New member, 1959 G12 questions!

[Whiskey98]

Hi everyone, I'm Peter, 24 years old and have finally decided to take the plunge into the world of vintage motorcycles to go with my love of vintage cars. Chose to swear allegiance to AMC motorcycles, much to my grandads annoyance who's more of a Triumph/Scott man!

I've owned an oily rag 1958 AJS Model 16 since June and it's been a joy, it even got me from Portsmouth to Leeds via Central London and the A1 without any snags whatsoever, wonderful bike.

Now as a long term project I've bought a 1959 Matchless G12 alternator model. Came with loads of bits in boxes but the bike is more or less complete, wiring needs sorting, there's no rear chain and the front forks are in situ but need a complete rebuild. I feel like this motorcycle was a half finished project when I bought it, the fuel tank is immaculate but then there's other bits that needs a fair bit of attention. My original plan was to fix it up and use it but now I'm leaning more towards a full restoration, I'm wanting polished chrome work, tinware repainted to the same standard as the fuel tank, and fully gone over mechanicals. The fella I bought it off said he tested compression and it was good, when I tried to turn it over with the kickstart the engine feels very dry, especially the contact between the cylinder and piston rings so I'm refraining from turning it over any more.

I'm also wanting to subtlety update the motorcycle, my plan is as follows
> Full restoration of the motorcycle
> 12v electrics
> Valve below oil tank outlet to avoid wet sumping, with a valve position switch to prevent starting with it shut
> Late 50s/Early 60s style clubman handlebars
> Taper roller steering head bearings
> Possibility of upgrading to 8.5:1 CSR pistons, and CSR carburettor jets

Someone has fitted a Siamese exhaust at some point which I'm not a big fan of so I'll be reverting back to an exhaust either side, possibly with megaphone silencers, and the Siamese exhaust will be appearing on the second hand market.

I'll probably have lots of questions about this motorcycle as I begin to restore it but here's a few I have now:

-The crankshaft: from what I understand, the 1959 crankshafts were basically made from plasticine and snapped if it heard you talking about it funny, and in 1960 they went to much better nodular iron shafts. If it came to it and I fancied one from the spares scheme, it says that the alternator crankshaft is suitable for models 1960 onwards. Would this fit a 1959 model or if not, what would be my options?

-Pistons: As I said earlier, I wouldn't mind upgrading the pistons to provide a 8.5:1 compression. What would your opinions be on this? I have heard someone say that new pistons are problematic on these engines and to go for NOS Hepolite ones when possible, is this true? There are plenty of listings on ebay for NOS 1959 650 pistons made by Hepolite and Mondial but no way of differentiating which ones are the high compression pistons and which ones are low, does anybody have any pictures of a CSR piston and a regular piston?

Many thanks
Peter

[SPRIDDLER]

Welcome, Peter.
I know nothing about twins (I'm a singles only fan) so won't attempt any wise words but if you haven't already found it there's masses of info and original factory manuals under 'Books' in the link below:

http://archives.jampot.dk/

On the same website look under 'Technical' then choose 'Pistons Rings Valves' where there are several articles on pistons.

One of those articles (link below) has piston illustrations and dims:

http://archives.jampot.dk/technical/Pis ... istons.pdf

Be cautious with adverts for NOS Hepolite pistons on auction sites. The Hepolite name is now owned by the motorbike spares company Wassell who have Hepolite branded pistons made for them and which are marketed in the original Hepolite design packaging.

[Mollbhan]

A 1959 G12 is an old bike, in bog standard form they have a very flexible engine, can happily go from 20mph to 80mph and probably beyond in top gear, I cruise mine at 55 to 60 which it seems happiest at. If the crankshaft has stayed good for 60 years it should be good for a few more given sensible riding , why do you want to tune it ? A modern bike would be faster,safer, more reliable and definitely stop quicker if you want speed.

[Whiskey98]

Hi Mollbhan, I guess I just want a performance period motorcycle so I can experience the ton up days for myself! That doesn't mean I'll be riding it at the limit constantly, far from it but I certainly wouldn't mind being a bit brisk with it on a summer weekend. It's true what they say about modern bikes but what they have in speed and reliability, they lack in character. As for the crankshaft, I always think prevention is better than cure, the last thing I want would be a broken crankshaft and bent valves 50 miles from home haha, I'm also unsure on the history of the motorcycle, for all I know it could have been off the road since the mid 60s

All the best
Peter

[Groily]

Ref your list of upgrades, I don't think anyone would argue about going 12v - makes a lot of sense, easier bulbs, batteries , good regulating options etc - although the advent of LEDs has made it possible to get semi-decent illuminations (depending on exact configuration) and low current consumption at 6v too.

An oil tap is one of those questions that get people going. I like them and use them, but the risk of the obvious is there unless a foolproof ignition cut-out or mag-killer is incorporated. They do get round the hassle of overfull crankcases after a spell in the shed.

Exhausts are a matter of personal preference I guess. I like siamesed pipes for easy access to the primary side if necessary, but don't like their tendency to rust at the splice over time. The period megas look and sound good I think, but my 2 twins are Ajays so don't have.

On the pistons, I've been running 8.5 JPs for 20,000 miles on my own 650, with no problems. Plenty of negative comment to be found about them, but if the cylinders are bored with skirt clearance to suit (mine were done by T&L Engineering in Beds, see ads in Jampot) I reckon they're fine. Fitted mine 9 years ago and have been happy, as in 'nothing to report' and haven't lifted the barrels in that time.

On the crank, not sure either if there is any reason why a new alternator one won't go in a '59 alternator motor. But someone who's more familiar with the early generation 650 will know if there is 'something' that causes a problem. My '61 dynamo model has a Club crank dynamically balanced with Thunder rods, and is about as unbreakable as these things can be I'd say.

A large part of what you do may come down to how much you feel like investing. Crank, rods, pistons etc, plus whatever might also benefit from being replaced (and there'll be 'stuff') can rapidly mount up to a high proportion of the value of the machine, and wouldn't be recoupable upon subsequent sale. I know that doesn't bother a lot of us who aren't in it with those things in mind, but . . .

I run very regularly with a fellow-owner with a very pretty '59 G12. It goes extremely well, he's happy to cruise it at 65ish on standard gearing and the acceleration isn't far off mine. (He's a lot lighter than I am, I suppose I should add!).
I also used to run regularly with a member who had a CSR, which represents the other end of the scale with the 650s. Yes, it was quicker and better-looking - but a significant enough difference to encourage expensive upgrades to a standard motor? I'm not sure.

On typical single-carriage-way roads, it's torque and flexibility I look for most, with relaxed cruising at around the 60-65mph mark where the roads allow. You can do a fair bit with the gearing to get to 'comfortable' for your own riding style and usage of the beast. For me, that has meant - after experiments in over-gearing - a 21T sprocket on the crank and a 19 on the AMC box. (23T and 16 or 17 was - I think - standard). Suitable gearing can be more useful than sheer power in terms of getting from A to B quickly on minor roads IMHO.

And whatever you do or don't do, the G12 will make the M16 feel very pedestrian!