[Fot] TR4 crank

[TeriAnn J. Wakeman]

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