Better to adjust valves for max clearance?

Nessism wrote: .......
I do agree with following the Kawasaki procedure. This is particularly important with regards to positioning the cams the way they specify during the adjustment. The common simplified method of simply pointing the cam lobe away from the bucket and checking the clearance that way is incorrect and will result in false measurements. Follow the factory specified method to assure the valves are set correctly.

+1 Follow the manual's instructions. That's the way I have done mine since day one. I figure that makes sense because doing it that way when the bike was brand new showed the clearances to be in spec which they would have been coming right from the factory. Ed

loudhvx wrote:

bountyhunter wrote:

loudhvx wrote:

bountyhunter wrote:

loudhvx wrote:

Nessism wrote: I disagree that more clearance will cause the valve to hammer into the seat. The cam profile determines the acceleration rate of the valve, not the lash. More lash means the valve just sits on the seal slightly longer is all.

The cam profile, at the heel, is round. This means zero lift per degree. As you enter the lift area, the profile gradually changes from zero to more lift per degree. If you skip over this change area, because the lash is too large, the lift rate, as seen by the valve, suddenly jumps from 0 to some positive rate. The more lash, the greater the jump. The greater jump, the harder the impact.

Just take the extreme cases to see it. Imagine an extreme lash of 1/8". As the cam nose swings around, it will whack the bucket., and conversely, as the valve closes, it will be moving very quickly, then suddenly stop as it hits the seat. Whereas, with exactly zero lash, the cam profile slows the valve down gradually to a complete stop, thus the valve will be closed without ever actually hitting the seat, but it will be closed and just barely resting on the seat.

Looking at it another, simpler way: the fact that valves are noisier when the lash is greater, tells you they are hitting harder. That's what generates the noise.

Hard to believe opening the clearance to the upper end of the specified range would cause any appreciable increase in wear. You're only changing it a couple of thousandths.

BTW: on the 750 twins the original spec was .002 - .004" but later opened up to .002 - .006" by Kawi so I guess that range is safe to run.

So if the lash distance is greater, the cam makes first contact with the bucket at a higher velocity... hence impact. The only way you would have no impact is if the cam was always in contact with the bucket (or shim in shim-over).

I understand the concept, I am just having trouble believing that a change of a couple of thou will have any significant affect.

"Significant" is subjective. The idea that there is no affect, is what I dispute.
Obviously valves wear, at least in some part, due to the impact of opening and closing. When two pieces of metal contact each other, there can never be zero wear. In addition, If you increase the speed at which they impact, the increase in the wear cannot be zero. So the idea of increasing the lash and seeing zero change in the wear rate is not possible.

My point, as stated earlier, and to the original poster's question, is don't try to out-think Kawasaki. Just do what they recommend. That is, not trying to hit the larger end of the range, or the shorter end of the range, but simply follow the lookup chart for new shim sizes based on old lash measurement and old shim size.

I'm all for people modifying their bike and doing re-engineering, but for a stock motor, there is no upside to varying from Kawasaki's shim chart, and only potential downside. The only reason I can even think of for not following it, is in the case of the 750 twin, where many shim sizes are harder to find than Jack links at an Ed Begley Jr. dinner party.

The OP's question was simply this:

If I look at the service manual it says "no change required" for the valves that are within the allowable range, but I'm wondering if I should change shims to bring their clearance closer to the highest allowed value, to allow for future wear.

And my answer was:

I keep valves on the higher gap. Valves tend to close down over time

I never stated at any point that he should go outside of the recommended range, rather that using the wider end of the range gives more insurance against a valve tightening up and burning a seat. I stand by that answer as it is correct in my experience.

I also said:

Hard to believe opening the clearance to the upper end of the specified range would cause any appreciable increase in wear. You're only changing it a couple of thousandths.

Again, I stand by that because it is correct to my knowledge.

I do not believe there would be any measurable increase in wear if one uses the upper specified limit compared to the lower limit. I have never seen any proof of this. If it exists, please post it.

bountyhunter wrote:

loudhvx wrote:

bountyhunter wrote:

loudhvx wrote:

bountyhunter wrote:

loudhvx wrote:

Nessism wrote: I disagree that more clearance will cause the valve to hammer into the seat. The cam profile determines the acceleration rate of the valve, not the lash. More lash means the valve just sits on the seal slightly longer is all.

The cam profile, at the heel, is round. This means zero lift per degree. As you enter the lift area, the profile gradually changes from zero to more lift per degree. If you skip over this change area, because the lash is too large, the lift rate, as seen by the valve, suddenly jumps from 0 to some positive rate. The more lash, the greater the jump. The greater jump, the harder the impact.

Just take the extreme cases to see it. Imagine an extreme lash of 1/8". As the cam nose swings around, it will whack the bucket., and conversely, as the valve closes, it will be moving very quickly, then suddenly stop as it hits the seat. Whereas, with exactly zero lash, the cam profile slows the valve down gradually to a complete stop, thus the valve will be closed without ever actually hitting the seat, but it will be closed and just barely resting on the seat.

Looking at it another, simpler way: the fact that valves are noisier when the lash is greater, tells you they are hitting harder. That's what generates the noise.

Hard to believe opening the clearance to the upper end of the specified range would cause any appreciable increase in wear. You're only changing it a couple of thousandths.

BTW: on the 750 twins the original spec was .002 - .004" but later opened up to .002 - .006" by Kawi so I guess that range is safe to run.

So if the lash distance is greater, the cam makes first contact with the bucket at a higher velocity... hence impact. The only way you would have no impact is if the cam was always in contact with the bucket (or shim in shim-over).

I understand the concept, I am just having trouble believing that a change of a couple of thou will have any significant affect.

"Significant" is subjective. The idea that there is no affect, is what I dispute.
Obviously valves wear, at least in some part, due to the impact of opening and closing. When two pieces of metal contact each other, there can never be zero wear. In addition, If you increase the speed at which they impact, the increase in the wear cannot be zero. So the idea of increasing the lash and seeing zero change in the wear rate is not possible.

My point, as stated earlier, and to the original poster's question, is don't try to out-think Kawasaki. Just do what they recommend. That is, not trying to hit the larger end of the range, or the shorter end of the range, but simply follow the lookup chart for new shim sizes based on old lash measurement and old shim size.

I'm all for people modifying their bike and doing re-engineering, but for a stock motor, there is no upside to varying from Kawasaki's shim chart, and only potential downside. The only reason I can even think of for not following it, is in the case of the 750 twin, where many shim sizes are harder to find than Jack links at an Ed Begley Jr. dinner party.

The OP's question was simply this:

If I look at the service manual it says "no change required" for the valves that are within the allowable range, but I'm wondering if I should change shims to bring their clearance closer to the highest allowed value, to allow for future wear.

And my answer was:

I keep valves on the higher gap. Valves tend to close down over time

I never stated at any point that he should go outside of the recommended range, rather that using the wider end of the range gives more insurance against a valve tightening up and burning a seat. I stand by that answer as it is correct in my experience.

Right.
You are recommending taking a different course of action than what Kawasaki recommends.
I am recommending doing what Kawasaki recommends.

By the way, it doesn't just start burning up a seat with no symptoms, and it does not just start burning up the seat continuously. The bike will stall at idle long before any valve can stay continuously open.

I also said:

Hard to believe opening the clearance to the upper end of the specified range would cause any appreciable increase in wear. You're only changing it a couple of thousandths.

Again, I stand by that because it is correct to my knowledge.

I do not believe there would be any measurable increase in wear if one uses the upper specified limit compared to the lower limit. I have never seen any proof of this. If it exists, please post it.

In my experience, setting the valves at a larger lash setting did not aprreciably lengthen the maintenance interval.
Also, lash settings which were initially larger than other valves ended up at about the same lash settngs after the same time interval.
Those two bits of anecdotal evidence point to increased wear on the valves which had larger lash settings.

But that evidence is not needed because common sense will tell you that impacting metal at higher speed will increase wear. Since we know that normal valve wear is significant, why would we want any chance of higher than normal wear, when there is no upside to it. Kawasaki has already determined what is a safe lash value, and being in the middle of the normal range is already at a higher safe lash value than the bottom of the range.

loudhvx wrote:
Right.
You are recommending taking a different course of action than what Kawasaki recommends.
I am recommending doing what Kawasaki recommends.

NO. I never said to set the clearances outside of the factory range, I said that I use the upper end of the range to minimize the chances of one closing down and burning a seat. Don't know how it could be clearer. Read what I said:

The OP's question was simply this:

If I look at the service manual it says "no change required" for the valves that are within the allowable range, but I'm wondering if I should change shims to bring their clearance closer to the highest allowed value, to allow for future wear.

And my answer was:

I keep valves on the higher gap. Valves tend to close down over time

I never stated at any point that he should go outside of the recommended range, rather that using the wider end of the range gives more insurance against a valve tightening up and burning a seat. I stand by that answer as it is correct in my experience.

But that evidence is not needed because common sense will tell you that impacting metal at higher speed will increase wear. Since we know that normal valve wear is significant, why would we want any chance of higher than normal wear, when there is no upside to it. Kawasaki has already determined what is a safe lash value, and being in the middle of the normal range is already at a higher safe lash value than the bottom of the range.

I have about 85k miles on my 750 twin and in that lifetime I had two cases where valves set in range at .0025 closed down below safe spec (to below .0015 that was my thinnest gauge) within the 3k mile check interval. That anecdotal evidence taught me it would be smarter to put the initial set point at the higher end of spec not the lower end. And FYI, the factory limit at that time was .002 - .004 and shims go in steps of .002" so a valve at .0025 given the next thinner shim would go to .0045 which was out of range for the spec at that time so I followed the manual. I read later that the range had been opened up to .002 to .006 which is what I now go by and I see why. I had two valves close down below spec because of the tight range limits.

why would we want any chance of higher than normal wear, when there is no upside to it.

The upside of using the wider end of lash spec of the allowable range is that it reduces the chance of a valve closing down too tight during the running interval between checks. I used to wonder why the interval was 3k on mine until I saw two valves close down. As far as I know, valves always go tighter and so the reason to put initial set towards the high end is because of that.

bountyhunter wrote:

loudhvx wrote:
Right.
You are recommending taking a different course of action than what Kawasaki recommends.
I am recommending doing what Kawasaki recommends.

NO. I never said to set the clearances outside of the factory range, I said that I use the upper end of the range to minimize the chances of one closing down and burning a seat. Don't know how it could be clearer. Read what I said:

The OP's question was simply this:

If I look at the service manual it says "no change required" for the valves that are within the allowable range, but I'm wondering if I should change shims to bring their clearance closer to the highest allowed value, to allow for future wear.

And my answer was:

I keep valves on the higher gap. Valves tend to close down over time

I never stated at any point that he should go outside of the recommended range, rather that using the wider end of the range gives more insurance against a valve tightening up and burning a seat. I stand by that answer as it is correct in my experience.

Right, as I said, your procedure is different than what Kawasaki recommends. When Kawasaki recommends "no change" you recommend change. That is the difference. That is the entire point of this thread.

Obviously, if a deviation from the manual can be statistically shown to be needed, then deviation is warranted, especially when Kawasaki alters the procedure. But the question is moot since Kawasaki has already altered the procedure as was deemed necessary, in the case of your 750 twin. So the rule would be to follow Kawasaki's new procedure.

The shim changing procedure is not just "get it within a certain range". It is spelled out as to when and if to change, and by how much.

Trying to out-think Kawasaki is what you recommend. In this particular case, I don't. That's where we differ.

Your anecdotal evidence tells you to do something different, even different from the new published procedure. My anecdotal evidence (based on 20 years of maintaining multiple KZ550's) says Kawasaki had the procedure correct (and has never had to change it), and going to the larger end of the range increased wear on the valves.

We have two very different bikes, so it's not surprising to have different opinions.

Incidently, the original post is talking about a ZR550 (rare in the U.S.), which is based on the KZ550. Your 750 twin uses shim over, but the bike in question uses shim under (like the KZ550's). Obviously, advice should be given based on the bike in question, and when data is not available, then the next closest bike would be next choice.

For anyone who rides their bike at highway speeds for about 20 minutes or so, getting off the highway and idling will show immediately if their lash is too small. The bike will not want to idle for the first minute after getting off the highway. That is a very good early warning that maintenance needs to be done.

bountyhunter wrote: ............ As far as I know, valves always go tighter and so the reason to put initial set towards the high end is because of that.

I have no personal experience with a KZ750 twin, but the valves on a KZ650 do not always go tighter. Sometimes they get a little looser, sometimes a little tighter. Overall they have actually gotten very slightly looser since the bike was new. I have only ever adjusted one valve, and that was to move it from the loose end of the clearance range to the center of the range. That was done at 4,500 miles. Here's a partial record of my clearances (see below). I can't find the latest readings, and it's time for me to check the clearances again. I count myself very lucky not to have needed to make a bunch of adjustments becasue the shim under bucket is not a fun task. :laugh:

I believe the valves are larger on the 750 twin and on the big 4 cylinder engines than those of the KZ650, and the valve springs probably also pack more punch, so that may be why they tend to get tighter over time. Ed

Nice to have time-series data like that! I have only one data point so far (not sure what the previous owner found, if he ever even checked).

I have say that adjusting the valves was a very rewarding experience. It's a little intimidating if you've never done it, but I understand my bike that much better after the exercise. It's really kind of incredible that these machines are so well crafted that after thousands of miles of mechanical wear we are still talking differences of hundredths (!) of millimeters in clearance.

Thanks Ed, I forgot to mention, on very rare occasions I've seen the lash increase as well, but only slightly, and not by more than a shim size. But what could cause that? Valve stem shrinking? I've always assumed it was a slight measuring error.

I take about 9 readings on each lobe heel. Straight away from the bucket and several different positions on either side over the course of several forward-only rotations, and it interesting to see how the readings differ. Obviously the heel is not perfectly round, or other valves' tension is causing the camshaft to not run perfectly concentric to the bearing. In other words, as other valves come under tension, they push the camshaft to a different position, or even slightly bend it... not sure which.

loudhvx wrote:

bountyhunter wrote:

loudhvx wrote:
Right.
You are recommending taking a different course of action than what Kawasaki recommends.
I am recommending doing what Kawasaki recommends.

NO. I never said to set the clearances outside of the factory range, I said that I use the upper end of the range to minimize the chances of one closing down and burning a seat. Don't know how it could be clearer. Read what I said:

The OP's question was simply this:

If I look at the service manual it says "no change required" for the valves that are within the allowable range, but I'm wondering if I should change shims to bring their clearance closer to the highest allowed value, to allow for future wear.

And my answer was:

I keep valves on the higher gap. Valves tend to close down over time

I never stated at any point that he should go outside of the recommended range, rather that using the wider end of the range gives more insurance against a valve tightening up and burning a seat. I stand by that answer as it is correct in my experience.

Right, as I said, your procedure is different than what Kawasaki recommends. When Kawasaki recommends "no change" you recommend change. That is the difference. That is the entire point of this thread.

WOW. When I said I didn't know how to make it any clearer, I guess I need to. I NEVER said to go outside the limits. I said that given the choice, lean towards the higher end of the range.

That get any clearer?

When Kawasaki recommends "no change" you recommend change.

depending on the allowable clearance range, there may be more than one shim size that would qualify as the "no change" position which means you have a choice different shim sizes that would be "no change", one would be .002" tighter clearance than the other. Like I sid in my example of a 750 twin: range is ,002" to .006". Shims come in sizes of .002". So if you have a clearance of .002"... you could choose to make no change. I DON'T RECOMMEND IT. I would go to the next thinner shim and go up to .004". But, clearances of both .002" and .004" would say "make no change". So you get to choose which shim size as both comply with Kawi specs.

I have never recommended anybody do anything against FSM and still don't. But I still would not recommend setting up new valves near the lower limit of clearance specs.

bountyhunter wrote: WOW. When I said I didn't know how to make it any clearer, I guess I need to. I NEVER said to go outside the limits. I said that given the choice, lean towards the higher end of the range.

That get any clearer?

Why do you keep repeating that? No one ever claimed you said to go outside of the acceptable lash range. Please point out where, if you think anyone did. That was never the question.

Please read the title of this thread. The original question of the thread was whether or not to set it to the maximum gap. The reason for the question is because of Kawasaki's recommendation, in the FSM, of no change, when the lash is within spec.

You say to change to the large end of the range. Kawasaki FSM says "no change". Why do you say those two courses of action are the same?