Does anybody have the correct procedure to adjust the valve lash on a 390 with adjustable rockers? I have tried to adjust them they way I would my old "C" but run out of adjustment. Is there a perticular amount of lash when the lifter is collapsed or is there just a 1 turn after contact is made adjustment? Any info would be great as I am stuck at this point. It is a 390 with 427 adjustable rockers and hydraulic cam.

Thanks
Jack


66 F250 Camper Special Custom Cab 390 4spd PS/PB

 

Jack: I seriously question the wisdom of using adjustable rockers on a hydraulic cam. If you mean also that you are using hydraulic lifters (HDLs from here out) AND adjustable rockers (ARs from here out), in my gentle opinion (pardon the pun) you're off your're rocker - literally. You cannot use successfully, for long, adjustable rockers and hydraulic lifters together!
Stop and think about it. HDLs take out any lash by compensating for wear, but ARs allow for expansion caused by heat - the 2 cannot co-exist.
Historically, 427s used ARs only for a few earlier applications, and later went to HDLs.
Tell us a little more about your setup (engine wise), and what your reasoning is for doing it this way.

 

Jack: An additional thought: Do you have a PI block? If so, you will NEED to run adjustable rockers, but that will require a NON-hydraulic cam. Otherwise, it's best run either a hydraulic sysem or a non-hydraulic system - but not a mix.

 

I have a rebuilt 390 block that the heads were milled that I dont know how much. I had problems getting the intake to fit which means to me I would need shorter pushrods so, instead of trying to figure out what size push rod I needed I would go hydraulic lifters and adjustable rockers similar to what the small block has. That is why I went this route. should I go back to the non adjustable's ?

 

Here is what I have done when running a hyd cam with adjustable rockers make sure the number one cly is at TDC and not in valve overlap.Then turn the rocker arm adjuster nut down just until you can with your fingers turn the push rod with a slight drag, then turn the rocker arm adjuster nut another 180 or half a turn, roll the engine over to the next cly ready to fire on TDC and repeat. Eric

 

Eric's right on his method of valve adjustment -- one thing noone has mentioned is that you can screw up your valve geometry when you mill your heads. When you change the dimension from the rocker centerline to the camshaft you change the angle of the rocker and the actual lift of the valve in relation to the lift of the cam.

If the heads have been milled <.010 - probably not a big deal. If they've been milled .030 or more you may need to check it.

 

Jack: Bill and Eric have given you excellent advice.

Bill is absolutely correct about the head milling, and it depends on how much. On one hand, the geometry does change at milling, and can have an effect. It really depends on the heads and the block.
Also, hydraulic lifters have that built-in clearance capability, so unless you mill more that about .030, you shouldn't have to worry about the pushrod length.
Now, if put in USED (well used, that is, with many many miles on them) hydraulic lifters after milling the head, you may end up with stuck lifters. That happens because the shorter distance makes the pushrod collapse the lifter further into the barrel, and any oil sludge there may make the plunger stick. So, after milling heads, always install new lifters.