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Silverstone/Challenger Crankcase seals

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  • #16
    Originally posted by Colin Sparrow View Post
    Mine was a one-off which had started life as a 24MX5C. No idea who converted it, but it was very nicely done. See LL 75. I think it had a re-ported long-stroke Challenger barrel; Druid's remarks explain the existence of the boost port.

    It actually handled quite well because it had about 2" longer wheelbase than a "real" Silverstone. I might still be about, it did get debated on here when it came up for sale a couple of years ago.
    Ah you mean lookalikes. The first time I saw a Silverstone advert in MCN in 1965 I wanted one! I converted my 24MX4 Challenger to as close to Silverstone specs as I could afford in 1972. Not easy on the wage I was earning then. I have the full history of the conversion in an old A4 size diary that I still have. I have a picture of the bike in there somewhere. I'll fish it out and put it on the web. It was never raced and was registered for the road. We could do daft things like that back then! I used to run round Edinburgh on it for two years till It was written off when a lorry ran into the back of me.

    Looking through my diary, an expansion chamber exhaust was only £6 direct from Greeves. A gearbox to replace the original duff kidney type from Stevens in London was £9.00. A 3 gallon tank from the same company was £5.00. Two wheels rebuilt with new 18" rims was only £12.00!

    It had Ceriani forks fitted when I bought it. I couldn't afford a new set so I just shortened the springs to get close to the correct angle. Despite that modification they still had a slightly "Easy Rider" look about them. It handled well despite this. It would do eighty with very little effort with a 46 tooth sprocket fitted. It was very prone to seizing though. I could never get it settled. I reckon the exhaust port was too big. It was originally an ex works bike I was told and had been modified (for the worse!). It was radiused at the edges but It ended up at +60 on the piston eventually and ran on the single dykes top ring as the lower ring kept breaking in the port.

    Great fun. Sorry for rambling on...


    David.

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    • #17
      I'm afraid I'm going to have to agree with Druid. In the drawings, there are some of the 'NN TT' cylinder with the boost port. There is also a drawing showing how to mod the piston to suit.

      My Silverstone had the port when I bought it. Every time I seized it, I had to spend ages cutting/filing the little window in the new piston! Two a penny in those days from the local motor factors and with trade discount!

      Regarding the Silverstone, they were almost a Yam beater in the hands of Jeff Went. Never seen anyone pull out such a lead after one lap of the Brands Grand Prix circuit and in the wrong direction (the Hutchinson 100 meeting)!

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