As many of you might recall from my dusty, pre-blog archives back in July, I somehow managed to get the engine coughing into life and the wheels to roll… which, let’s be honest, is the sort of miracle usually reserved for church fairs and tax audits. At the time, the blog wasn’t even a twinkle in my eye, so this is me playing catch-up—and trying not to fall asleep mid-story.
Push me Bohdan…. | BSA B40 350 Star
The grand plan had been to get the engine running before throwing more of my hard-earned cash and hours into this temperamental hunk of metal. Once that miracle occurred, I started tearing it apart, built an engine mount, and wrestled the engine out like it owed me money. The dismantling continued, mostly because the engine seemed to have a personal vendetta against me. I’d roped in my friend Mario—respected motorcycle mechanic and part-time saint—to help with the teardown and inspection. By now, I knew the clutch had decided to retire early: couldn’t pull it in, couldn’t roll the bike, probably sipping whisky in some long-forgotten corner of the gearbox. The transmission, on the other hand, appeared compliant enough to let me shift gears, which gave me hope. I even tried the old “kickstart while in gear” trick to loosen the clutch, but no dice—those 55+ years of hardened oil had turned it into something that could probably hold a castle gate shut.
I started by removing the timing cover… and I have to confess, I’ve never witnessed such a display of butchery on a set of Phillips head screws. It makes me think of what the outcome of a toddler wrestling a hedgehog might generate.
Enter the mysterious savior: the impact screwdriver. Who knew such a thing existed? (Apparently everyone except me.) You shove a Philips hex bit in, give it a whack with a BFH—Big Frickin’ Hammer, for those not in the know—and some clever little wedge inside magically imparts a twisting impact to the screw head. It’s a last-resort kind of tool… which, given the state of those screws, we were happily treating like a starter pack: maybe 6 out of 10 “last resorts,” and still counting.
I didn’t take many photos—nor did I bother with a video—because I was moonlighting as Mario’s apprentice mechanic. He was doing his best to keep his hands pristine, while I got to enjoy the full spa treatment of grease, grime, and questionable fluids.
If you squint at the clutch plates above, you’ll see the lovely little marks in the middle—souvenirs from 55+ years of cork-on-steel romance. There’s five steel friction plates and four double-sided cork plates, which, if you’re lucky, do a decent job of politely telling the engine to stop shoving power into the transmission when you pull the clutch. It’s one of those rare moments when I puff up with pride for being a Mechanical Engineer… and then immediately miss the good old days of manufacturing, before reality decided I should wrestle ancient BSA components instead of designing shiny new gadgets.
We didn’t dig too deep from this side—mostly because I was still trying to figure out which end of the engine to curse at—but a few nuggets of wisdom emerged:
1) The wire covering on the stator wires had apparently spent 55 years sunbathing and hardening into something approaching granite. Mario, in his infinite wisdom, suggested a heated razor blade to slice it off and free the three rebellious wires from the generator. Once liberated, a bit of new shrink wrap should keep them behaving… for now. If the wires throw a tantrum later, there are ways to cut back and resolder, but we’re hoping for a temporary ceasefire.
2) The primary chain—aka the timing chain—will need a proper once-over to check if the slack has exceeded BSA’s original specs. Shortening might be in order. In my later deep dive through the paperwork, I stumbled upon a service sheet. Seems BSA, realizing their earlier engineers might have been slightly optimistic, added a tensioner shortly after launch. Our engine, number 1318, just missed the memo; the sheet applied to engines 2501+. Mario was suitably surprised, and I felt like the poor sod had been handed a puzzle missing half the pieces. A retrofit is apparently in order—because of course it is.
The image on the left is about as revealing as a politician at a confession booth—turns out the outer cover hides bugger-all, since the next layer leads straight to the transmission. Since I could still shift gears (miracle of miracles), we decided the clutch was the main culprit and deserving of our full, greasy attention. For now, we buttoned it all back up and turned our sights to the top end—the valves, piston, and all the bits that like to remind you how much fun “disassembly” really is.
Mario, ever the sadistic mentor, assigned me “homework”: document the piston and start hunting for rings. Turns out we had a +020 piston—a hair bigger than the as-shipped STD. The piston itself is fine, but Mario reckons we might go bold with +040 rings and carefully size the ring gap… because apparently, measuring tiny gaps on a component that could have served as a medieval torture device is the height of fun. More on that nightmare later. (also reduces the risk of the +020 installing with a larger than desired/expected gap – I trust his experience over time)
I reached out to Walridge for parts, since we were replacing the exhaust valve, intake valve, and one particularly stubborn valve guide. A few other bits were on the shopping list, but those were the headliners. I asked about the ring set, and Mike—ever the practical joker—pointed me to a contact in the UK. Of course, why bother sourcing parts locally when you can wait weeks for international shipping and a generous side of jet lag for your patience? (Probably also because Mike didn’t have any on hand—he might sell his own teeth if anyone asked – for the right price.)
From: coxandturner.co.uk
You have a Hepolite #15544 +020 piston, so you need two 79.5 x 1/16” x .127” comps and a 79.5 x 5/32” x .127” oil. We wouldn’t advise gapping a +040 set down as the rings will just go out of round, if they don’t just snap when you try and fit them. Any spacers in te iol groove need to come out; our replacement oils are one piece slotted cast iron type, as were originally fitted.
To Be continued….
Keep following… so good to have you read this far… Thanks for the replies of encouragement I’ve received
Post is getting too long and would hate to lose your attention… more to follow
P.S. Attaching in pdf the presentation that Eleanor and I provided to the CVMG London section club… they were very pleased and it seems I’ve inspired some that wish to document their projects… lets see.