Catchpole specials

[Deleted User]

Hi Chaps
had a long conversation with Roy Lambert yesterday, and the subject of Catchpole specials came up. I know nothing about them, and can find virtually nothing on the interweb. Does anyone know how to point me in the right direction?

With many thanks

ATG

paul

ps/ Roger is rebuilding my engine for me with a few tweaks, had the most splendid, if expensive(!) day.

[David J Waring]

Paul,
To start the conversation rolling, here is a photo of John Catchpole taken from “Made to Limit Gauge” by George Stevens; just read the title !

[Deleted User]

The engine of the bike in the photograph is in my workshop now. When John Catchpole had it, he added weight to the flywheel, as I do in principle but using a different method. he made a special pair of cranks of heavier construction with a crankpin of 7/8″ diameter. Naturally this needed unique crankpin bushes with thinner than usual section. Rods are lightened and even had aluminium little end bushes. Inlet tract is polished out a bit and the inlet port bridges thinned.
Basically this incorporates all the traditional tuning modifications of the period, and is very well done. After Catchpole, it was owned by Derek Shire who used it to good effect in sprinting. For this purpose, the flywheel was reduced in diameter and the engine fitted with a TT Amac carb modified with a second jet to use alcohol and amyl acetate fuel. The barrel had been bored to top oversize and +60 short stroke pistons fitted. The bores and pistons were worn out so I skimmed a minimum out of the bores and have made a pair of pistons from castings in LM14. These turned out to be lighter than the previous short stroke items. The flywheel has had weight added again and the engine will have caged big ends and shimmed small ends. I have been a bit of a maverick all my life and prefer to think out my own solutions to problems, so my upgrades incorporate several non traditional methods, mostly to give a more free passage to the inlet.
With the blessing of the owner, this engine will have some of my thinking added to that of John Catchpole and Derek Shire. I feel privileged to be able to help ensure that this historic bike is kept on the road and retains its sporting character. I intend to write a piece for Yowl in the near future

[BRIAN MARSHALL]

Just to correct and fill in a bit more of this machines history, Derrick Genge Shire (NOT Derek) was not the owner after Catchpole. Arthur Breese owned and sprinted it after him but never achieved the same speeds, so he sold it to Derrick who kept it for many years. When he died Margret (another odd name spelling), his widow,passed it on to me. I was very concerned about what I considered to be dangerous and very extensive lightening work done by Derrick, as even the blades of the front brake and clutch levers were full of holes! In addition the frame had been very crudely modified, and I never sprinted it. I eventually sold it to Patrick Cravos a few years ago. I hope this sets the history books straight.

[BRIAN MARSHALL]

Further to my earlier posting I can now add more corrections and info about this machine. The carb was a Type27 twin-float Track Amal, repeat Amal overbored to one and five sixteenths and converted to take a second jet that comes in just under half throttle, Binks style. Main jet 1000, second jet 700. Special float needles to close quarter inch diameter holes in caps. Both floats will pass two pints of fuel in less than 10 seconds……The fuel mix used by Derrick was one gallon of Methanol (methyl alcohol),a quarter of a pint of Castrol M40 oil, and “half an egg cup” of Amyl Acetate. Main engine lube was by drippers and Castrol R40. Capacity was 647cc. Fuel consumption approx 4.5 mpg. Derrick bought it from Arthur Breese in 1962. When Derrick last raced it, in 1990, it was it’s first outing for 25 years, and this was at Bovingdon, Herts.. I bought it 15/09/99.

[Deleted User]

The January 1989 edition of ‘The Classic Motor Cycle’ has a obituary for John Catchpole written by Brian Woolley and Titch Allen with a fine photo of him with his 350cc Velocette-Villiers JC Special.
It’s almost worth buying a copy for the article on ‘The Crab’ !

[Author]

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