When is a mo­tor­bike not a mo­tor­bike?

The Shed - - Building A Motorized Trike -

This is one of the trick­i­est mo­tor­cy­cles you’ll see in these pages. It def­i­nitely looks like a mo­tor­bike and rides like a mo­tor­bike, but the trick is that it’s not made with a sin­gle mo­tor­cy­cle part. That’s the chal­lenge Kim ac­cepted when he set out to build it two years ago. He ad­mits to spend­ing a lot of time on in­ter­net fo­rums and this an­nual com­pe­ti­tion of­fered the kind of chal­lenge that fired up his en­gi­neer­ing cre­ativ­ity.

He’s al­ready build­ing a Harley-David­son bob­ber, which he’s nearly fin­ished, and while that kind of cus­tomiza­tion might sat­isfy some builders’ need for ex­pres­sion, Kim couldn’t re­sist the free­dom of hav­ing just one rule: you can build any­thing you like (apart from a death-trap) as long as you don’t use any mo­tor­cy­cle parts.

As soon as Kim found an in­ter­est­ing mo­tor and frame from some­one else’s stalled at­tempt, he was on his way. “The pre­vi­ous owner had done a great job but I had a dif­fer­ent vi­sion to his. I changed it a fair bit. I low­ered it quite a bit, changed the an­gle of the down­tube. In fact only the back­bone is the same. I like the line to the back axle.”

The bike, es­pe­cially with that ver­ti­cal down­tube, has a real vin­tage-racer vibe and Kim says that that was the look he was go­ing for. Hence the leaf spring front end. The bike uses the rear tyre from a fat-tyred moun­tain bike but he didn’t want to use the push bike’s mod­ern head­set and fork, so that be­came a stylish front end on one of his trikes.

Kim welded a box un­der the steer­ing head to lo­cate half a leaf spring. He cut down the leaves and re­duced the over­lap to make it softer. He also built the forks, and the rock­ers and rods that trans­fer axle move­ment to the spring. “The ge­om­e­try is amaz­ing,” says Kim. “It’s bru­tally low, so you have to be care­ful, but you can lean it right over and it re­sponds beau­ti­fully. It’s a real thrill.” That’s not en­tirely down to luck: “I cal­cu­lated the rake and trail and thought it should work.”

Kim loves two-stroke en­gines and the un­usual en­gine in this one hooked him im­me­di­ately.

“It’s a Wa­jax. They were com­monly used on fire pumps,” he ex­plains. “In the US they were called ‘Dis­ston’ and were used on two-man chain­saws with about a 2m bar. It’s a twin-cylin­der 180cc mo­tor and it puts out about 9hp [6.7kW]. It’s a re­ally in­ter­est­ing mo­tor.” Restor­ing the mag­neto would have been a big job so Kim fit­ted two old car-type ig­ni­tion coils, one feed­ing each plug. They are pow­ered from a bat­tery that lives in what looks like an oil tank. It’s a to­tal-loss sys­tem but Kim says that he gets about two hours of rid­ing out of it. Per­haps the most im­pres­sive part is not ob­vi­ous from the side view. When he bought the bike it had a gear­box with link­ages fash­ioned from Ford Es­cort hand­brakes. In­ge­nious, but it was in­clined to throw belts.

Kim had an­other idea. He in­stalled a con­tin­u­ously vari­able trans­mis­sion re­pur­posed from a wake­board­ing winch. The en­gine drives a cone on a shaft which is linked via a rub­ber belt to a cone fac­ing the other way linked to the rear axle. The belt finds its own ideal po­si­tion be­tween en­gine speed, torque, and the load on the rear wheel.

Best of all, all the en­trants in the com­pe­ti­tion will get to­gether at a meet­ing in Novem­ber to com­pare ma­chines and to race.

“It’s not slow,” says Kim. “It’s by no means the fastest, but it’s got quite a look about it and it’s a plea­sure to ride.”

“It’s a twin-cylin­der 180cc mo­tor and it puts out about 9hp [6.7kW]. It’s a re­ally in­ter­est­ing mo­tor”

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