Valve Clearance Changes With Cam Position

I have had my '82 KZ650 CSR for a few months now. It is factory stock and has 8,300 miles. It has electronic ignition, new spark plugs, and I have cleaned and synchronized the carbs, etc. The bike runs very well at anything over about 2000 RPM, and the idle is good.

But as I gently leave a stop sign the engine feels like one cylinder may be misfiring, or something is not quite as smooth as it could be. It is most noticeable at about 1500 RPM, and goes away as RPM increases.

I checked valve clearances and found 7 of them to range from .004" to .007", but the #4 intake seemed to have practically no clearance. This was with the cam lobe directly opposite the valve. The thinnest feeler gauge I have is .0015" and it would not go between the bucket and the cam. The bucket can be rotated, however, so I figure the clearance is more than zero.

I believe that this is causing the slight performance problem that I described above, but haven't had time to adjust the clearance with different shims yet. I double checked other clearances again and found them to be reasonably close to my first readings. NOW HERE IS THE ODD PART: I CHECKED THE #4 CLEARANCE AGAIN WITH THE CAM IN A SLIGHTLY DIFFERENT POSITION AND FOUND THE CLEARANCE TO BE .004", INSTEAD OF THE ESTIMATED .001" OR LESS, THAT I GOT EARLIER. Has anyone ever experienced this?

I suppose the cam is slightly out-of-round on the side away from the lobe. I would think the solution might be to run maximum clearance (.006") on this particular valve. As I shuffle and replace shims I want to get the clearances as correct as possible. Can anyone advise as to the best practice here? Thanks guys.

Very common. The way to check clearances is turn the camshaft while constantly trying to insert a feeler. The point the largest feeler will fit is used as the clearance measurement. This was how I was told to do it by a factory Kawasaki, not a dealer mechanic, in 1978. He said most valves are set too loose if you only measure with the lobe 100% opposite of the bucket. Anyway, this is the way I've done it for 30 yrs and it's worked fine with me.

At that mileage I bet cam clearance is not the problem.

That pilot jet hole in the carbs is awefully small, are you sure you COMPLETELY cleaned them?

Take out those pilot jets, soak them in carb cleaner, and blow the snot out of them with compressed air until they are all free and clean clean clean.

Also check the fuel level height in the carbs and make sure that you are not overflowing your carbs.

ALSO

Have you adjusted your pilot jets? I don't remember if the stock BS32's let you do that, but I'm pretty sure you can weasel your way in.

Hi,

Mine wasn't working at 100% on one cylinder and it was because the intake boot had a small leak.

Took 5 minute to check et tight back the bolt.

Don't know if it could resolve your problem but doesn't cost much to check.

Joce

I check my cams with the lobe opposite the valve.
If you rotate the cam more than 10 degrees you may
get more clearance.Some cam grinds have what an
expert called "quieting ramps".He did not go into
detail but said not to measure there and that was
why he wanted his grinds degreed in at .030" lift,
none less.

RonKZ650 wrote:

Very common. The way to check clearances is turn the camshaft while constantly trying to insert a feeler. The point the largest feeler will fit is used as the clearance measurement. This was how I was told to do it by a factory Kawasaki, not a dealer mechanic, in 1978. He said most valves are set too loose if you only measure with the lobe 100% opposite of the bucket. Anyway, this is the way I've done it for 30 yrs and it's worked fine with me.

A Good indicator is compression variance between cylinders. If you run into that situation it's a good idea to check compression and adjust clearance within the spec range to equal out the cylinders.

Here's an example:

Suppose spec is .002" - .006"

It's possible to have one point where you are say .006" but the rest of the base circle be more like .002". If the compression was low on that particular cylinder, it might benefit you set clearance to .006" at the tightest measurable location on the base circle.

It just depends on the situation you're dealing with and how fussy you want to get.

IMO as long as you don't experience any excessive ticking, it would be he way to go.

An engine with cylinder pressures balanced out as close as possible with be smoother running and provide a more balanced load on the crank.

I'm not saying in any way that Ron is incorrect. Just adding a bit more to his suggestion.

I don't feel that 10 crankshaft degrees from the point where the cam base circle is dead middle in line with the valve stem will put you into the silencing ram portion of the ramp.

Something you can try that might just open your eyes wide for a second is to clean the lobe and bucket or shim with brake clean. Then apply black majic marker to the lobe as far down each ramp as you can reach. Let it dry and then spin the motor over a few times. You'll see exactly where the contact points are.

Make sure you re-apply oil to the valve train after you finish...

Post edited by: larrycavan, at: 2007/08/10 17:10

I like the magic marker idea larry, you'll know exactly where the contact area is. If you do it by the factory manual (counting links, etc), where are you measuring on the lobe?

Bluemeanie wrote:

I like the magic marker idea larry, you'll know exactly where the contact area is. If you do it by the factory manual (counting links, etc), where are you measuring on the lobe?

Put the marker all the way down the lobe and onto the base circle of the cam.

I don't know if I answered your question. I'm not sure I understand what you mean.

People here are chatting about measuring with the lobe perfectly opposite the valve, some say slightly off, some say find the widest gap, etc. If you go by the factory manual for measuring (counting links, etc) where would the lobe be according to them? Opposite, slightly off, etc. Just wondering where the factory says the lobe should be?

I get what you're after now.

The clearance is measured on the base circle of the cam. The base circle is the bottom round portion, directly opposite the lobe. It extends from the end of the closing ramp, around the bottom to the beginning of the opening ramp.

What can happen is the base circle becomes non concentric. It could be ground that way or become worn that way over time from tight valves.

When the base circle is non concentric, you might see differences in the clearances when measured at different points along the base circle.

For starters, all valves need seat time to allow compression to take place but they also need to cool down. The intake valve get's some assistance in cooling from the fuel and air passing by. The exhaust gets cooled mainly by seat dwell time. That's setting aside any charge lost out the exhaust during TDC overlap that might give some very slight cooling affect. It would however, be practically immeasurable.

If the base circle were perfect, the lash measured at any point along the base circle would be equal.

It would take far too much typing to discuss the pros and cons of all the possible scenarios. Best advice I could give you is that when in doubt, favor the loose setting. If it's not making the valves tick. You're good to go.

Bluemeanie wrote:

People here are chatting about measuring with the lobe perfectly opposite the valve, some say slightly off, some say find the widest gap, etc. If you go by the factory manual for measuring (counting links, etc) where would the lobe be according to them? Opposite, slightly off, etc. Just wondering where the factory says the lobe should be?

Original 1973 Z1 Owner's Manual and FSM for 73-76 900's says to measure with cam lobe pointing directly way from the valve lifter.


FSM for 77-79 1000's says measure with marks on camshaft sprocket lined up with surface of cylinder head. This positioning of the camshaft sprocket should enable measurement of 4 valve clearances. Thereafter, rotate the crankshaft one turn until the sprocket marks line up again, and measure the other 4 valve clearances.

I have run into a few instances where the top face of the shim cup was worn into a "cup" on the face. Measure it one time and the clearance would be .004 turn the motor over, the shim cup turns and the "cupping" moved also and the clearance would measure .009 for example. Took a while before I figured it out but it's one of the things I check for now if clearances look funny in any way. Something to think about. Motor gets hot and the cups lose some of the heat treat, I was told, and they start to wear over time.