Valve lash vs. cam lobe position

Jeff: I had a '72 Honda CL450 years ago. I remember this old Italian Honda mechanic in Culver City, California who was so adept at tuning Honda CB450s and CL450s that he could adjust the valves externally just by listening to how much noise the tappets made while running! Impressive.

Suffice to say, I did not rely on my listening ability -- I took the valve cover off and used by eyes.

I'm not looking at a camshaft at the moment but IIRC when a lobe on one end corresponds to BDC the lobe on the opposite end of the cam has it's highest point on the spring and there is a lot of upward pressure on the camshaft via this cam. If there is any clearance at all in the bearings, the cam shaft is going to tilt and reduce the clearance on the cam that's on the BDC cylinder.

I don't know this for a fact but in the other post I was suggesting that it might give an indication of bearing wear or lack thereof. If you're gonna be pulling the cam(s) maybe some plastiguage and give us numbers. i.e. cam-bearing fit vs difference in 180 degree vs manual measurement of clearance.

I'll try to do the same when I finally get those two helicoils in for the cam caps on the GPz1100.

-Duck

The way to measure is to first determine what basic valve clearance you want. I go for .10mm. Turn the engine over slowly while constantly trying to insert the .10mm feeler between the bucket and cam. If any place throughout the entire rotation of the cam, the feeler inserts, then you have your clearance. Then try to insert a .15mm feeler throughout the entire rotation of the cam. If it doesn't insert at any point, then your clearance is correct at between .10-.15mm. I'll say it again, don't worry about marks, lining up anything to a certain point and measuring, and don't bother wasting time using in-between size feelers! Only use .05,.10,.15mm feelers ect. This is the way I was taught directly from Kawasaki factory mechanics, not shop mechanics, this was directly from Kawasaki.

In my opinion RonKZ650 is correct, you want a minimum clearance at the tighest point, no matter where that point is (not on the lobe obviously).

Ron, this approach works, but it's not the best approach for a sweet running engine. Some of the manuals offer a fairly wide range for valve lash - you don't want some valves at the very low end and others at the other end - you really want all 4 the same if you can. An example is the later KZ1000's list 2 thou (.05mm) to 6 thou (.15mm) - I would not ever want an engine running 2 thou on some and 6 thou on others - it will impact performance.

I have to agree with the minimum clearance theory. Here is my situation. After inspecting the cam lobe more closely, noticed some scuffing on the 90 degree portion (before and after the lobe) which is where I have roughly .05mm more clearance. On most valves, I have the least amount of clearance where the lobe is pointing opposite the bucket or 180 degrees away depending on how you view it. I believe it may be possible that the prior owner ran with "0" lash and wore the cams at this point. I believe it may be safest to measure at the minimum clearance point . . . correct me if I'm wrong. If I spec with the largest clearance, it's possible down the road that I'll have .05mm clearance (at the 90 degree marks) and .00mm lash on the 180 degree (lobe opposite bucket) which is not desirable. Is this .05mm difference on the cam rotation a serious problem? At the moment, I shimmed those valves .15mm minimum which is .20mm at the largest gap.

IMO if the clearance varies significantly (more than a shim step)
over the constant radius portion of a cam you've got other problems.

Things that come to mind are...
-Radius is not constant after all by design or wear
-Runout greater than spec as in a bent camshaft or ???
-Camshaft bearings out of spec as in worn*
-Camshaft axis not aligned as in wrong cap(s) installed
or cap loose/misaligned(guide pin(s) missing on correct cap).
-Head warped (you never know, it might happen

* As I mentioned in an earlier post, I suspect that the camshaft
might tilt as a result of pressure from 'lobe on' cam if the
bearings are worn. How much it might tilt and whether this is a
factor in clearance or a useful indicator of worn bearings, I do
not know. I suspect they would have to be pretty worn, like
0.003"-0.004" radial slop to give 0.002" play in clearance.

I will do my best to do some measuring in the GPz1100 when I get
to putting camshafts back in the head and report back.

-Duck

Thanks Duck for your input as you raise some valid points. It's possible the cam bearings are worn but I do not have any plastiguage to measure the bearing clearance. The engine was running good and the head was pulled to replace valve stem seals. At this point will probably reassemble and fire up. Good thing that it's not a daily rider so I could decommission and dig a bit deeper into it after the holidays. Let us know what you find out with your GPz 1100.

I'll chime in here with my $.02 The whole reason for valve clearance is to compensate for the different rates of expansion between the different metal alloys and temperatures in the valvetrain system. If there were no thermal expansion to worry about, the ideal valve clearance would be 0. Then the most lift and duration would be extracted from the cam lobe. By using valve clearance we are also reducing the amount of lift and duration that the cam lobe transmits to the valve. This is, however, the best solution without using hydraulic lifters (and they have their own set of problems.) The valve clearance is a figure derived by engineers alot smarter than I. This figure assures some positive clearance during all phases of operation, to prevent the valve from being held slightly open (negative clearance.) Obviously, a valve being held off-seat will have detrimental performance effects.
Of course, if the clearance is too great, then there are a few additional problems. First off, the valve will not be opening as far or as long as designed (low performance) Secondly, the cam lobe may begin to wear with excess valve clearance. If the clearance is grossly over-spec, then the cam lobe will impact the bucket (or shim in 900-1000cc) rather than smoothly ramp it open. Fortunately, valve clearances almost always decrease with wear as the valve-to-seat contact is where the most wear occurs.

So what you're really looking at here is minimum clearance. If the clearance you measure is below the min spec anywhere along the base circle of the cam, then it must be increased, or you run the risk of having a valve or valves being held off seat as things start to expand when the engine warms up. As for me, I always try to adjust to the minimum clearance possible, as it provides (although miniscule) a little more lift and duration from the camshaft. If you ride alot of miles, and don't like tinkering, then I'd adjust for the upper end of the clearance range. Then you won't have to mess with it as often.

As for the "scuffing" on the cam you have, well, I don't know. The faces of a camshaft are nitrided. Nitriding makes the surface of the cam very hard, and prevents wear. Nitriding is the hardest at the surface, and gets increasingly softer as the depth of the metal increases. If the wear is somewhere on the base circle, then you're probably OK. If it is on part of the ramp, then you're probably going to be needing cams soon. I have seen camshaft lobes wear COMPLETELY OFF in a matter of a few minutes of engine running. Once the nitriding has started to wear away, it wears exponentially faster, until there is no longer any friction (cam lobe gone)

I have little experience with the KZ650, so I can't speak about cam bearings specifically. Couldn't you take out (and label) the shims and buckets, and then bolt the cams back in and try to wobble them without the valves acting on them? I don't know if that will give enough room or not.

Great explanation B200driver. Another thing to note is the 650 doesn't use replacable cam bearings. The cam rides directly on the head surface and cam caps. So no possibility of changing what you have. So measure for minimum clearance around the entire rotation of the cam, set your shims and forget about it would be the thing to do.

Does your CB use a chain drive or gear drive off the crankshaft. Sounds like some slop in primary drive chain/gear. Common on older bikes. My KZ650 used to knock bad at idle from primary drive chain (hyvo style chain). Gear drive off crank is usually located on right side of crank, ala KZ900/1000. Chain drive typically from center, ala KZ650. Might want to check it out, but my mechanic told me is normal on older bikes.

B200Driver thanks for the details and I agree with your minimum spec clearance. RonKZ650 also has some valid points about the cam bearings as once they are worn, time to replace the head $$$ (ouch!). I'm not overly concerned with max performance so I'll shoot with the min .15mm and max .20mm to hopefully give a bit more duration between adjustments and cross my fingers the overspec .20 (somewhere along the cam) does not create any major problems. I should shoot for a safer .10-.15 spec but I have already been running like this for a bit with no obvious issues (for the moment). I'll see if I can get my hands on some plastiguage (after the holidays) and confirm cam bearing wear. Thanks to all for your time and input!