More crank problems

It's been almost exactly a year since I posted here so I'm long overdue for a new entry. I've made pitifully little progress and more backwards than forwards at times, but you may be interested in the latest problems with my Backwoods Ingersoll-Rand gas-electric.

In the previous post I showed it sitting on its elderly but intact and working Liliput OBB 2095 diesel chassis. These are fairly difficult to find nowadays and I was quite pleased to find this one - this was tempered with disappointment shortly after I made my last post when I dropped one of the power bogies and managed to crack all four of the plastic cranks. This was not a positive development.

You may just be able to see in the photo that there's a crack running from the centre boss up through the crankpin hole to the outside of the crank. The cranks seem be moulded in nylon and although it is possible to glue them (with the magic of Dr Mike's) this doesn't hold once the push-fit crankpins go in - I'd have been quite surprised if it had.

So it sat in the display case for months while I tried to think of a solution that didn't involve buying a new chassis. Now, I've been working on a couple of new kits recently and there was space on one of the etches for a few odds and ends, so I set to work to see if I could make a solution...

And I came up with these. They're a fold-up crank with 0.3mm pilot holes for the crankpin and the axles.

I wasn't sure how I was going to progress from there but it was a start. After the customary few weeks sitting in a drawer I doodled a design and started to turn up eight axle bosses. The Liliput axles are 1.50mm and I've bored them 1.3omm to give plenty of room for reaming out. I haven't decided on how to do the crankpins yet but I fancy some sort of screwed system rather than washers soldered on the end of plain crankpins I'd like to re-use the original plastic coupling rods if possible, so keeping them clear of the soldering iron seems a good idea. I've broken enough bits already.

The last photos show a soldered-up crank and the blank for one of the bosses, and pair of cranks, one with a boss soldered in place and trimmed and the other without its boss.

I think I've now worked out how to finish off the cranks and just need to solder up all eight cranks, fit the bosses and finish them off. I then have to work out how to fit them. I'd like to press fit them but I'm not sure about the tolerances required to get this just right so may depend on Loctite or lowmelt solder in the end. I also have to work out a plan for the crankpins an I suspect that doing those properly may take time (and money).