DeTomaso Mailing List: November 99, Message #234

You may have a valve tulipping, or a real soft seat. I have seen the tulip
happen on a 390 after 1500 miles on a rebuild. The fact you say it seems to
go away after trying certain fixes seems to put it in the valve train area.

To check the valves, remove the rockers and put a straight edge across the
valve tops. I realize 351's have canted, off-set valves, so do your best. A
valve pulling through will be fairly obvious. This assumes the valve height
was even when the heads were redone.

A soft cam lobe would show up like this, also. To check, look at the bottom
of the lifters you just replaced. If you spot one with a markedly different
wear pattern, that could be the culprit.

Hope you find your problem before something breaks.

Norm


At 08:33 PM 11/9/1999 -0500, you wrote:
>I have what I describe as a valve lash "clack", but have not been able to
>track down the source.  The engine was completely re-built by a local
>performance shop.  The sound slowly appeared a few months afterward.  The
>"clack" occurs above 1500 RPM and is louder when the throttles are open.  It
>is greatest when cold. Early on, when it was still mild, the engine builder
>shrugged his shoulders unconcerned.  Now, I'm no longer under warranty, and
>its worse
>than when I drove over to him.  I no longer share his nonchalance.  I
>initially figured it was just valve lash adjustment and did a quick
>inspection and just turned the valve adjustment in 1/2 turn more, and the
>sound disappeared but again slowly returned.  I have tried to identify the
>location of the "clack" with a stethoscope/probe - no luck.  It
>doesn't seem to be coming from under the valve covers, and sounds the same
>regardless of where on the engine I probe.  Along the way, I replaced the
>fuel pump-no
>effect.  I changed from the stock exhaust to the GTS headers/mufflers-no
>effect.  While I had the intake manifold off to switch to Webers, I replaced
>all the lifters, thinking that one of them appeared to be "soft".  The sound
>again went away for a month, but now has slowly reappeared.  Inspection of
>the valve train showed no anomalies - no signs of any wear really.
>
>I'm kinda out of easy trouble-shooting ideas - please give me a boost.
>
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