[DeTomaso] Preload.

[P. Rimov]

>From the Corral Net : Adjusting Hydraulic Roller Rockers


There's a procedure to go through to be sure the preload on the lifter and 
the pushrod length is correct because there's no adjustment in the system. 
Rotate by hand til lifter's on the base circle; once there, tighten by hand 
to zero lash (til it stops 'rocking' just barely); put torque wrench on and 
torque to 18-20 ft-lbs while counting turns. You should hit the torque in 
between 1/4 and 1 turn. If more than one turn you need to shim the rocker 
(pushrods are long); each .030" shim reduces amount to torque by about 1/4 
turn. If you hit the torque in less than 1/4 turn or you can't reach zero 
lash at all then your pushrods are too short. If it's the majority of the 
rockers, you need to order the right length pushrods. If it's just one or 
two you may be able to remove a bit of material from the bottom of the 
offending rockers.

&

1. Remove the valve covers, and pick a cylinder you are going to set the 
preload on.

2. Hand rotate the engine in its normal direction of rotation and watch the 
exhaust valve on that particular cylinder. When the exhaust valve begins to 
open, stop and adjust that cylinder's intake rocker arm.

3. Back off the intake rocker arm adjuster and remove any tension from the 
pushrod. Wait a minute or two for that hydraulic lifter to return to a 
neutral position. The spring inside the lifter will move the pushrod seat up 
against the retaining lock if you give it time to do so.

4. Now spin the intake pushrod with your fingers while tightening down the 
rocker arm. When you feel a slight resistance to the turning of the pushrod, 
you are at "Zero Lash". Turn the adjusting nut down one half to one full 
turn from that point. Lock the adjuster into position. The intake is now 
adjusted properly.

5. Continue to hand turn the engine, watching that same intake. It will go 
to full open and then begin to close. When it is almost closed, stop and 
adjust the exhaust rocker arm on that particular cylinder. Loosen the 
exhaust rocker arm and follow the same procedure described before in steps 3 
and 4 to adjust this rocker arm.

6. Both valves on this cylinder are now adjusted, and you can move on to 
your next cylinder and follow the same procedure again.

You can also use a cam wheel for step (2) if you know the exact valve events 
of you cam, not advertised, exact. For example if you know the exhuast valve 
opens at 43 degrees BBDC then using the cam wheel rotate the engine to 
43BBDC for the particular cylinder you are working then follow the rocker 
arm adjustment proceedures.

I believe some people like to adjust the rocker arms with a hot engine but 
usually when using the adjustable stud type rockers

>From Comp Cams : http://www.cranecams.com/?show=techarticle&id=2

Cheers

Paul