I have a 96 LT4. Recently I had the bottom end redone and a new cam from comp cams put in it. At about 800 miles on the new engine I hear a loud noise coming from under the valve cover. Turns out one of the rocker arms (all original, self aligning, 7/16", 1.6 ratio, rollers) came loose, turned a little sideways, and the valve chipped a piece off the edge next to the guide. It has been impossible (so far) to find another one just like it. The rocker arm stud is bigger than 3/8". Measuring the diameter of the opening in the fulcrum of the original rocker arm I get 25/64" (kinda weird, why doesn't measure 7/16"). The threaded top of the stud takes a 5/16" nut so the polylock has to fit that. Needless to say when I ordered a new set of rocker arms, and they sent me a kit for everything 3/8", nothing fit.

The 96 LT4 rocker arms are 7/16", self aligning, narrow body. I can find 7/16" but they are not self-aligning. I can get self aligning but they are 3/8". Both are available in narrow body. My choice seems to be - either I get 7/16" non-self aligning and get guideplates and install all new rocker arms on both heads OR get one 3/8" stud and one 3/8" self-aligning rocker arm and replace the one that broke with something that doesn't match all the others. Does NE1 know if the original studs have enough length under the nut head for a guide plate to slide under them and still bolt firmly back into the head? What about the pushrods? I've read that if you use guideplates you need hardened pushrods and I'm not sure if the stock rods qualify as hardened.

Any ideas or help is appreciated!

 

..... How about some pics ? ... I'm pretty sure the LT4 rockers are Metric ... 10mm ? .....

 

That may be true. I had read somewhere that early models of that LT4 were 10mm but the later ones were 7/16" and mine has a build date in Feb 1996. I assumed early would be Sept/Oct 1995. Either way I need to move forward with guide plates and new rocker arms or get a 3/8" stud and rocker arm.

I think I got some pics to attach.

 

And 25/64" is very close to 10 MM on the conversion chart.

 

..... The BIG question now is ... Why did it break ? ... what are the cam specs on your recent Comp Cam replacement ? ... Did you replace the valve springs also ? ... Rev it to the moon ? ..... Start a "Want To Buy" thread in the Parts for Sale section and see if someone already replaced theirs and has an original to sell .....

 

I'll have to get the cam card later for the specs. Yes to new valve springs. Didn't rev it over 3,000 RPM yet. The machine shop owner said don't go over 3,000 RPM for the first 1,500 miles. It's only been driven 800 miles so it's been driven gently so far. I think the only reason it chipped that piece off is because the lock came loose and the arm turned sideways a little. The valve kept hammering it on the corner instead of it riding on the roller. Don't know what else could've done it.

 

It's a 10 mm stud and a 8 mm nut on production LT4. IDK where you will replacement. It seems someone on the forum took a 10 mm rocker apart and transferred what he need from a new 3/8" rocker. There was a recall on the LT4 rockers I don't remember why. Crane was manufacturer

 

I've got the recall notice, it is Number: 96-C-07A. Subject is: Inadequate Retaining Load Holding Rocker Arm Roller Pin In Place. (The translation appears to be that the rocker arm pivot pin may move out and release the roller bearings into the engine).

It calls for use of new part number 12557779 Rocker Arms on certain Corvettes with the LT4 engine, both base and Grand Sport cars were included. This notice canceled a previous recall notice: 96-C-07 which called for installing Rocker Arms part number 12551311 which were also found to be inadequate.

 

..... If it were mine , I would replace the valve spring retainer and keepers on that valve .....

 

I just had the same thing happen to me and it looks like the same position rocker. I suspect the stock springs on mine.I will soon be changing them. just not sure how far down that rabbit hole I will be going yet