It has been a couple of months since I last reported on the 3F - Running trials have proven to be a bit of a trial...
A bit of time on the rollers, showed that there were no tight spots, but noisy.
The torsion link referred to by Will and Andrew was removed. (I was thinking about the motor flopping about, not torque, at the time...)
The motor is now held by some foam that keeps the top of the motor from bashing the walls of the firebox, and conveniently the torsion movement is fore & aft at that point.
Once I stopped the motor from resting against the bolt holding the cab to the firebox all was reasonably silent.
So far so good..., the 3F went on the layout.
Well, not so good... just kept falling off. So back to first principles, measuring back to backs, looking for the tender rubbing, out of square axles, etc...
Front set of driving wheels BtB was 17.93 - great for finding all the tight spots in the track, not so good for staying on the track!
The silver lining was I found a bit of track (old C&L flex) where the gauge was less than 18.83 at a key spot on the layout. This is now near the top of the "to be fixed" list.
Next was a trip to Dave Knight's where the 3F behaved, but not to exhibition standards, with the second pair of eyes we narrowed down the tender as the culprit.
Back home, I made some allowance for more lateral movement of the centre wheelset, but still all was not quite right.
Looking even closer, it appears that the springs for the centre axle of the tender are too strong, thus the tender is "light on its feet" or "porpoises".
At the front end this is partially controlled by the drawbar with the loco, but when the loco runs in reverse, the rear wheels will easily ride up over the rails.
So, that is where it stands today, next step will be to decrease the middle spring strength (this chassis uses the original Maygib springs) and continue trials.
However there is now coal in the tender and the boiler backhead has been detailed and installed.
"In the end, when all is said and done, more will have been said than done..."