[DeTomaso] Autopsy

[JDeRyke at aol.com]

In a message dated 5/18/08 7:12:12 PM, wkooiman at earthlink.net writes:

> These are the stock cast pistons.
> 
Cast pistons seem to only be able to take high rpms for a while, then they 
break, usually thru the oil ring drainback areas. In cast pistons, these are 
often sawcut slots while in forged pistons, they are drilled holes. I suspect the 
slots are too large and further weaken an already marginal piston. I've seen 
such pistons crack apart such that the whole crown continues to slide up & 
down as the cylinder fires while the rod is attached to only the skirts. The 
knocking is incredible as the loose crown smacks the head, then is driven down 
against the skirt by the explosion.
Second possibility is if you used stock valves. Both intake and exhaust 
valves are two piece, made of a separate head and a stem of a different kind of 
steel, friction-welded together. I've seen such valves in which the stem was 
non-magnetic while the head was magnetic. Under stress of higher rpms or heat- or 
both, these kind of valves break at the original welds, destroying the engine. 
Finally, stock valves use multi-groove split-keepers. These do not grip the 
stem tightly. Instead they hold the stem loosly, allowing the valve to move 
slightly during each cycle. This prolongs a valve job in a domestic engine, but 
again, at high rpms, the split keepers tend to pop out, releasing the stem and 
again, fragging the whole engine.

In your rebuild, I suggest using ONLY forged pistons and one-piece stainless 
steel valves with single-groove split-keepers, or always keep the revs down 
around 5000 maximum. This will give you a much more durable engine with spirited 
performance without breaking the bank.... or the block next year! And don't 
forget to save EVERYTHJING that unbolts from the blown block. There's about $1K 
of 'accessories' removeable from a trashed 351C, which you will need 
sometime. Sorry about the damage; better luck with the next assembly- J Deryke



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