So tonight was the night for preparing the new home of the piston and finalizing the decision on the rings, we’d a plan to meet at Mario’s garage for 3:30 sharp. Sharp, that is, if you go by Mario time — so naturally we got started closer to 4.
As Mario’s apprentice (read: gopher with delusions of engineering), I was on the tools and too covered in oil to take many action photos. You’ll have to make do with my rambling explanation.
The cylinder you see in the photo was already dressed up with three of the four bolts we were after (5/16″). The fourth one was still playing hard to get in the great junkyard of odd nuts and bolts Mario’s been hoarding since about 1974. He eventually fished one out and gave it a quick spa day on the wire wheel.
We were still rummaging through Mario’s treasure chest of doom — decades’ worth of orphaned bolts and nuts that looked like they’d survived at least two world wars. We’d managed to wrangle three that fit, and Mario had the fourth candidate spinning on the wire wheel, giving it a polish like he was preparing it for Sunday Mass.
According to the holy writ (the Workshop Manual), the head bolts are meant to be tightened down to 26 ft.lbs. The idea was to clamp the head onto the cylinder at that same spec, so the whole lot would behave like it was under proper working conditions before we started in with the hone.
But before all that, we did a wee science experiment with some long, delicate shims — each with a hole at one end so I could hang them off a scale. The numbers were something like: 1 kilo of pull with .004″, and about 2.5 to 3 kilo with .005″. In plain English: it proved the piston fit wasn’t a disaster. With the shim in place, we slid the piston up and down to check the gap stayed even across the stroke. It did — more or less — so we declared it “good enough to keep the piston from falling out,” and carried on.
Straight from the gospel according to BSA — the Workshop Manual for the Single Units — comes the holy word on what the ring gap ought to be.
We squared the rings neatly in the cylinder, poked in the feeler gauges, and had ourselves a measure. The verdict? About .028″. In other words: wider than a Scotsman’s wallet on payday. Clearly the rings have seen some miles, though who knows how many or when they first went in.
Rather than gamble, I’ve decided to order a set of +.040 rings from the UK. If they turn up and the gap’s too tight, we’ll break out the files and call it “precision fitting.” That’s the polite workshop phrase for what’s essentially fettling until the parts behave.
The photos above show our setup for the next step: clamping the cylinder in the vise with aluminium plates, then lining up the hone for its big moment. No video evidence exists — probably for the best — as Mario took on the role of oil-sprayer-in-chief while I manned the drill like a lad trying not to butcher his first woodworking project. Under his direction I eased the hone in and out of the cylinder, the goal being to smooth away the old marks and give the walls that lovely even crosshatch finish. By some miracle, it worked, and we were both chuffed with the result.
That wrapped up our afternoon’s graft. I broke everything down, released the cylinder from its compression bolts, and packed up the kit. Next step: rings on order from the UK and a patient wait for the postman. Until then, I gave the cylinder walls a good oiling back home — like tucking the old girl in with a blanket until she’s ready for the next round.
Ring Supplier:
Rings <rings@coxandturner.co.uk>
Home – Cox and Turner
Lastly, we had a look at the pipes I’d brought along for the front fork tool. At first it was a hopeless fit — like trying to squeeze a haggis into a teacup. But Mario, sharp-eyed as ever, spotted a raised weld seam inside the pipe. A quick trim to length and a bit of filing later, and suddenly it slid on like it had been made for the job. Magic.
The rest of the fabrication is now officially my homework — let’s just hope I don’t cock it up when left unsupervised.
On Saturday we’ve got the first gathering of the newly revived BSA Owners group under the CVMG banner, and Sunday is the last swap meet of the season. Fingers, toes, and maybe even spanners crossed that I turn up some good finds before the snow starts flying.
