Peter Allard and his 1950-something BSA "Gold Star" Bitsa.

“No, it's not an original BSA Catalina. I wish it was. It just a bitsa made from parts I'd been collecting for about 12 years. Maybe longer. The frame is actually a BSA A10 650 twin chassis, circa 1956. The engine is a 500cc BSA unit built up from a pair of B34 crankcases in the style of a big fin DBD Gold Star lump.

"To fit the engine, I had to cut out the usual piece of frame tubing to clear the oil pump. I fabricated a kinked replacement section. But there wasn't a lot else to do to the frame because A10 frames are essentially the same as Gold Star frames—except for some minor differences (the DB Clubman Goldie has lugs for rear-sets and no steering lock facility, for instance).

"For the engine, it had to be a big fin cylinder head. To my eye, they simply look the best. With the standard B31 engine, or the small fin head, the engines look too tall. But the big fin cylinder head looks much beefier, which was what I wanted. The rocker box came from a BSA B34.

"The basic 500cc (BB) B34, unlike the 500cc (DB) Gold Star, has a smaller drive side main bearing—which this one has. But I'm upgrading to a big bearing engine and am having the crankcases built up with weld ready for re-machining.

"There's nothing wrong with the small bearing engine, mind. They're pretty strong and reliable, and plenty of racers use them. And if you're stripping the engines regularly during a race season, you can check and replace bearings where necessary. But the big bearing engines are much stronger and need less bottom end maintenance, and I'm working my way up to "hot rodding" this one.

"The crankshaft is from NEB. Standard BSA cranks are built with the crankpins bolted between the flywheels. It's a generally reliable arrangement, but not as strong as the NEB crank that's pressed together. The crank, incidentally, was one of the most expensive parts of the build at around £500.

"This engine also has an Omega cast piston with around 8.5:1 compression (a forged Wiseco piston would be better, but they're around £150 each, which is roughly double the price). Most of the other engine internals are BSA B31/B33.

"Originally, I had the wrong silencer fitted, and that was strangling performance. But recently I've replaced that with a proper Gold Star silencer which has made a huge difference. The bike picks up much better and is still tractable at lower speeds with a strong and steady tickover. It really flies, in fact, and the silencer is more like an amplifier and rattles windows everywhere—which, of course, doesn't make me very popular first thing in the morning when I fire it up.

"Gold Star engines, note, won't run happily with just any old silencer, and they won't run well at all below around 4000 rpm. So the correct silencer is crucial.

"The tractability on this bike is helped by the 30mm Amal Mk2 carburettor. The Mk2 is a good carb, but ugly as hell. I might replace that sometime, with an Amal monobloc probably. But at the moment I'm reasonably happy with it.

"The forks are stock BSA. The front wheel and front brake came from a Norton Commando. The rear wheel is from a B31. I haven't got a proper seat sorted out yet. Just a piece of foam.

"The fuel tank, by the way, is a genuine Catalina item with, as far as I know, the original paint on it.

"The ignition and charging are by magdyno, and it's running on 12 volts.

"I don't know what the bike is worth. But I suppose I ought to insure it for around £4000-£5000 maybe.

"There aren't many Catalina style BSAs around now. Most people prefer the Clubman Gold Star look with clip-ons and rear-sets. Most of the Catalinas went to the USA, but some are coming back to be converted to DBDs.

"I prefer the Catalina look. The Clubmans can be a little heavy on the wrist if you're just using them locally to commute or something, which few people do of course.

"The oil filter on the side of the engine is just a temporary thing. The engine hasn't been fully run in, and I'm using the external oil filter to remove all the bits of whatnot from the rebuild. Later, when the bike has got a few more miles on it, I'll take the oil filter off.

"You don't really need external filters, but you do need to clean the oil tank every time you change the oil. By that, I mean that you ought to remove the oil tank and flush it properly with petrol or something. A lot of muck accumulates inside, and the tanks are easy to take off.

"A little tip for anyone running a B31, B33 or Gold Star is to carefully check the primary chain alignment. I work as a classic bike mechanic, and I often come across aftermarket parts that aren't accurately machined. It's the inner clutch hubs that cause the problem. They're frequently supplied with the taper in the wrong place. By that, I mean that the hubs stick out too far into the primary case, sometimes as much as 4mm. I usually have buy hubs in "bulk" and have them re-machined for customers bikes.

"I don't think it's important to have the engine sprocket and clutch hub/sprocket alignment any more accurate than, say, 1mm. But the better it is, the longer the life of the drive line, and the smoother the power delivery.

"One final tip is to replace the (single row) primary chain whenever it becomes slack. I'm not talking about immediately after a new chain has been fitted. I'm talking about when that initial bedding in is over and the bike has been used for a while.

"Drive chains don't wear out evenly. They get tight here, and get loose/slack there, and you can spend a lot of time trying to get the adjustment just right, and never get it how you
want it.

"I prefer to simply remove and replace the chain. Chains are not expensive and are generally long lasting (a couple of years or so). And while you're down there in the primary chain case, you need to check the nut on the engine shock absorber (they do come loose), and check that the clutch hub is tight.

"Lastly, always check the primary chain tension when the engine is hot, not cold, or it could pull up too tight when you're on the move."