452 valve clearances

[jusglazin]

Need some advice on a set of heads I recently had machined. I have a set of 452 heads that I had our local machine shop do a 3 angle valve job on and replace all the exhaust guides that were worn. They also machined all the seats and were suppose to check for cracks or any other problems. Once I got them back I took them part and cleaned up the bowls and re-installed the valves. I painted one of the heads and started to work on the last one, once I got to the last exhaust valve I noticed a small crack in the seat that extends into the head. Well I thought I would just take this one back to the shop and demand my money back for the poor inspection that was done. How could they machine the seats and not notice the crack?? Anyway I have another 452 that I was going to get done but after laying a straight edge across the one that I thought was good I see that the valves stems are not remotely straight or level. How much tolerance is allowed here? I would hate to have to change to adjustable rockers or should I just scrap both heads and start over ?

Thanks.,.,

 

[Meep-Meep]

You want the stems to all be at equal heights or really close - maybe realistically within .030" or better. Also having the stems too high will require shorter push rods, or as you pointed out, adjustable rockers to get the lifter preload correct.

Sinking the valves into the head not only hurts performance but may be evidence that a lot of material was removed from the seat. It has been brought up here many times that removing a significant amount of material form the exhaust seat on the factory hard seat heads destroys their resistance to unleaded gas because the hardened surface is ground away. I'm not sure how thick the hard surface is as that depends on the alloy and heat treatment process.

 

[jusglazin]

Thanks for the info, I just hate that I wasted my money getting these redone. I should have just put that money toward a set of aluminum heads but I guess I'll know better next time..

 

[Meep-Meep]

Yeah, I know the feeling. I just put a bunch of money in some 915's but I'm happy with them so what the heck.