The Recreation
‘Scarlet Runner’ replica
The Brooklands-type racer of Rick’s dreams had down-to-earth beginnings, based on the battered, corroded frame he was given 35 years ago (right), which had been dug up from a clay pit. The plan was to build a replica of Blackburne’s prototype racer of 1914 (see inset, bottom right) using an engine, bought from an autojumble, previously used to power a sawbench. Here are Rick’s latest jobs on the project...
1 The Thompson Bennett magneto came from the ‘sawbench’ power plant that included the engine and tank. It sparks but I doubt it’s been rebuilt – needs checking closely.
2 Someone’s been in here and repaired a broken slip-ring, but the coil is original and what looks like burnt sugar stuck on the steel armature core suggests ‘shellacitis’.
3 That’s when shellac coil varnish breaks down, goes sticky and spreads, gumming up the mag. I’m trying to stabilise and seal it with proper coil paint – but it’s a bad sign.
4 Primary coil resistance, from contact breaker centre bolt to earth, should be near zero, this is the thick wire coil and seldom goes wrong. Half an ohm? That’ll do nicely.
5 Brass HT output to earth gives a secondary coil resistance of 1200 ohms. I’d prefer 3500; it’s not broken, but may be shorting internally, reducing voltage.
6 I’ll take a chance – it may be fine for the bike’s limited use. Brass terminal looks right and gives the spark an easier path, reducing risk of further strain on coil insulation.
7 My swoopy Brooklands bars hit the glass drip feed on lock. I can do without it, but there’s no room for a plain elbow, either; the pump outlet is in the worst possible position.
8 Happily, pumps fitted on the left used mirror-image mountings, like this BSA one. They’re soldered, so I can swap it over and angle the pipe over the front of the tank.
9 But the pump wasn’t working anyway. I suspected the cupped washer. To dismantle, first unscrew the bottom – careful, there’s a strong spring inside.
‘THE PLAN WAS TO BUILD A REPLICA OF BLACKBURNE’S PROTOTYPE RACER OF 1914’
10 Unscrew the knob and the gland nut below it, and push the shaft down and out. As expected, the washer has broken into two pieces. Luckily, I have a spare.
11 Order of assembly: a spacer tube, smaller washer, cup (facing upwards), large washer and a nut at the bottom. Maybe Loctite the nut, they can come undone.
12 Guiding the plunger back up through the hole at the top is tricky. A thin screwdriver on top of the plunger can ‘steer’ the end of the rod toward the hole.
13 Another tank problem: of three bolt holes, one was filled with solder, suggesting a leak. Beneath the solder, the boss inside had broken free.
14 You can’t get inside the tank to heat the boss or clean the joint, so I drilled the boss oversize to take a tapped 3 /8in thread in the hole and made a brass bolt to fit.
15 Keep the head slim and tap a ¼in blind thread in the head end. Screwed into the old tank and soldered from outside, it gives a new bolt thread.