On This Day

Friday 25th August 1967

53 years ago

New Zealand motorcycle racer, Burt Munro set an under-1,000 cc world record of 184.087mph on his beloved streamlined Indian motorcycle, at Bonneville, Utah, US. This record still stands to this very day. Burt bought his Indian motorbike new in 1920 as a standard model Indian Scout which had a side valve engine of 600cc capacity. The price was ₤120 with acetylene lighting although he could have bought an electric lighting model but it was quite a bit more expensive at the time. The engine number was 50R627. In the 1920′s Burt started tuning the bike for speed and ultimately he had it exceeding 90mph in side valve form. In the mid 1930s Burt made patterns for an overhead valve engine conversion but initially he was quite disappointed as it was no faster than the original side valve. er overcoming the con-rod failures Burt then experienced engine big-end failure. As the lubrication was achieved by a total loss system, which had no direct feed to the big-ends and crank pin, with the result that the rollers often came out blued and fused to the big-end cage. Eventually Burt made new fly wheels and increased the diameter of the crank pin which was bored to feed oil direct to the big-ends. He also fitted an Indian Chief oil pump and in doing so changed it to a dry sump lubrication system. Over the years Burt gradually increased the bore and stroke which enlarged the engine to just on 1000cc capacity. Burt cast his own pistons using a large kerosene blow lamp and casting dies he made himself. Another modification was to the primary transmission. He made sprockets for this and fitted a triplex chain on the primary drive in place of helical gears as this was more efficient. The clutch was basically standard with extra springs fitted to cope with the extra power the engine was developing. In order to get closer ratios in the gear box Burt cut the layshaft and welded two pinions from an Indian Chief onto this Scout layshaft in order to get closer ratios on the three speed gear box. Originally the Indian Scouts had only two cams and this limited the valve timing so Burt changed this to a four cam system which allowed him to alter the valve timing on both the inlet and exhaust valves. Burt built four different streamline shells for the Indian Scout over the years.