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Lifter Installation
And
Valve Adjustment
You MUST
Check Lifter Pre-Load On Any Cylinder Head or Hydraulic Cam Installation!
New engines
from the factory can vary as can rebuilt or repaired engines. You can check
the following things that could change the height of the plunger in the
hydraulic lifter (pre-load):
- Cam base circle diameter
- Pushrod length
- Milled or resurfaced heads, block or both
- Faced-off valve stem ends
- Thicker or thinner head gaskets
- Several valve jobs done on heads
- Lifter height difference from lifter manufacturer
Install lifters with a liberal coating of Assembly Lube on the lifter face.
Apply motor oil to the lifter's pushrod seat. Lifter adjustments should
be made with the intake manifold removed, to better see all valve train
motion. Engines with separate adjustable rocker arms, such as the small
block and big block Chevy V-8 require installation and adjustment one cylinder
at a time! Don't tighten the adjusting nut down before adjusting the valves,
since over tightening can cause the valve to hit the piston when the engine
is turned over! (This causes bent or broken valves, pushrods, etc.) On engines
with shaft mounted adjustable rocker arms you should back off all adjusters
all the way before you install the rocker shaft assembly. Be sure the pushrod
is seated in the rocker arm seat and tappet before you start to make adjustments!
On hydraulic lifter cams, rotate the engine in the normal direction of rotation
until the exhaust lifter begins to move UP. Adjust the intake valve to ZERO
LASH with no pre-load, then tighten 1/2 more turn. Rotate the engine again
until the intake valve has moved ALMOST ALL THE WAY DOWN. Adjust the exhaust
valve to ZERO LASH, then 1/2 more turn. Repeat this procedure until each
cylinder is completed.
On engines with non-adjustable rocker arms you must have a lifter pre-load
of .020" to .060". Use the same procedure and sequence as above.
Pushrods for each cylinder are usually the same unless valve stem heights
are not properly matched. Be sure that the valve you check for lifter pre-load
isn't open. Allow a few minutes for lifter bleed down if this occurs. Some
installations require changing pushrod length, using adjustable pushrods,
shimming the rocker stands or shafts, installing straight screw-in studs
instead of stock bottle neck type studs, using Allen set adjusting nuts,
or machining the heads for adjustable rocker arms, studs and guide plates.
Hydraulic lifter cams usually do not require additional adjustment after
initial engine start-up.
To adjust VALVE LASH ON MECHANICAL LIFTER CAMS (also commonly called "solids"
or "flat tappets") follow the same basic procedure as above. Instead
of lifter pre-load and zero lash, use the valve lash specs printed on your
timing specs card. After engine fire-up, break-in and oil and filter change
you'll need to again adjust valve lash, and periodically after that.
Setting Lifter Pre-Load In Hydraulic Lifters On Engines WITHOUT SEPARATE
ADJUSTABLE ROCKER ARMS
Lifter pre-load (the distance the pushrod extends into the lifter) should
be between .020" and .060". Too little pre-load or no preload
will result in very noisy operation while the engine's running. Too much
pre-load will cause the engine to idle rough, have very low manifold vacuum
and poor low-end performance. It may also stall out when dropped into gear.
Torque all bolts for rocker stands, etc., to proper specs. Allow a couple
of minutes for the lifters to bleed down, to remove any oil contained inside
them. As always, NEW LIFTERS MUST BE INSTALLED ON ANY NEW CAMSHAFT!
Use the valve cover gasket surface of the head as a guide. Lay a metal scribe,
etc., flat on this surface. You'll need to make two marks so be sure your
reference point is flat and stable. Scribe a line on the pushrod. Unbolt
the rocker assembly and loosen up the bolts so the pushrod will stand free
in the pushrod seat of the lifter. Note that the pushrod seat in the lifter
will be forced up against the snap ring in the top of the lifter by the
plunger spring inside the lifter. Scribe another mark on the pushrod. The
difference between the two marks is the amount of travel that the pushrod
made into the lifter . . . the lifter pre-load! Measure this pre-load amount
with a machinist's pocket scale or dial calipers if you have them. .020"
to .060" is recommended. If the pre-load is too little measure the
amount of free-play between the rocker arm and pushrod and then add .030"
to this figure. You can then buy longer than stock pushrods by the amount
of extra length you need to achieve pre-load. Remember to add the .030"
to the total "longer than stock" length to allow for the extra
you need to get the right lifter pre-load! Check one each, intake and exhaust
per cylinder head. If your valve stem heights are uneven (check them by
measuring from spring seat to the top of the valve) or different from factory
specs (see the factory shop manual), then you'll have to check lifter preload
on each valve, on both heads.
If you're having a valve job done on your heads have your machinist check
the valve stem height. A properly done job should result in a straight edge
being laid across the tops of the valve stems with no excessive difference
between valve stem tops. On engines with pedestal or shoulder bolt mounted
rockers shims can be used to reduce pre-load. If pre-load is too little,
or there's none at all you'll need to use longer than stock pushrods. (Use
same measuring procedure as above) On engines with individually mounted
rockers tighten the adjusting nut or bolt to zero lash. Torque the adjusting
nut or bolt into place 3/4 or 1 full turn or rotation. This should put the
pushrod at the correct lifter pre-load. If you cannot get .020" to
.060" preload you'll have to use shims or longer than stock pushrods.
Again, use the previously mentioned procedure to order the correct length
pushrods.
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