Driveshaft Phasing?

[EEC]

I understand the driveshaft phasing and I have looked at 3 K100RS shafts including a new one at the dealer and none were perfectly phased. All were off perfect alignment by about one tooth. Is this acceptable?

 

Thanks

 

Dale C.

[smiller]

Exact phasing isn't super-critical unless you have a high driveshaft departure angle, not really the case with BMW motorcycles so I wouldn't sweat it. But since you've seen three (including a brand new one) that looks the same it kind of makes me wonder if the offset isn't intentional for some reason. I've never seen that before though.

[T__]

I understand the driveshaft phasing and I have looked at 3 K100RS shafts including a new one at the dealer and none were perfectly phased. All were off perfect alignment by about one tooth. Is this acceptable?

 

Thanks

 

Dale C.

 

Dale, I know very little about the K100RS (rode one once)..

 

On basic vehicle drive shaft U-Joint alignment there are a few issues that come into play..

 

First,, is the offsetting U-joint angles.. If the front U-joint is operating at 2° & the rear U-joint is operating a ½° angle then proper phasing probably has little meaning.. The reason you phase U-joints is to have one operating shaft angle (therefore mid shaft accel/decl per rev) offset the shaft’s second U-joint angle (decel/accel per rev).. If the joints operate at different angles then phasing is much less effective..

 

Secondly,, sometimes U-joint phasing is purposely skewed due to shaft angle offset in another plane (ie the lateral output centerline is different than the lateral input centerline).. This is usually due to engine or final drive offset from vehicle centerline for one reason or another.. Sometimes a mis-matching couple of degrees of U-joint phasing can remove a vibration or harmonic set up from lateral misalignment or lateral angular mis-alignment..

 

There is also the phasing issue under drive torque.. You really want the U-joint phasing closest under shaft loading at nominal drive loads.. In a rubber isolator type shaft the phasing can be skewed slightly so the U-joints match up to closer phasing under normal drive loads..

 

I don’t have an answer for you on your K bike question just thought a little understanding of shaft alignment & effect could help you..

 

Twisty