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Lotsoluck
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Had this piston hang up on me in the clutch in position. After the block cooled down it popped out on its own into the clutch out position and I was able to make it home. My manual mentions instances of pistons tying (???) in the casting on 81 on models preventing smooth clutch operation. Assuming tying means binding? Disassembled the external gearbox clutch activation hardware and cleaned and lubed all. Could not however remove the thrust piston. Is there a special tool to remove the piston, or any recommendations out there on removing it for service and inspection? Seems to be running ok now and maybe the cleaning and external lubrication applied might be sinking in, but I'm waiting for the other shoe to drop so to speak. Any help out there Airheads?
Thanks in advance.

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Ken

schrader7032
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San Antonio, TX
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Ken - Welcome! Are you

Ken -

Welcome! Are you talking about #2 here:

https://www.realoem.com/bmw/enUS/showparts?id=0487-USA-06-1993-2473-BMW-...

If so, maybe it's cocked in the bore. Not sure how to get at it if it doesn't want to come out on its own. I'm sure a complete transmission overhaul would allow you to get the back cover off so you could work at it from both sides.

The 1993 bikes were missing a circlip on the output shaft. A potential problem is that the bearing walks on the shaft creating binding inside the transmission. In the 1994/1995 timeframe, BMW decided to add the circlip back in...it was removed in about 1985.

http://www.largiader.com/articles/circlip/

If you were to take the transmission down, you could have the circlip added.

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Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2

Lotsoluck
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Clutch Drive Piston

Thanks Kurt. #1 is the issue. The engine S/N on my ride indicates it was made after the circlip issue was resolved. Thank God! I'll check out your other link. Thank you.

Ken

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Lotsoluck
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Clutch Drive Piston

Hi, Sorry, I thought you meant the second link you sent. Yes, item #2 is the culprit I'd like to inspect.

Ken

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Ken

schrader7032
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San Antonio, TX
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Snowbum has been keeping a

Snowbum has been keeping a list of bikes/transmissions that have no circlips during the 1984-1995 period. I would have thought that a 1993 model would be missing the circlip. The list is about 1/3 of the way down on this page:

http://bmwmotorcycletech.info/transmission.htm

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Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2

RickR90s
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I think the O.P. is

I think the O.P. is referencing the fact that the thrust piston is hanging up in the bore. Would this be caused by a missing circlip on the output shaft? The thrust piston's only role unless I'm mistaken is to press the thrust rod forward and disengage the clutch through the input shaft.

I too had this issue on my '93 R100RT. When fully warmed up, and with higher mileage, (started around 40k), my clutch lever felt very "notchy", when pulling and releasing the lever.

I removed the piston and had my buddy turn it down on a lathe, knocking off about .003" in dia. I can't remember the material of the thrust piston, but I don't think it was metal.

I rode the bike another 10k and the issue was gone.

FWIW,

RickR90s

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RickR90s

Twocams
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Doesn't the rod go up the

Doesn't the rod go up the hollow of the main shaft. To push on the pressure plate/clutch. If it does you could pull the transmission and push the rod and cup out. Dont know, never had one of these apart. My 84 VW rag top had the same clutch setup as the BMW bikes. Humm wonder why?

twocams

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Twocams
69 R69S 03 K1200GT
92 R100RT

Lotsoluck
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Gearbox Circlip

Hi Kurt, BMW started reinstalling circlips in September of 93. My engine is 01/94

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Ken

Lotsoluck
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I think the O.P. is

You are correct Rick. My symptom is exactly the same. Very notchy until it got stuck in. Engine cooled and it popped free. My difficulty is removing it for inspection. Nothing to grab on to. Figure the may use a tool? I have however have heard of others turning it as you suggested. Don't want to remove the gearbox unless it's absolutely necessary.

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Ken

Lotsoluck
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Doesn't the rod go up the

Thanks Twocams. Hopefully it won't come to this but you are absolutely correct.

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Twocams
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Well Ken, If you did have to

Well Ken, If you did have to pull the trans. Just think you could lube the transmission splines, replace that old rubber boot & get the rod & cup out. Its a win-win. Or you could spray something like PB Blaster Penetrating Catalyst in there and let it soak.Use some sandpaper to clean the bore out. What about using a propane torch and heating the rear cover. Ok that's all I got for this evening. hummm

twocams

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Twocams
69 R69S 03 K1200GT
92 R100RT

mark_weiss
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#1 is the clutch pushrod. One

#1 is the clutch pushrod. One of the problems which can occur is that the thrust bearing at the piston fails, the pushrod does not spin freely inside of the transmission input shaft (first motion) and the tip of the pushrod becomes friction welded to the clutch's pressure plate. Another problem is that the boot at the piston end of the pushrod fails and moisture intrudes the pushrod's bore. There is a felt sleeve which should be oiled on the pushrod, but with enough wetness this can fail and the pushrod and the input shaft's bore will eventually corrode. This causes sticking.

Yet another possiblity is that the piston's bore in the rear cover is worn, allowing the piston (#2) to occasionally hang up.

The piston and associated parts may be removed from the transmission's cover without the need to remove the gearbox. In this case, bore inspection is mostly by feel, but piston rocking is often detectable. The clutch pushrod is more difficult to remove. If the gearbox is left in place the swingarm will need to be removed. The pushrod will usually just clear the frame tube beneath the battery box. Replacing the pushrod, with a new felt seal, can be frustrating. The felt sleeve will seem as if it will never, ever, be able to be inserted. A strip of aluminum, cut from a can, can make a useful helper tool (as a sort of funnel).

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Mark
qualitycycleservice.com

Lotsoluck
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#1 is the clutch pushrod

Thanks Mark. We did find a good deal of water in the boot. Pressure washing I'm thinking as the boot looks fine. Sounds like you've had a bit of history with these. The clutch lever notchiness has gone away since we disassembled, cleaned and re-lubed everything externally for now. I did purchase a new piston in case this pops up again. From 81 on they don't show the felt ring, and in 88 the thrust bearing became an integral part of the piston. Question, any recommendations on a lubricant on the new piston during installation? Thanks again.

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Ken

mark_weiss
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Arizona
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Yes, the later models

Yes, the later models replaced the felt sleeve with a small seal. Also, the earlier four piece piston and x-ring seal was replaced by a piston with the bearing pressed in and no added seal. I do not know when the last change was made, my '82 has the earlier style multi-part piston.

Gear oil should be fine for the piston and seal. That is what keeps it lubed when in use.

Pressure washers, they are a common cause of corrosive damage at every place where our bikes have seals.

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Mark
qualitycycleservice.com

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