adjustable rocker arms on 390

[ken's1971]

my 390 in my engine has adjustable rocker arms but i don't know what to set them at, they seem to be hi performance pieces one of the previous owners put on. my MOTOR manual says the valves should be adjust to .010 on intake and .020 on exhuast but as far as i know 71 pickups with 390 did not come standard with adjustable rockers. So i'm abit confused about what is the correct setting for these rockers. Btw i already adjusted them to the above specs and the valves do make a tapping noise althogh not very loud. So does anybody know the correct way to adjust them. thanks

[heep70]

If they are tapping they are not tight enough. To adjust them, for each cylinder bring the piston up top on the compression stroke. Both intake and exhaust valves should be closed and the springs relazed. Grab the pushrod with your finger tips and start turning it while at the same time tighted the rocker arm down. Once the pushrod stops spinning, back off the adjuster 90 degress. You will have to do the process for each cylinder and valve set.

You can go a step farther if you have a really good ear. You can snug them down a bit more to get them just right. Each one will be a bit different. If don't have that trained ear you could get them to tight and eventually burn the valves. Your truck will run just fine with the first adjustment.

[DuckRyder]

You need to try to ID the cam, unless it is a solid (which no 71 light duty truck came with) you probably need to set them 1/2-3/4 turn down (preloaded) from zero lash.

No hydraulic cam should have clearance...

[ken's1971]

heep, thanks for the info, i'm not going to tear my motor apart to find out what kind of cam i have in it so it will have to do. The person who owned before me put on a cast iron 4 barrel intake and i can't seem to ID the heads they have what like like a brace of extra cast material running down the exhaust ports on the outside of the head. maybe its aftermarket heads i don't know. But i thought that all hydraulic cams and lifters had no adjustments on them, that only solid lifter and cams had adjustable rockers is this true?

[DuckRyder]

http://www.cranecams.com/?show=techarticle&id=2

[heep70]

heep, thanks for the info, i'm not going to tear my motor apart to find out what kind of cam i have in it so it will have to do. The person who owned before me put on a cast iron 4 barrel intake and i can't seem to ID the heads they have what like like a brace of extra cast material running down the exhaust ports on the outside of the head. maybe its aftermarket heads i don't know. But i thought that all hydraulic cams and lifters had no adjustments on them, that only solid lifter and cams had adjustable rockers is this true?

Yes, some hydraulic engine had adjustable rockers. Makes it nice when one wants to put a different size cam in.

The head ID should be located on the exhaust bank of the head in the middle. Four letters and sometimes a dash w/ a couple more letters. In fact they should be located on that web you are talking about. Let me know.

[willowbilly3]

If it is hydralic the methods mentioned are suffice, but if you want to be real accurate use a dail indicator and shoot for about .010 preload on the lifter.
I never had adjustable lifters on an FE hydralic but I did on a solid lifter engine and found out the sequence for adjusting them, as printed in my 1975 edition of Motors Truck repair manual, contained a typo and had transposed two of the valves in the sequence. The method they use is to put it on top dead and set half the valves, turn it 360 and set the other half. Probably not the best way on a hipo engine tho.