check to see if its pressurised, there doesnt appear to be much pressure behind it, I removed the hose to see whats going on, and although the rate was excessive, it wasnt that strong of a flow?

Done water pump seals a few weeks back, could this have anything to do with it?

Geebee, as said above, I only change 430 to compensate for those cling on's around the box :thumbup:

Well just sitting there running, there should be no pressurization of the gearbox, and only slight thermal expansion of the air within during warmup process.

There is always oil being slung about inside by the turning gears, and this is sort of why is may be best to run the vent tube uphill first, so even microvapors accumulate and return down, the other reason is to defeat to some extent any shock cooling effect and associated air space contraction of deep water! As the water must be pulled uphill first before the downhill entry would be allowed. This is not foolproof in DEEP water!

But back to yours, the crank area of a 2T both blows and sucks, essentially, an escape in one direction or the other is not good. Concieveably,a simple guage could be built to monitor these changes in gearbox pressure in inches or mm of water pressure rise or fall. In your case, seems bubbles would suffice!

I wonder if Neo did any cross reference to the seal that came out of his? It did look BLACK, and nitrile! And all that can even take things back to the oils used and the additives in them. That is another story! :rolleyes:

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So, bit of testing shows that the leak is pressurised, the bubbles were formed in the water, rate of one small bubble, maybe the size of a pea every one second.

The rich/lean problem appears to be solved, it bogs a bit in the higher gears but it should be tuneable out. The leak still has me baffled though. Crank seals or centre case gasket?

Or should I just do the whole cabum and do seals, bearings, the lot? Bearing in mind the bike was ridden hard before I got hold of her, Jono Richardsons 08 bike... hammered me thinks.

Runs well though, i just have this rather annoying problem of draining gearbox's. The long hose up over the cdi bracket and down seems to of done the trick to get me through tommorow's trial. Will investigate further afterwards.

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So, bit of testing shows that the leak is pressurised, the bubbles were formed in the water, rate of one small bubble, maybe the size of a pea every one second.

The rich/lean problem appears to be solved, it bogs a bit in the higher gears but it should be tuneable out. The leak still has me baffled though. Crank seals or centre case gasket?

Or should I just do the whole cabum and do seals, bearings, the lot? Bearing in mind the bike was ridden hard before I got hold of her, Jono Richardsons 08 bike... hammered me thinks.

Runs well though, i just have this rather annoying problem of draining gearbox's. The long hose up over the cdi bracket and down seems to of done the trick to get me through tommorow's trial. Will investigate further afterwards.

So I understand, you did this with the motor already warmed up and such, correct? Then ther should be no pumping process through the tube.

If you did not have it run up high prior, then that in itself could be a problem.

A leak is still a leak, and such as Neo's case, could well suck in oil to create some of the smoking you observe that you seem to consider unusual.

The seals are easily enough replaced, and barring any other symptoms of loose bearings asn such, I would take the simple route as Neo did.

The bearings should turn smoothly, no noise and no excess play. they probably start out at .003-.004 clearance and their service limit would be about twice that if you wanted to take a measure on them, but basically if you cannot detect a major movement in the flywheel side or the other, I would put seals in and run with it! Freshen the rings and or piston if you like! May need it!

Seems there could be a decent test process developed with the water scale here, wish I had thought of that on Neo's bike. Can't tell him anythin anyway, nutter!

Lest get back to this seal composition thing, Tony your basis please!

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Seals for crankshafts need to be made of viton due to the heat they face, nitrile seals harden & crack if heated where viton stays pliable

The difference in colours & design is down to individual manufacturers preference. I've never come across anyone doing them black but the current ones are quite dark

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Seals for crankshafts need to be made of viton due to the heat they face, nitrile seals harden & crack if heated where viton stays pliable

The difference in colours & design is down to individual manufacturers preference. I've never come across anyone doing them black but the current ones are quite dark

I do understand all that, makes one question? I take seals out of car engines all the time! Many are still black! Most have still made high mileage!

Others are brown and such, seems one never knows the actual composition, as I just go with the strict OEM part numbers and do not vary.

These things are simply disguared, no idea about origin. Commonly, poor oil change history is evident!

Same with the bikes for me, as unless someone has come up with some seal numbers to backtrace, I have no idea their content.

But I do have some some other ideas about the oil used and its seal conditioning properties! (or lack of) As this could be a potential issue!

Edited by copemech
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I've never had a crankseal fail on a sherco but do replace them as a precaution if doing the bearings, not sure why some people do have problems with theirs

You could be on to something as far as the effect of oils on the seal although I've used both ATF & proper gearbox oil in my bikes with none of the problems that Neo & Shercoman2k8 have had

I'm still not 100% sure the problem is caused by a seal as normally the oil gets sucked into the motor rather that forced out so it sounds plausible that the centre gasket is leaking, would have thought symptons would be the same.

Still seals are quick to change & always better to eliminate one thing at a time

Edited by tony27
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Had a quick read through these past few posts, Cope... The bike only seems to do it after the fans cycled in and out a few times, so she's definately warmed up, and it's too long for it to just be the expansion during warm up.

I held the breather pipe vertical for a minute or so, and kept the engine at a high idle... This pipe is about bar height and the oil still managed to work it's way to the top. Blocked off the breather for todays trial then we shall be doing the seals straight after. If this does not cure the issue, im guessing I should change the centre case gasket, yes?

I'm guessing that it's almost definately a leak from the crank case, the higher the revs, the faster, and with more pressure the flow. The lower, no flow atall. I have no noticeable loss of compression atall.

I use either proper motorcycle oil, or atf occasionaly... IIRC it's 15w40 ATF at the moment, but not cheap stuff. Around

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