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TR2/3/3A Moss Crankshaft pulley failure

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I hear ya'. There was a time I would have thought the same, and Moss is also very confused.

A damper is a heavy iron ring held to a steel hub with an elastomer...or rubbery...material. Every time the engine fires it puts a pulse into the crank, followed by the next, and the next. At certain speeds the frequency of the cylinder pulses matches the resonant frequency of the steel crank. It's hard to picture, as the crank seems very stiff, but like any steel part, it is similar to a very stiff spring. If you twist it at the right frequency back and forth, it increases the amount it stretches.

Piston aircraft engines often have warnings NOT to cruise at a particular RPM for just such resonant reasons. I've seen huge aircraft crankshafts sheared right off from resonance fatigue.

What I am trying to get at is that the load on the damper has very little to do with the pulley size, the fan, or anything like that. The resonant loads are an order of magnitude higher than any of these. So, reducing the bolt because of the belt or fan is just craziness.
 
I have this conversion kit installed and put it on and took it off 2 times inspecting the key position each time to see if it moved, of course the last time installed it probably did move!

I am worried about the pressing of the sleeve (1d) on to balancer (1c) there appears to leave a pocket that if the key is not indexed precisely could push the key back in the crank groove. This could allow the balancer to slip on the crank causing the damage to the crank seen in the other pictures of this thread. I wish that a spacer with the key pocket was made to hold the key in position until the balancer was in its final position on the crank shaft. The only other solution is to make a balancer that is full depth on the crank and fits the seal without the pressed sleeve.
 
HAWAIICJ said:
I have this conversion kit installed and put it on and took it off 2 times inspecting the key position each time to see if it moved, of course the last time installed it probably did move!

I am worried about the pressing of the sleeve (1d) on to balancer (1c) there appears to leave a pocket that if the key is not indexed precisely could push the key back in the crank groove. This could allow the balancer to slip on the crank causing the damage to the crank seen in the other pictures of this thread. I wish that a spacer with the key pocket was made to hold the key in position until the balancer was in its final position on the crank shaft. The only other solution is to make a balancer that is full depth on the crank and fits the seal without the pressed sleeve.
Click to expand...

i'm worried about the final key position too.
Number one: the spacer blocks your view of the key while tightening the pulley into position, so you can't be sure it hasn't moved.
#2. 1/3 of the key is not in the pulley slot. Which weakens the whole system From the get go.


any one know of a TR3A narrow belt crank shaft pulley, you can run without a fan extension?
 
If you can find a pulley hub that rides back farther on the keyway, you may actually save your crankshaft. The fact the Moss hub didn't ride far enough back may have spared enough of the crank surface to center a new, longer hub. That would be a good thing!
 
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