While my head has been at my porters, i asked him if he could find out why DS's have a tendency to loose lash on the intakes. I've seen severl posts that mentioned the intake lash getting SMALLER when doing routine lash checks, but no one mentioned why this is. I believe someone mentioned a possibility of the seats sinking up into the head, but that seemed the only guess. Well, i checked the lash just before i pulled the head on my 01 DS(less than 30 hrs on the quad) and found my intake lash to be .002" on one intake and less than .0015"(that was the smallest i could measure) on the other. The exhaust were .005 and .006.

My friend looked at it and says the valve itself is wearing against the seat. Actually kinda beating itself into a tulip, but nothing drastic. He said the seats look great and have no wear, nor are they "pulling" into the head. He measured the valve lengths to see if the stems stretched(this would cause a loss in lash), but they were to spec. He noticed the edges of the valves were blueing some indicating maybe a lean mixture or high temps, but the seat did'nt reflect this nor did the exhaust valves/seats, plugs(i sent them in the head), or the head pipes(sent them too).

He is currently looking into different valves(stk are ss, but not sure what grade) and maybe a neat type of shim-bucket like used on IRL cars. These would allow the use of Titanium valves and would be lighter than the stk shim/bucket setup. I'm keeping the stk valve sizes.

Just thought i'd shed a little light on the "mystery of the vanishing valve lash"...

 

I wanna mention that the wear on the valve is very minor. I think i made it sound worse than it is. Does'nt take much to cause lash loss though....

 

Boy, i thought someone would be interested in knowing. I was concerned about the seats pulling up into the head, as i've seen that before on bikes and cars. Now i just gotta find some good valves....

 

its not quite the mystery it seems, it has been talked about before but it has been a while and the old posts about it are probably just hard to find. but yeah all valve clearances decrease over time, I can't think of any scenario that would cause any motor's valve clearance to increase. the intakes are more prone and greater effected by tuliping because they are larger in diameter I suppose, because like you my exhaust clearance has never changed, even after 200 hours on the motor. but I've only had to adjust the intake once in that same time, not sure if that indicates a limit to how far they'll tulip or not.

stainless valves hold up much better, much stronger, more resistant to tuliping and wear. I plan on installing them the next time my head comes off.

the Web shim buckets are much lighter than the stock buckets, with titanium retainers and shim under the bucket so it can't be lost in the head in the event of major valve float or spring breakage. this kit really increases your rev limitations.