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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