does anyone have a procedure for measuring clearance in the assembled block.?
I have done valve to piston checks at10* btdc and 10* atdc
what is the protocol to check. some of the cams im seeing start valve openings as 24*btdc
I want to make sure I have clearance.
should I pick a cam then use its specs to check clearences in my engine as it is now ...to make sure it wont have valve to piston issues?
or check valve to piston contact at say 24* 14* 7* and at tdc.. then do the same after tcd..
and compare it to those same valve events on the cam?
for instance find max lift of new cam at crankshaft degrees then open my valves at that point. then open the valve till it hits the piston and measure the difference from max lobe lift..to find the clearance/margin/value.?
It is fairly simple, you just measure how much space you have at TDC and then use that number when you pick the camshaft. Typically you need to pull the valve springs on #1 cylinder and then use a dial indicator to tell you the space that you have for the valve with the piston at TDC. Look in the lobe spec part of the cam catalog and it will tell you the lobe lift at TDC. Multiply by the rocker arm ratio and that will tell you the valve lift at TDC.
Lobe lift at TDC depends a lot on duration rather than lobe lift. A cam with a lot of duration has to get the lifter moving up sooner than a cam with less duration. And rocker arm ratio is critical to this measurement since a high ratio rocker arm gets the valve moving a lot faster than a low ratio arm.
