Forum bmwbike.com

Purchased an R26 with unknown history (presumably restored). Bike vibrates horribly (literally dances around when idling, spilling battery acid all over the place).
After checking the usual suspects decided to strip the engine. All seems well (steel conrod with large counterweights, cranckshaft and bearings visually ok. Only concern is conrod:
Play at bigend is about 0.15 mm which seems ok, no up-and-down play discernable, but rod can tilt about 1 mm on small end side. Is this a problem ?
Another slight problem emerges from the long time between stripping and rebuilding and my fading memory: I found a 4 mm steel ball between the disassembled engine parts, but haven't got a clue where it came from or where to put it. Any suggestion welcome.

This is a group for singles only.Lot of experts here http://autos.groups.yahoo.com/group/bmw ... /messages/"
Harry

Hey jos,
does the 26 runs well? or do you have there also some problems?
Greetings
Rolf

Rolf,
I haven't been able to use the bike because of the vibrations. But it starts well, and the vibrations seem to be a little less at higher revs (possibly because of the higher frequency, it was still enough to kill a batterie in 10 or so miles)

A couple of things to check
- Was timing correct? Check marks when piston is at TDC
-Has crank been misaligned when last assembled?-check runout
-Was incorrect piston used in prior rebuild? let me know weight and I will weight an old one of mine
- Is nose of crank (where rotor for generator mounts) running true - I have seen them bent.
-Was flywheel mounted correctly ? Key way and key possibly damaged?
-All motor mounts tight with good rubber
-was cam timed correctly?
-review picture(original from Hugget I believe) does your crank have larger weights or does it look more like lined in area.

Good luck!

let us know what solves the vibration problem

Bob,
I've checked everything against the collective wisdom of this and other forums:
- ignition timing and advance mechanisme
- valve timing
- cranck and flywheel alignment
- crank balance factor (about 57 %)
- fitted new rubber motor mount
Piston is Nural 3rd oversize (69.44 mm) with 3 rings. Ring gap for oil ring is way out (about 0.7 mm) .
Weight is 240 gr (without rings and pin)

Hey,
it could be only the crancshaft, so bad vibrations. You are sure that you have the right counterweights?
Does the engine (maybe it is not to hear because of the vibrations) any noises?
I would put the cancshaft out and look at it, there could be that his counterweights are not parallel (mostly you can hear that, because the noise of the bearings, they are loud grumbling).
I think you have controlled valve and ignition timing (?).
Than there must be a bearing problem (because of the counterweights or something else).
greetings
Rolf

Hi Josh, is this your first R26? They are wonderful little singles but would viberate your teeth out . It is not unusual for the leading edge of the rear fenders to be pock marked with battery acid damage. Many of these models viberated so badly that the fenders would fatigue crack. Even the Isolated R27 would "walk" on its center stand with a twist of the trottle if it didn't pop back through the carb and stall first. If it starts, takes trottle, and doesn't make noise, then use it . If it makes power, then ride it to the nearest R26 owner and compare. Good Luck Josh, and best regards. Phil Cheney

Hi fellow R26 numb handed drivers. Mine ticks over nice and smooth then tries to self destruct on opening the throttle. I never mention this to admirers of the bike, who think it's such a lovely looking and smooth running bike! Recently shed the left footrest at 50 mph, luckily found all the bits.
Alan

Vibration problem partly solved !
One of the previous owners made a mess of the front engine mount, using shock absorber silent blocks to mount the engine. After restoring the engine mount to its original specs the level of vibration has dropped dramatically (actually not the level of vibration, but the propagation to the rest of the bike). Bike will now stay put when idling.
Thanks for the suggestions and support.