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valve clearances. whats going on?
i have a 94 suzuki dr125. i bought a manual specifically for the electronics but got curious the other day and decided to see if the valve clearances i been using before i got the book were the same w/ the clearances stated in the book. the clearances i used to use worked ok and were "intake-.08mm and exhaust-.13mm....now the book says between .08-.13mm but it also says the exhaust needs to be the same as the intake. i used to set the exhaust wider than the intake an it ran fine.so the other day i decided i wud set them both the same like the manually says to do i set them both for .08mm. i went for a ride shortly after,came back,checked them again, and the exhaust valve was closed up tight. so what im asking is do you think i need to ignore the manual and go back to a bigger exhaust valve setting like .08 and .13 or set them both the same but at a bigger clearance because riding w/ them both at .08 causes the exhaust valve to close. is my rocker arm threads bout gone? need new parts?
yes it states to set them when cold and i done that. FERRIS are you saying that wen the engine is at normal operating temp that there will be no clearance between the valves stem and rocker arm set screw? as in wen the engine is cold and i set both valve clearances for .08,go riding and come back and the exhaust is tight wen engine is cool again w/ no clearance at all that this is ok? and i shud take off again?cause i think not the clearances need 2 be right before i ride it. my question was if i set it at the specified clearance and it closes back up after riding an cooling back down what do i need to do. i kno this cant be good because it supposed to have clearance wen the engine is cold. i can set the clearance but when i come back and check it again the clearance is closed tight
i didn think ferris knew wt he was talkin about.its not only cracks but rocker arms and valves acutally wear down in size thx for the help tho i got what i waslooking for now i know to jus open the exhaust more
3 Answers
- bikinkawboyLv 79 years agoFavorite Answer
The exhaust is nearly always intended to be set a bit wider than the intakes. Not always, like with my Kaw KZ1000, but yes with my ZG1300 and Honda CM400A, as well as my old Studebaker cars, tractors, small gas engines and so on. Ferris is incorrect when he says there is supposed to be zero valve clearance when the engine is hot. Why? As soon as there is any valve seat recession or valve face wear, the valve is then being kept open. They are meant to have clearance for approximately 180 degrees of the cam lobe rotation, the middle of that range being opposite the highest point of the lobe. On either side are what's called clearance ramps ground onto the camshaft, which are meant to slowly take up the clearance before the lobe starts opening the valve in ernest. Way back in the old days or with cheaply made cams, they didn't have the clearance ramps and if you had too much clearance, when the lobe ramp hit the lifter or bucket, it was like kicking your front door open rather than opening it up slowly.
If you had no clearance when it was hot, then I'd go back to the wider clearance on the exhaust.
Source(s): I've been wrenching on engines for 45 years and have overhauled engines ranging from dinky weed eater engines to diesels having 300 pound crankshafts and 6 pound pistons. In other words, I have learned a thing or two in that time. - 9 years ago
Look, the idea is that when the engine is at its operating temperature, there will be no clearance and that doesn't mean that the valve is compressed. It means that if you were to add 0.01 to what you have, it would have a 0.01 gap (or clearance). But this is in an optimal situation, so if you find that when engine is hot you have 0.02 all round you'll be spot on.
If they are too tight the valves risk not shutting properly and when a valve isn't shutting properly it will let gas escape when it shouldn't (losing compression) then its seat will get dirty and then it will burn and the valve might even crack.
So, if you have to err, then err on the loose side. Having your tappets too loose will achieve that they will be noisy and they might open up (when real loose) a tad later than they should, but at least you won't run dangers of any sort..
To get back to your question, the exhaust valves always tend to heat up a bit more and so will expand more and so set them wider
EDIT: your rocker arm will need replacing when it breaks in two/ when it's so pitted it might ruin camshaft, when it moves sideway.. in other words you'll realize when it needs replacing. Make sure your tappets aren't gonna come loose while engine is running but make sure you don't strip them by tightening them too much AND never work on a hot engine or you'll strip things
Source(s): I have done a billion of them, including desmos - ?Lv 69 years ago
I am no mechanic, so take this for whatever you think it's worth.
Check the manual again, and see if you're supposed to set the clearance when the engine is hot or cold. An exhaust valve is going to get a LOT hotter than an intake. If you set it when it was cold, it expanded after it got hot. If the clearance is supposed to be set while hot, then run it up and down the road for 5-10 minutes, and go set them again.
