What causes "tight" valves?
Posted August 09, 2008 - 04:47 AM
Can someone explain to me how (if) valve clearances get tighter as they wear with shims? I have a 98 WR400 with a starting issue and several people have suggested valve clearance.
Also, how tight is too tight? The minimum spec in manual (for intake) is .15 mm and I have one that is .13 mm...?
Posted August 09, 2008 - 05:26 AM
Posted August 09, 2008 - 05:32 AM
Posted August 09, 2008 - 05:47 AM
Posted August 09, 2008 - 05:51 AM
Posted August 09, 2008 - 09:17 AM
Is this possibly normal?
Posted August 09, 2008 - 09:57 AM
I just finished double checking the valves and only one is slightly out of spec (.2 mm), as I was doing this I realized that I can turn the engine over using the crank nut fairly easy (probably not a good sign), but when I use the kick starter it will support my weight for a few seconds before bleeding off.
Is this possibly normal?
First off, if one of the valves is out of spec, adjust it. Quit telling us how much it is out of spec, remove the cams, and change the shim.
Posted August 09, 2008 - 11:12 AM
Posted August 09, 2008 - 12:09 PM
Posted August 09, 2008 - 02:39 PM
Posted August 09, 2008 - 05:19 PM
A one third (approximately) rotationj of the kick crank shaft will take the engine from the start of one compression stroke to the next. Since that's two revolutions of the engine, the ratio is 0.3:2, or 1:6. While that is nowhere near 200:1, the same principal applies. It's like trying to turn the crank nut with one sixth of the leverage of the wrench used.
When you are turning the engine over with the crank nut, you are turning it at a 1-1 ratio and when you use the kicker it is around a 200 to 1 ratio ( a number I heard somewhere a long time ago). So you are turning the engine over a lot faster and the compression doesn't have time to bleed off when using the kicker. Also since your in there do like Chikenstrips and a few others have suggested, get the valve back into spec, it won't get any better by waiting for someone to say it's OK the way it is. WR Dave.
Everything else said here is right:
Valves tighten because they wear at the seat and face, so the stem moves up into the head.
When the spec is .15 and the valve is .13, the valve is out of spec and needs shimming.
The intake valve being .02mm tighter than called for IS NOT the cause of your starting problems, even though it needs to be corrected.
The early FCR is a very fussy carb, sensitive even to changes in weather, and minor dirt invasions or just being slightly our of adjustment are 80% of all starting troubles on a 400. Weak ignition that demands a spark plug in very good condition is another 15%.
Posted August 10, 2008 - 04:43 AM