L-76 Engine Performance w/H & W Valve Adj.

[Geoff B.]

Re: L-76 Engine Performance w/H & W Valve Adj.

Got to drive today and didn't get far before I noticed a pretty loud clacking from the valves. I got back to the garage, pulled the valve covers and started checking all of the lash settings. Got to the 4I valve and saw the rocker nut had lossened by several turns. The threads on the stud and the nut look fine, so I'm guessing they have worn just enough that they need to be replaced.

Does that solution make sense?

Also, just doing a sanity check, when I am looking at the cylinders, I am assuming the exhaust valve is on the left and intake on the right, is that correct?

Thanks for any suggestions

[Stuart F.]

Re: L-76 Engine Performance w/H & W Valve Adj.

Geoff;

If one is used to big blocks you might expect to see an Intake after each Exhaust, or vice versa. On a small block it is not that way. Your best bet is to look for which intake manifold runner lines up with which rocker arm and which exhaust manifold outlet lines up with which rocker arm, i.e. on both banks it is: "E" "I" "I" "E" "E" "I" "I" "E".

It does sound as though you either have one bad rocker adjusting nut or, perhaps you did as I did and had two feeler gauges stuck together when you did that one. I'd try adjusting it one more time and see if it holds. You might also consider pal nuts to lock your adjustments. There is also a possibility that the stud has pulled loose from the head.

Stu Fox

[Duke W.]

Re: L-76 Engine Performance w/H & W Valve Adj.

Like Stu said - E-I-I-E-E-I-I-E and you can verify by looking to see if an exhaust or inlet runner is adjacent to the valve.

If you don't understand the valve sequence on the engine, you may have adjusted incorrect valves at some of the crankshaft positions, so you better go through the procedure, again.

Also, I have never seen a torque pre-load spec for the nuts, but IMO if a nut will turn with less than about 15-20 lb-ft, it should be replaced.

Duke

[Dan D.]

Re: L-76 Engine Performance w/H & W Valve Adj.

As I recall, some of the old Pontiac engines had the same rocker arm setup as Chevy, but you adjusted the valves by torquing the nuts to 15 ft. lbs. Always wondered why they did it like that and why different from Chevy. -Dan-

[Duke W.]

Re: L-76 Engine Performance w/H & W Valve Adj.

Pontiac actually developed the rocker ball/nut pivot mechanism for their new 1955 OHV V-8, and Chevrolet "borrowed" the design for their new OHV V-8 design because Ed Cole recognized the elegance of the design.

Pontiac valves are adjusted the same as Chevrolet - a specified fraction of a turn "preload" on the lifter from zero lash, and the nut is formed slightly out of round so that a certain amount of torque is required to move the nut so they don't loosen in service.

Maybe the 15 lb-ft you refer to is Pontiac's spec for minimum torque to turn the nut to keep it from loosening in service. If Chevrolet ever published a similar spec - I've never seen it.

Duke

[Dan D.]

Re: L-76 Engine Performance w/H & W Valve Adj.

Hi Duke,

Interesting story how Pontiac developed it. I never heard it before.

But back in the day me and one of my friends briefly helped out a couple of novice kids that were building a dragster. They had no money and even less brains. But they had this Pontiac engine installed in a home brew machine and we could not figure out how to adjust the valves. Doing it like Chevy's just did not seem to work for some reason. My friend looked in a service manual of some kind and it said to torque them to 15 Ft. Lbs. Didn't believe it at first, but we tried it and it worked fine. So I don't know. I know, it doesn't sound right. It was so long ago.

By the way, what do you recommend for pre-load on Chevy hydraulics? I always used 3/4 turn past zero clearance. Does that sound about right? I have a 327-300, but it has a mongrel cam in it. Has not been brought to life yet, but is close.

Also, I read you article in the Restorer and the follow-up threads on the forum (several times). Very, very good. Wished I knew all this years ago. Oh well, I probably wouldn't be rich even if I did. Thanks, -Dan-

[Duke W.]

Re: L-76 Engine Performance w/H & W Valve Adj.

Unless you frequently rev close to lifter pump up speed, anything between 1/2 and one full turn is fine; 3/4 is the average, which is fine. Make a dart board with rings marked 1/2, 3/4, and 1. Throw the dart and use whatever it comes up with.

The '64 327/300 in work to Special 300 HP configuration with the McCagh Special camshaft is making progress.

The OE 1.94/1.50" valve 461 heads are done and flow testing completed, and the numbers are good.

At 28" water depression the 0.45" lift flow numbers are 225/179 CFM for an E/I ratio of 0.80, and the ratio holds at lower lifts, which is right on target for the cam design.

Duke