Atlas Engine, Alternator and other improvements.

Information relating to the Matchless G15 or AJS Model 33 750cc twin. This also includes the G15 Mk II and the G15/45
Verbatim
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Atlas Engine, Alternator and other improvements.

Post by Verbatim »

I've been thinking about completely restoring a G15 CS (I'll refer to the engine as the Atlas engine), and I've been thinking about many aspects of the Atlas engine that I'd like to factor in when purchasing a project, apologies in advance I have several queries.

So, given the Atlas engine has an alternator, is it possible (and at all a good idea) to ditch the magneto setup in favour of a powerful alternator setup to run the whole bike from? I can already foresee a few advantages in this such as electronic ignition. Are there any substantial changes to the Atlas engine between it's inception and it's redudancy on the market and are there any modern improvements that can be retrofitted to the Atlas engine such as an improved oil pump?

My next query is the availability of replacement parts for the Atlas engine in the UK, let's say I bought a blown up engine or one in bits and decided to gut out most of it in favour of new parts and started with just the crank, cases, cylinders and head (with a only af few things like rockers etc.). Is it possible to source from new for example conrods, lightweight pistons, pushrods, valves, valve springs, bronze guides etc. as well as timing pinions/sprockets, cam chains etc.? Imagine if I wanted to completely renew all the parts inside.

Any pointers appreciated!
g80csp11
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Re: Atlas Engine, Alternator and other improvements.

Post by g80csp11 »

The Atlas engine when fitted to the P11 had alternator, most parts are available from Andover Norton
BillTS3
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Re: Atlas Engine, Alternator and other improvements.

Post by BillTS3 »

From about serial number 12100 (mid-year 1967) Norton switched from magneto to points-and-coil ignition with alternator. The late Atlas, G15/N15/33, P11 and early Commandos all used the same engine, with the exception that rocker oiling tapped into the head differently on the Commando. After about serial 131000 (mid-year 1969), Norton moved the distributor to the timing cover. Otherwise, no significant changes until the Combat of 1972.

Alternators are available from Andover Norton, Wassell and Emgo, among others
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Re: Atlas Engine, Alternator and other improvements.

Post by Groily »

Worth having a look at the Norvil catalogue for parts - they seem to have many things you might want, some of them at a price.
If you're going to go for new rods and pistons, it would be well worth getting the crank dynamically balanced - after all, these weren't the smoothest engines in the world right from the off.
On the alternator, probably best to go for a 200W job and a decent regulator/rectifier (Podtronics, A Reg 1 from Paul Goff, etc) if you're replacing those parts (and ditching the magneto).
Cheers, Bill
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John Donne
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Re: Atlas Engine, Alternator and other improvements.

Post by John Donne »

All Atlas's or G15, N15, 33 engines had alternator electrics or 12 volts with two Lucas MKZ9E batteries. The first Atlas Scrambler or G15CS, stamped engine, 107388 dispatched in October 1963 had 12 volt electrics. There is allot of electronic ignition conversion on the market, and there is also a complete kit of parts that can easily be used in place of the magneto. BTH have also made a replacement for the ageing Lucas K2F magneto. Get Brightspark to do a magneto for you, and your ignition problems will be solved. For any engine up grades, the oil pump is perfectly adequate, but you can also buy the later Commando one with the same size feed and return gears. Get the Paul Dunstal tuning book, as this has allot of upgrades that can be used on the Atlas engine. The magneto was dropped at engine and frame number 121007 or March 1967, the first P11. The valve gear ratio was changed at 125871 or about 1967. This used longer valves and shorter push rods. The change of ration gave another 1 to 2 bhp power increase. Use Commando valves and pushrods with the chrome valve stems. Use the later oil modifications. Six start oil pump gears, oil holes in the conrods, better oil control pistion rings, larger oil feed holes in the crankcases, and the change to smooth rocker arm spindles. All thses modifications were incorporated into the later Commando engines. Do not under any circumstances use the first Atlas issued conrods,as these can break. Used the later or Commando type. If you are worried about these, get them polished and shot peened as this is all the factory did when they raced this engine, or go and buy Corrello steel rods from America. RGM Motors do allot of engine upgrades, and there is also Steve Maney. His web site is www.stevemaney.com If you have the money he can build you a bullet proof engine, and he provides all engine component upgrades. There is also Mick Hemmings who is very well know for racing and building all Norton twin engines. If you want to keep the Atlas from so called blowing up, then be very conservative, in how you build it. I have being using Atlas engines since 1970, and the only thing that i have had happen was a cracked pistion on one of my original 7.6:1 pistions. Use the later Commando head gasket with the flame ring, and get the crankshaft dynamically balanced. Change the oil regularly, and use SAE 50 grade oil, add a spin on oil filter kit to it.You can also use the later Commando barrels as the 750 ones were heat treated and were much stronger than the earlier type. -)
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John Donne
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Re: Atlas Engine, Alternator and other improvements.

Post by John Donne »

The Atlas engine used in the G15, N15, 33, and the P11 series, was modified on the drive side, to take the AMC type alloy primary chaincases. This means the drive side crankcase's were machined differently to the standard Atlas drive side crankcases. There was also a large spacer that was used between the crankcases and the inner primary chaincase. This means the standard featherbed Atlas engine will not fit with the alloy primary chaincase into the AMC duplex frame. The G15 Atlas engine has three holes, and the featherbed one has six holes. Also the duplex frame used for the G15, was not the same as the G12 frame as the front engine mountings are different. 8-)
Verbatim
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Re: Atlas Engine, Alternator and other improvements.

Post by Verbatim »

All of you and especially John, wonderful knowledge I really appreciate this!
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Re: Atlas Engine, Alternator and other improvements.

Post by Verbatim »

Excuse my ignorance in advance I am totally new to these engines, John could I elaborate on the points you've made? I would like to do as much as possible myself, obviously things like crank balancing which I will certainly want to do I will have to outsource.
If you want to keep the Atlas from so called blowing up, then be very conservative, in how you build it.
Get the Paul Dunstal tuning book, as this has allot of upgrades that can be used on the Atlas engine.
Yes I would like to do a very conservative bulletproof build, the upgrades I'd want to do would be for the sake of reliability primarily, I don't need to squeeze out any extra power from the already stressed and overpowered unit! Does Dunstalls book cover this or is it (as I imagine) primarily concerned with racing and performance tuning (at the expense of reliability)?
This means the drive side crankcase's were machined differently to the standard Atlas drive side crankcases. There was also a large spacer that was used between the crankcases and the inner primary chaincase. This means the standard featherbed Atlas engine will not fit with the alloy primary chaincase into the AMC duplex frame.
The G15 Atlas engine has three holes, and the featherbed one has six holes.
So I understand that the G15 crankcases will probably fit the earlier G12 primary chaincase? And that the Atlas crankcases were probably modified to fit them?
Get Brightspark to do a magneto for you, and your ignition problems will be solved.
Unless I'm mistaken for the sake of reliability I'd prefer to go to a strong Alternator setup without the mag. What did they do later with the former Mag placement on the engine, did they just block off the port/hole to the crankcase? I'd also like to go to an electronic ignition.
For any engine up grades, the oil pump is perfectly adequate, but you can also buy the later Commando one with the same size feed and return gears.
I would want to do this, so the Commando one would be an upgrade right? And thats from a 750 combat?
This used longer valves and shorter push rods. The change of ration gave another 1 to 2 bhp power increase. Use Commando valves and pushrods with the chrome valve stems.
This all bolts on over from the Commando to the Atlas/G15 engine? Would it stress the engine more, if so I may stick to the older valves, I was thinking about bronze valve guides as well.
Use the later oil modifications. Six start oil pump gears, oil holes in the conrods, better oil control pistion rings, larger oil feed holes in the crankcases, and the change to smooth rocker arm spindles.
I didn't quite understand this part, the six start oil pump gears (what/where is this?), oil holes in the conrods (is this a mod or stock on the commando/combat conrods), piston rings, larger oil feed holes (is this a modification to the crankcases or again something that came in the later Atlas/G15 cases) and the change to smooth rocker arm spindles (again is this a later upgrade on the commando/combat engines or a case of an aftermarket upgrade or polishing etc.).

Is it a case of sourcing all these parts for a commando/combat engine and retrofitting them to the atlas head / crankcase etc.
Do not under any circumstances use the first Atlas issued conrods,as these can break. Used the later or Commando type. If you are worried about these, get them polished and shot peened as this is all the factory did when they raced this engine, or go and buy Corrello steel rods from America.
Use the later Commando head gasket with the flame ring, and get the crankshaft dynamically balanced. Change the oil regularly, and use SAE 50 grade oil, add a spin on oil filter kit to it.You can also use the later Commando barrels as the 750 ones were heat treated and were much stronger than the earlier type. -)
So from what you've said a lot of the original Atlas engine can be swapped out/discarded. If I read you correctly, I can use the cylinders from a 750 combat and they are identical in appearance and fit, just materially superior? The crank, is this also interchangeable from a Combat in which case I should use a Combat 750 crank and conrods and lightweight pistons (any idea from where?). Internal head parts such as rockers, valves, rods can be swapped over from a 750 combat?

Lastly the G15 gearbox, clutch basket etc, was this originally directly sourced from a G12 and if so can it bolt over from a G12 onto the G15, likewise are there any upgrades to the gearbox that can be done? Anyone tried a 5th gear or is this wishful thinking? :)

Slighly off topic, it's the G15 I'd like to build and lightly modify, one thing I'd like to do is to drop the front a few inches as it'll be primarily for road use and the bike is quite tall, has anyone tried this is this a good idea at all? I imagine it would reduce rake and increase the flickability (and instability) of the bike. Are the original G12 teledraulics shorter than the long roadholders used on the G15 CS?
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John Donne
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Re: Atlas Engine, Alternator and other improvements.

Post by John Donne »

If you want to improve the Atlas engine use all the later or post 1966 modifications. Do not use the spigoted barrels as they will leak oil. Get the spigot machined off, and add the spigot ring fillers to the cylinder head.The part number is 25494, these fill the spigot recess in the cylinder head. Change the four head bolts by the spark plugs to 3/8 and get rid of those 5/16 head bolts, with the correct washers.The barrel and the cylinder head will have to be modified to do this. All the Commando barrels have this modification done. Use the Commando cylinder 061705, as this was modified for the use of high performance camshafts. These replaced 060396A.The 3/8 cylinder bolts are torqued to 30 ft lbs, and the 5/16 bolts are torqued to 20 ft lbs. Use Colesbro bronze valve guides, and add valve stem oil seals to the inlet valve guides 062726. Do not put them on the exhaust valves as the valves will stick in the guides. Make sure the inlet valve guides are machined for the oil seals.
For the crankshaft, get it crack tested, Magnofluxed, and then have it Tuftrided. The crankshaft can then be polished all over, to stress relieve it.
You can also get a one piece crankshaft made or supplied by Norish Racing engines. For the main bearings use the SKF Superblend or NJ306ETN, these have a barrel roller on them, so that the crankshaft can flex. These are supplied by all Norton retail outlets. All Norton twins can use these bearings. You may also need a spacer for the end float. SKF NJ306 or NJ306E, FAG NJ306, NTM NJ306 Hoffman R306L, RHP NF306, are the different makers of thedse bearings.The new bearings are 2 dot single lip roller bearings, and should be assembled with the lip into the crankcase in both cases.Main bearing part number is 063114.Used on all Norton twins from October 1971. The designed crankshaft fitted end float for the new arrangement is 0.010in to 0.024in. (0.254mm to 0.609mm)
For the head gasket use 063844 or the "Flame Ring" head gasket, as this replaced 064071.When installing the flame ring head gasket, both head and barrel must be thoroughlly cleaned with lacquer thinner or a similar cleaner. to remove all the grrease and oil. The new flame ring head gasket must be installed WITHOUT GASKET CEMENT. Issued by Norton in March 1974. Smooth out the inlet side of the cylinder head where the valve guides are so that the oil can flow much faster down the oil return to the crankcases. 8-)
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John Donne
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Re: Atlas Engine, Alternator and other improvements.

Post by John Donne »

If you are going to get a G15CS, N15CS or a later G15CSR, get one that has an engine and frame numbers from 123 onwards. This will have the later Lucas RM21 alternator, coil ignition, and the 930 Amal Concentrics. It will also have the later oil system modifications, with the pressure feed to the rockers, and the larger crankcase oil feeds. It will also have the LUCAS 54418910 A/R unit, with the Lucas 4CA CB assembly. This self destructed after about 1500 to 2000 miles, but it gave amazing accelleration.The later 54425657 A/R unit is the best of the three (54419340)that were used. from 1967 to 1968. The later two have a datam point so the CB gaps could be set more easily. This can be very easily converted to a Boyer, Pazon, or any other electronic ignition, as the ignition mushroom was a standard Lucas issue part. There are three types of these mushrooms. One had two plain bushes, one had one bush and needle roller bearings, and one had two needle roller bearings for the A/R units drive shaft. The coils will have to be changed from 12 volt to 6 volt for more voltage for the ignition. Change the coil bracket 033008 behind the oil tank, and make a much stronger one as the original will fall apart, and drop into the road, as it breaks into about six or more pieces. The Zenor diode charging system can be changed to a Boyer Powe Box, or a Petronix box, so the Zenor diode, can be replaced by an electronic control. Hence the no need for a Zenor diode heat sink.
The G15 engine does not use a G12 chaincase, but one made for the G15 models, that was adapted from the G12. The later models also had an added stud to stop the chaincase moving around. Buy a complete bike, as putting one together from parts is fraught with allot of difficulties.
Change the gearbox's small bearing in the main gearbox housing, for the layshaft to a roller bearing, or a superblend one as Norvil calls it. Change the G15CS gearbox sprocket from 17 teeth to 19 or 20 teeth. The engine sprocket can be change to the G15CSR of 22 from the G15CS one of 21. 8-)
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