KZ650 cafe-racer

It may sound strange, but having the new OEM cylinder head and valves I decided to perform valves leak test. Therefore I installed all valves (without valve seals, sure).



Then I performed a classic leak test using gasoline.



Intake valves seem to be tight, but couple of exhaust valves after some time shown signs of not complete tightness:

Then I performed the test in which combustion chambers are to be filled with liquid and compressed air are to be blown into intake and exhaust ports. I didn’t like the idea to use water on brand new valves so I filled the chambers with kerosene.



This test takes more activity from the tester, but it also shows results much quicker than classic test. It confirmed the result of the classic test. It’s likely that valves became tight during the work of the engine, but I didn’t wish to take risks. I decided that even fine lapping compounds I have at hand will be coarse for the job, so I made my own compound from the mix of “coarse” polishing compound and oil. This soft “lapping” left no scratches but only shimmering traces on the valves and it did the trick, so all valves became tight.

Here is short video in before/after style. In second part I used improvised restrictor to create a pressure in ports.

Since I “lapped” every valve to a specific seat, now every set has it’s numbered compartment in the box I use for storing cylinder head components. This box has seen quite a lot of valves, a very useful thing as it’s compartments could be easily readjusted for 8 or 16 valves. Here it is with a set of parts ready for final assembling:





And to finish this part of the story here is a little illustration where curiosity could lead the man. So far I have three KZ750 cylinder head and one KZ650 cylinder head. Three of them have complete set of valve shims and one had only 7 shims. And when it came to making inventory of valve shims I became curious about shim sickness distribution. So I measured all shims, printed the table to fit shims and here we are:



Kawasaki KZ650-750 (including ZR750 Zephyr and ZR7) valve shims range from 2.00 to 3.20 so we could say that distribution of shims is slightly shifted from the centre to thinner ones.

Well, I since I was couple of times asked via email about KZ650 secondary shaft damper rubbers, I wrote a kind of article about them.

So the subject of these posts 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.



However, I wonder: why Kawasaki didn’t bother to indicate 92075-1227 as part number that supersedes 13098-029?

In the course of KZ650 engine pre assembling preparations I had yet one job to do: cleaning oil pan (came from 1991 Zephyr 750 and has ports for oil cooler), transmission cover and bearing cap. Bearing cap and transmission cover looked not bad after being washed with gasoline and soaking cleaning solution I use for aluminum parts, however they needed to be brightened a bit.

However, the oil pan was a rough case: it’s insides were all bright and nice after gasoline, cleaning solution and high pressure washer, but outer surface was a mess of grey aluminum, dirt and oxidation, and remains of old paint, that no pressured gasoline, nor pressured water were able to remove,. My first idea was to treat it with glass beads blasting. But the closest workshop that could do the proper job is placed some 25 kilometers from my garage; and with only one part to blast and all that snow that we’ve got in the middle of the winter (not mentioning low temperatures) glass beads blasting didn’t seem to be a very bright idea. And anyway, I don’t like the finish after glass beads blasting, I like my oil pans to be semi polished.

So I replenished my abrasive supplies and proceeded to the work. Couldn’t say it was an easy cake, but as Terry Pratchett’ Nac Mac Feegles were used to say: “Just that? Nae problemo!”. To give you idea of what was done, here are photos in pairs “before” and “after”:

Doing the work, I had to constantly remind myself: we are not going to polish the pan, we just make it look decent… Looks like I managed to persuade myself not to do polishing, however I indeed did some sandpapering to remove casting flaws like this:



The pan looks pretty nice after I finished with it.

I also painted an oil plug (which was made not removable in case of Zephyr 750) to increase its corrosion protection.



And here are the bearing cap and transmission cover I mentioned in the beginning.Just clean parts ready for further usage.