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I didn't intend my meaning to imply that a gap didn't get bigger as it got hotter - of course it does. My meaning was that it is hard to visualise why it does. I suspect my knowledge of physics is better than most people on this forum.

The laws of physics say that a gap expands when it gets hot. (Just why this is I personally find hard to visualise - logic could just as easily tend to make one think that it got smaller). So a gap decreasing on an engine with increasing temperature must be generally considered to be something...

I don't have enough knowledge of vibratory-type matters to really comment. However my intuition would make me inclined to think that a pump etc. meant to take racing stresses would not be prone to break so easily from vibration.

Braggarts I don't mind if they know what they are talking about. Braggarts who don't know anything are the annoying ones. For more than 40 years I have accepted without thinking about it too much that a tappet's clearance reduces when it gets hot. But is this true? The rule in physics is that...

Ivymike - I think your last comment makes a lot of sense and I strongly suspect that this is the basic reason that racing cams have higher ramps/clearances etc.

Mike H - Maybe I shouldn't have used the word "sheared". But there still is no answer to the original question of why the oil pumps repeatedly failed. The main question wasn't - "Where is the vibration coming from"? It was - "Why is the oil pump breaking"? Or maybe I have totally misunderstood...

Raptor - This still doesn't explain why the pumps sheared.

The amount of tappet clearnce must match the amount of lift on the opening and closing ramps of the cam lobe. The ramps can clearly be seen on a lift/vel/accel graph of a lobe. They show up a horizontal constant velocity trace if the cam lobe is measured without any tappet clearance. There is no...