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If you listen to some forum ‘experts’ if you are going to model in P4 everything has to be compensated or sprung or it will all fall off and everyone will point at you and laugh! Of course the closest that these people get to regarding springs are the ones in their oh so comfy armchairs that they never seem to get out of.

The reality is somewhat different but before I go into that it’s probably best that I share my finding of how model railway vehicles run. Of the three options Sprung vehicles do run best, then compensated and finally rigid when it comes to trackholding. Visually though the order is a little different as while sprung still looks best, I find rigid vehicles look smoother than compensated ones where due to a single solid axle all the track imperfections are transmitted to the body.

It seems then that Compensation is perhaps outdated and I certainly wouldn’t bother with compensating a wagon these days. Leaving sprung and rigid as 2 viable options. Sprung being best but not always necessary. I have a theory that any form of flexible chassis is primarily there to compensate for us not building things square in the first place and when it comes to machine produced RTR wagons most of the time you can just pop some new wheels in and they will work as can be seen here –

So before we fix anything we should really see if it needs fixing at all, however some RTR is a bit more tricky and the prime culprit here is Lima with their underlength axles. So using a lima PGA as a victim here’s what to do.

First thing is P4 wheels just wont fit. However Lima did mold a boss on the back of the axle guards so one option is to carefully cut this away with a circular saw in a minidrill and deepen the axle holes with a special tool such as Ed’s tool. However Lima also modelled a lot of their wagons too high so in an attempt to kill 2 birds with one stone the original axleguards were removed completely.

lima-cutoutI tend to use the Bill Bedford springing units but if mounted to the floor they wont fix the ride height problem. The trick is to mount them to the top side of the floor not the bottom and cut holes for them to poke though. The angled shapes are there so that the wheel doesn’t hit the floor. This mounting to the wrong side of the chassis idea also works for Bachmann TTA’s too. brassmasters-jigYou shouldn’t expect springing to sort out sloppy workmanship because it wont. Getting the axles parallel in all 3 dimensions is still important and a handy tool to help with this is the Brassmasters axle spacing gauge as seen above.

BB-cambrian-modI always solder the bearing in to its carrier and file it down a bit for clearance. The original Lima suspension moulding was distorted to adjust the height so I decided to replace them with spares from a Cambrian SSA kit that I had. These are very thin, plastic mouldings, so a few strips of square 40 though strip were glued in place to act as spacers. It goes without saying – dont bung the springs up!


The finished (ish) chassis. The SSA kit also yields the rather heafty brake gear brackets too. Obviously the body needs work but that’s for another day.

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7 years ago

Hi Jim,
Excellent, just what I needed to read. Springing is a future goal for me, but, I was betting on 9′ and 10′ wheelbase 4-wheeel wagons running without problems provided they’re sufficiently weighted and my track laying is smooth.
It’s always good to see another of your updates in the Inbox.

6 years ago

Jim, what make of replacement cast buffers have you used on your PGA project Please?