Jumping Timing Chain

I recently did a head rebuild, and upon reconstruction, my cam chain jumps. It will jump once per full revolution. I'm wondering if there's something going on with the timing, or if my automatic tensioner has gone out.

This is a 1982 GPz750, new valves, cut seats, new shims, gaskets, etc (full rebuild).

sounds like the cam chain is not running on the crank sprocket......likely off to one side of it...IMO

Id have to agree with turbo king. but could be the tensior.

Obvious stupid question - did you release the tensioner after you put it back in?

Do you have the top cover installed when you turn the engine over? There is a tensioner on the bottem of the valve cover that pushes down on the camchain when installed.

How does one go about "releasing the tensioner"? And yes, I have tried it with the valve cover installed, same issue.

How do you know your cam chain is jumping after one revolution of the crank? The crank turns twice for every one cam revolution.

If your cam chain is jumping doesn't that mean the valve timing relative to the crank is shifting? That being the case, do you know if you have had contact between the valves and pistons? Ed

How do you know your cam chain is jumping after one revolution of the crank? The crank turns twice for every one cam revolution.

When completing the rotation (turning the crank by hand), the chain will be taut, then something *pops* and the chain goes very slack.

If your cam chain is jumping doesn't that mean the valve timing relative to the crank is shifting? That being the case, do you know if you have had contact between the valves and pistons? Ed

I do not know if I have had contact between the valves and pistons. As far as I know, the timing has been spot on since forever. But then again, I've only put about 1000mi of the 36000mi on the bike.

freakinbike wrote:

How do you know your cam chain is jumping after one revolution of the crank? The crank turns twice for every one cam revolution.

When completing the rotation (turning the crank by hand), the chain will be taut, then something *pops* and the chain goes very slack.

Of course it does, that's the cam going over center and the valve springs rotating the cam.
Perfectly normal

If your cam chain is jumping doesn't that mean the valve timing relative to the crank is shifting? That being the case, do you know if you have had contact between the valves and pistons? Ed

I do not know if I have had contact between the valves and pistons. As far as I know, the timing has been spot on since forever. But then again, I've only put about 1000mi of the 36000mi on the bike.

To put it simply, you're seeing problems where there are none. No experience and a little nervous maybe?

.

By jumping I thought you meant jumping a tooth on the sprockets. In other words, what I have always heard referred to as "jumping timing." That's why I asked about valve/piston contact - it seems impossibly to me for a KZ engine to jump a tooth on the cams every revolution of the crank without causing a nearly immediate valve disaster.

After reading Steell's posting I re-read this thread. I now think you are not saying the cam chain is actually slipping over a tooth on the cams, but merely getting tighter and looser as the engine rotates. As Steell points out, this is normal. That is why when adjusting the manual tensioner provided on some KZ's (like my KZ650-C1) the crankshaft needs to be oriented in a specific position in order for the slack to be taken up by the tensioner before the pinch bolt it tightened. Ed

Ok, well that's good to hear. I have an automatic tensioner, I thought it was supposed to take up the slack so that the chain doesn't fall off.