Bad lifter?

[Dan Pepper]

I adjusted my valves today (66 L36) and found the first rocker (front) on the left side fairly loose. Following the normal GM protocol - I loosened it until it clattered, then tighened until it stoped, then cranked 1/4 turn at a time until one full turn of the nut was completed. Here's the catch - the nut rides high on the stud compared to the other rocker nuts. That is to say, no threads are showing on this valve, and all the other rockers show about 1/2" of threads. On top of this, when I shut the engine down, this particuar lifter seems to bleed faster to the point where the rocker arm is noticably looser than any others. I could crank it way down before the engine would begian to bog, but I left it adjusted at one full turn past clatter.

Is this something I should be concerned about?

PS- Went through this exercise trying to chase down a persistant miss at 1500 RPM. Igintion seems fine - valves seem all okay - except for above...

[Jack H.]

Re: Bad lifter?

This could be a DANGER sign.... Originally, the factory press-fit rocker studs in. If your engine has been rebuilt with the cylinder heads gone through, there are those machinests who 'think' they can determine if it's safe to re-press rocker studs to cut assy costs. In my book, any machinest worth his salt in terms of experience with vintage engine work, does NOT hesitate to go the extra mile (at your expense) to rebuild the cylinder heads and either drill/tap the stud holes for screw-in rocker studs or press and pin the rocker studs in to MAKE SURE they cannot lift up/out under dynamic exercise.

If you've got a rocker stud that's lifting (look carefully at it's height compared to adjacent studs), STOP!!!!!!! Don't fire this engine and do NOT drive the car. It's about to let go with the net result being you're going to turn push rods into pretzels kiss/crack valves into piston heads and maybe see even worse damage (crack the head, break a piston rod and tear into the block's water jacket).

IF you've got a rocker stud that's lifting, you got REAL LUCKY catching it before all (*&& broke loose! My advice would be to pull both heads, take 'em to a skilled machinest and have ALL of the rocker studs removed and replaced with threaded style studs if you're serious about using/driving this car.

If the rocker stud isn't lifting (measure to be sure), there's something else that's funky....

[Dan Pepper]

Re: Bad lifter?

Jack-
Thanks for the input. Thankfully(?) the stud is the same height as the rest of the studs. The engine/heads are original at 52k miles... hmmmmm.

[Craig S.]

Re: Bad lifter?

Jack - we are talking a big block engine....3872702 oval port heads...it would have screw in studs......but your explanation is great for small blocks!....Craig

[Joe L.]

Re: Bad lifter?

Dan-----

Craig is correct. All big blocks use screw-in studs so a "stud-pull" cannot be your problem. It's still possible for the kind of "thread exposure" difference between the studs to be "normal", but only if it was always that way. If you didn't change any parts, then you should have returned to about the same "thread exposure" taht you had originally. Otherwise, I'd say that the only 2 possibilities that I can imagine are either a bad lifter or a bad cam lobe.

[Joe L.]

Addendum

Dan----

You did insure that the rocker stud is fully seated and torqued to spec on this particular stud, didn't you?

[Mike McKown]

Re: Bad lifter?

This type of hysteria is comical but sad. Re-read the post! The stud can't be pulling, if the nut doesn't have threads showing, it is "maybe" pressed in too far. Stud depth has nothing to do with the safety of running the engine unless it is pressed too far to break a water jacket.

[Wayne K.]

Is the pushrod correct ? *NM*

[Craig S.]

Re: Bad lifter?

Mike - the studs are not pressed in at all, this is a big block with threaded rocker studs...Craig

[Jack H.]

Daah--he DID say L36!!!!!!!!! *NM*

[Craig S.]

Re: Daah--he DID say L36!!!!!!!!!

Yep, and with that new linkback feature Terry added, well, easy to check. But, hey, I have had my share of misreadings too!...Craig

[Robert Willis]

Re: Addendum

Did someone put a truck (Heavy Duty Truck ) push rod or a tall deck engine push rod in the engine at sometime ? I think they are about 1/4 inch or so longer.

http://members.kos.net/willisb/

[Jack H.]

Thanks for the PRODE, Craig!!!! *NM*

[Craig S.]

Re: Thanks for the PRODE, Craig!!!!

Hey - I only do it to someone I totally respect Jack! (LOL). It is exactly the type of thing I do, then think what a doofus I am!....Craig