"30-30" Valve Lash: ADDENDUM,To All .........

[Joe C.]

......who replied to my post below.

Jerry B.: Yes, the engine did have more midrange power with the wide lash settings. Yes, I realize that bottom end power will suffer with a tighter valve setting, but that's fine with me. If I wanted more bottom end power, then I would have bought a Corvette with the L75 engine instead of the L76. Also, the engine was beginning to detonate slightly due to the lack of overlap with the emasculated valve lash settings, and I didn't want to back off the timing as a "band-aid". The engine has never detonated with the correct lash setting. The only problem is, why did the lash change so quickly??????? I like the lumpy idle. I don't mind the driveability "problem" at low RPM's. I like the way the cam comes on at the top end. I don't care about the 8-9 inches of idle vacuum. I have no fuel injection to worry about, and I have no power brake booster to worry about.

Joe L: Why don't you like "Posilocks"? Is there any specific reason? I can tell you that they were all tight when I readjusted everything yesterday. So I have to eliminate them as the cause of the lash widening.

Again, I repeat, that if I knew that these springs were so much stiffer than stock, then I would never have let the machinist install them. I was told that they were "slightly stiffer than stock, and perfectly safe to use with pressed in rocker studs". So, if the studs have already started to pull out, then it is too late, and WHAT'S DONE IS DONE. So........stop beating me up over it.
What I have to do now is determine whether the studs have, indeed, already started to pull out. I am asking you for a method of determining this. If it is not too late, then I WILL THROW THE DAMN THINGS AWAY AND PUT IN THE STOCK SPRINGS. If it is too late, then I'll leave the go*damn things alone, and pin the studs, or put in screw-ins.

Here Are The Facts:

1. Lash was initially set at .028", using Williams/Hinckley method, on 10/15/02, odometer 00000 miles.
2. Lash was set yesterday at .025", using Williams/Hinckley method, odometer 00827 miles.
3. Yesterday, BEFORE readjusting, I laid a steel straight edge across all 16 rocker nuts. Each bank was flat, by eyeballing. So, if the studs ARE pulling, they are pulling very evenly.
4. Yesterday, BEFORE readjusting, I measured the lash as follows: .039-.039-.040-.034-.044-.038-.035-.036-.036-.030-.036-.040-.038-.036-.034-.034

When studs pull out, DO THEY USUALLY PULL EVENLY, or do one or two usually pull first. Or, is there really no way to tell.

Any good, non speculative advice here is much appreciated. Thank you in advance.

Joe

[Mike McKown]

Re: "30-30" Valve Lash: ADDENDUM,To All .........

My limited experience with studs pulling is you will have one or two go first. Not all of them.

A suggestion: Pull several of the push rods on the valves that have the wider lash and roll them across a piece of plate glass or chuck them into a drill press and look for runout. If you see any you may have found your problem.

There is an installed height spec for the studs but I don't know what it is offhand.

I've never used posi-loks but have heard they will back off if not installed properly. I've heard what Clem suggested is the proper method.

[Joe L.]

Re: "30-30" Valve Lash: ADDENDUM,To All .........

Joe-----

The reason that I don't like "Posi-Locks" is that they're usually not so "Posi". They DO loosen up and the WILL loosen up if they are not used with studs that are perfectly flat on the top (stock GM studs are NOT perfectly flat on the top and they are hard to make so while installed on the engine). The stock-type self-locking nuts are equisite in their simplicity and work perfectly (as long as they are not worn out). I feel that they are preferred over any other type of locknut. The problem is that, for wrench clearance reasons, they cannot be used for roller rocker arms. That's really why the posi-locks were developed in the first place----to address this requirement.

Rarely, do all the studs in the engine pull out to the same degree, assuming that any pull out, at all. While your springs are a bit heavy and certainly higher rate than stock, I don't think that necessarily means that they will cause stud pullout (and, I never said that they would). Keep in mind that the original GM #3927142 springs (which are similar in spec to the ones you have) were designed for use with the GM #3927140 SERVICE-only camshaft. Also, the 3927140 camshaft was intended for use with 68-69 Camaro Z-28s with 302 engine. No Camaro 302 engine was ever originally fitted with screw-in studs. All were press-in type. So, this cam and springs were intended for use with engines that DID NOT HAVE screw in studs.

The bigger problem with the springs is that they exceed the requirement for your engine. In many cases, higher performance parts can be used in street engines without having any negative effect (except, perhaps, for cost). However, more is not always better and racing or high perfomance components are not always without compromise when used in a street application. Valve springs are an example of this. For many applications the higher spring pressure will produce no positive benefit for a street engine. However, it may produce negative results. Increased camshaft wear, increased valve seat wear, and pulling of pressed in studs are three POSSIBLE effects of higher-than-necessary valve spring pressure. Increade camshaft wear and increased valve seat wear are really the bigger issues, though. If you were to decide to change valve springs, it's quite inexpensive and relatively easy to do without removing the cylinder heads. The choice is yours; I don't think that it's something that you have to do.

[Mark #28455]

look for signs of wear

Although therte is some break-in wear on any new camshaft, I suspect in 800 miles this would be a few thousandths of an inch. You have some valves with up to 0.016". Did you initially lube the cam with some assembly lube (and the lifters too), are the valve ends still unworn? I had a set of aftermarket valves that failed heat treatment and wore to the point that the rockers almost knocked the keepers loose - go figure!

I would start looking at the 2 or 3 valves with the most change as that's where the evidence would be most obvious.

Hope this helps,
Mark

[Joe C.]

Re: "30-30" Valve Lash: ADDENDUM,To All .........

Mike:

I think that Clem found the problem! I did not tighten as he recommends. I had another local engine builder tell me the same thing. It makes sense that the Posilocks would all back off a few thou if not tightened properly. It also makes sense that 1 or 2 studs would pull first, not all. That was my "common sense" way of thinking about it, too. I just wanted to hear your experience to confirm my "theory".
I'll readjust 'em tomorrow, a third time, and tighten the Posilocks as per Clem.

Thanks again.

Joe

[Joe C.]

Re: "30-30" Valve Lash: ADDENDUM,To All .........

Joe:

That is a very good explanation, and squares perfectly with what Clem said, and others. I'm about 99% sure that the Posilocks are the problem, as they have all backed off fairly evenly between .005-.010.
I'll either reset the Posilocks as per Clem (easy method) OR install stock stud nuts and change back to stock springs.
Thanks again!

Joe

[Joe C.]

Re: look for signs of wear

Mark:

Thanks for the response. The engine runs too well, and there is no mechanical problem. Yes, I generously lubed everything with assembly grease, and the cam and lifters with the grease supplied with the camshaft. I ran the engine in using the standard method.
I have isolated the "problem" to incorrectly set Posilocks, which have subsequently backed off by a few thousandths all-around. I will possibly replace with fresh stock stud nuts, or readjust as per Clem Z.

Joe