Club Triumph

Hi. If a valve clearance is too large, what metal part on metal part is making the excess noise, or is it a few things please?.

Thanks for any replies.

Dave

well the rocker arm hitting the stem will always generate a noise but the bigger the gap the faster the arm is travelling so producing a louder noise. To prevent any noise there needs to be no gap but then there would be no room for thermal expansion or valve settling and risk valves not closing completely....

Thanks Glang.  I always assumed that's what made the chatter, though if I have a hose to ear and top of valves I don't think I hear much, so was wondering?.

There normally isn't any separation between cam lobes/tappets/pushrods/rocker adjuster screws when running to make any noise, I assume?.

Dave 

Correct, no other gaps, which I assume is achieved just by gravity as I cant think of any springs or other means.....

I don't think it's purely gravity. The pushrod has a cup one end and a dome that fits in the follower at the other. Both of these are shapes that attract an oil film and hold by surface tension or suction. So the easy places for a gap to develop are the rocker to valve and the follower to cam. Given that the valve spring has pushed the mechanism back, inertia will encourage the follower to rest against the cam and the rocker to separate from the valve.

Yes it makes you wonder how it works on upside down or radial engines in aircraft.... Also wouldnt it be better to have the gap between the cam and followers (effectively like a OHC) as theres more surface area in contact so less wear rate?