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Mr. A. Bevington of Lesser Ashton writes in: "I am thinking of taking my taking my 1939 Manx Brooklands Excalibur onto Stage 3 tuning - what used to be called Race Level 20 in the Hurley-Pugh Race Tuning Manual which I have secured a copy of.
I have already fitted a replica Benito sport camshaft, and a rather non-standard 2.5" Wal Phillips fuel injector in order to run a suitably porky ethanol/petrol mix. The cylinder capacity has been increased to 1209cc using a machined-down Foden piston at 17.5:1. Naturally I have increased the diameter of the oilway and pipes as per and beefed up the brakes a little by fitting a hand-built fifteen-leading-shoe hub and Bohmerland wrought-iron wheels, though the original forks do flex a bit under heavy braking. The Excalibur has been dynoed at 166bhp and is quite capable of an 9.8 second standing quarter mile with a terminal a tadge under 144 mph. Of course by this time, the entire oil tank has been scavenged and the motor has to be shut down, but it goes to show how incredibly robust the old H-P is, eh?
I am now thinking about a Druid supercharger - there seems to be space where the Faraday starter is at present. I'm lucky enough to have got hold of one of the original works thermionic ignitions s/no AP3308. This is in poor condition and may not be salvageable. Any comments at this stage, or should I just suck it and see?"
Indeed it goes to show. Try and get a modem motorcycle to perform like that and you would soon have a crankcase full of swarf. And though your pluck must be admired, I must say that many of the modifications you propose are quite out keeping with the spirit of Hurley-Pugh. However, I am bound to offer assistance, even in your case.
Personally, I've never seen a Hurley-Pugh tuned past Race Level 16, or "Killer" as we like to call it, as it was the Level that "Killer" Steerforth used to qualify in the 1938 TT, and the subsequent disqualification still rankles all these years later, I can tell you. Back in the 1930s, when I was apprenticed at FFS Ltd, the only official tuning outfit I may say, we saw Race Level 20 as really quite unnecessary to a rider of the proper calibre, If it couldn't be done with a riffler file and 2s 6d we didn't need it anyway. But if you must vandalise a priceless piece of British Engineering History, throw away those nasty Bohmerland wheels - the ornamental spokes are typically German and will let you down. You'd do much better to use our 3/8" brass spokes in standard H-P rims, which H-PO&EC has made by Pratchett & Son, of Sheffield.
If you must use a supercharger, discarding the Faraday follows works practice but kick-starting an H-P is not for the weak or slovenly. You might want to remove the incorporated boot scraper, or purchase a pair of the Club's 18g steel shinguards. And for the Lord in Heaven's sake fit the injector more than 17" from the head and rearwards-facing - I distinctly remember a foolhardy American getting his right leg blown off when one spat back on the overrun.
I hesitate to ask how you came by the very rare thermionic valve electrical ignition. That serial number says it was built by Alaric Pugh himself in 1933, an early unpatented prototype. The thermionic valves are, sadly, no longer made, although Sovtek can help with equivalents from the MIG 19 avionics. There is little doubt the unit performs well, despite occasional HT arcing problems - with 144 kV kicking around, it's best to wear a heavily rubberised macintosh, gloves and galoshes, and still avoid putting your feet down while it's raining.
Do make sure you keep all the original parts carefully, so your Manx Brooklands Excalibur can one day be returned to its original, perfectly adequate specification.
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