{"id":473,"date":"2025-09-19T13:50:26","date_gmt":"2025-09-19T17:50:26","guid":{"rendered":"https:\/\/blog.brainwalkers.ca\/?p=473"},"modified":"2025-09-19T13:55:55","modified_gmt":"2025-09-19T17:55:55","slug":"engine-clutch-dismantle-beginnings","status":"publish","type":"post","link":"https:\/\/blog.brainwalkers.ca\/index.php\/2025\/09\/19\/engine-clutch-dismantle-beginnings\/","title":{"rendered":"Engine \/ Clutch dismantle… (beginnings)"},"content":{"rendered":"\n

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\u2026 which, let\u2019s be honest, is the sort of miracle usually reserved for church fairs and tax audits. At the time, the blog wasn\u2019t even a twinkle in my eye, so this is me playing catch-up\u2014and trying not to fall asleep mid-story.
Push me Bohdan\u2026. | BSA B40 350 Star<\/a>

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\u2019d roped in my friend Mario\u2014respected motorcycle mechanic and part-time saint\u2014to help with the teardown and inspection. By now, I knew the clutch had decided to retire early: couldn\u2019t pull it in, couldn\u2019t 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 \u201ckickstart while in gear\u201d trick to loosen the clutch, but no dice\u2014those 55+ years of hardened oil had turned it into something that could probably hold a castle gate shut.<\/p>\n\n\n\n

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I started by removing the timing cover\u2026 and I have to confess, I\u2019ve 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.<\/p>\n<\/div><\/div>\n\n\n\n

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\u2014Big Frickin\u2019 Hammer, for those not in the know\u2014and some clever little wedge inside magically imparts a twisting impact to the screw head. It\u2019s a last-resort kind of tool\u2026 which, given the state of those screws, we were happily treating like a starter pack: maybe 6 out of 10 \u201clast resorts,\u201d and still counting.<\/p>\n\n\n\n

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I didn\u2019t take many photos\u2014nor did I bother with a video\u2014because I was moonlighting as Mario\u2019s 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.<\/p>\n\n\n\n

If you squint at the clutch plates above, you\u2019ll see the lovely little marks in the middle\u2014souvenirs from 55+ years of cork-on-steel romance. There\u2019s five steel friction plates and four double-sided cork plates, which, if you\u2019re lucky, do a decent job of politely telling the engine to stop shoving power into the transmission when you pull the clutch. It\u2019s one of those rare moments when I puff up with pride for being a Mechanical Engineer\u2026 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.<\/p>\n\n\n\n

We didn\u2019t dig too deep from this side\u2014mostly because I was still trying to figure out which end of the engine to curse at\u2014but 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\u2026 for now. If the wires throw a tantrum later, there are ways to cut back and resolder, but we\u2019re hoping for a temporary ceasefire.

2) The primary chain\u2014aka the timing chain\u2014will need a proper once-over to check if the slack has exceeded BSA\u2019s 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\u2014because of course it is.<\/p>\n\n\n\n

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See the wire going from the generator and through the body.<\/mark><\/strong><\/figcaption><\/figure>\n<\/figure>\n\n\n\n
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The image on the left is about as revealing as a politician at a confession booth\u2014turns 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\u2014the valves, piston, and all the bits that like to remind you how much fun \u201cdisassembly\u201d really is.<\/p>\n<\/div><\/div>\n\n\n\n

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Mario, ever the sadistic mentor, assigned me \u201chomework\u201d: document the piston and start hunting for rings. Turns out we had a +020 piston\u2014a 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\u2026 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)<\/p>\n\n\n\n

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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\u2014ever the practical joker\u2014pointed 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\u2019t have any on hand\u2014he might sell his own teeth if anyone asked – for the right price.)<\/p>\n\n\n\n

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From: coxandturner.co.uk

You have a Hepolite #15544 +020 piston, so you need two 79.5 x 1\/16\u201d x .127\u201d comps and a 79.5 x 5\/32\u201d x .127\u201d oil. We wouldn\u2019t advise gapping a +040 set down as the rings will just go out of round, if they don\u2019t 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.<\/p>\n<\/div><\/div>\n\n\n\n

To Be continued….

Keep following… so good to have you read this far… Thanks for the replies of encouragement I’ve received <\/p>\n\n\n\n

Post is getting too long and would hate to lose your attention… more to follow<\/em>

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.<\/p>\n\n\n\n