rear main seal and valve adjust questions - - Excellence in Motion
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post #1 of 4 (permalink) Old Nov 25th, 2007, 4:01 pm Thread Starter
Join Date: Oct 2007
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rear main seal and valve adjust questions

I'm a long time airhead wrench and would know this stuff if the bike was 20+ years old, however this K stuff is all new to me.

main seal History
I just pulled the transmission on my 98k1200rs with 31k tracking an oil leak only to find it dry in the housing. There was a lot of oil on the transmission bottom and back. I found what I think to be oil in the cavity behind the clutch slave cylinder and there was no gasket between the clutch slave cylinder and the transmission. This seems to be the sole source for the leak. My gut reaction is to stop now before I pull the clutch and screw up something that is not broken.

Can oil get in this cavity from the transmission or must it be brake fluid from the slave cylinder? The clutch pushrod seemed dry.

Would you continue to pull the clutch etc to change the seals anyways, or leave well enough alone?

valve history
I checked my valves and have

one exhaust that goes at .09 and no go at .10 -- factory calls for .10 to .12
one intake that goes at .05 no go at .06 -- factory calls for .06 to .08

also have two valves .01 loose, but I know this is not an issue.

Would you bust this down for 2 valves less then .01 tight?

wait and see if they change?

When valves are found tight, how much out of spec are they usually?

Thanks for the advice.
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post #2 of 4 (permalink) Old Nov 25th, 2007, 6:06 pm
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The leak there will probably be from the slave cylinder seals. This is bad news because fluid eventually gets down the pushrod shaft, on to the clutch, clutch slips and you have to dismantle everything. You might be seeing a drop in clutch fluid level at the reservoir. Main seal leak is more visible at the bottom of the casing.

There's no gasket on the slave cyl. flange originally, but now you can get one with a new slave cyl. It matters little though, because you really want to stop any fluid being forced down the pushrod hole in the drive shaft. I actually drilled a couple of small holes in the casing to let fluid out and act as a warning tell-tale, it might just save a clutch plate too.

If you leave well alone, the worst is your clutch will start slipping one day, you'll need a new plate anyway, and at least you know what it is and you would be wise to do the O ring and main seal at the same time. It's possible to replace the slave without going inside and it's a matter of luck if you caught it early. My '97 KRS was at 36K and I decided to do the lot.

I couldn't understand how you explained your valve clearances. If they are within the range or say a thou" outside I'd leave them. If you look up the list of bucket sizes (yes $$s not shims!) on, you'll find you can't get them spot in the middle of the range anyway. A race shop might lap down the buckets, but it's uneccessary on road bikes and more clearance is better than less.

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post #3 of 4 (permalink) Old Nov 25th, 2007, 7:07 pm Thread Starter
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I already pulled the transmission and the clutch cavity is still dry.

The valve measurements are go / no go. Two valves are les then 1 thou under spec and two are les then 1 thou over spec. I'm not worried about to much clearance but wonder if I should worry about the tight ones yet.
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post #4 of 4 (permalink) Old Nov 25th, 2007, 8:23 pm
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Location: Atwood, Ontario, Canada
Posts: 398
If it indeed is your clutch slave cylinder leaking, then you definitely want to replace the transmission seals that were exposed to the leaking fluid. The brake fluid used in the clutch circuit will quickly break down the seals. If it was me, I would replace everything once you are in there, main rear seal, the o-ring on the main shaft and transmission seals that could have been exposed to the leak.

Valve clearances - out of spec is out of spec. I'd make it right. You may not need any new buckets, sometimes by just swapping some around, you can get everything in spec.

Brent Boshart
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