No Subject

[Ted Borck <tborck@domain.elided>]

> Date: Sat, 12 Jun 1999 01:01:25 -0400
> From: Doug Rasmussen <DougRasmussen@domain.elided>
> Subject: Re: Uncorked exhaust - warped valves
> 
> Message text written by Ted Borck
> >If the exhaust pipe is short enough to allow [relative] cooler air to
> reach the *hot* exhaust valve(s), the exhaust valve may warp.

<snip>

> Ted,
> 
>   This is a very logical explanation, but do you REALLY know that valves
> warp because of exposure to the cool air or are you just speculating that=
> it may happen?

Doug,

If my understanding of thermodynamics is correct - in order for metal
to expand *evenly* when exposed to heat, heat must be applied *evenly*
over the metal's surface area.  

Best example I can think of at this moment would be a hot soak oven at
a steel mill.  Or putting your crankshaft timing gear in your oven
(wife "what's that smell?") in order to expand it enough to slip over
the nose of your crankshaft (it's been in the freezer - not
necessarily an IHC V8).

Conversely in order for hot metal to cool and contract *evenly,* the
heat transfer to the cooler medium (valve seat, valve guide, ambient
air) must be uniform throughout the surface area.

Remember exhaust valves operate at temperatures which has the valve
heads glowing red hot.

If an engine stopped leaving an exhaust valve in the open position, it
would be possible for a *short* exhaust pipe - or - missing exhaust
manifold to allow cool air to enter the exhaust port and unevenly cool
the head of the valve and possibly cause the valve head to warp.

Carrying the image further, the hot open exhaust valve head would be
surrounded by the hot cylinder head exhaust passage (and thus
protected from too rapid cooling) except where the open valve head is
adjacent to the exhaust port and possibly exposed to cooler air, and
uneven cooling.

Considering how much effort it takes to replace cylinder head
valve(s), If I were running short exhausts or with no exhaust
manifolds, I would be ready with the shop rag plugs.

Ted Borck	tborck@domain.elided