I have an 850 mk2a with a belt drive and am getting oil contamination from the crank.
I thought you would have to break the motor down to change this seal. I now believe you can change from in the primary drive.
Can anyone shed any light on this? It is contaminating my clutch.
Stu

Yes, the crankshaft drive side oil seal can be replaced from the primary. Are you using a breather check valve? If not, I would highly recommend one. You'll find once you do, your oil leaks will mysteriously disappear. I doubt you will even have to replace the oil seal.

If you are replacing the seal, get a rubber one rather than the original "tin" ones, as they tend to seal better....Steve Maney does them as he's in your neck of the woods

bigstu wrote:I have an 850 mk2a with a belt drive and am getting oil contamination from the crank.
I thought you would have to break the motor down to change this seal. I now believe you can change from in the primary drive.
Can anyone shed any light on this? It is contaminating my clutch.
Stu

hi stu are you sure the oil is not coming down the clutch pushrod

I used to regularly replace the crankshaft oil seal, about every 2,000 miles. Finally, I installed one of the Motormite brake vacuum check valve. The oil leaks stopped for about 200 miles. Eventually, I went with a Yamaha XS 650 PCV valve. No more oil leaks. The problem is not the seal. It's the positive crankcase pressure that causes the oil leaks. Not only does the crankshaft seal quit leaking when you use a proper PCV valve, so does everything else on the engine.

Hi , Be very interested to know how you get on with this problem , got the same going on just now with my mates 750 which i am trying to fix ,on seal no3 now it also has belt drive ,this bike was fitted with a check valve and i removed it and still it leaks cant see the purpose of this valve maybe someone can enlighten me , hope you get it fixed Brian

brf1957 wrote:cant see the purpose of this valve maybe someone can enlighten me

There has been so much written on crankcase breathing. Searching just on this site will give you plenty to read.

bigstu, you should be able to get the rubberised seal from any bearing shop. Just give them the dimensions which are; 1 3/16 x 1 3/4 x 3/16, or in metric; 1.18 x 1.75 x 3/16. I got one and it was about £3.00 if I recall correctly.

I believe that the part No. ML118175 will get you the rubberised seal also.

Been a while since I had my primary off, but I'm about to do it again for a gearbox rebuild. Am I hearing that this seal can be done from the primary side with just the primary off? Does it just pry out with a screwdriver or pick or the like?

For $3 I guess I'd invest in a seal while I'm in there. Appreciate any guidance. Thanks - B

BrianK wrote;

Does it just pry out with a screwdriver or pick or the like?

Basically yes. On my bike it's not a particularly tight fit, and I have done it this way at least twice. I also put a smear of silicone on the shoulder afterwards, but I'm not sure that this is necessary.

Thanks Reggie - Brian

Thanks for the advice. It is time to fit a breather. I am intending fitting the XS 650 breather when I can figure who to buy from in the UK. I think I will replace the seal anyway after fitting the valve. Does anyone know where I can scource this over here?

Just a note to Brian...The engine breathes in and out with the pistons going up and down. If you fit a 'one way' valve then in essesnce this alows the engine to breath out but not in, which, as the revs increase, turns the pressure in the crankcase from positive to negitive, or less positive anyway....this means that oil is less likely to be forced out through weak points. They say it can even increase the performance of your engine as a poor breathing engine is in effect a 'restrictor' to easy rotation.
I think I have got the concept of 'positive crankcase ventilation' about right here..?
Stu.

Yes, I run a "Krank Vent" - made for Harley - on my Commando. Seems to do a good job. If I'm gonna have the primary off, though, why not replace the seal?

bigstu wrote:Thanks for the advice. It is time to fit a breather. I am intending fitting the XS 650 breather when I can figure who to buy from in the UK. I think I will replace the seal anyway after fitting the valve. Does anyone know where I can source this over here?

Just a note to Brian...The engine breathes in and out with the pistons going up and down. If you fit a 'one way' valve then in essence this allows the engine to breath out but not in, which, as the revs increase, turns the pressure in the crankcase from positive to negative, or less positive anyway....this means that oil is less likely to be forced out through weak points. They say it can even increase the performance of your engine as a poor breathing engine is in effect a 'restrictor' to easy rotation.
I think I have got the concept of 'positive crankcase ventilation' about right here..?
Stu.

You nailed it, Bigstu.

Glad to hear you've opted for a decent PCV valve. You'll be very happy with the results. Hope you can find a supplier in the U.K.

I bought one of those Yamaha PCV valves but had installation issues - I no longer remember exactly what - so I threw it on my Ducati and bought a Krank Vent for the Commando. Both bikes doing well, FWIW (the Duck never had any oil leakage problems, at least, once I put in all O-rings I'd omitted during reassembly and put a bit of Yamabond on the cylinder base gaskets).