Working on my Corvette LT4 engine, it says in both the GM factory manual and the Hayes manual, to tighten the rockers to 18 ft-lb after reaching zero lash. When I did this, I noticed that on some of them, the valve spring compressed a little during the final torquing. OK or do I need to start over?

 

If you have the original factory LT4 valve train in place, that is the correct procedure. It could be that the lifters will relax a little after it is running.

 

are you setting valve lash while the cylinder is at TDC?

 

Good point. I assumed that. With torquing them down, it really does not have to be at TDC. I don't think about the factory LT4 lash too much.

 

I have the original LT4 valvetrain and I did set the valves at zero lash, using Method 1 as described on Shoebox's site. Putting the LT4 torque method aside, is it OK for valve springs to compress a little while adjusting the valves since the lifters should bleed down when the engine is running?

 

That procedure sounds wrong to me. Maybe they mean the locks get torqued to 18 ft-lbs?

 

The stock LT4 rocker adjustment is different than the LT1 or any other SBC. After reaching zero lash you simply torque the rocker nuts. It will automatically set the preload.

 

The only down fall to that method is if it's on a high mileage engine, the lifters will bleed down rather quickly when you are torquing them down. Which will make it very easy to set in to much preload..

 

With the stock LT4 rockers there is not such a thing as too much preload. The rocker studs have shoulders that lock in the factory correct preload.

 

The procedure on my site is really not for the factory LT4s. You just torque them down, like was already mentioned.

 

Ahh, so the LT4 setup isn't adjustable. That clears a few things up.