classic motorcycle forum

The Mk XII-C & XV-C engines show a lot of potential but suffer a major handicap. There was never an alternative alloy piston for them. To repeat myself yet again, replacing the original cast iron piston with an alloy version transforms these basic Villiers engines. The alloy 25C piston drops straight into the VIII-C, the 196 Super Sport into the 1E & 2E plus several aftermarket piston firms made an alloy version for the original 175 Sport but there is nothing for the XII-C/XV-C. (The XV-C is the single exhaust port version of the XII-C).

The XII-C  has the best breathing of all the pre-war C series. It sports the MW carburettor, the same size as used on the earlier 175’s and the 196’s of its time and Villiers made an appropriate exhaust for it but the times were against it. Two-strokes were looked down upon, fashion decreed a Brooklands flavoured exhaust system and four -strokes were de rigueur.  No one was interested in them.

Nowadays we see the potential for a tongue-in-cheek fun little bike but it’s too late for riders with average finances. Financing small batch piston manufacture is a bit beyond us. Pity about that. So close yet so far.

The first registrations I have around the GY 7000 mark date around the first half of 1936. Can’t get much closer than that. As I wrote earlier I can only broadly date when an engine was produced from registration dates. The registration dates are surprisingly varied, there can be a several month difference between consecutive engine numbers. It is very broad brush. Not that it matters that much as Villiers didn’t make annual model changes and the actual date of manufacture is irrelevant for maintenance and repair purposes.

As for the aluminium flywheel magnetoes yes, Villiers made them alongside the brass variety. Again, it’s not really relevant detail for maintenance or repair so I take little notice. Of far more interest are the paired numbers on flywheel and backplate to ensure you have a factory pair. Mix’n’match can cause problems here.

I can see the engine numbers stamped across the crankcase halves in one of the photos. This makes it a postwar production. Villiers changed how they identified and numbered their engines in the immediate postwar years.
It’s built to Mark VIC (6C) specifications that had a much smaller carburettor than the later Mk VIIIC and has the reversed inlet manifold of the later industrialised versions. Excellent for the lawnmowers it was built for but not a motorcycle engine and not viable for motorcycle use.
Finally, most postwar Villiers motorcycle engines can be identified as to year of manufacture, what bike it was fitted to and so on but to my knowledge no one has done this with their industrial engines. Perhaps the Lawnmower Club knows more.
Not exciting news I know but these old lawnmower versions turn up with great regularity as old lawnmowers lead very gentle lives compared to their motorcycle brothers.

Not the first time it’s been on flea bay. Much the same ridiculous price as last time.Needs a LOT of work to finish.
But then again, you only have to find one unwary buyer.

Hi again Ralf,
I don’t think it is a Brooklands crankshaft. I can’t see Villiers making a full circle crankshaft in that fashion when they had their own forging shop in house. Forging a full circle crank would make a much sturdier foundation for what they had in mind. Parts 214/219 go down that track. That’s my thoughts anyway.
Your piston is intriguing. I don’t recognise the part number but that’s no surprise, and the 14.22mm gudgeon pin is 9/16”, a fairly common oversize repair on the standard Villiers 1/2” pin. I’ve seen that one on a few old engines.
The 96mm overall height is more or less the standard Super Sport piston dimension while the 46mm compression height is more or less the old plain Sport compression height. Perhaps it is a true Brooklands piston. How frustrating not being able to get original Brooklands data.
Last thing, what is the piston diameter?
I did have thoughts it could be a 196cc Super Sport piston but I think that’s a step too far.
Cheers,

Both my “T” Sports have the standard triangular inlet port as shown on your right cylinder as does the solitary Super Sport cylinder I have.
I’ve always believed this was done to smooth out and quieten the inlet gas flow. That squaring the port as on the L/H one causes a sharp cracking sound and disrupts the gas flow. True or not I can’t bring myself to make any sort of irreversible alteration to an original cylinder so I’ll never know.
Two-stroke technology has advanced so much that no matter what is done to these old three port deflector piston engines they are not remotely competitive so I tune for sweetness and dependability.
Last question. Is the crankshaft plain or drilled for lubrication purposes?

What an interesting engine. As you surmise it’s not ” pure “ Brooklands but something built up with available parts. Nothing wrong with that as long as you understand what you are doing.
It’s easy enough to identify all the various parts, about the only tricky bits are the Brooklands head and piston. It’s not easy to tell them apart from their SuperSport equivalent. The head is not too hard, the obvious difference is the length of the cylinder head bolts. 4” on the Brooklands, 2&5/8” on the Super Sport.
I have no practical information on the pistons. I’ve never seen original factory Brooklands or Super Sports pistons, only aftermarket Super Sport. I have a new aftermarket Super Sport piston to hand but how accurate a replica is it? There is always a whisper of doubt.
It’s easy enough to run through a Villiers parts list to check out the rest. I have the No 22 parts list which is laid out like an Excel spreadsheet so is effortless to see what bits and pieces are interchangeable between what engines. Makes life easy. My copy came from the VMCC Library.
I’m not quite sure why you are concerned about the year of manufacture. As it’s not a factory original does it matter? It would be nice to know its provenance but is it essential?
Cheers,

Thank you for the confirming information and photos.
Further to the advice already given the middle photo seems to show the red wire being crushed with a possible cut through the insulation. Instant failure if it has. It needs to be laid down deep and as close as possible to the back plate. There must be no chance of contact with the rear of the flywheel. I also believe its current location is preventing the flywheel from seating properly hence your problem there.

Villiers also fitted a rubber grommet where the red wire enters the points box so as to eliminate any chance of a short circuit occurring. You now have the additional green condenser wire coming through the same hole. I would think carefully how you could improve the present layout.

The external condenser is an old and successful competition mod. There are a few others I could list if you wish. All aimed purely at improving reliability and dependability.

Finally, wear in the moving points pivot hole causes the ignition timing to wander back and forth. Check yours for wear. Later points boxes are bushed and bushes are available from Villiers Services. Space is tight but if you have the facilities it is possible to rebush the early bronze boxes. Sloppy timing reduces power.

I think the coil is fine, your red wire is the problem.