[DeTomaso] Quenched Head Rework or Tweaks???

[JDeRyke at aol.com]

In a message dated 1/1/09 11:43:14 AM, tborcich at msn.com writes:

> What kind of valve failure rate do the OEM values have once their three and 
> a half decades old? I recall they're two piece, and have read that some opt 
> for one piece valves....I'm ok with
> the OEM's for now if their dependable at this age.
> 
They really don't fail on a time schedule; its more from a sudden increase in 
stress. There are two modes: first, the weld holding the heads onto the stems 
fails under higher-than-normal stess (read, performance and rpm increases). 
Second, the OEM valves use multi-groove split-locks which not only shear now 'n 
then but also release the valve stem -again under higher than stock rpms. 
Both these failure modes will drop the valve into a cylinder while running, which 
usually completely destroys the block and sometimes at least that head. 
Aftermarket far-east-made stainless valves can ALSO be welded two-piece and 
fail the same way as the OEMs do, with even less testing & inspection, so when 
buying, look for a definite statement that says 'one piece stainless valves' 
or 'billet stainless' valves. So far, the cut-rate-shops have not yet lied 
outright in their advertisements.... 
Good one-piece U.S-mfgr stainless valves will cost from $12 to $20 each and 
will always be made with a single lock groove, so you'll also need 8 pairs of 
new single groove split locks. Be very suspicious of $6 'stainless racing' 
valves! OEM retainer washers will work, as will stock springs, but I recommend new 
springs and if you're also changing cams, get the combination of parts 
recommended by the cam grinder. For OEM, use Boss 351 stuff (except for valves). 
FWIW- J DeRyke



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