[TR] harmonic balancer?

[Randall]

>     Let me ask:  Just what is  a harmonic balancer?

Well, first of all, it's a misnomer.  There are some engines that do require
an external balance weight but AFAIK Triumph never used any of them.  So,
what we are talking about is a "harmonic dampener" (or damper if you
prefer).  On a Triumph motor, it has nothing to do with balance.

So, what is a harmonic dampener ?  Well, it dampens harmonic vibration.
Basically, a healthy crankshaft will "ring" like a bell if you rap on it
just right (which some old-time engine builders used as a check for a sound
crankshaft : a cracked or flawed crank won't ring).  And each time a
cylinder fires, it's rod thumps the crankshaft like ringing a bell.  At
certain rpms, the thumping matches the frequency the crank rings at, and the
ringing gets louder and louder.  (Not actually audible AFAIK, but the same
principle.)  The ringing of course adds extra stress to the crank (over and
above the rods pounding on it) so under some circumstances the total stress
can cause the crankshaft to break.  So, the "harmonic dampener" dampens the
vibration (ringing), reducing stress on the crank and (hopefully) keeping it
from breaking.

But, as best I can tell, the dampener is useless on a nearly stock
street-driven TR2-4A motor.  They simply do not (cannot) get operated under
the conditions that lead to cranks breaking (basically prolonged full
throttle operation at a particular rpm well beyond factory redline).  So the
harmonic dampener (on a TR3 motor) is primarily a racing part.

> I am also 
> guessing it can be added (to the hub?) at a later time.

True enough, but by the time you find out you need one, you'll also be
rebuilding the engine.

>     For the current time, I think a big, heavy-duty, and 
> exactly centered washer will suffice.

I thought that too; but experience proved I was wrong.  The washer pulled up
against the end of the crankshaft and did not clamp the hub tightly enough.
Even though there is a key between the hub and the crank, there is always
some play in the keyways, so the hub can vibrate back and forth.  Mine
eventually wore out the crankshaft, keyways and hub.

Randall