tracking down oil leak on transmission - - Excellence in Motion
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post #1 of 7 (permalink) Old Dec 2nd, 2010, 1:54 pm Thread Starter
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tracking down oil leak on transmission

I am in the process of rebuilding my 85 k100rs and am currently trying to track down the source of a slow oil leak that has accumulated on the top of my transmission. The photos show the results from at least 40k miles and at least 10 years. It never dripped oil. The oil "stain" shown in the photos is the extent of it so, while it is large, I assume the leak is slow.

As you can see, the clutch area and the mating surface to the intermediate housing are clean so the oil is not coming from there. The blurry photo shows the intermediate housing. On the intermediate housing the oil is only within the cavity in which the alternator and starter sit. The outside of the intermediate housing and its connection to the engine are very clean all the way around.

To me, it doesn't appear to be coming from the connection areas of the starter of alternator.

I am guessing that the gear oil is coming out of the plastic cap on the top of the transmission. Strangely the cap itself is very clean but I can not think of any other source.

Any comments are appreciated but my questions are:
Has anyone else experienced leakage from this hole beneath the cap?
Is this cap some kind of breather hole that has a normal amount of fumes escaping that might accumulate like this over time?
Should I just clean it off and then keep an eye on it or is there any reason to open up the transmission and look deeper?

thanks as always. This forum has been a great find.
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Last edited by kringb; Dec 2nd, 2010 at 1:55 pm. Reason: added photos
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post #2 of 7 (permalink) Old Dec 3rd, 2010, 9:59 am
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It looks like its coming from the plastic cap as far as I can tell. That's the breather/overflow outlet on the top of the transmission. Doesn't look like its any cause for concern, possibly too much gear oil in the case at one point or another? Has the bike every tipped over?

I would just clean it off, and not worry about it. Have you been filing it properly? The rear spring compression adjuster is the dip stick for the gear box...

There has been some suggestion that synthetic oils weep more in the gear box but I don't think there is anything conclusive.

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post #3 of 7 (permalink) Old Dec 3rd, 2010, 11:54 am Thread Starter
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thanks lukeman, that sounds good to me and I will rest easier without worrying about it. The bike was never on its side but it is possible that I slightly overfilled it on occasion. At every oil change I always precisely measure the amount recommended in the clymer manual but I don't always double check with the dipstick after running the bike. I probably have not always completely drained it before adding the full amount.
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post #4 of 7 (permalink) Old Dec 3rd, 2010, 12:02 pm
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Have you looked at the crankcase breather hose? It is just ahead of the tranny and they are well known for cracking/leaking.

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post #5 of 7 (permalink) Old Dec 3rd, 2010, 1:21 pm Thread Starter
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That breather hose is cracked but not yet all the way through. I may replace it now but I don't think that is related to this problem. The intermediate housing creates a big wall between that breather and the stain.
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post #6 of 7 (permalink) Old Dec 3rd, 2010, 3:39 pm
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I'd guess the bike took a nap of some duration.

When I bought my K1100RS, I rode it up the coast from Malibu to San Francisco to a friend's house. He's got a lift so I gave the bike a thorough once over once I got there. The bike had been serviced at Ventura BMW about 1,500 miles prior. (Bike came with receipts.) The idiot mechanic at Ventura BMW had filled the transmission to the brim. No oil came out of the breather cap.

(Ventura BMW had also installed the front tire backwards. Needless to say, I wouldn't recommend them for service.)
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post #7 of 7 (permalink) Old Dec 3rd, 2010, 4:17 pm Thread Starter
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I'm not sure what you mean by "nap". It has been my main source of transportation for over 15 years and it has never been layed down. I don't even use the side stand so it hasn't even been leaning.

Your comment about being filled to the brim and not leaking is puzzling though so I guess I won't rest easy after all.

I need to remove the Intermediate housing to get to the sprag clutch so maybe I will discover more as I move along.

There may be a problem in the transmission but there are no other symptoms. Because no body has said it is a screaming warning sign of transmission problems I will plan to clean it up and keep an eye on it and see where it starts from, if it continues.
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