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Old March 3rd, 2021, 01:32 PM   #1
Gearbox Paul
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Valve clearance question

I just completed the valve clearance adjustment on my 08 250r. The bike has 21000 km (about 13000 miles). I'm not the original owner and I don't have any maintenance history on the bike. So I don't know if the valve adjustment was ever done on this bike.

When I first checked the clearance, all intake valve were within spec. But all exhaust valves were too tight, with some well below the acceptable range of 0.22-0.29 mm. On one of the exhaust valves on No. 2 cylinder, the clearance was below 0.127 mm (0.005") which is the smallest feeler gauge I have. Yet the bike ran fine.

I didn't have a shim kit when I did the work, so I went to the two local motorcycle shops in town to buy the shims I needed. Unfortunately, their shim supply was not complete, and I didn't get all of the shim sizes I was hoping to get. And there is no Kawasaki dealer nearby. Anyhow, I completed the work with the shims I could get and ended up with all but one exhaust valve in spec. The valve that is out of spec is on cylinder no. 1 and its clearance is between 0.178 and 0.203 mm. That's better than it was before adjustment, but still out of spec. Running out of time, and not having any other shims available, I elected to put the bike back together.

Which leads to my question: how soon should I correct the remaining valve that is out of spec ? Given that the clearances are much better than when I first measured them, my gut tells me that I don't have to rush to correct this right away. But what if I wait until next winter (I typically ride about 2000 miles per year) ? Is that too late and am I running a serious risk of damaging something? What if I wait until the next scheduled valve service in 7500 miles?

I appreciate your input. Sorry for the long thread.
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Old March 3rd, 2021, 02:51 PM   #2
Triple Jim
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The clearance tends to shrink with miles, so valve that's at 0.178mm will be the weak link. Once it gets to where it's zero with a cold engine you'll start to get the typical symptoms of hard starting, and difficulty with idle until it warms up.

It would have been best to not put it together until you had it shimmed properly, but at this point you could keep an eye on the compression, and if it starts to drop on that cylinder before the normal service interval, take it apart again.
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Old March 4th, 2021, 01:36 PM   #3
Gearbox Paul
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Thanks Jim. That approach makes sense to me. Now that I know what shims I'll need, I can order them and plan the work for (hopefully) next winter.
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Old March 5th, 2021, 05:47 PM   #4
SibSerge
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I think the danger of the too small of a gap is that when the engine is warmed up and the valves do not fully close you will have the gas blow by which of cause is not good by itself as you lose power but what is worst it might be burning the mating surfaces which can potentially take it to a point where the valve would not seal anymore even with a proper shim.

I would fix the shim asap.
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Old March 5th, 2021, 07:26 PM   #5
Triple Jim
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Quote:
Originally Posted by SibSerge View Post
I think the danger of the too small of a gap is that when the engine is warmed up and the valves do not fully close you will have the gas blow by which of cause is not good by itself as you lose power but what is worst it might be burning the mating surfaces which can potentially take it to a point where the valve would not seal anymore even with a proper shim.
Yes absolutely. But these engines increase clearance when warm, so you notice the symptoms when cold before it gets so bad that it does it when warm. That's why I suggested keeping an eye in it with a compression tester.
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Old March 6th, 2021, 09:22 PM   #6
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Quote:
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Yes absolutely. But these engines increase clearance when warm, so you notice the symptoms when cold before it gets so bad that it does it when warm. That's why I suggested keeping an eye in it with a compression tester.
Got you, Jim.

Why is the clearance increasing on these engines when hot ? Would not the thermal expansion actually decrease it ? The only explanation I could come up with this statement is if the aluminum head is "swelling" more than the steel valve stem due to the expansion coefficient of aluminum being higher than steel. Could you elaborate ?
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