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what do these do sorry but im a joiner not mechanic

b1zbaz wrote:what do these do sorry but im a joiner not mechanic

They increase the lift of the cam, if you imagine that a rocker on an overhead valve engine merely turns the up push of the cam into a down push on the valve, if the ratio of levers is changed (from say 1:1) to 1.5:1 then the cam's lift is converted into an increased push on the valve. It is supposed to be the equivalent of a wilder camshaft without taking the whole engine apart, i.e. bolt on performance. The roller is in the tip of the rocker that bears onto the valve stem and reduces the friction losses.
I'm no mechanic myself but it is amazing what you can pick up from books, I'd recommend David Vizard's Tuning The A Series Engine.
(Actually it's also amazing what you can pick up from toilet seats)

Cheers Mark