Piston to Valve (PTV) clearance check
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This is a simple test to do while you are
doing the cam degree. It is much more accurate than using clay
especially since the modular motor requires much less piston to
valve clearance than a pushrod engine. We have seen engines
running with 0.010" of clearance at 6500RPM and the valves never
touch the pistons (though we recommend at least 0.020" to be safe) Using the cam degree instructions slowly rotate the crankshaft between 0 and 20 degrees after TDC in the range shown below:
Now for this entire range stop the crank rotation every few degrees and press down on the rocker arm to push the valve into the piston lightly. Record the difference as show below: In this first photo the rocker is not depressed yet and we see a reading of 0.063" approximately.
Here the rocker is depressed and we see a reading of 0.097"
Taking the distance/difference between these 2 points we find 97 - 63 = 34 or approximately 0.034" of piston to valve clearance. While that is tight it usually is a safe spec for the modular below 6500RPM or so. To increase this clearance you will either need to retard the cam or notch the piston. |
