I need to know the gap on adjusting the valves on a 425ci engine

caddy, olds or johndeer?

1978 coupe deville cadillac.

hydraulic lifters, no gap.
zero lash on push rod with valve backed off, warm engin.
why are you adjusting them?

I'm going to have the heads redone.

have you ever adjusted hydraulic valves befor?

are these self adjusting valves.

the lifter that drives the push rod into the rocker is pumpped up by oil pressure and keeps the valve adjusted.

OH LORD HELP ME! :-(

hee hee:)

most ofthe big block GM's are the same try this:

http://www.justanswer.com/chevy/180in-best-adjust-valves-1978.html

You got hydraulic lifters. You gotta put each cylinder at TDC and then just walk the firing order one cylinder at a time. When you get to each cylinder turn the intake push rod with your left hand and tighten the rocker with your right. Now when all the play is out between the push rod and lifter, you’re gonna see that the push rod is getting harder to turn. Now you gotta tighten the rocker some more. A quarter of a turn to half a turn should be good, but don’t forget that the additional turning has got to be from the point when you first noticed the rocker was gettin hard to turn. Now you gotta do the same for the exhaust. From there just continue to walk the firing order, using the same procedure till all the cylinders are done.

just zero lash, no add. turns.

I’m sure you know this, but I just wanted to be sure you did. Firing order is 1 8 4 3 6 5 7 2 .

now that you have the procedures for adjusting the valves. Please let us know how it turns out for you.

Is that caddy fuel injected?

no

We're here to help you "Breanna". Everything you need to know has been posted already. Simply just tell us what you are missing. If you can't do that, then get the car to a "PRO".

Back it off till it clacks then tighten it up till it just stops clacking then give an extra XX amount of turn. I only give mine about 1/2 turn extra. The rockers make a clacking noise with no preload when you hit 0 lash it stops clacking. The extra amount of turn gives you the .030-.060 preload that hydraulic lifters need to operate correctly. It's been done this way on SBC and BBC since the early days.