Valve lash on "425" nailhead.

[Guest]

What is the valve lash on a "425" cu. in. nailhead. I installed a Kenny Bell cam and lifters and had to use adjustable push rods and hydraulic lifters and I am uncertain what the clearance should be. Down to zero and leave it there, or go a turn and a quarter/half after zero.....or what??????????????????????

[The Old Guy]

A good rule of thumb is half the lifter travel. Most lifters have .090 and your push rod probably has a 5/16-24 thread. If this is the case ,one turn will be .040 and should work just fine<p>[ 05-22-2002: Message edited by: The Old Guy ]

[NTX5467]

For what it's worth, the stated spec on Chevrolet V-8s for lifter adjustment is something like 2 turns preload after zero lash. This is supposed to basically center the lifter piston in its available travel in the lifter body.<P>Most of the hot rodders only put about 1/4 turn preload on them for more rpm as at higher rpm, the lifters can pump up (i.e., the lifter's internal piston will be pushed higher in its bore with higher oil pressure) and not allow the valve to seat at those higher rpms, hence the reason for less preload. This is an old hot rod trick from way back for the Chevy V-8s to get the engines to rev higher.<P>From my own experiences, I like 1/2 turn preload rather than 1/4 turn preload so you don't have to go back and do it again later. The whole idea is to get the slack (i.e., "lash") out of the valve train so it's quiet and stays that way.<P>As you bought an aftermarket cam and lifter set, I would suspect there should be some recommended adjustment setting in the instructions. Using a stock adjustment for an aftermarket high performance hydraulic lifter might not be optimum as their lifters might have a different size oil bleed hole or other features to keep them from pumping up at high rpm. <P>In one respect, as long as there is enough preload to keep the hydraulic lifter valve train at "zero lash" at all times and operational temperatures, that's all that is really needed, but some preload will be necessary to keep the piston from constantly being against the snap ring that keeps it inside the lifter body. In the absence of any recommendations from the cam/lifter manufacturer/vendor, you might experiment some.<P>If you adjust the lifters with the engine running, you can try some of the "stoppers" that might be put on the ends of the rocker arms to decrease the amount of oil splashing around. Plus some cardboard to hopefully keep some of the runoff from getting on the exhaust manifolds and inner fenders. Otherwise, be sure to have some of your favorite engine degreased on hand. Setting the preload with the engine running is the best way to do that adjustment, just don't force the preload on the lifter too fast.<P>Enjoy!<BR>NTX5467