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post #3 of (permalink) Old 12-12-17, 10:17 AM Thread Starter
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Join Date: Nov 2017
Posts: 23
Re: how to determine pushrod length, 351W, nonadjustable valves, rollercam, hydraulic lifters

I called my local machine shop expert and asked him the same question. He said the exact same rules for adjustable vs non adjustable rockers apply. First, get the valve in question to the base of the cam lobe. Then either:

A. tighten down the rocker bolt until all play is removed from the pushrod, then look for another full turn before the bolt gets to full torque rating

B. use a pushrod measuring tool, adjust it until there is zero lash (with the rocker bolt fully tightened down), and then the pushrod length should be 0.050" longer than that.

That's it, he said, no other guesswork.

I was asking him about hydraulic tappet theory, and mentioned a few things that were bugging me. ("it's impossible to compress a pumped up lifter in a vice, it won't compress no matter how hard I try!", "even when I leave a lifter on a cam lobe, it takes all night for it to pump back down!", "won't putting 0.050" of preload on it when the cam is on the base, cause the valve to slightly stick out and never fully close?")

he said, "how cold is your engine oil?" I said, "garage temperature". He said, "and what is that?" I said, "about 40 degrees F". He said, "lifters change how they work dramatically when the oil starts to heat up to 250F. You can't judge them when they're cold. This is why hydraulic lifter engines run so poorly when they are cold, the lifters don't work right until they get warm engine oil in them. Don't try to fix a lifter issue with heavier weight oil, under any circumstances, fix the pushrod length."

I'll be darned. Never thought of oil viscosity changing how the lifter works.
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