> Date: Sun, 27 May 2001 15:43:51 -0500
> From: Pat Bibbs <PatB@iewc.com>
> Subject: [oletrucks] Hydraulic Lifters
>
> I'm a semi-novice on this subject.
> I have set lash on standard lifters but I'm not sure about hydraulic one.
>
> A new rebuild, new Comp-Cam roller lifters and Crane roller rockers.
>
> Engine has not been started yet.
> I understand that it is zero lash, I know how to make sure the valve is
> closed.
> When I run the nut down on the post, how far should I turn it?
> Until it doesn't rattle, then a half turn ? Then set the set screw ?
>
> I just want to make sure I don't go too far.
Hydraulic lifters actually have "negative lash", that is, you turn the
rocker nut down past the point of zero lash. On a hot rod like you're
working on, half a turn is usually what you want. A stock engine would
probably be better with one full turn. The difference is that having
less preload makes it less likely to float a valve if you overrev the
engine, and hot rods are more likely to be overrevved.
I follow the firing order (engine NOT running), starting with the #1
rockers when #1 is in Top Dead Center (TDC) firing position (both valves
closed and not trying to open). Loosen the adjustment nuts till both
rockers will rattle...then tighten one at a time till they just contact
the valve and pushrod, then half a turn more. If you don't have the
intake manifold on yet, you can look at the lifters, you should see the
plunger just a little bit below the retaining ring in the top of the
lifter. If the lifters have not had oil in them yet, you will also be
able to push the rockers down at the pushrod end, and make clearance
between the valve and rocker tip--this is ok! because when you prelube
the oiling system, and the lifters fill with oil, you won't be able to
do this any more.
After you adjust both rockers for cylinder #1, then turn the crankshaft
1/4 turn, and adjust #8, then 4, 3, 6 5, 7,2.
It sounds like you also have posi locks, the tall nuts with the set
screw in the middle. To tighten these things properly, you have to back
off the nut about 1/4 turn, then using a big wrench on the nut, and an
allen wrench in the set screw, you screw the set screw in so it contacts
the stud, then tighten both the nut and set screw at the same time. You
will have to try it a few times to get a feel for how far to back off
first--the goal is to have it be tight (about 40-50 ft lbs torque
applied to the big wrench) as the nut reaches the point of half a turn
past zero lash. It's hard to explain, but you need the nut adjusted to
the proper position when it's tight (half turn past zero lash), and you
need the nut tight (pulling hard on a box wrench). If you just tighten
the set screws after adjusting the nuts, then the nuts WILL back off,
and you'll hear some neat rattling noises and have to adjust the valves
again!
Hope this gets you started...
Jim
oletrucks is devoted to Chevy and GM trucks built between 1941 and 1959
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