Kawasaki KZ650 cafe-racer. Timing chain tension system.

Earlier models of Kawasaki KZ650 as well as its even more famous brothers Z900, Z1 and Z2 (KZ900, KZ1000, Z750) have roller timing chain which, unlikely to modern silent timing chains (also known as hy-vo chains) needs quite complicated system of guide sprockets and rollers to be silent. Here is illustration from KZ650 part list:

Let’s simplify it to view of only guide rollers and sprockets.

As you may see, Kawasaki KZ650 cam chain tension system has three guide sprockets (positions 4 and 5 on picture above) one rubber guide roller (or idler wheel, position 10) and one rubber tensioner roller (position 12).  Sprocket 4positioned above cylinder head, sprockets 5 a placed between cylinder head and cylinder block and axle of rear sprocket is simultaneously axle of tensioner wheel bracket (12). Idler wheel 10 position is between cylinder block and crankcase, right above crankshaft timing sprocket.

Engine I have  for my KZ650 cafe-racer project has low mileage and its guide rollers and sprockets are in perfect condition and rollers still are quite soft after forty years.

I had no questions about sprockets, but as I prepared replacements for all rubber parts in engine I was wondering: should I have to replace those timing chain guide wheels as well?

Quick search showed that OEM rollers for KZ650 are no more available, but there are quite a lot of aftermarket replacement parts for Z900, Z1 and Z2.  However,  even as tension systems of KZ and it’s bigger brothers looks quite similar, part numbers for lower guide rollers and tensioner rollers are different. Idler wheels for KZ650 has part number 12055-004 while bigger Z-s have 12055-002 for that roller. Same is situation with tensioner wheels: part number for KZ650 is 12048-015 and for Z-s it is 12048-001.   It’s not uncommon situation when identical parts have different part numbers, but such situation always needs some proof digging, so I made as deep search as I could.

From KZrider forum I learned that Z900 and Z1  have tensioner rollers of smaller diameter than KZ650 roller, but with same “wheel center” to “bracket axle” offset. That was promising information, especially counting that I already have PMC manual tensioner which solve the question of smaller diameter, but looked like no one clearly knows if lower guide rollers are identical or not.

I also found that Liska Racing (USA) makes replacements for KZ650 lower idler roller and tensioner roller and their tensioner roller  has sprocket instead of wheel. PMC (Japan) also makes replacements for these parts (with tensioner sprocket instead of wheel to), but with compatibility indicated for Z1, Z2 and Z900 models.

I was quite sure in compatibility of KZ650 and Z1 tensioners and I had couple of other parts in list that I wished to order from Webike (PMC dealer), so I decided  to clarify by the way  the question of KZ650-900-100 lower  guide rollers (idler wheels) compatibility, thus I ordered  timing chain tension components from Japan. Order arrived within a week and it counted these PMC parts:

The rightmost part is not related to this article, about it I’ll write in one of the next posts.  Here are photos of PMC tensioner sprocket VS OEM tensioner wheel. It’s clear that they are compatible:

But simultaneously one may ask a question: is it safe to use sprocket instead of wheel? Answer is YES, and main proof is in earliest OEM Kawasaki KZ650 manual  which is dated by 1976, while motorcycle sales started in 1977. That means that manual was illustrated with photos of pre-serial motorcycles.

On page 52 of that manual you may find this illustration:

And another one is on page 140:

So, as you may see, pre-serial KZ650 had tensioner that was equipped with sprocket identical to 17 teeth front and rear guide sprockets. I could only guess that Kawasaki switched sprocket to rubber roller only due to economy of production.  PMC tensioner sprocket also has 17 teeth so we may say that we are back to the roots with it.

And now time to clarify another question: is lower rubber wheels of KZ 650 and 900-1000 models identical despite different part numbers? Answer is, unfortunately,  NO.

They have the same thickness and axle diameter and identical axles, but their outer diameters are different. KZ650 roller body diameter is 52mm and lip diameter is 56mm while Z900-Z1 wheel has body diameter of 46 mm and lip diameter of 50mm.

I have to pay tribute to PMC: even holding their roller in hands it’s impossible to distinguish it from OEM part, it made as complete copy of it, including all markings.

I also compared softness of this new wheel and that I removed from my KZ650 engine and looks like I have no reason to replace original roller by new, however, I still thinking about Liska Racing  guide roller which is upgraded by roller bearing similar to sprockets…

 

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