Valve Lash adjustment

[Joe L.]

Re: Valve Lash adjustment

I take ARP's advice at face value on my racing engines and use polyloks. I think they are a PITA but I haven't had any failures.

I'm not familiar with the GM studs. I assume they have a hex at their base for wrenching. How does the radius from the hex to the shaft compare to that of the ARP studs?

Jim

Jim------


The GM threaded rocker studs have a hex base for both small block and big block studs. No GM threaded stud was ever of the "hex-less" type; those are aftermarket only.

The shaft-to-hex radius of the ARP studs is significantly greater than the GM studs. However, I've never heard of any problem with breakage of the GM studs. The small block studs have 7/16-14 thread into the cylinder head and 3/8-24 top thread. Big block are 7/16-14 thread into the cylinder head and 7/16-20 top thread. The big block studs can be used for small blocks in conjunction with aftermarket rocker arms.

[Joseph F.]

Re: Valve Lash adjustment

Many thanks to all who replied. Will definitely use self-locking nuts. Went to Poly-Locks so many years ago I forgot why. Probably on advice of local hot-rodders! I seem to recall the lash going out of adjustment after some spirited driving and the Polys seemed to hold adjustment better. But this may not be exactly true. Thanks again!

[Jim D.]

Re: Valve Lash adjustment

Many thanks to all who replied. Will definitely use self-locking nuts. Went to Poly-Locks so many years ago I forgot why. Probably on advice of local hot-rodders! I seem to recall the lash going out of adjustment after some spirited driving and the Polys seemed to hold adjustment better. But this may not be exactly true. Thanks again!

That's been my experience with running them for the last 45 years on my 60.

[Jim L.]

Re: Valve Lash adjustment

Jim------


The GM threaded rocker studs have a hex base for both small block and big block studs. No GM threaded stud was ever of the "hex-less" type; those are aftermarket only.

The shaft-to-hex radius of the ARP studs is significantly greater than the GM studs. However, I've never heard of any problem with breakage of the GM studs. The small block studs have 7/16-14 thread into the cylinder head and 3/8-24 top thread. Big block are 7/16-14 thread into the cylinder head and 7/16-20 top thread. The big block studs can be used for small blocks in conjunction with aftermarket rocker arms.

'Mornin' Joe,

Thanks for the info about the GM rocker studs. The smaller radius of the GM studs concerns me and I'll stick with ARP.

Reason being that I experienced a rocker stud failure on a (relatively) small radius stud once. No idea what brand. However, since switching to the larger-radius ARP stud, I haven't had any other failures.

I read once that using roller-trunnion rocker arms placed unusual loads on the rocker studs and because of that, the BB studs were recommended in high output applications. There was no explanation of the physics of the loading so I don't know if that's true or not.

For me, it's academic since I'm required to run stamped rockers in vintage racing (they check...). So, 3/8" ARP studs, stamped rockers, polyloks, and 6000 RPM..... no problem.

Jim

[Duke W.]

Re: Valve Lash adjustment

Joe,


Remember, this is a " hot " setting.

Ray

There's no difference between hot (idling) and cold valve clearance on a Chevrolet engine with cast iron block/heads and steel pushrods as explained in the paper - link listed above. So you can do them cold with the engine off, and the paper explains a sure fire way to index the crankshaft to ensure that each lifter is on the base circle for each valve that is being adjusted.

Duke

[Joe L.]

Re: Valve Lash adjustment

There's no difference between hot (idling) and cold valve clearance on a Chevrolet engine with cast iron block/heads and steel pushrods as explained in the paper - link listed above. So you can do them cold with the engine off, and the paper explains a sure fire way to index the crankshaft to ensure that each lifter is on the base circle for each valve that is being adjusted.

Duke

Duke-----


...and Chevrolet service manuals only specified the "cold and engine not running" procedure. I'm quite sure that's how it was done at the engine factories, too.

[Joseph F.]

Re: Valve Lash adjustment

Thanks again to all who replied. Some additional thoughts - vehicle has 186,000 miles. Engine has been rebuilt twice during this time. All of the valvetrain has been replaced, however, I have incomplete records of the rebuilds and am not sure when rocker arms, pivot balls, and pushrods were replaced. Some may actually be original parts. Should these be replaced during valve lash adjustment? Any issues with getting proper parts?

[Joe L.]

Re: Valve Lash adjustment

Thanks again to all who replied. Some additional thoughts - vehicle has 186,000 miles. Engine has been rebuilt twice during this time. All of the valvetrain has been replaced, however, I have incomplete records of the rebuilds and am not sure when rocker arms, pivot balls, and pushrods were replaced. Some may actually be original parts. Should these be replaced during valve lash adjustment? Any issues with getting proper parts?

Joseph------

First of all, make sure you keep the rocker balls and rocker arms together as they come off the engine

Check the rocker arm valve end for wear. If there is any "grooving" seen, even minor, replace the rocker arm.

Check the rocker arm ball socket (which interfaces with the rocker ball) for any "grooving" or spalling. If any is observed, even minor, replace the rocker arm.

Check the rocker balls for any "grooving" or spalling on the convex surface. If any is observed, even minor, replace the rocker balls.

If either the rocker arm or rocker ball is in need of replacement, then replace BOTH the rocker arm and rocker ball.

If you have usable rocker arms/balls, use them on exhaust positions. Use new rocker arms on the intake positions. Of course, if you don't have 8 usable rocker arms/balls then you will have to use some new rocker arms/balls on the exhaust positions.

If any need to be replaced, I recommend Crane Nitro-Carb rocker arms. The only stock-type rocker arms currently available for small blocks from GM are the guided type. These cannot be used with mechanical lifter engines or engines equipped with push rod guide plates.

[John D.]

Re: Valve Lash adjustment

The '57 to '63 fuel injected cars using the original style '097 cam valve lash setting. First of most of you know that the FI's run on engine vacuum.
Take the vacuum away from them and they suffer.
Could site many examples and mention names of DB members here that have suffered but I won't.
12-18 minimum. We have found out that a little looser settings bring the FI's alive and they have a really nice idle.
13-19 to 14-20. Depending on how good someone is using the feeler gauge. Thanks, John D.

[Joseph F.]

Re: Valve Lash adjustment

Joe,
Thanks for the in-depth info. As you can see, I have owned this vehicle for quite a while ( purchased when it was not quite 2 yrs. old). Had no idea in the early days that I would keep it forever. Around 100,000 miles, I had pushrods cracking and actually crumbling at the rocker arm end. Any idea why this happened? Now that I am approaching 200,000 miles, can it happen again or was the original problem a fluke? Hopefully this discussion is of value to others.

[Joe L.]

Re: Valve Lash adjustment

Joe,
Thanks for the in-depth info. As you can see, I have owned this vehicle for quite a while ( purchased when it was not quite 2 yrs. old). Had no idea in the early days that I would keep it forever. Around 100,000 miles, I had pushrods cracking and actually crumbling at the rocker arm end. Any idea why this happened? Now that I am approaching 200,000 miles, can it happen again or was the original problem a fluke? Hopefully this discussion is of value to others.

Joseph------

Your engine originally used pushrods GM #3837152. This is a very old part number which dates back to 1955. These were "not very good" pushrods and, in my opinion, should never have been used with special high performance engines. But, they were.

If you replaced the pushrods after 1963 (which is likely since you say you had 100,000 miles on the engine at the time) and you used GM pushrods, you should have received GM #3796243 which replaced the 3837152 in January, 1963. The 3796243 were originally used for special high performance small blocks in 1962 and, soon thereafter, replaced all small block push rods. The 3796243 were excellent pushrods with hardened stems and are quite "bullet-proof". They can be identified by a circumferential BLUE stripe (which likely won't be visible after long use in an engine). These pushrods were even used with LT-1 engines with guide plates. Engines with guide plates absolutely require pushrods with hardened stems.

If your engine now has the GM #3796243 pushrods, then I don't think you have anything to worry about unless you find some that evidence any wear or damage, particularly on the ball ends.

The GM #3796243 was discontinued quite some time ago and replaced by GM #14095256. While the 3796243 were "one piece" type pushrods (they were not actually one piece but they appear like one piece), the 14095256 are welded-ball type pushrods. While welded ball type pushrods make some folks uncomfortable, these were actually used in PRODUCTION for many later small blocks including 1985-86 Corvettes and I know of no problems associated with them. These are EXCELLENT pushrods and I would not hesitate to use them. The "downside" is that they GM list for $18.83/each. The last GM-available "one-piece" type pushrod I know of was GM #14044874 but it has been discontinued without supersession. This was a SERVICE-only pushrod that, as far as I know, was never PRODUCTION-validated.

As an aside, in case some of you are wondering how an apparently later GM pushrod part number, the GM #3837152, was replaced by an apparently earlier GM pushrod part number, the GM #3796243, wonder no more. The GM #3837152 was released in late 1954 and the 3796243 was released in late 1961. Part numbers in the series 383xxxx were used for engine parts and released "out-of-sequence" at the very beginning of the small block era.