Curtis Frame article from Cycle Canada Showcase

First a monoshock then a real shocker for Honda builder
by Jim Colbert

Full sized image of article below

It wasn't until he'd spent 150 hours fabricating a gasket, new valve seats, cam caps and oil passageways that Jim Brokensha began to wonder if putting a 16 valves in an eight-valve Honda engine was worth the trouble.

A 42-year-old North Vancouver resident, Brokensha would have settled for a stock '69 Honda motor to fill his Curtis monoshock frame. Then he heard about the 16-valve kit made in England by Piper FM Ltd., and ordered one.

The kit Piper sent, as it turned out, was a prototype and lacking in several areas. It came with no head gasket. The camshaft caps were too thin and the stainless steel valve seats had to be replaced by aluminum/bronze seats. The head had no oil drainage system.

Brokensha realized what he would be getting into by proceeding with the 16-valve conversion, but proceed he did. And, after making the necessary adjustments to the kit and to his engine, he chose to give his whole bike the damn-the-torpedos treatment.

Thus four Amal Mk II 32 mm carbs were installed in place of the 28 mm Keihins. Brokensha, a perfectionist (if you saw his Curtis-frame Cinvent in Cycle Canada November you'll understand), modified the Amals by drilling the main jets and installing Holley acceleration pumps. The pumps are activated by home-made throttle shaft cams.

To insure cool running he mounted a Derale oil cooler and a gigantic 16 litre oil tank under the seat. Oil prices being what they are these days, he's content to use seven litres of 20-50 Valvoline racing oil at a time.

The position of the monoshock meant two oil tanks had to be joined together under the seat to create the desired capacity, but there was still room for the battery.

To increase ground clearance and because the starter wouldn't budge the 12:1 MTC pistons anyway, brokensha moved the alternator inward four cm by boring out its centre and removing the starter gear. Careful cutting lightened the alternator for quicker throttle response. the transmission and clutch were left stock, but the rear-set shift linkage uses aircraft-type spherical rod end joins for precision and lack of play. Esthetically, the bike is as clean and as eye-grabbing as anything you're ever likely to see on the streets of Vancouver. "Everything has to match," insists Brokensha. "Even the carb angles have to match the bike. It's important. It looks professional."

It was with a little bit of luck and a lot of searching that brokensha acquired an early sand-cast, rather than die-cast, Honda engine. It's matte finish is favourably contrasted by the mirror-like black, red and green Interpart fairing and Rickman tank. The Shelby-Dowd aluminum wheels, partically hand-made Winning Performance exhaust and Yamaha TZ750 tachometer leave no doubt that this is a no-fooling-around street racer.

And the performance prooves it. With 100 horsepower moving only 204 kb, acceleration is clean and crisp from low rpm right up to about 8,000 at which point is stutters and lets you know it wants t obe shifted. Handling is neutral and very stable. In a word, excellent.

Too excellent. "It's happy at about 100 miles per hour, but where can you open it up? It bugs me... "

Cycle Canada Showcase Article

Curtis monoshock frame bike, image from Showcase
Curtis monoshock frame, image from Cycle Canada article

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