Another Crank pin proof of concept

The next round of experiments with Percy will require yet another new set of connecting rods. I’ve been wanting to experiment with a new style of connecting rod and crank pin for years and this seems like a good time to do it. North American eight-wheelers seemed to have had two styles of crank pins. […]

Percy’s New Frame

The one place where Percy admits surprisingly tight tolerance is in the relationship between axles and frame. Dropping the original axles into the slots, I find they have a nice running fit with very little discernable fore-and-aft movement. Both #622 and #10 have bearings running in guides, soldered à-la English etched kit to the insides […]

Friction for Percy

The question Percy and I have been grappling with is this: I strongly believe that 622 and 10 both spontaneously lost their quartering, causing them to lock up; how is this possible? Let’s review what we’ve learned so far: There is substantial play between the original crank pins and the connecting rods, as well as […]

Percy and the loose drivers

The more I drill Percy on the test track, the more the little engine mystifies me. Up until now, I’d cherished the theory that a shifting driver could cause it to lose quarter and ultimately bind the mechanism. To probe this theory, I deliberately reamed one of Percy’s front drivers (the geared axle) so it […]

Percy throws a rod

Earlier, Percy sheared off a crank pin. So, conjecturing that this meant the fast starts and stops were causing the wheels to get out of quarter sufficiently to put some force on the crank pin, I continued to replicate #10 and #622. Both of those have brass crank pins, but I turned some for Percy […]

Percy shears a crank pin

With Percy’s continued resilience to poor alignment, my approach will be to continue to replicate the construction of #10 and #622 until I can make it fail in the same way. This week, I turned some 3 mm axles, having no such stock material in my collection. It turns out to be harder than expected […]

Percy gets compensated

There is a widely held belief among proto:scale modellers that equipment works better if it is compensated or, better yet, sprung, or even better yet, compensated and sprung. It stands to reason that wheels that are able to stay on the rail are less likely to find the ballast. However, in an email, Rob Kirkham […]

Percy’s new connecting rods

One of my theories has been that Percy’s loose connecting rods were more forgiving of minor perturbations in quartering or crankpin eccentricity. So, I printed the middle experiments (8 degrees out of quarter and .022″ off eccentricity) with the thicker crankpins that allow only minimal clearance. These are about 20% bigger than the original crankpins. […]

Percy and the bad drivers

The question of tolerance continues to interest me. With those loose connecting rods, how tolerant is Percy of misalignment of the wheels, or uneven crankpin eccentricity? It turns out, Percy is not only tolerant, he’s indifferent! I didn’t have a front axle with the original crankpins, P87 wheels and the gear printed on, and so […]

Percy and the crankpins

On disassembling Percy, the first surprise was how loose the connecting rods were on the crankpins. I’d read, and have probably reiterated, that the finest line is the one that separates running clearance from slop. I’d always imagined that where crankpins are concerned, it really mattered. I’ve now tried four different crankpin sizes in Percy’s […]