clutch balance

[ISAMEMON]

due to a uninsured job accident I have not been able to ride or wrench for almost a year and I will have to sell my recondiotned 78 R-80. I did sneak out and ride it over the weekend, only a few miles, dont tell my wife

But I do have another bike an 85 R80 RT that I dissassembled about a year ago ( before accident) and I need to put it back together and probabally sell too
was noticing, that somehow over the past year that my paint marks have dissappeared on the clutch pressure plate. It might have happened when I was cleaning everything, a year ago had made some mental note, and then I was gone
So isnt the balance critical to these bikes, and if so, how would a person rebalnce it.
thanks

 

[PGlaves]

See if you can detect any of the original factory marks - white or yellow paint smudges. Not likely but worth a very careful try.

Then, maybe a good machine shop can balance it.

Or, trial and error - because that's all that's left.

It's a little late to mention this - but when I take one apart I apply paint - but then use a small pin punch to mark each piece. Pin punch marks don't wash off like paint does.

 

[72828]

Hi Paul,

Just a quick question that might also help here.

When completely renewing the clutch assembly aft of the flywheel (just done on a '75 R75/6), my "trouble-free" approach was to simply replace the entire package. It was a bit pricey, but after 35 years of service, it was most likely due.

Given that these parts are made with reasonably close tolerences and semetric about the crankshaft centerline, is balancing really that much of an issue? Past experiences doing the same thing on an R100/7 and R100GS seemed to show good results.

Just curious.

Thanks for your insight!

Rgds,

Marley

 

[ISAMEMON]

I should have punched it, but was expecting to put it back the next day, wiht paint marks on it, alas its been a year and the paint did not stick

Marley made reference to putting them back wihtout attention to marks

I dont want to have problems, and tranny was just rebuilt ( last year)

what would be the negative effects of out of balance or harmony

when you get a new clutch , what is in in balance, are we assuming you will line it up with some mark on the flywheel if present ?

thanks Paul I like all your posting and articles in ON

 

[PGlaves]

Hi Paul,

Just a quick question that might also help here.

When completely renewing the clutch assembly aft of the flywheel (just done on a '75 R75/6), my "trouble-free" approach was to simply replace the entire package. It was a bit pricey, but after 35 years of service, it was most likely due.

Given that these parts are made with reasonably close tolerences and semetric about the crankshaft centerline, is balancing really that much of an issue? Past experiences doing the same thing on an R100/7 and R100GS seemed to show good results.

Just curious.

Thanks for your insight!

Rgds,

Marley

Everything is manufactured to tolerances - what BMW decides is "good enough." They then take the extra step of marking the three parts: flywheel, pressure plate, clutch cover - so that they can be assembled with the three marks as close to 120 degrees apart as you can arrange them. This is to prevent stacking tolerances so that all the heavy spots align or all the light spots align.

In my experience it does make a difference. Voni once had an R80/7 that had a vicious vibration at certain engine speeds I couldn't get rid of. After a couple years of field events at rallies almost every weekend all summer it needed a clutch. I pulled it apart. I marked the three pieces. Once it was cleaned up I discovered that the three factory marks had been lined up - not separated. I put in a new disk only, but correctly dispersed the factory marks, ignoring mine. That vicious vibration absolutely disappeared.

Enough imbalance at this location will increase wear on the engine rear main bearing and on the transmission input shaft front bearing along with their associated seals. It is a true crapshoot as to how much risk there is - because that depends on how close to balanced each piece is, and how stacked the heavy spots are.

Worse - the psychology is such that you feel the slightest vibration, wonder if it is the clutch, and wonder if taking it apart and putting it back together differently will make it better or worse.

No good answers except to try very hard to find the mark on the flywheel at least, and to then replace the pressure plate and clutch cover with new ones with visible marks. Two out of three is better than nothing. Then at least you have only three options for the flywheel.

 

[72828]

Thanks Paul,

I appreciate your help.

I guess that I will tear the rear end off of this R75/6 once again and look for the marks. I'm gettting pretty good at it.

As this is a '75 version, can you please provide some insight as to what the flywheel, pressure plate and compression plate marks look like? Will they be obvious on all three parts?

I would think that the greatest challenge will be the flywheel mark as it is 35 years old.

Thanks again,

Marley

 

[PGlaves]

Thanks Paul,

I appreciate your help.

I guess that I will tear the rear end off of this R75/6 once again and look for the marks. I'm gettting pretty good at it.

As this is a '75 version, can you please provide some insight as to what the flywheel, pressure plate and compression plate marks look like? Will they be obvious on all three parts?

I would think that the greatest challenge will be the flywheel mark as it is 35 years old.

Thanks again,

Marley

BMW's suppliers have not been consistent in how they marked things over the years. Generally however it has been a smear of what looks like white or yellow paint. The last Airhead clutch I installed had what looked to be a small child's thumb print in white paint. Not with fingerprints, but about that size and shape.

That said - how does the bike feel at 3,500 or 3,800 or 4,000 or 4,200 rpm. Does a vibration come and then disappear as you gently accelerate through these rpm ranges. If not - have some coffee and leave the wrenches alone.

 

[72828]

Thanks again Paul,

This is one of those project bikes that is slowly coming back together. I am waiting on the heads to come back from the shop and then I will finish up the project.

It's just sitting in the garage waiting for its top end. I guess that it is better to take the rear end off now rather than later and yes I am one of those people that will question those errant vibrations and wonder about the clutch installation.

Best regards,

Marley

 

[Rinty]

A buddy of mine, a long time BMW rider, had a highly modified K75S that had had a bunch of mysterious things wrong with it, and had been disassembled at least once. The clutch and flywheel had multiple marks on them, and after it was back together, he thought it was buzzier than before. A couple of techs rode the bike, and thought it felt like a normal K75.

My buddy kept complaining, and, on my suggestion, he took the clutch / flywheel assembly to a machine shop to have it balanced. The shop had to make a special rig to attach it to their balancer, and got it balanced on the first try. After re-assembly, my buddy found the bike to be perfectly smooth, but he was rear ended a month later, and the bike was written off.

He now rides a Wee Strom.

 

[72828]

Well, the R75/6 is now back in bits and pieces and guess what. NO MARKS on any of the new factory parts.

I did find the flywheel mark, but with no marks of ANY kind on any of the new BMW parts, I guess I get to go with the trial and error process.

Marley

 

[88bmwjeff]

Two out of three is better than nothing. Then at least you have only three options for the flywheel.

I ended up having to do this on my 88 R100 RT. No matter how hard I looked, I could not find a mark on the flywheel/clutch carrier. I was new at wrenching on the bikes, so I didn't mark the parts before I removed them.

 

[r60us]

Well, the R75/6 is now back in bits and pieces and guess what. NO MARKS on any of the new factory parts.

I did find the flywheel mark, but with no marks of ANY kind on any of the new BMW parts, I guess I get to go with the trial and error process.

Marley

I've also encountered the new parts dilemma. Not much you can do. Just for interest sake, before assembly, place the diaphragm spring in the flywheel and notice how sloppy the fit is. If the diaphragm isn't centered in the flywheel, I would think it could be a source of vibration. Obviously this wasn't a concern for BMW but it has always bothered me and as an experiment, last year when assembling an R100/7 and an R60/5, I centered the diaphragm and took up the clearance by wedging several equally spaced tiny 5mm long slivers of cardboard around the edges of the diaphragm and trimmed off the excess height flush with the diaphragm. The total weight of the cardboard didn't move the pointer on my gram scale, so they won't affect balance should they escape and move around. Unfortunately to do this the engine needs to be out of the bike and placed "face down" with the flywheel in a horizontal position so the cardboard stays in place during assembly. I know it sounds stupid and probably a coincidence but both engines are really smooth runners - smoother than other rebuilds with new parts. Who knows...

FWIW. YMMV

 

[From MARS]

When I replaced some of the clutch parts on my '93PD, a string was run thru the center of the flywheel with the clutch parts (minus the clutch plate) stacked and screwed lightly together. When suspended with the marks 120 degrees apart, the unit hung to one side. After rearranging the parts (moved the clutch housing and spring plate marks closer together to offset the flywheel) it hung level. The bike is back together and it is very smooth.

There is a thread describing this on here. Maybe a search will bring it up.

Edit: I ran a search and it brought up this:
http://forums.bmwmoa.org/showthread.php?t=32881&highlight=clutch+balance
Hope it helps.

Tom

 

[RecycledRS]

How do you get the string or rope centered exactly???

 

[PGlaves]

How do you get the string or rope centered exactly???

Maybe with a cone - or maybe you don't, exactly - but close is a lot better than not close. If you want "exactly" take it to an automotive machine shop that specializes in blueprinting engines and they can give you exactly. It will more than double the parts of the clutch - but you will get exactly - or at least almost exactly.

As my good friend and Best Man at our wedding once said, "It isn't like we're trying to send a man to the moon or something. This is a problem that can be easily solved by throwing money at it."

 

[ISAMEMON]

the string idea is intersting, kind of like an old car wheel balancer in tought
ill have to look at the cheap way now, out of work adn selling my old "reconditioned" 78 R80
and no short cuts were taken with that one

 

[From MARS]

the string idea is intersting, kind of like an old car wheel balancer in tought
ill have to look at the cheap way now, out of work adn selling my old "reconditioned" 78 R80
and no short cuts were taken with that one

Sorry for being slow to reply. The idea is exactly like the old wheel balancing machines.

I used a piece of 1/4" rope with a 1/4" fender washer held on one end by melting the rope and forming a ball on the end of the line. After running the line through the center of the flywheel and up through the pressure plate, spring plate and clutch housing, I suspended the unit and measured from the bolt holes in the flywheel to get centered. The parts were held together by screwing in the clutch bolts (loosely). Then, I moved the parts around to find the optimum arrangement.

The flywheel must be reinstalled in the original position for timing purposes, but the arrangement of the rest of the parts can be changed.

Hope this helps.

Tom

 

[ISAMEMON]

thanks guys

I trully believe in what PGraves says, wish I had the money (unemployed).
So thanks Mars for the work around, Ill have to try it

 

[TGHSMITH]

I used the cone from a lawn mower blade balancing and sharpening kit(Ace hardware) first tried it on the spindle that came with it(didn't work) so I drilled a small hole in the cone tip and strung a line and used it as a dangle balance, the cone is stepped and needed to be worked a bit to get the flywheel to fit well, everthing looked great so I moved the peices and the balance was off, so back to the first placements and into the bike, smooth sailing....

 

[From MARS]

thanks guys

I trully believe in what PGraves says, wish I had the money (unemployed).
So thanks Mars for the work around, Ill have to try it

You're welcome. Good luck.

Tom