1. British Bike Build
UPDATE October 2024
Sorry folks. I've just noticed that the first few posts in this Blog have disappeared during our website update and the remaining posts have, somehow been incorrectly renumbered. I have recovered the missing pictures but the text is lost.
I will try to find time to rewrite the early posts and rebuild the blog.
Again, apologies for the cock-up.
Neil
Here's what I can recall up to the new 'POST 1
In 2014 I got the urge to build another bike – over forty years since I built my NORBSA. I fancied a big single, like an old BSA 500, in a Norton frame.
Matt soon found a frame on eBay, complete with forks, wheels and a registration document.
Finding an engine wasn’t so easy. Eventually, I located a Vincent Comet engine ‘for spares or repair’ on eBay for £4000 - much more than I wanted to pay, but a few days later, I saw a Comet-engined NORVIN for sale at £36,000. Suddenly, £4k for an engine didn't seem so bad.
The engine seller was an English guy living in Austria, selling parts for old classic English bikes. He’d heard of me from the P4 days and was also the designer/manufacturer of the recent, £60k, new version of the Brough Superior.
We agreed the deal and he shipped over the engine.
POST 1.
Well, that's the engine and gearbox mounted. Primary chain is trial fitted OK, rear sprockets are in-line, looking good and all is Hunky Dory. Next up, it's the primary drive chain case. As I've said earlier, I'll be running the 'O' ring chain dry so there will be no need to make it sealed and leak-proof. I have a few ideas, starting with a piece of 10mm thick aluminium plate for the inner casing.
As is the way with this project it'll evolve as I progress - hopefully without too many dramas and without too much metal flying across the workshop into the scrap bin.
From what I have here, I can determine the centres distance between the engine crank and gearbox mainshaft, the allowance I need for chain stretch and clearance around the chain. It make sense to follow the profile of the engine crankcase and to use the existing mounting threads.
There are several ways to transfer the screw hole positions in the crankcase to the plate. The simplest is to just press and rub the hole with your grubby finger. It'll leave a witness mark of the holes. I did the same with the front edge of the casing.
Because the plate is 8mm thick - about 3mm thicker than the comet or BSA inner chaincase castings, I have to machine clearance for the chain.
No fixing holes yet - it's just sitting there, but clearances are OK and I've allowed for about 15mm chain adjustment. You can see that I've made up an aluminium ring to replace the rollers in the clutch bearing. It make life much easier when the parts are on and off all the time.
OK - next challenge - to drill the mounting holes at the front of the plate to line up with the six, 1/4" whit threads in the crankcase.
If you recall, I already had the hole positions roughly marked on the front side of the plate by transferring their positions from the grubby marks on the original paper template. So I drilled one of them right through. I then mounted the plate with one screw, assembled the sprockets and chain and swung the plate to it's optimum position to centralise the chain run. I tightened the single bolt and gave the plate a tap with a hammer above the position of the little pointed screw, thus making a centre-pop mark on the engine-side of the plate. Off with the plate again and drill another hole at the newly marked position.
Here's my method for drilling accurately positioned and sized holes.
1. Amplify the original centre pop with another whack on the bench.
2. Drill right through the plate with a small drill. Here, I'm using a long 2mm drill allowing the plate to 'float' and align itself for a perfectly perpendicular hole.
3. Use a Step Drill (an Imperial one in this case) to open the hole to 1/4", cutting half way through from both sides. If you're careful, the next step on the step drill will de-burr and leave a nice clean chamfer on the hole.
It may be difficult to see in the pictures but I decided to make the inner and outer plates level and in-line below the centre-line of the inner plate. But, I reduced the height of the top edge of the outer plate by 1/2" - and re-drew the curve at each end. I've decided to make the side wall in two halves and weld them together at the seams. The bottom half will simply be a strip of 3mm x 78mm aluminium, rolled at each end to between the forward end and rearward end of the centre line of the rear plate. The top side wall however will be a slightly more complex shape. I'll start with a paper pattern. Clear as mud - I know.
That's plenty good enough. I'll make it slightly oversize anyway, and trim it after it's shaped.
It's much easier to work aluminium if it is annealed. I was taught to heat it gently until it's hot enough to blacken a piece of wood then let it cool naturally. An IKEA pencil works fine.
Top and bottom sidewalls taped in position and the fit ain't too bad. I just have to trim them a little and set the welding clearances. I learned how to gas-weld aluminium forty years ago but I reckon Tig would be much tidier on this job. I'll have to ask a mate to help out on that.
I'm starting to wonder if the cover is gonna be a little bulky and industrial-looking so let's call this the Mk 1 for the time being
And here it is. It's not quite as inelegant as I expected. I found a local welding company who made an excellent job of Tig-ing the joints with enough penetration that I could dress off the welds and give it a quick polish.
Not too shabby.