The subject of this post is Kawasaki KZ650 secondary shaft dampers. These dampers are positioned between two couplings: one of them is connected to the crankshaft through the primary chain while other seats on the secondary shaft. So these rubbers are pretty important since they in combination with clutch basket dampers damp jerks in both directions: from crankshaft to gearbox and from gearbox to crankshaft. Also these rubbers cease vibration of primary chain and since engines of motorcycles like KZ650, KZ750 and ZR750 Zephyr aren’t equipped with primary chain tensioner this function of dampers are of importance too. The less are vibrations of the primary chain, the less is its distinctive rattling sound that could be heard on idle even on motorcycles which carburetors synchronized all right.
So it’s obvious that secondary shaft rubbers, once they become hard, have to be replaced. Part number for KZ650 secondary shaft damper rubber is 13098-029 and as one may check, it’s already marked as “not available” on websites of such big parts suppliers like Partzilla, MAS and CMSL. And there are no part numbers that Kawasaki marked as superseding for this part number.
Anyone who bothered to check parts lists , will find that part numbers for both, inner coupling and outer coupling (also called secondary sprocket ) of secondary shaft are identical to the part number of the same parts for KZ750, GPZ750 Zephyr 750 and ZR7. However, the part number for damper rubbers in question for these bikes is different, it’s 92075-1227. To add more havoc, it’s pretty hard not to notice that KZ650 rubber is longer than rubber for KZ750/Zephyr 750. Here they are, 92075-1227 secondary shaft damper in comparison with original KZ650 rubber.
Therefore, one might have a question like: “What the hell is going on and could I use 92075-1227 instead of 13098-029?” If shortly, the answer is yes, one may use later 92075-1227 rubbers to replace early 13098-029 dampers even if Kawasaki didn’t state this fact clearly. But let’s do some explanation.
We have to ask ourselves why Kawasaki replaced longer rubber with a shorter one? Answer for this question might be found in the course of visual inspection of parts. Damper housing consists of two parts, or couplings, with every rubber placed between the blades of outer and inner couplings, thus momentum from the crankshaft is transferred through rubbers. Outer coupling is fixed on inner coupling by circlip which prevents outer coupling from axial movements.
If we take a closer look under the fixing circlip of our KZ650 damper housing, we’ll find that it “ate” the trace in outer coupling. It’s not natural and could mean only one thing: there was excessive axial pressure which pressed outer coupling against circlip.
Now let’s take a look at the ends of dumper rubbers. New shorter rubbers have ends with rounded edges and so had original KZ650 rubbers when they were new. However, one or both ends of used KZ650 rubbers became mostly flat and the ends’ edges became much sharper. Therefore we could quite rightfully guess that these rubbers were under the pressure and that pressure deformed them.
During the work of the engine outer and inner couplings squeeze rubbers by blades. And if uncompressed rubber is already fit tight between the bottoms of both couplings, being squeezed by blades it tries to expand in axial direction and therefore creates axial pressure on couplings. Add to this potential heat expansion and we’ll get a pretty plausible explanation why Kawasaki replaced longer damper rubbers with shorter ones in KZ750 models.