A chain reaction
With the return of the Rudge’s rebuilt crankshaft, Rick was ready to nail the old Brit single together. Should be job done by lunchtime, surely...
The crank looked fantastic as I eagerly opened the box from Alpha Bearings. They had made a super job of it, but now it was up to me to match their work and I knew there were some tricky jobs facing me. You see, although everybody says British bike engines are easy to work on, it’s only a halftruth. Yes, they have few parts, but this breeds over-confidence. Back in the day, any kid who could lay hands on dad’s Ford Pop toolkit would think nothing of spreading his engine across the yard on a Saturday to do a rebuild or ‘tuning mod’, but building these engines to give their best takes thought, care and attention to detail. Max Nightingale at Alpha Bearings had convinced me to have the crankshaft professionally rebuilt, his point being that the fit in the flywheels was suspect. Doing the job, it turned out that the drive-side crankshaft had also worn slightly oval, making the main bearing a loose fit, so Alpha hard-chromed and reground the shaft. At £532 plus VAT it wasn’t cheap, but they have made a very good job of it and that’s just what it costs.
Rudge bearings are supposed to be a tight fit on the shafts and in the cases. To prevent tightening up after fitting, C3 clearance bearings are required; these aren’t always easy to get, but Paul Horton at rudge.parts supplies them; the snug fit prevents the crank moving to assess end-float, so I had first to assemble the bottom end with the old bearings which had worn to a sliding fit. Too much end-float is bad news, putting side-thrust on the conrod, but it was comforting to find that the original shims still gave the correct figure.
The Rudge oil pump is another area for caution – a worm-driven, reciprocating plungertype, backlash here reduces an already mediocre supply. The new pump, again from Rudge Parts, is precision-made to provide as much oil as possible. It costs £375 but it’d be foolish to spend so much on the bottom end and trust an 80-year-old pump to keep it all healthy. Rudge engines have compression plates as standard and it is important to check there is adequate clearance between the head and piston crown; our piston had some bruising. It seemed to clear with the thick head gasket fitted, but relying on selecting the right gasket for piston safety troubled me, so I fitted a thicker compression plate and standard thin gasket. Opening two valves with one rocker means that the stem lengths have to be matched to slight variations in the rocker pads, otherwise the valves won’t open together; and the valve timing? I spent two evenings trying to figure that out. To do it in the frame you need a pinion puller because it takes a few tightenings and removals to get right and a custom-made depth gauge because the frame prevents you going in perfectly vertically and with a domed piston that means you get a different reading every time. Drilling a bolt straight through the middle to take a spoke ‘plunger’ proved the answer but it’s still a faff because you need two rods – the one long enough to measure down near bottom centre hits the frame before the TDC setting can be checked.
The Pitman manual says set at the exhaust opening point and the rest follows, but I’d advise checking closing and the inlet timing as well. Ours has a good cam and followers and came out near enough. There’s more wear in the rocker spindles that appeared on the bench, a set of spindles and bushes is on the way from the Rudge club so the head can’t go on just yet but at least the tricky bits are done.
‘I KNEW THAT THERE WERE SOME TRICKY JOBS FACING ME’