daver clasper Posted October 16, 2020 Share Posted October 16, 2020 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 Quote Link to comment Share on other sites More sharing options...
glang Posted October 16, 2020 Share Posted October 16, 2020 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.... Quote Link to comment Share on other sites More sharing options...
daver clasper Posted October 18, 2020 Author Share Posted October 18, 2020 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 Quote Link to comment Share on other sites More sharing options...
glang Posted October 18, 2020 Share Posted October 18, 2020 Correct, no other gaps, which I assume is achieved just by gravity as I cant think of any springs or other means..... Quote Link to comment Share on other sites More sharing options...
RobPearce Posted October 18, 2020 Share Posted October 18, 2020 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. Quote Link to comment Share on other sites More sharing options...
glang Posted October 18, 2020 Share Posted October 18, 2020 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? Quote Link to comment Share on other sites More sharing options...
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