When I originally made the magnet suggestion last Monday, I wasn't sure if
it would work. The stainless that I've had the chance to hit with a magnet
haven't been magnetic, so I figured it was worth a shot. The last
metallurgy class I took was almost 30 years ago, and my memory is showing
signs of fading. (grin)
The idea for stainless exhaust valves came from a conversation I had with
the engine shop doing my Spitfire 1500 rebuild in 2002. They suggested
stainless exhaust valves as part of making the engine happy with no lead
fuel. Since Spitbits offers stainless valves, I bought 4 and let the engine
guys do their thing. As several previous posts have pointed out, given the
low mileage most Triumphs get, making a special point of reworking the head
probably isn't needed.
BillG
Newalla, OK
-----Original Message-----
From: spitfires-bounces+bill=gingerich.us@autox.team.net
[mailto:spitfires-bounces+bill=gingerich.us@autox.team.net] On Behalf Of
Michael Porter
Sent: Wednesday, August 06, 2008 2:31 PM
To: Steve Beswick
Cc: spitfires@autox.team.net
Subject: Re: [Spits] Stainless test
Steve Beswick wrote:
> To those who have recommended using a magnet to test valves:Stainless
Steel
> is magnetic. How do you think magnetic knife bars work?
>
Umm. Sort of. Austenitic stainless steels are not magnetic in their
annealed form, but become weakly magnetic with working, but not as
strongly magnetic as ferritic stainlesses or other carbon steel.
The more an austenitic stainless is worked, the more magnetic it
becomes. So, it's true that a magnetic test won't identify a stainless
valve from a carbon steel valve.
As for the original question, I don't think a stainless valve is
necessarily a mandatory item for unleaded operation, and depending upon
the stainless alloy, might not actually be the best choice, as some
stainlesses are not as hard as better carbon steel valves, and the valve
face may deform around the valve seat over time. In any event, simply
assuming that "stainless" is better is not necessarily true. Any valve
with Stellite hard facing is probably just as suitable.
Cheers.
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