I understand what you have said and was told by Laystall Engineering the
same thing about "Nitridable steel alloys," yet empirically have found the
following. I went through 3 cranks in quick succession. Each lasted 7,000
miles of hard street driving and weekend autocrossing. I was using a rev
limit of 6800 rpm with a TR-4 engine in a Morgan. each of the cranks had
been magnafluxed, was standard size ( had the factory radii on all the
journals) and two of them had been shot peened in the radii. In each case,
after 7,000, almost like clockwork, a vibration that had not been present in
the engine upon assembly appeared. Pulling the pan and #4 rod cap revealed a
crack in the inside rear radius of the rod journal. The next crank I used
was "deep case nitrided". It has run over 30,000 miles on the street, all
hard miles, and over 30 race weekends, all using a 6800 rpm rev limit. The
rods, pistons and pins were all lightened a lot, the rods over 1/2 lb. each,
mostly off of the big end. This crank is still good and passes mag. I have
seen 4 or 5 unmodified street TR-3s and 4s with broken cranks and twice
that number which would not pass mag, none of the engine that we have
rebuilt with nitrided cranks have cracked or broken, to my knowledge.
Regards, Greg Solow
----- Original Message -----
From: Mark Palmer <mgvrmark@hotmail.com>
To: <vintage-race-digest@autox.team.net>; <brian@uunet.ca>
Sent: Monday, July 10, 2000 8:08 AM
Subject: RE: Spridget 1275 crankshaft
> Group,
>
> A few years ago, after breaking two MGA cranks, I did extensive research
and
> analysis of crankshafts. I'm sure everyone here has reported their
personal
> experience accurately, and that experience is as valuable as any "theory".
> But there are some immutable laws of physics that override some of the
> speculative thoughts expressed in some previous messages. To clear up a
few
> myths:
>
> In a 3-main 4-cylinder engine, BY FAR the most destructive stresses on the
> crankshaft are caused by the reciprocating masses acting at high RPM. In
a
> nutshell, it is NOT horsepower that is breaking these cranks, it is high
> RPM. The inertial forces are proportional to the engine speed squared --
> e.g. 8000 RPM creates over twice the amount of stress as 6000 RPM (8**2 =
> 64; 6**2 = 36). Lots of other considerations came up in the analysis, too
> much to detail here.
>
> An obvious implication -- lighten the reciprocating masses. Running stock
> pistons & rods isn't a real good idea at high RPM. Lighter forged
aluminum
> pistons, and aftermarket racing rods will reduce the stress on the crank
> considerably.
>
> Another myth: nitriding EN 16. It will have relatively little benefit.
> Conventional nitriding only works when the steel has a fair amount of
> certain alloying elements (notably chromium or molybdenum). EN 16 doesn't
> have either, so it won't form the beneficial nitrides you're looking for.
> That's why Runciman noted that "it hardens less than EN40. EN 40 B
nitrides
> very well (3% Cr, 0.6% Mo). The correct method for heat treating EN 16,
or
> any other non-alloy or low-alloy steel, is Tufftriding -- but very few
heat
> treaters still perform Tufftriding. There are a couple other methods that
> may work, but I don't have enough data on those (I Tufftride my cranks).
>
> Another myth: that EN 40 is somehow "more rigid" than En 16. All steels
> have essentially the same modulus of elasticity. In simple terms, they
are
> all "equally rigid". Certainly some are STRONGER than others, and heat
> treating affects strength -- but the modulus of elasticity remains
> essentially the same at 30x10**6 psi for all steels.
>
> One more: balancing. Yes, it's a good thing, and there is no reason not
to
> balance ... but it does relatively little to reduce the stresses on the
> crank. It DOES tend to reduce the force that the engine transmits to the
> frame, and hence it "feels smoother". But the inertial forces due to the
> reciprocating masses in the engine are still there, and just as large as
> ever.
>
> When I was studying this a few years ago, the "billet crank" manufacturers
> in the U.S. were Moldex, Scat, COLA, and LA Enterprises. I think some of
> those may be out of business now. In England, the billet crank source was
> Phoenix. I have heard good things about Moldex and I own one Moldex
crank,
> not installed yet, but appears to be well made. The typical billet crank
is
> made of 4340 steel (in the U.S.), nitrided, and shot peened. In the U.K
> they typically use EN40B.
>
> One of the most critical aspects which determine life of a crank,
> particularly a poorly-supported one like a 3-main 4-cyl, is the fillet
> radius of the journals (particularly the main journals). A common mistake
> occurs when a machine shop regrinds a crank, and reduces this fillet
radius.
> It should be kept as large as possible, without disturbing oil flow out
of
> the bearing. On the MGA, 5/32 radius was a good number. A fillet of
1/16"
> will reduce life by something like 80%.
>
> Another avenue for improving fatigue strength is shot peening of the
fillets
> (journal surfaces are masked). This works even better if the crank is
> properly heat-treated first (e.g. Tuffrided or nitrided if appropriate
> alloy).
>
> Hope this helps you, Brian, and clears up some of the mis-information out
> there. For what it's worth, I have chosen to use NOS factory cranks in my
> MGA engines (these cranks are EN16), had them Tufftrided and shot peened,
> and theone currently in my car has done about 50 race weekends with no
> cracks (yet). I try to limit myself to 6500 RPM but go to 7000 when
> necessary. I use aftermarket rods & pistons. Not sure on the
availability
> of NOS cranks for the A-series, I got mine from England.
>
> Regards,
> Mark Palmer
> BSME, MSME
>
>
>
>
> >From: Jim Runciman <Jim.Runciman@donhad.com.au>
> >Reply-To: Jim Runciman <Jim.Runciman@donhad.com.au>
> >To: "'Brian Evans'" <brian@uunet.ca>, Taiju Kobayashi
> ><portago@xc4.so-net.ne.jp>, vintage-race-digest@autox.team.net
> >Subject: RE: Spridget 1275 crankshaft
> >Date: Sat, 8 Jul 2000 20:01:48 +0800
> >
> >I note the exchange on this subject regarding spridget cranks and think
> >that
> >you may be considering unnecessary expenditure. I run an A series 1275
> >engine in a Cooper S and I stopped using the EN40B cranks about 10 years
> >ago. The EN16 cranks have proven far more durable.
> >We wedge the crank and nitride it (doesn't come up to the same hardnes as
> >the EN40 B unit), balance the rods ( I have a set of Carrillos in one
> >engine) and make sure the flywheel runout is no more than 0.001".
Obviously
> >everything is balanced.
> >I use one of two US sourced cams and we have an engine that produces
+135HP
> >on 100 octane fuel and will rev to 8500 if required. In ten years I have
> >had
> >no blow ups and the only incident with a crank was a crack started to
> >propogate from the corner of the keyway in the end of a crank but it was
> >picked up before any damage ensued.
> >These engines are running 30 tto 50 hours between strips and they are
super
> >reliable.
> >problem with th e EN40B cranks is that they are too rigid for the BMC
> >engine. The material is fantastic in almost any 5 bearing engine.
> >Hope you find this of interest.
> >
> >Jim Runciman
> >Jim.Runciman@donhad.com.au
> >Phone:08 9279 7611
> >Fax:08 9279 7173
> >
> >
> >-----Original Message-----
> >From: Brian Evans [mailto:brian@uunet.ca]
> >Sent: Saturday, 8 July 2000 12:12
> >To: Taiju Kobayashi; vintage-race-digest@autox.team.net
> >Subject: Re: Spridget 1275 crankshaft
> >
> >
> >While I had good luck with stock BMC crankshafts when I was running them
> >from the outright failure point of view, I often had to show up with
three
> >or four cranks to find one that wasn't cracked after magnafluxing (what
is
> >it about magnafluxing that cracks so many crankshafts? pisses me off...)
> >
> >I do know from talking to guys who ran works BMC cars in Canada in the
good
> >old days than Cooper S EN-40B nitrided cranks were lifed at three or four
> >races, which suggests that simple fatigue is the real answer here. The
> >stock cranks are old, they have a lot of miles on them, and they weren't
> >designed to last seasons of racing at high HP levels, which I believe is
> >more important than RPM's alone.
> >
> >I too am probably going to be shopping for a billet crank soon. Who do I
> >call, who has the good prices and delivery, and who has the quality?
> >
> >Thanks, Brian
> >
> >At 09:55 PM 07/06/2000 -0400, Taiju Kobayashi wrote:
> > >Dear fellow listers:
> > >
> > >We have been racing a Spridget w/1275 motor quite successfully, however
> >the
> > >crankshaft was chopped twice in 2 years.
> > >The crankshaft is nitrided and balanced, and we kept it revved under
> > >7500rpm. And the engine is professionally built and maintained by
> > >ex-Formula 3000 engineer.
> > >
> > >Now that the well-prepared stock crank proved themselves unreliable by
> > >nature, we are in search of a steel billet or some other better
> >crankshaft.
> > >Does any of you have recommendation or real experience with that sort?
> >Let
> > >me know how it works.
> > >We also keen to know what were wrong with our stock crankshafts. Any
tips
> > >to avoid troubles?
> > >
> > >Cheers,
> > >
> > >Taiju Kobayashi
> > >Tokyo,Japan
> > >'69 Tecno Formula Ford(coming soon)
> > >'63 AH Sprite MkIII(our friends', myself as 2nd driver for endurance
> >race)
> >
> >Brian Evans
> >Director, Strategic Accounts
> >UUNET, An MCI WorldCom Company
>
> ________________________________________________________________________
>
>
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