G12 with a mystery motor

[robcurrie]

Have you removed any pieces of cloth that might have been put in the ports for protection?

Rob C

[bob]

The lack of engine number is most likely that the crankcases are from spares dept. parts . Probably the engine thru a rod or similar and it was rebuilt using new crankcases . Hence no numbers .

Your seizure , Your going to have to start at one end and work your way thru .
Take off the primary case ,
You will know when removing it if the alternator has fused together .
If thats OK , then remove primary chain , and try to turn bare crank . .
Keep breaking the investigation into small component parts and work thru the system ,
Engine only has crank , magneto and valve gear to operate ,
Then onto primary side , its unlikely to be clutch , so move to bare gearbox ,
lastly Rear wheel .
Theres nothing left after that .
Its got to be somewhere along that route .

[Papulski2]

Hi and thanks for everyone's help.
The explanation for no serial # makes total sense.

Today I connected the clutch cable. I found that when in gear and depress clutch the rear tire won't turn so that's not good.

Removed the primary case. That came off easy. Removed primary chain. The primary chain was tight, I mean TIGHT! Not sure how tight it should be but I couldn't get it back on. The good news is the engine turned by using wrench on crankshaft nut. A little hard but wasn't stuck, got easier as I moved it back and forth. When in neutral the clutch turns freely. When in gear and depress clutch the kickstart will go down once then lock up. Depressing clutch causes the clutch plates to loosen which I believe is correct. Could a tight primary chain have caused my problem?

The sprocket on crankshaft has 21 teeth and on clutch has 42 teeth. The primary chain measured 33 1/2 inches.

Looks like my next move is to figure out if something's wrong with gearbox.

Anyone have a schematic using a 2 wire alternator? It is Lucas. There's a # on the rotor....54212006. Also 5 71

[Mick D]

Hi

That's progress

The primary chain should have had 3/8" play in it - a tight chain will make the gearbox and engine harder to rotate however as you say that with the clutch disengaged and the bike in gear you can't turn the rear wheel then you have a problem with the gearbox.

Check that the over tightened primary hasn't bent the main shaft which is now causing the clutch basket to foul the inner primary case.

I'm surprised that the kick start moves when in gear with the clutch disengaged but the rear wheel doesn't.

You're going to have to bite the bullet and strip the gearbox, they're a very simple design and there's plenty of info online, take loads of photos as you disassemble it, that way if you don't diagnose the issue someone on here may be able to from a photo.

I'd be looking for a broken gear tooth or damage to the main or lay shafts, particularly a bent main shaft if the primary chain was that tight.

Regards Mick

[ajscomboman]

The 21 tooth sprocket is sidecar gearing, will leave the lights like a scalded cat but will vibe like buggery at about 55-60. Try to find a 23 or 24 tooth engine sprocket. A very tight primary chain and I mean bow like, will pull the g/box mainshaft against the sleeve gear and make it tight to turn over. As for the kickstarter jamming that could be a worn pawl. All simple fixes compared to a frozen motor, so it's a bonus.

[Groily]

Agree totally with ajscomboman on this.
Or - maybe? - you could up the gearbox sprocket to say 19? I say that because I am in fact running a 21 up front, with a 19 on the 'box on my '61 Mod 31.
It's quite a decent overall ratio but does require a 67 link primary chain. Rear chain is a 98 and a new one I just fitted, along with a new drum/sprocket and all three bearings, goes on just nicely at close to minimum adjustment with a new primary chain on too (which is what you want ideally).
Original gearing would I think (but happy to be put right if it's wrong) have been 23-42(clutch)-16 g'box (or 17 on CSR) - 42 rear sprocket. The 42s you can't easily play with, but there are loads of options on the simple sprockets, especially for the gearbox.
What I would say from experience though is that a 24 on the crank with anything more than 17 max on the rear is too high (for this heavy bloke when going uphills into the wind, anyway!)

Doesn't sound as if there is too much to panic about there - and it looks a very handsome beast to me, a nice addition to any shed. Congrats!

You raised a question about the lack of battery earlier, which hasn't been picked up on yet . . .
The electrics might actually be fine, as you don't HAVE to have a battery in circuit for the lights to work. They'll flicker at low rpm, and only work when the engine's running, but things might indeed be better than initial thoughts suggested.
If you have an alternator with 2 wires off - and you can check that for sure with the primary cover off now - then I'm guessing it is running at 12v, or there is a 6v regulator/rectifier fitted somewhere, instead of the original simple rectifier. Or maybe there is a capacitor somewhere, which was a way round fitting a battery on some competition bikes. This says that the wiring you have got might not conform to anything in the Archives, but I wouldn't worry, because with the magneto for the sparks, the basic charging side of an alternator system can be done very simply. It may indeed have been done - you'll only know when you're further in to the process and can identify what parts are fitted. Plenty of folk here to help on that, especially if you carry on posting good pix!

[ajscomboman]

I have to admit Bill, 19 g/box did cross my mind but not tried the option so shy'd away from suggesting it. I think that it'd be the easiest and cheapest way to go to raise the gearing though.

24 engine and 17 g/box is ok on a bike running 10.25 :1 pistons but a bit too tall for lower comp pistons. It's the combination I'm running on the CSR but I've done away with the twin carbs and gone back to a single carb. This has made the bike so much better lower down the rev range and it's actually a nicer bike to ride now. Doesn't look quite as sporty but the way it now rides and pulls low down, I can live with the trade off.

[Papulski2]

thumbnail_IMAG2213.jpg

[Papulski2]

thumbnail_IMAG2219.jpg

Removed the spring cups and pressure plate. Removed friction plates. Removed nut and washer on shaft. I can't get this last part off. It's loose but is hung up on something. Any ideas what I'm doing wrong?

[Mick D]

Hi

The clutch centre may be stiff on the main shaft spline or there may be burrs there - either way an extractor will sort it:

http://www.amoc-parts.com/store/comersu ... duct=21783

Regards Mick