Need quick valve help

13 replies to this topic
  • Supafreak_711

Posted December 17, 2005 - 10:04 AM


Hey, my dad and I have his bike apart and are checking the valves and we have a question about the feeler gauges. We can get some in that are considerable outside the specs (which would make sence because of the problems we have been having) but we arent sure if we are just compressing the valve spring and making the gap bigger. Do we just keep getting bigger gauges in there untill the next one wont fit? Or just go untill you have to push the gauge in. Thanks, we are using the manual but couldnt figure this out. I guess we will start putting the carb back together and see if there are any posts when we are done.


  • UK STU

Posted December 17, 2005 - 10:45 AM


when u got the bike timed up the gauge should slide in with very little restance

  • Supafreak_711

Posted December 17, 2005 - 11:02 AM


So the guage should fit in easily? (but the next size would be to snug, right?). I think we were compressing the valve springs a little bit when we were putting in the bigger gauges, do you want to compress the springs at all? or just get the biggest gauge in without pushing on the springs?

Thanks, I'm trying to get through my first valve check

  • Supafreak_711

Posted December 17, 2005 - 11:35 AM


Ok, we just went with the biggest gauge that would go in without much struggle. looks like both exhaust valves were around .17 mm (to tight). Would it make sence that being to tight would be causing the bike to pop alot while starting (big pop in exaust pipe).


  • Ronin 26

Posted December 17, 2005 - 11:36 AM


No you do not want to compress the springs at all. Slip in gages that push and pull smoothly, if you have to force it in it's probably compressing the spring. It takes awhile to develop a proper "feel" for the actual clearance. If you have a micrometer, or caliper set it to .010" and run a .010" feeler gage through a bunch of times to start the feel development if your not comfortable.

  • Supafreak_711

Posted December 17, 2005 - 12:22 PM


Ok I think we got it. We figured out that there was a pin on the cam that was sticking out a bit opening one exhaust valve just a tad when it should be fireing. Thanks for the help, now we just gotta remember how it all goes back together. I guess we will know when we get it together :applause:


  • CycleWriter

Posted December 17, 2005 - 12:28 PM


There's no way you could compress a valve spring by inserting a feeler gauge without bending it unless the feeler gauge you're using is as thick as a screwdriver blade.

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  • grayracer513

Posted December 17, 2005 - 01:08 PM


You can squeeze one size larger guage into the gap between cam and lifter than the gap actually is without too much difficulty. The correct feel is something like you would get if you put the feeler guage on a flat piece of metal, rest the end of a 3/4" wrench on it, and pull the guage out from under it.

If the pin you mentioned (the auto-decompression pin) was lifting the valve, you were not checking the valves at TDC on compression as you should have been.

  • Supafreak_711

Posted December 17, 2005 - 02:44 PM


Uhh ohh..... We had it at TDC (im sure of that), haha I guess that pin was supposed to stick out. Dangit, looks like my dad will be opening the motor back up (hes the one that said he didnt need the manual when I asked him about it). well... this sucks.

Thanks, I guess you saved me a "why is the auto-decomp not working" post.

  • Supafreak_711

Posted December 17, 2005 - 02:56 PM


Yea, just tried starting it... your most definately right. Is it just supposed to stick out far enough that the other side of the pin is flush with the surface? Thanks, we would have spend hours trying to figure this out. Haha you should have seen the look on my dads face (i walked in just as he was putting the seat back on). I wish I took a picture.

Well im off to the garage..... again...

  • grayracer513

Posted December 17, 2005 - 07:17 PM


The auto decompression mechanism is very simple. At speeds below idle, the pin protrudes enough to raise the left exhaust valve off its seat during the first 50% or so of the compression stroke, cutting the cranking compression from around 190 lbs. to more like 100, making it easy enough to crank that a small electric motor would be able to do it. Once idle speed has been reached the flyweight on the exhaust cam is moved outward by centrifugal force, and in so doing, retracts the pin so it no longer contacts the lifter at any time, and the engine runs on its full, normal compression.

With the engine off, the pin normally extends far enough to lift the left exhaust valve from the seat from a point near BDC to a point around 60 degrees BTDC. Anything else is abnormal. But, that's why the valves must be checked at TDC instead of some random point in the rotation.

  • Supafreak_711

Posted December 17, 2005 - 08:02 PM


After closer inspection, the pin was broken (I didnt look at it, but my dad said he had to order a new exhaust cam). I guess I will wait and see if with the new cam our problem is solved.

Thanks for the help,

  • MountainMax

Posted August 04, 2006 - 12:51 PM


Thanks for that great explination, i wondered myself how they worked.

  • Nitroused383

Posted August 04, 2006 - 03:59 PM


Feeler gauges are designed to run with some resistance. The average resistance on a feeler gauge should be 12lbs of resistance. By the way 12 lbs of resistance isn't a lot.

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