Clunk when overrun/acceleration

[Adamastor]

Hi there once again... I hope I am not creating too many threads but here is another doubt that has arrisen:

- I never had before any bike shaft driven, so this might be normal or not.
-> If I de-decelerate and then accelerate I hear a clunk coming from behind. Apart from the noise I can also feel a little vibration on my feet.
Is this normal on cardan driven bikes?

If I put the bike in gear and try to rotate the rear wheel I only get about 2cm (0.8 in) of distance measured on the ground between stops. This doesn't sound too much, is it?
where could this clunk come from? Is it safe to run the bike like that?

Many regards, and thanks once again for the help...

Sergio

[Bob_Roller]

The 'clunk' is not normal on a shaft drive bike .

The .8 inch 'free play' at the rear wheel is not uncommon .

There is a spring loaded ball and socket type assembly on the cardan shaft, that takes up any shock, or jolt in the drive train during shifting .

Possibly a weakened spring allowing the assembly to pop, or rotate a half revolution when it gets loaded, then seats again .

[Adamastor]

If I rotate the rear wheel, in no gear, in both directions I hear a small "tak" noise coming from the rubber boot. It looks almost like there is some play in there.
Could it be this play that makes a louder clunk when driving the engine/bike?

[Bob_Roller]

There are four 12 point bolts that secure the drive shaft to the transmission output flange, see if you can feel the four bolts through the rubber boot .

There have been instances where the bolts became loose .

Also, if the swing arm pivot bolts aren't adjusted properly, the universal joint inside the boot, can contact the swing arm tube itself .

[Adamastor]

Also, if the swing arm pivot bolts aren't adjusted properly, the universal joint inside the boot, can contact the swing arm tube itself .

-> Wouldn't I feel the rubbing and/or some drag on the wheel?

And yes, I could feel the bolts. The most certain suspect would be a worn spring? This would cause the clunk when the rear wheel doesnt match the engine revs? (both on overrun and acceleration) ?

(I know I ask too much... I will have to pay you all a six pack one of these days when you come to Portugal ehehe)

[Bob_Roller]

You wouldn't necessarily feel anything by moving the rear wheel .

Usually you will hear a clicking, or light scraping sound from around the rubber boot, when you rotate the rear wheel through a few revolutions, if the pivot pins aren't adjusted correctly .

[Adamastor]

I will go for a little walk to test how this goes...

If forgot to mention, when I bought the bike and changed oils, there wasnt much oil on the driveshaft, I drained only about 70ml when it is supposed to have 150ml, right?

[Bob_Roller]

I think the specified amount of oil is 150-180 ml .

[Adamastor]

Got back from the test ride (not walk, lol). What I felt:

-> I only feel the clunk at lower revs, bellow 3000rpm

-> At about 2000rpm (and below)  I feel on my feet some rattle and a bit of vibration noise.
She always done that, and I assumed these engines are supposed to vibrate a lot (specially this one with a lot of miles on it).

-> Since I done the spline lube job, I re-centered the swing arm pivot bolts with equal space on both sides (between the swing arm and the bike frame). It was not scientifically tested, but seemed ok.
If it is not 100% centered could with the lower revs higher vibration be touching somewhere? Could it be that I didnt torque the inner bolt enough and it is a bit loose?

When I changed all the oils I saw no metal neither on the gear box, driveshaft or final drive.

Apart from that I actually enjoyed this little night ride and I would love to take her tomorrow to work (35 km distance).

Any ideas arise?

[Bob_Roller]

Usually the universal joint, or what ever else can make contact with the swing arm housing, will make noise all the time, rpm range shouldn't be a factor .

The swing arm pivot bolts get a pretty good torque value, I think it's in the 100 foot/pound range, so if you just snugged it up, you may want to torque it a bit more .

You may want to look the bike over for loose fasteners, elsewhere, like the exhaust system, engine mount nuts, if you have a rubber hammer, try tapping around, and see if you can hear anything vibrating, I had a loose baffle in one of my mufflers, that wouldn't start vibrating until the engine got to around 4000 rpm, took me quite a while to locate that one .

The center stand can be a common source of vibrations, if the springs, and the attach hardware is loose, or worn .

[Adamastor]

The swing arm pivot bolts get a pretty good torque value, I think it's in the 100 foot/pound range, so if you just snugged it up, you may want to torque it a bit more .

Hi Bob once again, this might be dumb asking (or not) What does need all that torque? The swing arm pivot pin or the 27mm locking nut? (I torqued hard the locking nut but left the pivot pin hand tight)

Have we found my problem?

[Bob_Roller]

The pivot pin has a torque value of : 10-12 N/m, 7-9 foot/pounds .

The lock nut : 100-110 N/m, 72-79 foot/pounds .

That's out of the BMW shop manual .

I don't know if you can get the full torque valve on the lock nut, without slipping off, but needless to say it's torqued pretty tight .

[Adamastor]

Just came from the garage, and checked out the pivot pins and locking nuts.
Did a more precise centering and then hand tightened the pivot pins. I think they were a bit loose. The 27mm locking nut was torqued hard (dont know how much).
I guess hand tight would be near 10/12N/m and I don't have anything that measures 100 N/m so I torque it hard with a large tool.

Its a bit too late to go for a walk, but tommorow morning I will get back to tell you if the clunk improved or disappeared. It would make some sense to happen if the pivot pins were too loose, right?

The other noise on the driveshaft might be normal play when you rotate the wheel from one direction to the other..

[Bob_Roller]

Turning the wheel by hand when the transmission is in gear, you get a bit of noise when you get to the end of the freeplay .

[MrRiden]

Just to confuse things I'll toss this out of left field. Is the engine mount bolt tight? Did someone rubber mount the engine or are there solid spacers between the frame and crankcase.
Returning to left field,
rich