Yup. I don't exactly recall the alloy I used most often but it was
something like AM435 (but don't take that to the bank--my neurons are
notoriously toasted). I'd be happily tapering the nose on a guide when it
would suddenly grab the toolbit and rip itself to shreds. Or you'd ream
one with a perfectly straight ream and get .002" taper top to bottom in a
2 inch guide. Maddening. If you get guides that have been precisely
machined for the valves you're using you can get away with just driving
them in without honing to fit in the head. But on bike engines we found
that you can't just ream bronze guides once they are in the head. If you
have to ream to fit, you need to leave it a bit undersize and hone. That's
work for a really good shop, though I did it myself with the big sunnen
rig we had. Dinky little arbors with tiny little stones. You'd probably
screw the guide up worse by just reaming than driving in ones that are
honed to size. The big open question is the condition of the head and how
much interference fit you have. Too loose and the guide might shift and
won't dissipate heat well. Too tight and it deforms and you're back to
honing.
With a really good guide material and proper fit you can cut most of the
guide out of the port, increasing flow dramatically. I've never tried any
of this stuff on a TR3 motor--or on any cast iron head for that matter.
Probably folks like Kas, Greg Solow, Hardy Prentice, and other TR Wizards
are snickering because they know far better what these goofy motors take.
Though Jon certainly ranks with the rest of the wizards, and it sounds
like he pretty much agrees on Bronze.
-----Original Message-----
From: T.R. Scratchings [mailto:wob@dandrade.freeserve.co.uk]
Sent: Monday, June 09, 2003 1:55 PM
To: Bill Babcock
Cc: fot@autox.team.net
Subject: Re: bronze or steel
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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