13.5-1 and valve shims

6 replies to this topic
  • Diode663

Posted December 20, 2005 - 09:56 PM


I recently did a top end and used the wiseco 13.5-1 piston. The bike cannot be started by a human being. We finaly got it started by towing it behind a truck in gear while kickstarting it. It ran like a champ until it was warm and then I turned it off to cool down. Then I tried to start it up again.. no dice. So I thought about the research I did on the hi compression piston and I figured no one would condone such a mod if it was imposible to start like this. The kick locks up with compression and takes a bit of standing on the kick start to get through it. So I came to the conclusion that something was arye.
So I I checked the valve clearences and all of them were in spec but the lifter under the decompression nipple (wich I belive is why it wont kick over) there is excessive gap.
I didnt test the clearences before I tore the bike apart but my friend says it was a tad noisy. Im not sure why I didnt have a similar problem with this before. I suppose the hi comp piston exagerates this. I do know that the valve isnt stuck open because the bike has amazing compression. So do I just get a new shim and go with that and be good?
So if I have .508 clearence and there is a 175 pad in there Should use a 205 pad? Oh yeah and this is on an 04 450F
Also is it true the crf450 shims will fit this bike?
Thank you a bunch guys.. Im so close to getting this thing working again.

  • grayracer513

Posted December 20, 2005 - 11:52 PM


I don't know how you got to be .30mm out of spec unless you changed something or mixed the buckets up, but your math and your theory about your exess cranking compresion are both right. If you have a 175 shim in that valve now, and your clearance is .50mm, you need a 205. And the CRF intake shims do fit.

  • Diode663

Posted December 21, 2005 - 04:09 AM


Thank you very much gray. Im not sure either. But It must have been like this before I took the bike apart as well. Because the only time I took the lifters out was when I reseated the shims, but I only took them out one at a time to avoid confusion. Im just willing to bet its never been checked which upsets me, but as long as it holds compression and can be adjusted out that should be good no?

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  • 642MX

Posted December 21, 2005 - 06:41 AM


I don't think its the piston. I noticed that mine was a little harder to kick, but nothing like you described.

  • Matt96xr6

Posted December 21, 2005 - 08:35 AM


IF you can kick it over and it will not start, check the hot start plunger in the carb. Make sure it is not stuck.

If you cannot kick it over, double check the cam timing.

  • grayracer513

Posted December 21, 2005 - 10:19 AM


If you cannot kick it over, double check the cam timing.

That's a good point, too. If the cam was installed one tooth advanced, the auto-decomp will reseat the exhaust valve too soon, and will not release enough compression.

The extra clearance could contribute to that, but not as much as the timing could.

  • Diode663

Posted December 21, 2005 - 04:09 PM


I checked out the timing.. everything was in order the lobes were in the correct spot as well as the timing dots. Im guessing the decomp nipple doesnt press down the valve soon enough. I will let you know what happens.

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