engine rebuild problem: valve "slap"?

So I got my new piston rings and started putting the engine back together. Got up to the cylinder head assembly and installed the cams, making sure to follow the manual at every stage. Once the cams, upper cam chain guide and cam tensioner were in I decided to turn the crank to see how everything worked. At TDC of 1 & 4 cylinder the exhaust valves of 2 & 3 "slap" up against the cam lobes, and vice versa at TDC of 2 & 3. I applied engine assembly lube on everything including the valve shims so I wouldn't think that it was a lack of lubrication. I certainly don't want to continue to assemble the motor and try and start it with this happening. Anyone have any ideas????

Did you adjust the tensioner before doing this?
If not, then it's probably the pressure of the valve springs on the cams making them "snap" until they take up the slack.

Now if you're saying there is lots of clearance between the valves and the cams, and then the valves suddenly release and smack the cam, then the only thing I can think of at the moment that would cause this is bent valves.

I did not adjust the cam tensioner. How do you do that? Adjust the lock bolt??
so, we tried removing the cams again, making sure the cams were correctly positioned and the valve shims well-lubed... same thing. The sequence of "slapping" is: #1, #2, #4 and #3.... all on the exhaust side. The intake side seems to not be doing it.
I wouldn't think that it were possible that the valves became bent while the cylinder head just sat there. I cleaned them but that's it.
Help!!! I'm SO close!!!

so I'm wracking my brain trying to figure out what the problem is... I think it must have something to do with the cam chain tension... How do I adjust it? I can't think of what else it might be... I mean, if my cam shaft were off 180 it wouldn't cause this problem would it?

Nope, you can't have the cams 180 degrees out, at least as long as the marks on both cams line up.

When you removed the tensioner, did you retract it all the way and tighten the lock bolt to keep it retracted? And, did you loosen the lock bolt to let the tensioner take up the slack and then re-tighten it after installation?

I didn't do either of those things. Can I just take it off and redo it? Or do I have to take the cams back out? I know this sounds like a stupid question.

First thing I'd try is adjusting the cam chain tensioner like it says in the manual.

I don't have a manual that covers you bike, but if I recall correctly you just loosen the lock bolt so the spring loaded tensioner can take up the slack, then re-tighten the lock bolt.

Maybe someone else with a manual will chime in, my memory is a little rusty so I may be wrong, I sold my 77 KZ1000 in 1982 so it's been awhile

When you talk about an engine rebuild, did that include new valves? The valves need to be ground to a specific length in order that they can be shimmed where the proper clearances will result. Most common cause of things being off is that the cam chain didn't have all the slack pulled out. You can count 28 links till you are blue in the face if you have the chain with slack down in front of the chain sprocket on the crank. I have done this DOZENS of time thinking the chain was tight. If you have the idler assembly on up on the top and the chain is loose, it isn't likely to jump if you turn it over by hand but you WILL see it bunch up. If the chain jumps a link or two, you can end up bending valves. To adjust the tensioner, you are supposed to take the engine to where #4 piston is at TDC. Loosen the locknut on the tensioner from the left side of the bike and back out the bolt that the lock nut holds. Turn the engine over by hand using the bigger 17mm nut on the end of the crank under the points cover. There is a spring on the plunger that pushes the chain tight that will spring out and find the slack part in the chain. After turning the engine over a time or two, tighten the bolt and then the locknut.

it didn't include new valves... before I tore down the engine I had inspected valve clearances and they were all within spec. I deduced that the cause of my low compression were my piston rings and disassembled the engine down to the crankcase. I got new gaskets and new rings and cleaned a lot of the grime from the motor, including the valves.
I will tinker with the tensioner and get back to you all.... thanks so far...

Pull the head and bench set the cams. (Valve Clearance)

One cam at a time. DO NOT put in both cams in when
bench setting. Make sure you have the head shimmed
off the bench 1/2 in. or more.
As you turn the cam you will be abule to see just
what is going on with the valves.

If you cleaned all the carbon of the head and valves
your valve clearance is probably way off.
If you benched the head and did not shim the head of the
bench you most likely bent a valve or two.
Good Luck

XENU

Bicycle Lee wrote:

At TDC of 1 & 4 cylinder the exhaust valves of 2 & 3 "slap" up against the cam lobes, and vice versa at TDC of 2 & 3. Anyone have any ideas????

If you have valves that are actually pressure loaded then suddenly breaking free of the pressure and the buckets fly up, slamming the shim against the base circle of the camshaft....causing a noise.....STOP! You have something seriously out of wack and there's probably damage done.

That scenario is not the same as simply having tight valve clearances. Which is it?

It sounds to me your valves are hitting each other, read cams out of time, and one valve is being held a bit then being released to snap back into the seat. I did this with my first Z1. Bent the valves too....chris3