{"id":503,"date":"2025-09-21T17:56:27","date_gmt":"2025-09-21T21:56:27","guid":{"rendered":"https:\/\/blog.brainwalkers.ca\/?p=503"},"modified":"2025-09-21T17:56:28","modified_gmt":"2025-09-21T21:56:28","slug":"engine-clutch-continued","status":"publish","type":"post","link":"https:\/\/blog.brainwalkers.ca\/index.php\/2025\/09\/21\/engine-clutch-continued\/","title":{"rendered":"Engine \/ Clutch – Continued"},"content":{"rendered":"\n
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With the engine now containerized like some dodgy artifact in a museum, it\u2019s my turn to review the pile of bits and start plotting the grand rebuild. First order of business: order the parts we think<\/em> we know need replacing\u2014because nothing says \u201cconfidence\u201d like putting quotation marks around the word know<\/em>\u2014and then begin the glamorous job of cleaning decades of grime.<\/p>\n\n\n\n

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Some of the parts are on backorder, of course, but only 2\u20133 weeks. Which, in the world of vintage motorcycle restoration, is practically same-day delivery. Either way, they\u2019ll arrive well before reassembly\u2014assuming I don\u2019t lose half the bolts down the garage floor cracks first.<\/p>\n\n\n\n

Piston Rings<\/h2>\n\n\n\n

I wish my Father-in-Law was still around to fill me in on the \u201cstories.\u201d Funny how time slips by and it\u2019s the little details you miss\u2014the daft repairs, the shortcuts, the why on earth did you do that?<\/em> I\u2019m left piecing it together like some forensic mechanic, reading the tool marks and spotting the non-standard bodges. The piston, for instance, was definitely swapped at some point. Back in the early \u201960s, that was no big deal\u2014most bike owners knew how to change pistons and rings. Getting more than 30,000 miles out of one was pure fantasy. These days, engines happily chug past 100K, and most owners think \u201cmaintenance\u201d means changing a lightbulb or trading the whole bike in for a shinier one. The art\u2019s been lost, along with the smell of burnt oil baked into your fingernails.<\/p>\n\n\n\n

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Here\u2019s Mario checking the piston-to-cylinder gap with a set of shims. We could squeeze the piston in with 0.003″, but it refused to slide through. At 0.005″ it was just loose enough to remind us we weren\u2019t working with Swiss watches. That gave us our working range.<\/p>\n\n\n\n

The plan now is to hone and clean the cylinder, which, of course, will probably nudge the gap a little wider. Nothing like a bit of suspense to keep the rebuild exciting.<\/p>\n<\/div><\/div>\n\n\n\n

And this is where the \u201cscience\u201d (or, more accurately, years of stubborn trial and error) begins\u2014with the rings. The piston is a +020, the first step up from factory STD. Back in the day, BSA gave you STD, +020, and +040, before politely suggesting you re-sleeve and start again at STD. Since this engine was running well enough before, this is really more of a maintenance check, made necessary by the 55+ years it spent sulking in a shed. The cylinder only needed a light deglaze\/hone, and the piston itself was still in good nick. But either way, there was no way we\u2019d reuse the old rings\u2014they\u2019ve had their day.

This piston has three grooves: the top two take identical rings, and the lower one is for the \u201coiler,\u201d complete with a dainty little spacer. (See linked piston image for your daily dose of vintage metallurgy. – My piston diagram)<\/p>\n\n\n\n

Piston Dimensions<\/a>Download<\/a><\/div>\n\n\n\n

Here is a link to a youtube that explains a lot, but you may not have time or interest as it’s getting deeper into the advanced mechanic \/ engineer details.<\/em>
Piston RING GAP – HOW and WHEN to adjust it + GAP CHART – BOOST SCHOOL #6<\/a><\/p>\n\n\n\n

The rings, in case you missed piston school, do two very simple but life-saving jobs: they dump excess heat into the cylinder wall (since this engine is air-cooled and couldn\u2019t chill a pint if it tried), and they keep combustion gases from sneaking past the piston like freeloaders at a football match. Trouble is, metal isn\u2019t really solid\u2014at least not when it\u2019s getting roasted alive\u2014so you have to allow for expansion between \u201csitting pretty\u201d and \u201crunning like hell.\u201d That gap will close up as the engine heats, and if you don\u2019t leave one, the ring ends will crash into each other, buckle up or down, and shove against the ring lands. I\u2019ve seen the aftermath: entire pistons turned into confetti. The last thing an engine wants is chunks of feral metal bouncing about in the combustion chamber.<\/p>\n\n\n\n

So, instead of +020 rings (which might leave us with a comedy-sized gap), Mario suggests we go with +040 rings and file them down to fit. Custom job. His rule of thumb is about 0.002″ per inch of bore diameter. The ring manufacturers, naturally, insist on 0.004″ per inch. Who\u2019s right? Neither, both, and somewhere in-between. Like most things with these bikes, it\u2019s a cocktail of theory, trial and error, and the grumpy wisdom of mechanics who\u2019ve been at it since the \u201960s.<\/p>\n\n\n\n

For now, I\u2019m holding off on ordering the rings until we\u2019ve cleaned and honed the cylinder, so we can actually get accurate measurements instead of guessing and praying.<\/p>\n\n\n\n

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To the left, you\u2019ll see the clutch pressure plate\u2014posed with four driving plates stacked up like pancakes and five driven plates sulking in the background.<\/p>\n\n\n\n

I gave the driven plates a spa day with some very fine 140-grit sandpaper, just enough to scrape off 55+ years of fossilized muck. The driving plates still need their cork thickness checked, but at a glance they look fine\u2014like they could actually do their job without bursting into tears.<\/p>\n<\/div><\/div>\n\n\n\n

Word on the street (or at least on the internet, where truth and nonsense live side by side) is that finding good-quality clutch plates these days is a right pain. So the fact mine cleaned up nicely feels like winning the lottery\u2014minus the money, glamour, and champagne. The bright side? They\u2019re dead easy to remove, replace, and adjust\u2026 or so I say now, before future-me learns otherwise the hard way.<\/p>\n\n\n\n

Shiny Wheels (Rims + Spokes + Hubs)<\/h2>\n\n\n\n

When I was scrounging for parts, I hauled my wheels up to Walridge to see if any of the $109 specials they had lying around would fit my bike. Spoiler alert: they didn\u2019t. But after poking about with Mike, we confirmed both of mine are WM2-18 rims. Naturally, they\u2019ve got different center hubs and probably demand different spoke packages\u2014because BSA never missed an opportunity to complicate a simple job. Forty spokes apiece, just to keep me busy swearing.

A quick bit of math (or masochism) tells me new rims are $149 each, plus about $85 for a spoke set. That means I\u2019ll need to strip the hubs, restore them, and then rebuild the wheels from scratch. And let\u2019s not forget to measure the hub offsets\u2014usually 3\/16″ or 1\/8″ from centerline\u2014because nothing says \u201cfun weekend\u201d like trying to true a wheel that\u2019s fighting geometry itself. All in, it\u2019s about $250 per wheel, plus elbow grease and a steep learning curve. The old rubber might do for a couple of trial runs, but after that I\u2019ll need new tires unless I fancy sliding into a ditch on 50-year-old rubber.<\/p>\n\n\n\n

Tools – Construct<\/h2>\n\n\n\n

Up front, the job is to replace the seals; in the rear, it\u2019s mostly about polishing up the chrome \u201cdecorative\u201d bits\u2014which is just BSA\u2019s way of saying extra parts to rust and annoy you.<\/em> Of course, both ends require some bizarre, special tool to disassemble. Because why would you use a wrench when you can invent medieval torture devices instead?

So, off I went to the Metal Supermarket and picked up a couple lengths of pipe to sacrifice in the name of engineering. The plan? Start grinding and hack-sawing away until the tool I need finally emerges from the scrap, like Excalibur from a block of steel. More details to follow\u2014assuming I don\u2019t saw through something vital, like my patience.<\/p>\n\n\n\n

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The Adventure shall continue….<\/p>\n","protected":false},"excerpt":{"rendered":"

With the engine now containerized like some dodgy artifact in a museum, it\u2019s my turn to review the pile of bits and start plotting the grand rebuild. First order of business: order the parts we think we know need replacing\u2014because … Continue reading →<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_s2mail":"yes","footnotes":""},"categories":[1],"tags":[],"class_list":["post-503","post","type-post","status-publish","format-standard","hentry","category-uncategorized"],"_links":{"self":[{"href":"https:\/\/blog.brainwalkers.ca\/index.php\/wp-json\/wp\/v2\/posts\/503","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/blog.brainwalkers.ca\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/blog.brainwalkers.ca\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/blog.brainwalkers.ca\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/blog.brainwalkers.ca\/index.php\/wp-json\/wp\/v2\/comments?post=503"}],"version-history":[{"count":3,"href":"https:\/\/blog.brainwalkers.ca\/index.php\/wp-json\/wp\/v2\/posts\/503\/revisions"}],"predecessor-version":[{"id":515,"href":"https:\/\/blog.brainwalkers.ca\/index.php\/wp-json\/wp\/v2\/posts\/503\/revisions\/515"}],"wp:attachment":[{"href":"https:\/\/blog.brainwalkers.ca\/index.php\/wp-json\/wp\/v2\/media?parent=503"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/blog.brainwalkers.ca\/index.php\/wp-json\/wp\/v2\/categories?post=503"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/blog.brainwalkers.ca\/index.php\/wp-json\/wp\/v2\/tags?post=503"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}