TeriAnn,
You are absolutely correct about wanting to stay away from any crankshafts
natural frequency.
Operating in this range will induce crankshaft 'whip' and severe bending
moments into the crankshaft. Breaking the crank somewhere in the middle is
quite typical of this failure mode as the nose of the crank and the rear of
the crank are bending 180 degrees out of phase with each other. Flywheel
bolts that shear as a result of stretching is another indicator you are in
the natural frequency zone. No amount of nitriding or any other surface
treatment known to mankind will stop it breaking.
Lots of racing boat people learn this lesson quickly! Trying to run at a set
RPM range that coincides with the cranks natural frequency! Extremely
expensive mistake when it can be avoided by operating a few hundred RPM
higher or lower!
Cheers...
Kind Regards
Peter Vucinic
TR-4
_______________________________________________
fot@autox.team.net
http://www.fot-racing.com
Donate: http://www.team.net/donate.html
Archive: http://www.team.net/archive
Forums: http://www.team.net/forums
-----Original Message-----
From: fot-bounces@autox.team.net [mailto:fot-bounces@autox.team.net] On
Behalf Of TeriAnn J. Wakeman
Sent: Thursday, 3 May 2012 2:29 PM
To: fot@autox.team.net
Subject: Re: [Fot] TR4 crank
On 5/2/12 7:42 PM, Tony Drews wrote:
> As I understand it, the stock crank will live pretty much forever if
> you shift at 5,000 RPM. If well prepared (good radius between bearing
> surfaces and the rest of the crank, possibly nitrided as well), it
> will live a number of seasons shifting at 5,500 RPM. When you start
> running it to 6,000 RPM, that's when the longevity drops pretty
> quickly - a season or two is about it before the #4 journal section
> goes. Some last longer than others. Sometimes when it goes it
> doesn't take out much else, sometimes it kills the block and a rod or
> two.
>
> Tony Drews
I don't remember the RPMs and I can't find them in my notes so my numbers
will be a little iffy.
The way I heard it is that stock granks hold up well below the 5000 RPM red
line. A little above 5000 RPM (5200ish?) there is a strong harmonic that
tends to break the crank at the base of the flywheel mounting flange. The
common way to tame this harmonic is with an aftermarket harmonic dampener.
At full acceleration I commonly shift at 6000 RPM.
My crank has a dampener & is nitrided and has held up well so far.
It is my understanding that there is a second major harmonic around 6200 to
6400ish RPMs that wants to break the crank in the middle. I stay away from
that harmonic because I don't think even a nitrided crank would hold up to
that one for long.
Wishing I could find my notes on the subect,
Teriann
_______________________________________________
fot@autox.team.net
http://www.fot-racing.com
Donate: http://www.team.net/donate.html
Archive: http://www.team.net/archive
Forums: http://www.team.net/forums
Unsubscribe:
http://autox.team.net/mailman/options/fot/pvucinic@netspace.net.au
_______________________________________________
fot@autox.team.net
http://www.fot-racing.com
Donate: http://www.team.net/donate.html
Archive: http://www.team.net/archive
Forums: http://www.team.net/forums
Unsubscribe: http://autox.team.net/mailman/options/fot/mharc@autox.team.net
|