[DeTomaso] Autopsy

[Will Kooiman]

The valves are one-piece Ferrea stainless.  I don't think the valve failed
first.  It's possible.  I'm not convinced, though.

 

What about the melted rod bearing and the black journal?  The #3 + #7
journal obviously had problems.  Have you ever seen a rod journal overheat
when you lose a piston?

 

Will.

 

  _____  

From: JDeRyke at aol.com [mailto:JDeRyke at aol.com] 
Sent: Monday, May 19, 2008 1:28 AM
To: wkooiman at earthlink.net; detomaso at realbig.com
Subject: Re: [DeTomaso] Autopsy

 

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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