Weird valve clearance problem help

The previous summer my bike started becoming difficult to start when it generally started after a half second on the starter. It also started popping from the exhaust and or carb. All symptoms, or at least as I understand it, of valve clearance problems. checked the clearances on all on them but I didn't have my FSM on me so I checked each cam lope while pointed away from the bucket (perpendicular) and these are the results:

exhaust: #1(.13mm) #2(.15mm) #3(.13mm) #4(.10mm)
inlet: #1(.08mm) #2(.06mm) #3(.08mm) #4(0mm)

So boom, there's the problem right? I decided, that I should do this over again but follow the FSM instructions just to be sure and these were the results: (cam lobes are pointed at more of a 30 degree angle to the buckets)

exhaust: #1(.13mm) #2(.15mm) #3(.13mm) #4(.10mm)
inlet: #1(.08mm) #2(.06mm) #3(.08mm) #4(.08mm)

WTF? everything is exactly the same reading BUT Inlet #4 is at minimum spec, how in the world is there no clearance when it's pointed away and .08mm clearance when at 30 degrees away? And how do you shim that? even if I shim it to a smaller shim by say, 10mm, the variance would be .10mm when pointing away and .18 when 30 degrees.

Sorry I hope this makes sense. Anyone have any ideas or advice?

How's the compression look? Do a leak down test too, if possible. I suspect carbon buildup on a valve maybe causing the differences.

Compression seemed fine, I tested it before I pulled everything. fairly close to 150 across the board with slight variances.

If carbon is keeping the valve from closing properly, wouldn't it be tight across the travel of the whole cam lobe? It seems too consistant that it's always zero clearance when pointing away from the bucket and .08mm when pointing 30 degrees on either side. Although, I really have no idea what I'm talking about, so you advice is appreciated and an explanation is welcome

I pulled the cams and I'm going to test to see if they are within spec.

You can get shifts in clearance based on cam chain tension. The camshaft actually can ride up and down a bit on either side based on chain tension which is related to what the other valve is doing (if it's pushing down on a spring).

If I recall correctly, you can get some compression effect from the other valve at 30 degrees off TDC. This one is from a 750 twin.

bloglos wrote: The previous summer my bike started becoming difficult to start when it generally started after a half second on the starter. It also started popping from the exhaust and or carb. All symptoms, or at least as I understand it, of valve clearance problems. checked the clearances on all on them but I didn't have my FSM on me so I checked each cam lope while pointed away from the bucket (perpendicular) and these are the results:

exhaust: #1(.13mm) #2(.15mm) #3(.13mm) #4(.10mm)
inlet: #1(.08mm) #2(.06mm) #3(.08mm) #4(0mm)

So boom, there's the problem right? I decided, that I should do this over again but follow the FSM instructions just to be sure and these were the results: (cam lobes are pointed at more of a 30 degree angle to the buckets)

exhaust: #1(.13mm) #2(.15mm) #3(.13mm) #4(.10mm)
inlet: #1(.08mm) #2(.06mm) #3(.08mm) #4(.08mm)

WTF? everything is exactly the same reading BUT Inlet #4 is at minimum spec, how in the world is there no clearance when it's pointed away and .08mm clearance when at 30 degrees away? And how do you shim that? even if I shim it to a smaller shim by say, 10mm, the variance would be .10mm when pointing away and .18 when 30 degrees.

Sorry I hope this makes sense. Anyone have any ideas or advice?

First, .08mm =.003"

The FSM method is still using the base circle as check point. All it does really is position the cams so that you can check 4 valves from on positioning of the crank.

What you report indicates the base circle isn't concentric on that lobe. In theory you should get the same lash reading anywhere on the base circle. In reality, it can vary, especially with aftermarket cams that have been around a long time. Generally you don't see that much on OEM cams.


I have seen cams that have varied .003" lash readings from the base circles not being concentric. On some old Andrews cams, I've seen it as much at .005".

You really do want lash present when the lobe is fully away from the bucket, even if that means more than spec when checked a the FSM positioning. The potential for that particular tappet to be a little noisy exists because the lash would be wider than design as the lobe comes onto the opening ramp.

Bountyhunter is on to something. There is oil clearince at cam bearings and when you are measuring clearance at one valve the other 3 valves are pushing up on the cam at the other end. This can cause the cam to tip and that can give you an odd clearance measurment. It's important to remember you are looking for the maxamum clearance between the bucket and cam. If you need to move the lobe around a bit to find the max. clearance, its no big deal.

893cv wrote: Bountyhunter is on to something. There is oil clearince at cam bearings and when you are measuring clearance at one valve the other 3 valves are pushing up on the cam at the other end. This can cause the cam to tip and that can give you an odd clearance measurment. It's important to remember you are looking for the maxamum clearance between the bucket and cam. If you need to move the lobe around a bit to find the max. clearance, its no big deal.

I'm a little confused now. I understand what you are saying about the odd clearance measurement, but did you mean I should move the lobe around until I find the min clearance rather than max? Wouldn't I want to shim based on the least clearance which is 0mm at the lobe perpendicular to the bucket?

So say the problem valve is shimmed with a 2.60mm shim. Based on my measurements which 0mm clearance at perpendicular and .08mm at 30degrees from perpendicular either side. Which do I shim for? 0(min) clearance or .08 (max)?

Do as larry says.
Set the clearance with the lobes pointing 180 deg from the lifters.
Ignore all other mesurements as it only adds un-necessary confusion.
You can run up to 0.18mm with no trouble, try to keep clearances above 0.10mm.
Forget any other advice regarding cam position etc as it is over complicating the issue,is mostly crap and won't have any significant effect.

Per Larry C: The potential for that particular tappet to be a little noisy exists because the lash would be wider than design as the lobe comes onto the opening ramp.

How does one compensate for this situation, as I have a noisy tappet on #1 or #2, but haven't isolated it to the exact location yet? The last check, all measurements were within spec. so I covered it back up, and am tolerating the noise for now.

The only other thing I can think of that may give the difference in gap is may be the shim itself is starting to deteriorate/spall so maybe take it out and check it?

I grew up with Tim Pestotnik, who was called "the motorcycle man" and was a factory Kawasaki race mechanic for a while. Tim was killed a few years ago out in CA in a motorcycle accident, but none of this matters. He said pretty much opposite of Larry, and that was to check clearance as you slowly rotate the engine and take the point of max clearance as your spec, spin your engine with the 17mm nut, constantly check clearance on a valve and if at any point you get the .10-.15mm feeler to fit and the larger feelers do not fit, you are set. Tim said most engines were set too loose due to doing the other way. Whether this way is correct or the other which would give much more clearance in some engines is debatable, but I think it's 6 one way, half a dozen the other and doesn't make $0.02 worth of difference.

what you are saying with 0mm clearance is actually nil? correct? do you know the size of the shims yet with #4 giving you nil? for instance, I had to have a base to start on because I was also getting nil on a couple shims. but I had no idea what sizes I would need to correct this without a "spare"shim to start out with.