R100 Clutch pushrod too short?!?

Thanks for checking out this post. Bear with me as I provide the background details...

An acquaintance of mine, who knows that I tinker with Airheads, brought me his R100"RS" in a box. The quotation marks are there because by VIN it started life as a 1981 R100CS. It was bought if from someone who built it up from spare parts, and my friend has been riding it for six or seven years. In that time I think he has needed two clutch jobs - he rides quite hard, and then someone opened up the transmission when he thought there was a problem there. I do not believe it was put back together correctly as he now had problems such as false neutrals between every gear. He took it, all together and running, to another garage BMW mechanic. That person opened up the gearbox and threw up their hands.

The bike, in pieces, then came to me to be sorted out. For later in the story, I did note that the bike had the later (post 1981) style gearbox and clutch, and I assume flywheel as well.

The transmission has been sorted out by a professional who said it was a nightmare. I also replaced the clutch as the one that came to me only had a few hundred miles left on it.

I put it all back together, something I have done many times. When I inserted the clutch pushrod into the tunnel through the transmission, instead of making contact with the clutch, it went all the way inside and disappeared! There was nothing left sticking out of the back end to engage with the clutch actuating arm. I checked the length of the rod and it is 227 or 228 mm which I believe is the correct length for this bike.

I cannot think of a reason why this would be. If I cannot come up with the reason, the only solution I see is purchasing a longer rod and cutting it down to size. The later BMWs (1995 and up) had longer rods that should do the job (they are the same diameter).

But before I go that route, which may make me feel temporarily smart for finding a solution, but then eternally puzzled as to why the problem occurred, does anyone have any thoughts? All ideas are appreciated!

Can you take some pictures of the clutch parts you're dealing with? Are they similar to what's in this diagram?

https://www.realoem.com/bmw/enUS/sh...0_2474_BMW_R_100_T&diagId=21_0086#23131464167

This is a picture of the pushrod I replaced on my /7 about 5 years ago...it's 205mm long, so clearly if you have something that is longer, it must be the right part.

I will post some pics.

The clutch pushrod in the photo you sent appears to be part no. 23 13 1 232 089 (Max's fiche) which is for pre-9/80 models and is 205 mm long. It also has the cut out for the felt ring.

The clutch pushrod I have in my hands - I believe it to be part no. 23 13 1 241 844 (Max's fiche) is for post-9/80 models and is approximately 225 mm long. There is no cutout for the felt ring. This seems to have been done away with at that time.

Here are pics of the parts that came to me, some have been refurbished, and have been put back on the bike. The transmission cover in the photo with the clutch parts is a broken and then repaired cover that was replaced with an undamaged one during the rebuild....

And a two more pics...

OK, looks like you're are using all the right parts.

I tried finding some good words from Mr. Cutter on the Airheads archive...about the only thing I could find was someone who said that his pushrod went too far in. The end result was that he installed the diaphragm spring backwards. Could that be something you could verify?

Of course I think I installed it correctly, but I will entertain any hypothesis. I will check tomorrow.

More puzzle pieces...

The first time the clutch was done, these spacers were found attached to the little arms protruding from the clutch plate (21 21 2 302 200). These were put back in place at that time. The second time the clutch was done, they were left out. The performance did not seem to suffer for their absence. I have not seen them before, nor are they on the fiche. I did not replace them in the clutch assembly this time either...

Reading from my Haynes, it mentions that sometimes spacers (0.2 - 0.4mm) were needed to space out correctly the cover plate when used with the strengthened flywheel on assembly. When the later model cover plate was available, the spacers were eliminated. So, if you have the original cover plate, then it would seem that the spacers are needed. The cover plate is #5 in this diagram:

https://www.realoem.com/bmw/enUS/showparts?id=0435-USA---2474-BMW-R100 /T&diagId=21_0067

If the clutch plate is too thick, the spring gets flattened too much as you bolt it up, moving the center too far forward. The same effect happens if there isn't enough room for the clutch plate because other dimensions are too small. Those spacers will increase the room for the disk, moving the center of the spring rearward.

I had this problem one other time, on a GS with a modified or aftermarket clutch. The engagement was just in the wrong place, and I used washers to restore the spring geometry to normal. Post the part number on the flywheel, if it's still legible.

Kurt - Thanks for solving the spacer mystery! Do you know how I can tell if I have the earlier or later style of cover plate?

Anton - As I will be taking it apart tomorrow, I will check to see if I can find a number on the flywheel. Is it in any particular spot? Hopefully it can be seen without removing the flywheel. I will also try to check the clutch plate thickness. PS It was your website that showed me that the clutch pushrods got longer over the years but stayed the same diameter - so thank you for writing that page. But for this situation I would still rather fix it the right way.

Thank you for all of the education and ideas thus far!

CaptDistraction said:

Kurt - Thanks for solving the spacer mystery! Do you know how I can tell if I have the earlier or later style of cover plate?

Click to expand...

I'm afraid I don't...Haynes doesn't give any more specifics. As the part number was unchanged, that wouldn't even help. My guess is that the earlier '81s had this problem and that it got corrected soon thereafter. A check of Snowbum's site seems to have an answer...look at the big red box near the top of the page:

http://bmwmotorcycletech.info/clutch.htm

clutch problem

Hi guys , getting into to this a little late, but I have just recieved my Oct copy of classic bike,and in a maintence collum much the same fault, the guy had put the diaphram spring in backwards !! so no plate to push on, hope this assists ,Jimmy sorry wrong post should be for clutch push rod too short,

Jim -

I did the swap-a-roonee for you...move your post from the camshaft thread over to here.

thanks

many thanks kurt, i did try by cancelling etc but nothing seemed to work , again thanks, you do good work Jimmy

It's been a week since I made the first post. I am grateful for the opinions thus far. I'm back now with more information and more pictures....

One issue was brought up was whether I have the strengthened flywheel. Here are some pics of the flywheel and the numbers on it. If someone can tell me if this is the older version or the strengthened version, I would appreciate it.

"...sometimes spacers (0.2 - 0.4mm) were needed to space out correctly the cover plate when used with the strengthened flywheel on assembly. When the later model cover plate was available, the spacers were eliminated. So, if you have the original cover plate, then it would seem that the spacers are needed..."

Here are pics of the housing cover plate. Can you tell if it is the original (requiring use of spacers) or the later model?

And now the question I should have addressed first... the simplest explanation is the most likely, and many have asked if I installed the diaphragm spring backwards. Here is a series of photos showing the view after the transmission is removed followed by removal of each successive piece of the clutch pack... I believe that it shows that the diaphragm spring is installed correctly.

AntonLargiader said:

If the clutch plate is too thick, the spring gets flattened too much as you bolt it up, moving the center too far forward. The same effect happens if there isn't enough room for the clutch plate because other dimensions are too small.

Click to expand...

Here is the clutch plate. If measurements would help I can provide them.

And here are some other measurements to add to clues to figure this out...

1) The transmission shaft (that engages with the clutch) is about 23mm.

2) I thought it would be helpful if I could describe just how "short" the clutch pushrod is. So I whittled a wooden rod that was much longer than necessary. I then inserted it through the transmission until it fully engaged with the clutch. I did this initially to figure out what length pushrod I would need to make - I realize now that is not the best solution - better to figure out what is actually the problem. But by doing this I can see just how much the stock pushrod is coming up short.

The stock pushrod is about 225mm long

My wooden replacement shows that I would need a pushrod that is about 260mm long to fully engage the clutch actuating lever on the back of the transmission.

That is a difference of 35mm (or 3.5cm or 1.38 inches). I'm not sure I fully understand how the previously mentioned spacers work, but looking at how thin they are, I don't see how they could make up for this 3.5cm difference.

I am looking forward to reading your thoughts given all of these new exhibits - thanks!!