While Trisha is taking oodles of cash at Bristol today (wishful thinking: the show hasn't started yet) I feel a bit better after my sojourn in hospital with kidney stones and have returned to the chassis. Up to this point I hadn't spent any time getting everything to whirl around or to and fro as appropriate (other than a quick check that it would roll with the rods on).
I have spent some time working out how the motor will fit, and I have an idea for the pony truck, but before all that I spent time to get the side play control washers in place. There is very limited clearance between the crosshead and the front coupling rod boss, so the side play has been limited as much as possible.
I found that occasionally the rolling chassis would jump as something interfered with something else. A great deal of detective work showed that it was the con rod hitting the lower slidebar. If the driven axle moved sideways then the recess at the end of the slidebar didn't align with the plane that the con rod was moving in and it would cause a momentary bind. The solution was to make the recess slightly larger, restrict the side play on the driven axle and ensure the con rod big end was in the correct lateral place. I did this by using a hex faced tapped 10BA crankpin bush with the head inside the coupling rod and length adjusted so that it was just proud of the coupling rod which was secured by another hex faced reduced bush. The con rod was slipped over that and secured with a round faced bush cut to length. Good job I have a stock of these !
The result is a free rolling chassis.
I now need to fit the motor mount and final details (injectors, sandpipes, axlebox oilers) then final cleaning and spraying. I'll cut back the excess crankpin lengths when all is finally assembled.