A question that I have been unable to find an answer for:
I have installed a mechanical cam that requires .020" valve lash hot. For initial setting I´d like to set some sort of lash cold and warm the engine up and check the lash at operating temp.
Crane cams catalogue advices that for alloy block/heads you can subtract as much as 0.012" from hot lash and use that value for cold lash setting. This is a general value and should be approached with caution :-). Now, my cam is not a Crane cam and naturally extreme caution
Does anyone have real life experience about the matter ?
Anywhere around .010" should be fine for a starting setting.
Basically what you are trying to do is set the max hot lash that won't make a bunch of clatter. Reason for the max is to stretch out the adjustment interval. If they close up too much due to wear you can either burn a valve or develop a miss. The spec gives you .020" to play with. You can close that down a good bit if they are too noisy. Frequent adjustment due to wear isn't as much of an issue as it once was, however you don't want to go much under .005" cold or hot. Usually hot will be bigger but it depends on the materials of the heads, valves and seats.
Jim
"If they close up too much, due to wear". Please explain ? When cam lobes, lifters and valve train wear, clearance increases ?
Cheers, Art.
Head gasket crush and valve seat recession tighten up the valve clearance over time. Lifter, rocker, camshaft and pushrod wear loosen the clearance but these seem to advance more slowly.
Valve and seat wear may be less than it once was but it still occurs and it takes up the clearance in the valvetrain, to the point where the valves barely close. Then heat transfer from the valve to the seat decreases and valves get burnt. This is the main reason why you periodically adjust the valves when you have solid lifters. Thought you motorcycle guys would know that.
Jim
The older motorcycles didn't seem to need it as often as these newer bikes.
Maybe because they don't wind as high and therefore have lighter valve springs.
Jim