The Story of our Sprint bike

The engine was revised each year:-

Mk1:- A very neat (but not very durable) 250cc'ish rotary vane compressor was mounted on the primary cover and directly driven off the end of the crankshaft through an internally toothed coupling. Carburation (methanol)  was by 1 1/8" WalPhillips fuel injector. In this form it ran numerous times at RAF Topcliffe and once each at Esholt and Santa Pod. It occasionally reached the finish line without breaking either a tooth coupling or the compressor itself. The compressor breakages were terminal resulting in having to buy new ones, which at  £5 was more than a week’s wages for a poverty-stricken apprentice. After about 3 broken compressors a re-think was essential.

Mk2:- As well as a different compressor arrangement for 1965, I decided to convert the heavy duplex down tubes to a single tube, at the same time fitting shorter, rubber element forks (these were from an obscure 50cc French moped). The compressor was now a rotary lobe type of about 210cc displacement, mounted behind the barrel and driven at a little over engine speed off an extension to the crank via V-belt. WalPhillips fuel injector again. This compressor was capable of any engine speed without self-destructing and should have been better - but wasn't! 

It somehow never developed the power of the Mk1. In this form it ran mainly at RAF Topcliffe. More re-thinking was necessary!

Mk3:- This time a second-hand Roots compressor was fitted (as opposed to the Shorrock C75 which was desired but way beyond my financial means!). This compressor was mounted in front of the motor driven by toothed belt with a speed reduction. A hybrid homemade SU/WalPhillips injector was fitted. Whilst being exceptionally reliable this arrangement did not produce particularly good power, probably due to the compressor being a bit worn out and not efficient at the lower speed. This, in addition to my homemade injector being very difficult to set up and the induction tract being a bit too long, resulted in the bike only having a couple of outings in 1966 (again at RAF Topcliffe).

 "By now I was losing interest and moving on to other things, so it went under the workshop bench from 1967 until Bonhams auction (in 2014). Whilst I had the privilege of competing against some of the top racers of that period, I did not pose much of a threat to them! The benefit to me was the engineering challenge, more than riding the bike. "

"I seem to recall its best time was in Mk1 form and was the wrong side of 15secs!”  (Richard Goater)

Since the 1960’s It has been a non-runner with a few engine parts missing (main components of the supercharger installation, clutch, kick-start etc) and Tim had never planned to get it going or riding it. However, the frame has been powder coated and new engine plates cut, tiny tank added, new seat fitted and generally smartened up. It looks the part, but wouldn’t it be great to get it fired up …even if it didn’t set any records. 

So, would it ever run? The simplest solution would be just to replace the engine with something else. That’s the easy route but then it’s not the same.

Stephen outlines the challenges ahead 

First, that front end needed a rethink! While the wheel/drum was acceptable the step-thru style leading links suspension was seriously worn, and top and bottom head bearings looked borrowed from a push bike. (turns out they were - and a few balls short!) 

The engine initial inspection revealed that part of clutch is present, the important bit as the rest of the clutch looked the same as later 250/350/450s (Later discovered it wasn’t !). Turning the engine over made a horrible noise - the crank was turning on the bearings with the main bearing seized solid and possibly a worn crank! 

 Searching for gears was interesting There might be some inside but they could not be found using the gear lever! 

Other issues included an oil dip stick tube replaced by a brass fitment as used in domestic water system, the points cover had been glued on and the Castrol R oil in the sump had reverted into natural crude state, i.e. black goo,  in the bottom of the sump. It became clear the engine would require a complete strip down and may well just not run if too many issues are found – there is a limited budget

The rear end was Ok apart from the chain rubbing on the frame. This means the engine would need moving across – and then also repositioning the wheel as well. A frustrating chore.

A fine mixture of decomposed oil and alloy corrosion was not pleasant

  However, the good news was the head and barrel were in good condition and although the mains were shot the big end was fine - which was a big relief ! 

The Ducati motor is generally straightforward to work on despite the fiddly shimming required for the bevel drive. Although there are timing mark for the valves, there are no marks at all for the ignition - and the points are the other side to where the timing disc goes which doesn't help.

  The hunt started for the missing clutch centre drum. It turned out that the 200 Elite motor which was made for only 2 years employed a totally different clutch than all the 125/175 and 250 singles of the time. Bugger! One was eventually tracked down in Holland and its wasn’t cheap. 

Now we have a complete clutch – and big end  -thanks to Adrian Smith for making up the spacer where the  alternator and flywheel should have been. .

By the time the engine was complete, covid-19 had done it worst and the Heritage Sprint for 2020  had to be cancelled. So, with no kickstart and not trusting the well-worn mechanism anyway, further engine work was left until some starter rollers were located.

With great delight the moped forks were replaced by a set of much modified Honda CG125 (big thanks to Roadstar of Dover for these). The original front wheel was machined internally to take proper wheel bearings and the CG spindle and yokes fitted with correct bearings in the headstock. These mods mean the bike is slight taller at the front and about 4 inches longer. The fairing brackets were re-worked to make it more secure and prevent it fouling the bars. 

So, it’s a bit different now - gone are the massive 6v coils a proper set of clip-ons fitted new forks with 3cm of travel!!  It’s got a carb with all its bits inside and even a working petrol tap!

Finally, on 24th July 2020 the bike was started for the first time since 1967 … it has only taken 53 years and a pandemic to get it sorted!