My 1954 R 68 is now "alive" but little problems have arisen with the clutch and transmission. Having adjusted the clutch cable/mechanism to the desired settings, once running, the clutch looses adjustment (i.e. does not fully release) resulting in difficult/noisy gear selection and the rear wheel commencing to turn, with force.
When the motor is stopped and the bike lifted onto the centre stand, the clutch and gearbox work ok when the gears are selected. The clutch appears to be original, is 4mm thick, in reasonable condition, (uncontaminated) and operated by six (6) new springs. The cable is new, together with the pushrod assembly. During the restoration process, the box was not opened, as all appeared to be functional. All seals were replaced.
The scenarios are.... loose flywheel, incorrectly shimmed crank...too much end float on the crank...warped/distorted clutch plate ...and/or excessive end float on the gearbox shafts.
I think that the gearbox will need to be removed.
Any clues?
PeeVee
Transmission problems: BMW R68
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Han Verhagen
Re: Transmission problems: BMW R68
Bonjour Philip,
On the plunger models I have only experience with a R25/2.
Of coarse all your senario's may apply. However the symptoms you describe could be explained by the front end of the pressure bearing touching the input shaft of the gearbox. This may happen if you forgot to install the small ball (Kugel) in between the the two parts of the pushrod.
On the plunger models I have only experience with a R25/2.
Of coarse all your senario's may apply. However the symptoms you describe could be explained by the front end of the pressure bearing touching the input shaft of the gearbox. This may happen if you forgot to install the small ball (Kugel) in between the the two parts of the pushrod.
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Allan Atherton
Re: Transmission problems: BMW R68
I would look at the actuation - first the clutch adjustment and next the thrust rod.
I adjust the clutch by screwing the handlebar lever adjuster all the way in, then screwing the transmission lever adjuster inward until the handlebar lever depresses the clutch, then I screw the handlebar lever adjuster out until the correct play is reached at the lever.
In the course of doing that, if the transmission lever adjuster cannot push the clutch far enough apart to completely disengage it, you will feel that and know that something could be amiss with the thrust rod.
I saw a bike that could not be shifted because its clutch thrust rod had become seized, then twisted at the thin place where the felt seal fits (photo below). More commonly, the tip of the thrust rod wears down and shortens the rod.
I adjust the clutch by screwing the handlebar lever adjuster all the way in, then screwing the transmission lever adjuster inward until the handlebar lever depresses the clutch, then I screw the handlebar lever adjuster out until the correct play is reached at the lever.
In the course of doing that, if the transmission lever adjuster cannot push the clutch far enough apart to completely disengage it, you will feel that and know that something could be amiss with the thrust rod.
I saw a bike that could not be shifted because its clutch thrust rod had become seized, then twisted at the thin place where the felt seal fits (photo below). More commonly, the tip of the thrust rod wears down and shortens the rod.
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Philip Vergison
Re: Transmission problems: BMW R68
Allan,
Your advice about transmission "actuation" proved to be correct. After removing the gearbox, it was determined that the clutch thrust rod had broken in the vicinity of the felt seal, after partially seizing. This partial seizure explains the squeaking sound from the box not long after the bike was initially kicked back into life.
The broken rod looks almost identical to the photograph you posted. And there are obvious score marks in that section of the rod close to the thrust bearing.
Fortunately, we have a spare rod and felt seal for installation AFTER it has been checked for fit.
Thanks for the advice.
PeeVee
Your advice about transmission "actuation" proved to be correct. After removing the gearbox, it was determined that the clutch thrust rod had broken in the vicinity of the felt seal, after partially seizing. This partial seizure explains the squeaking sound from the box not long after the bike was initially kicked back into life.
The broken rod looks almost identical to the photograph you posted. And there are obvious score marks in that section of the rod close to the thrust bearing.
Fortunately, we have a spare rod and felt seal for installation AFTER it has been checked for fit.
Thanks for the advice.
PeeVee
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Philip Vergison
Re: Transmission problems: BMW R68
Allan,
Just a note to let you know that your "guesstimate" about transmission actuation proved to be correct. Upon removal of the 'box, the thrust rod was removed in TWO pieces, having broken where the felt seal sits. There was evidence of the rod seizing/nipping up within the gearbox, which led to twisting forces that snapped the rod.
With a new rod and seal in place, the gearbox was re-fitted, the clutch adjusted and the machine kicked into life.
The bike has subsequently been on numerous trips around where I live, and has well and truly lived up to its reputation as a sporty machine in the true BMW tradition!
PeeVee
Just a note to let you know that your "guesstimate" about transmission actuation proved to be correct. Upon removal of the 'box, the thrust rod was removed in TWO pieces, having broken where the felt seal sits. There was evidence of the rod seizing/nipping up within the gearbox, which led to twisting forces that snapped the rod.
With a new rod and seal in place, the gearbox was re-fitted, the clutch adjusted and the machine kicked into life.
The bike has subsequently been on numerous trips around where I live, and has well and truly lived up to its reputation as a sporty machine in the true BMW tradition!
PeeVee