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Old 05-04-2013, 09:02 PM
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lifter rotation on new cam

Installing a new comp cam and lifter combo into a Pontiac 400. Mild cam with .425 lift. I read on a different website that all the lifters should rotate when turning the cam by hand. This is done by properly installing the cam, applying cam lube to the lobes and dropping the lifters in the bores but not installing the pushrods or timing gear. Then simply turn the camshaft in the correct direction by hand. Would such a slow turning of the cam with no pushrods installed be sufficient to rotate the lifters. This test was suggested as a preview of potential problems with lifter /cam lobe mating. Anyone try this before assembling the remainder of the engine for the first start up?

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Old 05-04-2013, 09:15 PM
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I've never heard of it or tried, did you?
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Old 05-05-2013, 12:29 AM
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Never did it, except to verify the lifter to bore clearance at 0.0015", but it sounds like a good idea. If the bore is too tight or too loose, the lifter won't spin properly and the whole mess is doomed from the start.
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Old 05-05-2013, 07:37 AM
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The weight of the lifter alone will not put enough pressure on the cam lobe to spin the lifters in the lifter bores. The cam lobe will push the lifter up in the lifter bore and the cam lobe will lose full contact with the lifter on the return flank of the cam lobe.

Extrapolate that into a situation when the engine is running:
If the lifter (follower) fails to follow the cam lobe at high RPM because of inadequate valve spring pressure, the lifter will be lofted over the nose of the cam lobe on the return flank of the cam lobe and the valves will not fully return to their seats before the cam lobe starts lifting the valve again. That is what is know as "valve float" .
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Old 05-06-2013, 10:03 AM
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Quote:
Originally Posted by frankOne View Post
Installing a new comp cam and lifter combo into a Pontiac 400. Mild cam with .425 lift. I read on a different website that all the lifters should rotate when turning the cam by hand. This is done by properly installing the cam, applying cam lube to the lobes and dropping the lifters in the bores but not installing the pushrods or timing gear. Then simply turn the camshaft in the correct direction by hand. Would such a slow turning of the cam with no pushrods installed be sufficient to rotate the lifters. This test was suggested as a preview of potential problems with lifter /cam lobe mating. Anyone try this before assembling the remainder of the engine for the first start up?
I would be very surprised if you would see lifter rotation under the circumstances described. With no spring load to press the lifter into the cam with more than the force of gravity on the lifter; I'd expect that the interface forces wanting to cause rotation would not be high enough to overcome the tackyness of the lubrication that will want to prevent rotation.

Bogie
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