Re-adjust Valve Lash or Not?
W.C. - After nearly 600 miles on a new 383 stroker motor, I am considering readjusting the valve lash but am not sure if it is REALLY necessary. It uses a hydraulic Lunati cam (.495 average lift). I have heard from some that this should be done and from others that it is not needed on a hyraulic cam. Any feedback about this or personal experiences would be most appreciated...thanks in advance:)
B.S. - Wes, I know there's alot of opinion about this topic, but there is one thing that is certain. You are not really adjusting "valve lash" on a car with hydraulic lifters because the preload that you place on the lifter plungers allows the engine to run at "zero lash", which means there is no clearance at all between the top of the valve stem and the tip of the rocker arm when the valve is closed (unlike an engine with solid lifters).
As I mentioned, what you are adjusting is "preload", which is the measured amount that you depress the plunger in the valve lifter body after you've tightened the adjusting nut just enough to remove all the slack out of the valve train.
It is my experience that it is very easy to put too much preload on the plunger if you use the "can I still spin the push rod with my fingers" method of determining when all of the slack is taken up before you tighten the adjusting nut the specified amount of additional turns (another highly debated topic ranging from 1/4 of a turn to 3/4 of a turn). Its best to actually watch the lifter plunger to see when all the slack is out. The second that the plunger moves down off of the locking clip that holds it in the lifter body you have removed all the slack.
Those who say re-adjustment of the preload on hydraulic lifters are basically right. But, if something loosens up during the breakin period (like an adjusting nut backing off a bit) you might well have to re-adjust the preload. But this is not common. The thing to remember here is, "if it ain't broke, don't fix it"... if your valve train is not making any of the tell-tale clicking sounds associated with being out of adjustment -- leave it alone!
I just finished rebuilding my 350, and I actually had to replace one hydraulic lifter (a real pain in the butt, having just put the whole engine back together 400 miles ago). This lifter actually accumulated enough of the break-in period metal shavings from the innards of the engine to start sticking, resulting in a valve that would not completely open!
So, my advice is this:
1. Leave your valve preload adjustment alone and just keep an ear open for any signs of valve train noise that would indicate trouble.
2. Change your oil and filer at least every 500 miles for the first 2,000 miles on your new engine. You'd be surprised how much shiny silver stuff can accumulate in there!
<.> Good luck!
S.C. - Bob is absolutely right, and gives some good advice. The only thing I can add is I change the oil and filter right after the cam break in period(20-30 minutes) and I'm still amazed at all the metal gleamings, lint, and other stuff that comes out of a new rebuilt engine.
K.T. - In general I keep an eye on what GM does. They don't readjust the lifters on new cars so neither do I unless there is a specific problem. The American Pontiac engines could get another 600 rpm on the top end before valve float just by setting the lifters 1/4 turn down. It worked for me. Higher rpm Chevies no doubt would see some improvement as well. With carbs and distrubutors it's the same. Set them up to factory specs for the particular engine then make small changes until the desired results are found. There wouldn't be so many red hot headers if this route were taken.
Archivist: Tom Wilson
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