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Discussion Starter #1 (Edited)
I picked up a cheap, 02 trackbike from a friend. Hasn't been running in a while so I'm going over everything before I get it back out there. When I was checking the valves most of them were close to the stated spec, either tight and within spec or just on the tight side of outside the spec. All except one of the rear cylinder exhaust valves. I measured it multiple times to make sure, and it came in at 0.09mm (0.10mm wouldn't fit). The spec for the exhausts is 0.20 - 0.30 mm. I've never had a valve measure this far out of spec on any of the bikes I've done.

Is this so far out that it's concerning for the valve being being burned or starting to burn? Do I need to do something else to verify this, ie take the head off?
 

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Sounds like you need to check the shim and fit a shorter one if necessary. Just one valve being that far out, though. Not good.
 

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I would do a compression check. If it isn't low compared to the other cylinder, it might not be an issue.

I've seen valve clearances all over the map on different bikes and cars. You never know what previous owners have or haven't done.
 

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pull the bucket and see if the shim has walked or if it's a giant shim for some reason
 

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I would also suggest a compression check on both cylinders. If, for example, the valve was open whilst in storage there may be some rust film on valve seat. Shold show up as lower compression. If so don't run the engine as you may burn valve seat, adjust valve clearance and perhaps run the engine a bit to clear rust film, check clearance - if it gets wider it is or was rust.... if compression improves re check valve clearance etc... you need compression to get better and valve clearance to be static.... if not your looking at valve re lap.....
One of the problems with not using modern machines is the rust that can set in on steel etc cos of ethonol in fuel... piston rings can suffer also if engine left idle... short idle times can be sorted with an Italian Tune up, a good thrash!
 

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Discussion Starter #8
I would also suggest a compression check on both cylinders. If, for example, the valve was open whilst in storage there may be some rust film on valve seat. Shold show up as lower compression. If so don't run the engine as you may burn valve seat, adjust valve clearance and perhaps run the engine a bit to clear rust film, check clearance - if it gets wider it is or was rust.... if compression improves re check valve clearance etc... you need compression to get better and valve clearance to be static.... if not your looking at valve re lap.....
One of the problems with not using modern machines is the rust that can set in on steel etc cos of ethonol in fuel... piston rings can suffer also if engine left idle... short idle times can be sorted with an Italian Tune up, a good thrash!
Well the bike has run some since it sat, just poorly, so I don't think that's the case. The carb bodies are in the shop for an ultrasound bath. Everything was pretty dirty.

I guess the move that everyone's suggesting is to adjust the lash so it's in spec, check the compression, and go from there. Fingers crossed.
 

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A compression check should be done with the engine at operating temperature. If for some reason you don't want to run it you could do a leak-down test instead.
 

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Discussion Starter #10
A compression check should be done with the engine at operating temperature. If for some reason you don't want to run it you could do a leak-down test instead.
If the valve is indeed burned wouldn't there be a significant difference between cylinders, enough that even a cold test would show something is wrong? I have a tester on the way, but I don't have a compressor so would have to take it somewhere to have a leakdown test done.
 

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If it were me, I wouldn't bother shimming it until I did a compression test. If you change the shim before the test and the compression is low, you'll need to re-disassemble everything you just finished assembling.

Given that there is some clearance, albeit minimal, it suggests that the valve is fully seated. If the clearance was excessive, it would suggest that the valve was not fully seated. My point is that the engine is most likely mechanically sound enough to get a decent indication of whether or not the head should come off. If it doesn't, then change the shim.

It probably goes without saying that if the compression is okay and you change the shim, it would be a good idea to check it after a few hours of run time.

FWIW, I have always done compression tests cold with the throttle slightly open. I'm sure there are a lot of variations on this theme, but that's always worked for me.
 

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Discussion Starter #12
If it were me, I wouldn't bother shimming it until I did a compression test. If you change the shim before the test and the compression is low, you'll need to re-disassemble everything you just finished assembling.

Given that there is some clearance, albeit minimal, it suggests that the valve is fully seated. If the clearance was excessive, it would suggest that the valve was not fully seated. My point is that the engine is most likely mechanically sound enough to get a decent indication of whether or not the head should come off. If it doesn't, then change the shim.

It probably goes without saying that if the compression is okay and you change the shim, it would be a good idea to check it after a few hours of run time.

FWIW, I have always done compression tests cold with the throttle slightly open. I'm sure there are a lot of variations on this theme, but that's always worked for me.
I left the bike mostly disassembled while I'm waiting for parts. It has manual CCTs, so all I should have to do is loosen those, pop the cam out and change the shims, then re-measure everything.

I don't even have the carbs back on yet as I just got them back from the shop and am waiting on some parts, so I was just going to compression test it as-is, pretty much the same as with the throttles fully open I'd guess.

Yeah, I'm hoping it's nothing major. If the compression checks out I have a couple track events left this year I'd like to run it at, I'll just re-check it after those if it runs fine. I guess worst case I can get a used head on ebay and learn how to replace a valve on this one. It's just really weird how far out of spec that one valve is. Only 2 out of the remaining 7 valves need to be adjusted, and they're just barely on the tight side.
 

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I had an '83 CB1100F many moons ago. I'm not sure how many owners it went through before me, but it had about 33K on it. I checked the valves about a month after I got it, and one exhaust valve was right about .0015", the rest were in the .004" to .005" range.

Those old Honda F motors ran hot, so I figure the engine was overheated at some point, the one valve got hot enough to stretch a bit, and the cycle repeated itself over time. That's just a guess, though.

I adjusted the valves on a 1970 BMW R75/5 about a month ago. The owner had the engine rebuilt less than 1000 miles ago by a well known rebuilder. Intakes are supposed to be .005", exhaust .008" (if I remember correctly). Anyway, all the valves were at about .010". The head bolts were fine, no metal in the oil, etc. So the pushrods shrank, the cylinders stretched, the valves got shorter, the cam lobes are wearing out disproportionately, or something else entirely. Who knows? I adjusted them and it runs fine.

Sometimes engines do funny things and it's difficult to figure out why. If vehicles always worked the way they were designed to, there wouldn't be mechanics and Internet forums...
 

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Discussion Starter #14
So, finally got around to working on it again today. That rear CCT is a real pain. Adjusted the clearance on the offending valve and did the compression test. 195psi in the rear cylinder (the one with the tight valve) and 200psi in the front. Looks like everything should hopefully be ok.

Hopefully will run right now that the carbs are clean too, just need a couple parts. Assuming it does will run it at the track and measure the valve lash it again.
 

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BTW, thanks for the continued updates. There's been a lot of threads that just die, so you never find out what the resolution was.

It sounds like you're in good shape. It will be interesting to see if the problem child behaves itself.
 
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