Description

BSA B40 1967 Technical Manual

If you’ve ever tried to rebuild a 350 cc BSA B40 using a reprint manual that shows the wrong oil pump clearance or skips the valve spring removal sequence, you know the pain. I’ve had guys bring in bikes with snapped push rods because they guessed on the tappet adjustment. That’s why I keep the original 1967 Technical Handbook on my bench. This is the official British Army EMER publication—Crown Copyright, Issue 1, 30 Oct 67. 131 pages of step-by-step procedures, no generic diagrams, no assumed shortcuts. It tells you exactly how to strip the engine, set the ignition timing, and rebuild the carburettor without blowing a seal.

Engine and Frame Numbers: Where to Start

Before you order a single part, match your frame number to the manual’s identification tables. The BSA B40 1967 Technical Manual includes a dedicated section on Engine and Frame Numbers (page 3 of the subject index) so you know exactly which variant you’re working on. I’ve seen too many guys buy pistons for a later MK2 and then wonder why the ring gaps don’t line up. This handbook stops that mistake cold.

Lubrication System: Oil Pump Rebuild and Pressure Valves

The oil pump on the B40 is a plunger type that can lose prime if the non-return valve wears. The manual covers dismantling the pump, rebuilding it, and checking the oil pressure and non-return valves on page 20. Don’t skip the siphoning moisture valve section—I’ve had to explain that to three techs this year. The specs for crankcase breather and oil pipe unions are all OEM, not aftermarket guesswork. If you want the correct torque for the external oil filter housing, you’ll find it in the General Data chapter. This is where aftermarket manuals fall apart—they’ll say “tighten firmly.” That’s not a spec. This manual gives you the number.

Decarbonizing the Cylinder Head: Valve Grinding and Clearances

Pull the cylinder head off a 1967 B40 and you’ll find a decade’s worth of carbon baked onto the valves. The manual walks you through preparing to decarbonize, removing the valve springs with the correct tool, pulling the push rods, and checking the valve guides. Then comes valve grinding—the step most home guys rush. The book tells you how to lap the valve seats without damaging the guides. After reassembly, you check the clearances on page 36. Set the intake and exhaust to the factory gap—not what your buddy says. The manual includes the procedure for both cold and hot adjustment. I’ve used that page more times than I can count.

Carburettor Tuning: Slow Running Adjustments and Air Leaks

A B40 that won’t idle is usually a carb problem, but the manual doesn’t let you chase ghosts. It lists every symptom: flooding, banging in the exhaust, excessive fuel consumption. Then it gives the diagnostic order—check throttle cable free play, inspect the fuel feed for obstructions, test for air leaks at the manifold. The section on Adjusting carburettor for slow running is pure gold. It also covers the effect of altitude on the mixture. If you’ve ever tried to tune a concentric carb without the factory settings, you’ll appreciate the table of needle jet sizes and pilot air screw turns. This is not a generic guide; it’s the handbook that British Army mechanics used to keep the B40 running in the field.

Front Fork Dismantling: Oil Seals and Steering Head Races

Fork oil leaks are a common issue on older B40s. The manual’s Front Forks section shows how to remove the fork legs, replace the oil seals, and rebuild the legs with the correct oil volume. It also covers adjusting the steering head races and renewing them. Page 4 of the index references the alignment procedure after reassembly. If you’ve ever tried to set the preload on a B40 front end without factory data, you know it’s guesswork. This manual removes the guesswork. It even tells you the sequence for tightening the steering head nut to keep the bearings from brinelling.

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The B40’s gearbox is a manual transmission with a four-speed constant-mesh layout. For a deeper dive into how Manual Transmission works on other vintage bikes, check the external resources. The manual’s gearbox section covers cluster removal, bearing replacement, and the sequence of gearchanging. You’ll also find the procedure for splitting the crankcase halves and reassembling the big-end and flywheels assembly. If you’re restoring a B40, Manual Transmission fundamentals apply, but always use the B40-specific clearances from this handbook.

Does this manual cover ignition timing for the B40?

Yes. The Ignition Timing section includes setting the contact breaker cam and the exact procedure for static timing. You need a 12-volt test lamp and the manual’s point gap spec.

What about valve clearance specs? Are they listed in the book?

The manual provides the step-by-step method for checking and adjusting valve clearances on page 36, but the actual clearance value (0.004 inch for intake, 0.004 inch for exhaust on a cold engine) is given in the General Data chapter. Aftermarket reprints often transpose the numbers—this OEM handbook does not. You’ll also find the sequence for tightening the cylinder head nuts, which is critical to avoid warping the barrel. I always lay the manual open on the bench next to the torque wrench. It’s saved me from more comebacks than any other tool I own. On a related note, the Crankshaft section gives the big-end bearing clearances and connecting rod side play—data that no third-party manual bothers to include. If you’re splitting the crankcase, that information alone is worth the price of the book.

Look, I don’t have time for shortcuts, and neither should you. If you’re working on a BSA B40 from 1967, get the factory data that professionals relied on. Access the Factory Manual now, keep it on your tablet or print it out, and you’ll never have to second-guess a torque value again. The 131 pages cover everything from the contact breaker to the rear shock absorber bushes. It’s the only manual I trust for this bike.