I've got a GM headbolt set that I will be using to bolt on a set of Vortec heads. These bolts already have the thread lock on them, but I was wondering if I needed to apply some silicone to the threads of some of the bolts. Maybe a bolt that might fall into a water jacket?

 

Bad idea. Thats a great way to screw up the torque readings, by gumming up the threads. It's not needed.

 

never seen that before on a bolt. i bet it's sealer and not thread lock, but it'd be about the same. you wouldn't want RTV because it'll fail over time. if you use anything use a non hardening sealer like PST from loctite or a similar liquid tefelon sealer.

 

All of the head bolts in a SBC go directly into the water jacket. They MUST have sealer on them, otherwise coolant will leak past the threads and into the crankcase (rocker gallery). They all need some sort of non-hardening sealer (NOT silicone) applied to the threads. I'd suggest either Loctite PST (automotive pipe thread sealer with Teflon), or Permatex 300 (brown gooey gunk).

There is no issue with torque readings.

As far as why GM put some sort of something on their the threads, I have no clue. I can't read their minds. They do some really weird things sometimes.

 

I agree with ede, use PST, never had a leak with it on the bolts. also, using somehting like that on the threads will give you a more accurate torque because it lubes the threads, dry threads tend to bind before reaching the desired torque, the torque wrench indicates proper torque but it isn't really right.