Valve clearence check?

Not ALWAYS required

The reason to check it is because you don't want the valves to hit the pistons.

If you're buying valve train parts (cam, timing gears, timing gear advance, lifters, pushrods, rockers, valves, valve springs, valve spring retainers) that have been proven in the past, you probably won't have a problem. You could still buy the correct parts, and have the timing gears advanced so far, that Mr. Piston meets Mr. Valve! Since there are so many variables in the valve train, it's a good idea to check it.

The "old school" method of checking piston to valve clearance, is with a lump of modeling clay. Stick it on top of the piston where the valves will be. Then assemble the head & install it on the block WITH a used head gasket. Now hand crank the engine over 2 complete revolutions (720 degrees). Then take the heads off and measure the thickness of the clay, at it's thinnest point. That is your piston to valve clearance. BUT remember that with juice lifters (hydraulic), there is a cusion of oil between the lifter plunger & the bottom of the lifter. If your lifters pump up, it will cause the valves to extend further into the bore & thusly be closer to the piston.

Now you get the idea why cams & valve trains are like so much smoke & mirrors!!!!!!

68COUGAR
 
What are you changing? May just be as simple as making sure the preload is correct.
 
Allow me to clarify.

What I meant was, If it was all oem parts why then would you need to verify the clearance. I want to replace my lifters but I was reading up on the process and it stated that I should verify the clearance.
 
why change the lifters? I read where they are good for close to 200,000 miles. That said I replaced mine when I rebuilt my engine.


If you are only changing lifters you only need to verify the preload. which means that you put the valve on the heel of the cam lobe and then tighten the pushrod/rocker to zero clearance.

torque for stock rocker is 25lbs.

This is extracted from the instructions provided by Doug Macmillin with for installing his roller rocker kits. (Doug sells a Roller Rocker Kit and provides great service) http://v6power.net/rr1.htm

"From Zero Lash: Take your Torque Wrench and tighten to 15 ft-lbs. Notice position of wrench when starting and when finished … it needs to be between 1/3 to 1-1/8 full turns from the original “ZERO LASH” position, and ideally between 1/2 to3/4 of a turn.

if it takes less than 1/3 of a turn with no shims, you need LONGER PUSHRODS. "

Even though I only bought the milled pedestals from Doug he helped me figure out what was wrong and guided me in fixing my preload issue.



My max milled Crane pedestals used with roller rockers are only torqued to 20lbs max.
 
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