I’ve been trying to track down a localised vibration problem with my ‘91 K75RT for years (not the purpose of this post) and as a last resort I thought I’d check what’s behind the timing case cover as it’s possibly about time to do so (115000 km) ... and who knows?

Took off the cover and all appeared normal at first glance. The chain tensioner isn’t extended very far, implying that there’s not much wear in the chain.

Took out the torx screws on the chain top guide rail and found there’s virtually no wear at all. Reassuring! Next step was to remove the chain tensioner, followed by the tensioner blade with its plastic face and the plastic chain guide. The problem is I can’t remove the chain tensioner. Haynes says compress its piston and withdraw it. It compresses about 1/8 inch (it’s not extended much further than that) but the unit only comes out a little way and there’s not enough clearance from the tensioner blade. Clymer says to pivot it clockwise and disengage it from the tensioner blade. Same thing - no clearance. I tried pulling the tensioner blade off its mount as far as it would go and that allowed the chain tensioner unit to come out quite a bit further, but not enough to remove it. Besides it was placing lateral stress on the tensioner blade plastic face and I was afraid that might break.

The only way I can see getting the tensioner unit off is to remove the lower cam chain sprocket but I’m reluctant to do that. Some would say to just put it all back together and forget it. They’re probably right but that phrase "Peace of Mind" crops up. Because I’ve gone this far I really would like to check the other guides and give the tensioner a flushing as there is a certain amount of rattling from the area.

However there’s something else about the tensioner unit that I’ve noticed. It is different from any of the pictures I’ve seen of them in Clymer or elsewhere. What’s different is that it has a blind orifice in the top right hand corner and a metal plate on one side that’s held in place by either a rivet or a screw. If it’s a screw then the head has been ground off. Is there something else about this thing that’s different that I can’t see? Like is the shaft that inserts into the oil supply longer than what’s usual, preventing it from easily being withdrawn?

I want to post a photo of it but I'm not sure how to do it. Help please.

If anyone has any experience with this or any ideas or suggestions I would really like to hear from them.

After removing both screws the tensioner should normaly be easy to remove,
unless some mods have been done.

No mods have been done. Owned the bike since new and this is the first time the timing chan cover has been off.

Any tips on how to post a photo of it?

Just 2 socket head screws and it should come off the engine. Have sent PM with email address for photo.

Thanks Rick. Photo on its way. As you'll see it's quite a different unit from what Inge K posted. And, yes, both socket head screws were removed.

And thanks also Inge. I didn't get your photo immediately because I'm still on 'steam-powered' internet. (dial up)

the link for how to post pictures etc



might have to wait a few days though



http://k100rt.aforumfree.com/t998-posting-pictures-and-movies

Well I have never seen one like that I will post it here to see if any one else has any idea.
As can be seen there is a small ratchet sys to prevent the tension droping away when oil pressure is lost.
Inge how about you?

Thanks for posting the pic Rick. I was just getting the hang of what charlie99 sent for posting pics.

I'm so glad that what I have is different. It just adds to my persecution complex.

I can pull the unit about 3/8 inch away from the engine body but it won't clear the shaft running between it and the engine body. It's close but not quite.

I have just spent an hour or so searching REAL OEM without any luck. It looks like it is factory from the plate on top, it is the same as other tensioners.
You say it has a shaft behind the body of the thing, do you know if it is a peg to locate or does it turn. All others I have seen have the 2 socket head screws holding it on and not even a gasget it just faces onto the engine over a hole for the oil pressure.

MLR wrote:
I'm so glad that what I have is different. It just adds to my persecution complex. .

love it ....many of us have them i figure .....

Have not seen one like this before, no. Can clearly see that the ratchet mechanism
have been changed.

Improved.....?....remember how Bohumil`s ratchet mechanism did look like anyone?

The problem seems to be underneath the tensioner, another change.....can`t move this one straight down as the previous version.

I`ve would have put a tiny screwdriver blade behind the side/top of the ratchet blade to release the ratchet mechanism.
Then compress the tensioner, and keep it compressed......I`m using a small zip tie to secure them before mounting.

See if this can make enough space to remove it.

Maybe the oil gallery is spigoted on this one, when CF posted pics of a sectioned K100 in general discussions this link was with it http://www.motor-design-mark.de/BMWK100.htm maybe the 8th pic down shows the front of the engine. worst case scenario may be to unbolt the lower chain rail and remove as a set. perhaps the rear lug on the tensioner is catching somewhere.

Well, I've resolved the situation with the mysterious chain tensioner.

I decided to 'damn the torpedoes' and loosened off the lower (exhaust) cam sprocket. It allowed enough lateral movement in the chain to pull the tensioner unit free. K75cster, you were right in that there is a spigot on the back of the tensioner unit which extends into the engine 3/8 inch that created the problem for me.

HOWEVER, if you recall in my first post I mentioned a blind hole in the upper right corner of the tensioner unit. There's a tab in there that I couldn't see that, when pushed to the right, releases the ratchet mechanism allowing the piston to be compressed completely. That would have given sufficient room to allow the tensioner unit to be removed.

I'll attach some pictures later to show you the scoop, and for future reference for the possible one other person in the world that has the same tensioner unit.

Many thanks for your thoughts and efforts on this. It is greatly appreciated!

....... MLR

P.S. There was absolutely no wear on any of the plastic guides!

Done some research: that is the standard chain tensioner on the K75`s
(never worked on any of those).
And the spigot acts as housing for a one way valve.

A new lesson for me, and I guess a couple of others.

Thank you for clarifying this further Inge. Looks like Darwin was right in that there can be significant genetic differences between siblings (i.e. K100/K75).

Below are some pics:

Tensioner body showing spigot and internal ratcheting:



Piston unit with ratcheting:



Upper right hole in tensioner body showing ratchet release tab:



Overall unit:

Would it fit a K100?

ReneZ wrote:Would it fit a K100?

The interesting part would be drilling out the engine block, to get space for the spigot.

Fair enough, was thought of. It seems it is a better construction that the original ones fitted, particularly the 'ratchet part'.

Sorry I didn't take a picture of the K75 engine block showing the oil port area.

Any suggestions on what kind of sealant to use on the timing case cover and the water pump cover? Permatex makes several types and they all seem to say that they do the same thing.

Hi MLR,
I like 'Drei Bond' sealant as recommended by BMW; had good results with it.
Cheers,
Paul.

Thanks Paul. Never seen it before but I'll cast around a little further for it.

Regards ..... MLR

Another alternative.....Permatex Black RTV...which I`ve used for this, with good results.