Clutch failure R90S

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adrian967
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Clutch failure R90S

Postby adrian967 » Sun Jun 10, 2018 2:23 pm

Bugged,
3 miles up the M1 and the clutch fails..the last time it went was when the spokes broke on the clutch plate even though there was plenty of meat on the linings...is it time to renew pressure plate and all the bits?
I can do the job myself and can have the gearbox out in little over an hour.

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CharlieVictor
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Re: Clutch failure R90S

Postby CharlieVictor » Sun Jun 10, 2018 3:52 pm

It's not a very expensive job if you do it yourself.
1978 BMW R100S "Naked"
1999 W65L "Twin with a kick"

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Re: Clutch failure R90S

Postby Jockboxer » Sun Jun 10, 2018 5:41 pm

Does the friction plate have life left in it? Check with a caliper / micrometer against specification. If so, then you might get away with a sh pressure plate. Give Motorworks or Sherlock a call and have a chat / see what they've got?

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Rob Frankhamr
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Re: Clutch failure R90S

Postby Rob Frankhamr » Sun Jun 10, 2018 8:19 pm

Sorry, I'm probably being a bit dim... but... spokes on the pressure plate??? Not sure what you are referring to...

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Mark Esposito
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Re: Clutch failure R90S

Postby Mark Esposito » Sun Jun 10, 2018 9:00 pm

I'm guessing but my money would be on the "fingers" of a diaphragm spring.

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Re: Clutch failure R90S

Postby adrian967 » Sun Jun 10, 2018 11:30 pm

The bit with the lining on ...4 spokes I think..the last time these sheared

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Rob Frankhamr
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Re: Clutch failure R90S

Postby Rob Frankhamr » Mon Jun 11, 2018 12:26 am

Hmm,

The bit with the lining on is the clutch friction plate and on the R90S, this is a solid disc (apart from some small holes). The later clutch disc (post 1980) does have six spokes but this shouldn't fit on the R90S. Could it have been an aftermarket replacement I wonder?

Images of the clutch discs can be found on this page... https://www.motorworks.co.uk/vlive/Shop ... 5_20_CA_30 (the later disc is on page 2)

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Re: Clutch failure R90S

Postby Jockboxer » Mon Jun 11, 2018 2:58 pm

The bit with the lining on ...4 spokes I think..the last time these sheared
I assumed you meant the diaphragm. A friction plate failure is usually caused by the splines shearing either on the plate or on the gbox input shaft. This is a well known BMW foible. You need to pull the gbox back and remove the clutch for inspection.

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Re: Clutch failure R90S

Postby adrian967 » Wed Jun 13, 2018 7:50 am

Further to the failure.....splines have failed on the gearbox input shaft taking the clutch friction plate with it..is it an easy fix?

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Rob Frankhamr
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Re: Clutch failure R90S

Postby Rob Frankhamr » Wed Jun 13, 2018 9:46 am

Further to the failure.....splines have failed on the gearbox input shaft taking the clutch friction plate with it..is it an easy fix?
Sadly the answer has to be no, it's either going to be a relatively easy but expensive fix or much more involved but somewhat less expensive.

Firstly, the clutch disc will have to be a straight replacement... no other real option.

As far as the input shaft goes, it depends if you feel competent to rebuild the box. It's within the skills of a competent amateur wrench but does require a couple of special tools (to whit an output shaft puller, a shimming plate along with a precision depth gauge and a BIG torque wrench to loosen/re-tighten the output flange nut... not to mention a certain amount of brute force :smile: ). While you're in there, you'll probably want to replace the bearings, seals and shift mechanism springs as a matter of course.

The alternative is to buy a replacement box. A rebuilt box is going to set you back around £500.00 (+P & P of course) but it will save you a lot of hassle. Alternatively, you could probably source a second hand unit but then you run the risk that it will have similar (or different) issues.

At the end of the day, you pays your money and takes your choice. The joys of running a 40 odd year old machine [-o<

The only other thing to say (and excuse me if I'm teaching grandma...) you must replace the gearbox with a pre'80 - smooth sided box. The later box with ribbed sides will not fit to the earlier clutch/flywheel.
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Rob Frankhamr
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Re: Clutch failure R90S

Postby Rob Frankhamr » Wed Jun 13, 2018 9:58 am

Further to the last, I don't know where you are based... as you can see, I'm in the middle of Scoland and I surmise from the M1 reference that you're quite a long way south... but I do have a spare smooth sided box. I took it out of my R60/6, replacing it with one I'd rebuilt earlier, at the last major overhall. The old box feels a bit loose but has no known major issues. My intention is to rebuild it as a spare when I get time.

If it would keep you on the road, I am quite willing to loan it on a temporary basis while you get yours sorted... the only issue is transport.

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Re: Clutch failure R90S

Postby adrian967 » Wed Jun 13, 2018 12:15 pm

Very generous offer Rob, I've spoken to Roger Bennett who is local to me, and he is going to take a look next week...he thinks it's not too bad from my phone description. Will keep the group posted if anyone is interested.

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Re: Clutch failure R90S

Postby adrian967 » Wed Jun 13, 2018 12:17 pm

An addition to the job...my 90s has a light flywheel and later clutch adapted by Keith Shaw some years ago.
No visible spring on the clutch arm.

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Re: Clutch failure R90S

Postby Mark Esposito » Wed Jun 13, 2018 12:26 pm

Very generous offer Rob, I've spoken to Roger Bennett who is local to me, and he is going to take a look next week...he thinks it's not too bad from my phone description. Will keep the group posted if anyone is interested.
I'm very interested, please keep us posted.

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Re: Clutch failure R90S

Postby Mike D » Wed Jun 13, 2018 12:46 pm

If buying another gearbox, it doesn't have to have s smooth casing. My 1978 R100 RS has a ribbed box and as I bought new, I know it's original. But as Rob said it DOES need to be suitable for the heavy flywheel models.

The obvious way to check is to compare the clutch arm mechanism as the are different. The input shaft is also different.


Mike

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Re: Clutch failure R90S

Postby adrian967 » Wed Jun 13, 2018 2:02 pm

Yes Mike but mine is a smooth case, light flywheel with later actuation arm..no visible spring.
Thanks

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Re: Clutch failure R90S

Postby Mike D » Wed Jun 13, 2018 7:37 pm

Sorry Adrian, I missed that post where you said you had a light flywheel fitted.

Mike

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Rob Frankhamr
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Re: Clutch failure R90S

Postby Rob Frankhamr » Wed Jun 13, 2018 10:19 pm

An addition to the job...my 90s has a light flywheel and later clutch adapted by Keith Shaw some years ago.
No visible spring on the clutch arm.
Ah... that explains a lot of things... notably why the friction plate has 'spokes'...

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Re: Clutch failure R90S

Postby Jockboxer » Thu Jun 14, 2018 10:24 am

I thought so! This is is from the ukgser forum.

2x airhead gearboxes for sale
Evening all,
I have two pre 81 gearboxes to sell,
Both have really nice internals and will be fully refurbished with new bearings ,seals and camplate springs,with a roller upgrade.
Casings will be vapour blast cleaned.
I can offer these with either an early smooth case or the later ribbed type,
One of these on an exchange basis from motorworks is £510
Or an extra £144 if you don’t have a serviceable unit to exchange.
My price is £420 each plus post or collect Melton Mowbray
Some pics to illustrate the different casings and the finish once vapour blasted.
Pics 1&2 are the later ribbed case
Pic3 is early smooth case.
Neither box is kickstart

Mike is a first class engineer. Give him a.call on 07786 340692

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Re: Clutch failure R90S

Postby adrian967 » Thu Jun 14, 2018 11:29 am

Thanks Jockboxer

Will give a call if mine doesn't pull through

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Rob Frankhamr
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Re: Clutch failure R90S

Postby Rob Frankhamr » Thu Jun 14, 2018 7:07 pm

Thanks Jockboxer

Will give a call if mine doesn't pull through

The problem there is that the gearbox you have is a 'hybrid' it has the internals (or at least the input shaft) and rear cover of a post '80 'ribbed' box installed in a smooth pre'80 casting. That's the only way to make the 'lighter' clutch work with a smooth box. You could-

  1. Install a post '80 ribbed box direct or
  2. revert to the old 'heavy' clutch/flywheel combination with a replacement smooth pre'80 box or
  3. have your existing box rebuilt.
What you can't do is simply bolt up another pre'80 box... it won't work.

Sorry to be a Jonah

Rob
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Re: Clutch failure R90S

Postby adrian967 » Thu Jun 14, 2018 9:23 pm

Yes I know that Rob....I may need to find a good box builder....what causes the failure anyway? I think Siebenrock were in there last (3 years ago)whilst doing other work.
Couldn't see any grease on the splines.

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Re: Clutch failure R90S

Postby Jockboxer » Fri Jun 15, 2018 8:40 am

As i said ... Get in touch with Mike to discuss options. I doubt it there's anyone in the UK who knows more about airhead engineering.

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Re: Clutch failure R90S

Postby Rob Frankhamr » Fri Jun 15, 2018 9:26 am

Yes I know that Rob....I may need to find a good box builder....what causes the failure anyway? I think Siebenrock were in there last (3 years ago)whilst doing other work.
Couldn't see any grease on the splines.
That's probably it then... although it is an area naturally prone to wear and gease on the splines can only put off the invevitable for so long. As for other causes, apart from the obvious defective component, a dragging clutch wouldn't help, nor would unmatched gear changes and, of course, a heavy right hand will mean more wear. It's very difficult to aportion blame without knowing the use a bike has been put to over the years. A bike that is used extensively in town or on country roads or, for that matter in a racing type scenario...any use where there are frequent gear changes and heavy acceleration/engine breaking will experience quicker spline ewear than one that is used for constant speeds on a motorway.

The other thing I would definitely want to look at is the input bearing. any radial movement there would cause rapid spline wear.

Good luck

Rob
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Mark Esposito
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Re: Clutch failure R90S

Postby Mark Esposito » Fri Jun 15, 2018 9:31 am

Are there any early warning signs of this type of failure or airhead models that are more prone to this.

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