I don't have many miles on my rebuilt TPI 350, as it is a weekend driver. However yesterday I cranked it up and noticed a pretty loud tapping coming from the drivers side. I took the valve cover off and the last rocker arm stud was broken and both pushrods were bent. I haven't had any trouble out of this engine other than this. I ran the casting number off the block when I pulled it and found out it is a Vortec block from 1996 and up. I replaced the heads with a set of Vortec's that had been reworked for a 500+ lift cam. Everything else seems fine. the only warning I got was the tapping sound that I had never noticed before. What would cause this and do you think it happened at start-up yesterday? I took the car out for a spin last weekend with no noticable problems. The car hasn't been run hard as I'm still in the break-in process. This is on a 1992 z28. The valve train consist of comp roller tip rockers, pushrods, and roller lifters. Any help on this will be appreciated.

 

What part # rockers are you using? Do you have screw-in studs & guide plates?

 

I can tell you what happen to me about a month ago but this may not help you because different engines and parts ... me 6 you 8.

Anyway, I had a collapsed hydraulic valve lifter (at the time didn't know about it) that stripped the rocker arm studs twice (replaced and happen to the same one again). My push rods were not bent so I could see the action while the engine was going. I notice that a few of the rockers was not being lubed and others slightly lubed.

Long story short... I had three collapsed hydraulic valve lifters (internal springs destroyed) and seven clogged. I ended up replacing all hydraulic valve lifters, one push rod, and one rocker arm stud.

So check and see if you have a good flow of oil pumping/ squirting from your push rod/ rocker arms.

As far as start-up ... it may have worn down over a period of time and finally gave during start-up.

 

They are Comp roller tip rockers #1417-16. Studs are screw-in, no guide plates.

 

What cam are you using and was anything done to the vortecs to allow for more lift. i.e. grinding down the guide boss by about .200.

The only thing i can think of, others can probably think of more, is that you were maxing out factory lift. i.e. the guide boss was coming into contact with the retainer and preventing any further valve lift while the cam was still trying to open the valve. That would explain the bent pushrod. The stud may have then taken excessive heat as the spring-to-tip contact of the rocker was then the fulcrum point. The stud eventually gave out.

That is just my speculation. I have no clue if thats even possible. I do know that maxing the lift on vortec heads is not hard to do and can cause valvetrain geometry issues with the pushrod if left unchecked.