We use an alloy called Colsibro, which is soft, wicks away heat like copper
and is an absolute ^*&#$rd to machine.With chrome or tufty valve stems, we
can use very high lift on a very small guide/stem clearance without wear or
sticking problems. These guides ain't cheap, but they are lovely to behold
and easy to fit.
Jon Wood Classic Racecraft
----- Original Message -----
From: "Bill Babcock" <BillB@bnj.com>
To: "'Brad Kahler'" <brad.kahler@141.com>; <fot@autox.team.net>
Sent: Monday, June 09, 2003 9:26 PM
Subject: RE: bronze or steel
> Actually, grey cast iron is usually used instead of steel, and it's
> usually chilled. The choice of materials has more to do with production
> cost than performance. Cast iron is easier to ream and machine (it's
> generally done dry) and it's cheaper. Phosphor bronze is challenging since
> it grabs the cutter and often overheats. It's hard to get a bronze guide
> to have parallel sides since it heats up the reamer and the guide as it
> goes. They should be reamed undersized with lots of coolant and then honed
> to fit--in the head. People often have bad experiences with bronze guides
> pumping oil and assume it's early wear, when it might be inadequate
> cooling during reaming.
>
> You can set up phosphor bronze (or better yet, an alloy of bronze that
> includes a little nickel to increase the hardness and wear resistance) to
> have tighter clearance than cast iron since it is less likely to seize,
> conducts heat better, and beds quickly. That means the seat can be thinner
> to flow better without wandering and losing seal. It also means you're
> less likely to burn your exhaust valve.
>
> All that is fairly philosophical and my comments are all based on building
> motorcycle racing engines, not tractor motors, where we always used fancy
> bronze alloys and were real, real careful about getting heat out of the
> exhaust valve and keeping the intake seat very thin. But then we were
> getting more than 200HP/liter with carbs just to be in the ballpark of
> competitive.
>
> I doubt the guide material matters in these engines, but you're looking
> for the "best" meaning superior performance and not ease of use, it's
> unquestionably bronze.
>
> -----Original Message-----
> From: Brad Kahler [mailto:brad.kahler@141.com]
> Sent: Monday, June 09, 2003 12:24 PM
> To: fot@autox.team.net
> Subject: bronze or steel
>
>
> Amici,
>
> What is considered best for racing, bronze valve guides or
> steel valve guides?
>
> Thanks
>
> Brad
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