1957 Maico Iron Barrell Scrambler BUILT BY JOHN CALDWELL


John writes: Hello Siege,
Nice picture, I don't remember the girl going coming out of the parts dept..... It was purpose built to compete in the Premier Lightweight class.

The rules allow for 7" travel up front and 4" rear travel. The original Earles type forks were replace with later units and the early very short swing arm was replace with a later square barrel type. As per the rules the main part of the frame remained the same. After that particular muddy event at Washougal I decided to make a few improvements to the frame. The battery tray was removed and the frame strengthened in that area and an aluminum air box was fabricated along with an improved air filter system. The rules allow for a pipe with two cones, so I fabbed up a down pipe prototype along the lines of the 77 250. It works well and allows the motor to really rev out. As per the rules it runs a 34mm carb and to accomplish this the intake was enlarged as the original was only 28 mm. I also increased the size of the transfer ports. The head is an aluminum type and has been modified to my own design. I run a PVL but this is going to be changed to another type that is programmable.

The original "M" type motors are ok but there is room for improvement, they use a 3 plate clutch and a single non roller primary chain. The rods are long and thin and the big end bearing is a strange affair, as well next to impossible to find. The motor is narrow and the transfer slots are narrow at the base. Because of this I decided to use a square barrel lower end, That gave me an upgraded transmission, primary chain and clutch. I was also able to take advantage of the wider port slots and increase the transfer port area of the cylinder by welding up the lower section of the cylinder and widening the port sizes.

Shortening the stroke with the square barrel lower end meant shortening the cylinder. There was lots more done but I don't want to divulge all my tricks. When originally built it ran 13 / 58 gearing but when I changed the pipe design I was able to drop to a 56 on the rear. All in all a fun bike to ride and is quite fast as race results have proven.

Cheers, John

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