Hello all,
I have 2 sets of Crankcases. I was hoping to use one of one set to get my C15T back into service, but on inspection they are different. My current crankcases have the part numbers 41-8 and 41-10, the set I was hoping to use have the part numbers 40-8 and 40-10. Whereas the primary sides look much the same the timing sides look very different.
I am guessing the the 41-x part numbers are the newer, can anyone tell me when the 41-x parts came into production and are there any pitfalls in using the 40-x crankcases instead of the 41-x crankcases?
Cheers
Bill.IMG_3813.JPG
I believe the 41 marked (its a raw casting number not a finished part number) cases came into use in 1960 when the B40 model was introduced, new parts introduced with the B40 model were given part numbers starting with "41". Previously, new parts introduced for the C15 a year earlier were given part numbers
starting "40".
The "41" marked crankcases are fully interchangeable with earlier "40" cases, it's just a new slightly stronger casting to allow it to be machined to suit either C15 or B40.
The telltale sign that all the castings in your pics are pre 1962 and therefore interchangeable is the lack of the extra screw at the bottom of the cast rib dividing engine and gearbox.
PS, any reason for not using the original crankcases?
Hello Rupert,
Thanks for the information it's much appreciated and interesting to know when and why the changes came about.
Having reread my post, I can see that I didn't explain which cases were original or otherwise.
The 41-x cases are the original ones from my bike. It suffered from leaks, oil burning and other ailments so I decided to overhaul it and re-gear the gearbox from road ratios to the factory trials wide ratios. Once stripped I found lots of stripped threads and one completey sheared thread boss at the bottom of the gearbox section. I got a local shop to build up the boss with weld so that I could grind it to shape and drill and tap it to the original BSCy thread, you can see that repair in the picture. They built it up OK but then decided to clean it up by grinding the front face, unfortunately they also ground a dip into the mating edge of the case in that area, there's a dip of about 0.5mm that's 5 or 6 mm long.
I had the 40-x cases and considered using them as they're in reasonable condition, then I spotted the differences. I'm now thinking about trying to level the dip, perhaps with JB Weld or similiar and stick with the 41-x cases.
So I guess the question is, do I try and salvage the 41-x cases or take the easier option and use the 40-x cases, although that will mean splitting the original cases and moving the crank shaft over, which I was trying to avoid.
I would appreciate your input.
Regards
Bill.
On balance I'd probably salvage the original cases, all the defects you mention can be overcome.
The ground away jointface I would build up with weld then dress it back by hand, all you need is a welder who has lost his angle grinder....
Seriously, it's not that difficult.
A couple of other minor factors - the earlier cases would have been fitted with an oil pump with thick suction tube and one-hole sump filter. The later cases would have a pump with thin suction tube and two-hole filter.
Not an insurmountable problem to change things over but easier to stick to original spec.
Many thanks for the further advice, it's much appreciated.
I will use the original cases and get the welding done, making sure that all grinders are safely locked away.
Best regards
Bill.