Grb Velocette

GRB VELOCETTE

BSA Gold Star lovers sneer, Matchless thumper advocates swear there’s nothing to compare with their machines, and one Royal Enfield “Bullet” owner we know won’t say one way or the other. But the Velocette in one of its many forms is still the machine for many enthusiasts all over the world.

Such an enthusiast has a motorcycle machine shop just three blocks from the CYCLE WORLD offices. Dick Brown, who operates GRB Engineering, 1650 Babcock St., Costa Mesa, CA 92627, makes his living by doing special/prototype machining for individuals and motorcycle importers, and also makes high quality chopper and custom accessories.

When Dick rides a motorcycle it’s for pleasure, and after scrutinizing his “toy” and bashing around Saddleback Park for a couple of hours, we reaffirmed our like for the Big Single in general, and the GRB Velocette in particular. It’s an individual machine of, by and for an individual person.

It’s difficult to detect much that isn’t standard by looking at the outside of the engine, but an excellent machinist like Dick doesn’t let little things like the fabrication of non-standard parts worry him. He wanted a reliable, big, play bike and that’s exactly what he wound up with.

I have always liked certain design features of the Velocette even more than my favorite Single, the BSA Gold Star. The degree of engineering in this motorcycle, which was originally produced in 1935, bristles with beautiful specifications like a “square” bore/ stroke ratio (86 x 86mm), finely pitched helical timing gears, a rather high camshaft location which permits the use of very short, light pushrods, and an extremely narrow and rigid pressed-together flywheel assembly.

In spite of the high camshaft location, revability in the original design was hampered by the fitting of hairpin-type valve springs which limited engine rpm to about 6800 without valve float. However, with coil valve springs, my Gold Star revs quite happily to over 7500 rpm.

Dick’s Velocette has been modified to accept coil valve springs, and a 34mm Mikuni carburetor now replaces the standard 1-3/16-in. Amal Monobloc. Standard Velocette scrambles cams provide a broad, flat power band, and a specially constructed exhaust system which terminates in what looks like a Brooklands “can” gives just the right amount of back pressure to lower the point at which the power really starts to come on, as well as quiets the exhaust’s bark.

But the biggest surprise about the GRB Velocette’s engine is in the bottom end. Early model Velocette MSS flywheel halves give an increase in stroke from 86mm to 96mm, and to get things back into proportion a late model connecting rod, which is shorter than the early MSS item, is employed.

A Machinist’s Interpretation Of An Ideal Play Bike

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This modification necessitated the use of an MC forged piston which is produced for the BSA Gold Star. Because the Gold Star had an 85mm bore, an oversize piston has been fitted. The Velocette combustion chamber is “flatter” than the Gold Star’s, so the 9.5:1 compression ratio is now up to 10.2:1—great for high quality American gasoline, but a trifle high for the gasoline generally available in the wilds of Baja, California.

Dick uses an old MSS Velocette gearbox and runs a final overall gear ratio of 5.60:1. Other ratios are 3rd, 7.45; 2nd, 9.81; and 4th, 14.32. At 7000 rpm the theoretical top speed is in the region of 95 mph, with a low gear low enough to climb just about any hill likely to be encountered while out cow trailing.

Other interesting features are a set of modified Velocette scrambles forks which now give an inch more travel than the standard ones, an oil tank from a 350 KTT Velocette road racer and three sets of wheels.

For general cow trailing Dick fits the wheels pictured: a 3.50-21 up front and a 4.00-19 rear. When the urge to go skidding corners at the dry lakes strikes, he puts on a 3.50-19 front and a 4.00-19 rear. And when it’s time to visit the desert Dick puts on a 4.00-19 front and a 5.00-16 on the rear! The gearing stays the same wherever he rides.

There are probably more machines similar to Dick’s in the area...we’d like to try them all! |<5