We had a bronze threaded business that was inserted like a heli-coil into
the stock chilled cast iron stock guide then reamed. They stopped all the
problems we had with guides. Best thing I ever did for those engines.
Well,......... okay,one of the best things.
----- Original Message -----
From: "Bill Babcock" <BillB@bnj.com>
To: "'T.R. Scratchings'" <wob@dandrade.freeserve.co.uk>
Cc: <fot@autox.team.net>
Sent: Monday, June 09, 2003 8:15 PM
Subject: RE: bronze or steel
> 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
|