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
Posts: 18
Joined: Fri May 02, 2014 3:13 pm
Location: London, UK

Re: Atlas Engine, Alternator and other improvements.

Post by Verbatim »

John thank you so much for all this info!
The new flame ring head gasket must be installed WITHOUT GASKET CEMENT.
:) I barely use the stuff anywhere if I can, usually just where the crankcases split.
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.
Unfortunately I've bought something of a basket case G15 CS (actually an N15 but it will be a matchless when I finish) that has been severely plundered! Only thing left of the engine is some crankcases (118), cam shaft and cogs. I have however rebuilt a complete Honda starting from just a frame so I am confident given a few years it can be done, kind of a hobby where I buy bits in at a time and sort them out one by one. It also means you really learn the bike back to front inside out.

I think from everything you've said I can go straight to getting a combat 750 cylinder and head? Is this the same with the crank? I'm not sure a Nourish crank is not overboard for me.

As for camshafts, I will probably want to stick to the Atlas camshaft, I've read the Combat cam shafts are more aggressive leading to the crankshaft flexing, helped by the bearing like you say but I'd like it to be super reliable at the expense of some performance, 50hp is more than enough for me.
User avatar
John Donne
Posts: 303
Joined: Wed Oct 29, 2003 12:00 am
Location: SURREY UK

Re: Atlas Engine, Alternator and other improvements.

Post by John Donne »

The standard Commando barrell is fine, the Combat cylinder head uses 32mm ports, which may be a tad on the large size for you. You can clean up the inlet ports and may be a polish.Nortons get most of their power from their cylinder heads. The camshaft from a combat will not fit the Atlas cases, as the CB's are on the end of the camshaft. Use a billet camshaft and have it Nitrided, or the chilled iron one is perfectly ok. The Dunstal camshafts used needle roller bearings and an oil feed where the Atlas breather is. For the rocker you can have them lightend and polished and use a spacer where the Thackery washer is used.
For piston only use the ones with oil holes and not slots, and the later better oil control rings. Build it right and it should rock totally. The slotted type pistons have been known to part company with their crowns, if reved. The desert racers also added a breather out of the inlet rocker cover. 8-)
User avatar
John Donne
Posts: 303
Joined: Wed Oct 29, 2003 12:00 am
Location: SURREY UK

Re: Atlas Engine, Alternator and other improvements.

Post by John Donne »

RGM Motors and Walridge Motors supply a mushroom tappet adjuster, for the Norton twin engines. This is very good modification to make, when the cylinder head is being overhauled. There can also be used with an alloy lock nut to save weight. 8-)
Verbatim
Posts: 18
Joined: Fri May 02, 2014 3:13 pm
Location: London, UK

Re: Atlas Engine, Alternator and other improvements.

Post by Verbatim »

I meant to reply earlier but I was in Italy and unable to get to a computer for long enough.

So given your suggestions can I condense all that info and see if it makes sense? Also the bits I didn't catch or make sense out of?

Cylinder Head

-Post 1966 Atlas head (if I get an earlier one can it be modified for oil etc.?).
-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.
-Colesbro bronze valve guides, and add valve stem oil seals to the inlet valve guides 062726. (But not on the exhaust side)
-RGM Motors and Walridge Motors mushroom tappet adjusters.
-Commando valves and pushrods with the chrome valve stems
-Head gasket use 063844 or "Flame Ring" head gasket
-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.

Cylinder

-From a 750 Combat

Bottom end/Crankcases

-Post 66 crankcases (as I have earlier ones can the oil feed hole be modified/enlarged, will this need to be done on the head also?)
-Combat type Conrods.
-Combat oil pump or standard atlas pump.
-Pistons with oil holes and not slots, and the later better oil control rings. (Are these also the Combat ones)
-One piece crankshaft made or supplied by Nourish Racing engines (I called them this is quite expensive and overkill for me I may stick to the standard crank in which case dynamic balancing of course).
-Main bearings SKF Superblend or NJ306ETN
-Crankshaft, crack tested, Magnofluxed, and then have it Tuftrided

Other
-Electronic ignition of one sort or another.
-Change the coil bracket 033008 behind the oil tank, and make a much stronger one.

Things I didn't quite understand or missed out:
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
-Is there a bolt on upgraded alternator that can be bought or does a standard one suffice?

Anything else I missed out ;)
User avatar
John Donne
Posts: 303
Joined: Wed Oct 29, 2003 12:00 am
Location: SURREY UK

Re: Atlas Engine, Alternator and other improvements.

Post by John Donne »

The cylinder head that you have written after my suggestions will work out for you. The later Atlas cylinder head has the recess deleted, but the pre 1966 ones still has a recess for the spigot rings. If you can only get an earlier one you can get the spigot ring fillers for the cylinder head. A Commando cylinder head will fit, but the cylinder head has the oil feeds to the rockers on the side by the hatching, and there may also not be provision for the bolt 030424 and the washer 000010. The oil feed to the cylinder head will have to use a Commando one. The Atlas head steady and the G15 head steady is a totally different part. There is also and earlier G15 head steady, and the later reinforced type that is retailed by Norvil under p/n 032284. or headsteady assembled. The Combat head may not work, as listed above, as the Commnado's use a totally different head steady.
Your crankcases if they are stamped 118 then they will have the later enlarged oil holes, so these will not need to be modified. The main bearing are of the Superbleand type and they are availbale at any Norton parts supplier. For the pistons use the standard Commnado 8.9.1 pistons with oil holes and NOT slots. These have the better oil control rings and the slots are bigger and deeper than the Atlas ones. Get the crankshaft Dynamically balanced at 85%, not statically balanced as the dynamically balanced crankshaft is better. You could also weight match the pistons and the conrods if you want to be that particular. Use electronic ignition, or a Brightspark prepared magneto.
The gearbox Superblend bearing is retailed by Norvil, and it is the small one that fits in the main gearbox casting under the large mainshaft bearing that the mainshaft attaches to the gearbox sprocket. Just ask Norvil for one. Use the Lucas RM21 alternator and it will fit into any G15, N15 primary chaincase and get the later welded up rotor, as the earlier rotors can fall apart. You can also use a Boyer power box, or a Postronics unit to get ride of the Zenor diode, and the rectifier. The standard Lucas 6 volt MKZ9E batteries are not availbale any more. Do not be tempted to use to use two six volts in series, but use a single 12 volt battery, as there is one that will fit the G15, N15, battery compartment. It may be a bit of a fiddle to get it in, but you can file the top lip of the battery box to make it fit better.
Get a copy of Paul Dunstals Tuning book, and American published INOA Tec Digest, as this will be a huge help to you. 8-)
User avatar
John Donne
Posts: 303
Joined: Wed Oct 29, 2003 12:00 am
Location: SURREY UK

Re: Atlas Engine, Alternator and other improvements.

Post by John Donne »

The heavy weight twins had an improved lubrication system from engine and frame number 116372.The amount of oil circulating through the engine had been increased considerably because of the following modifications.
1, Larger diameter oil feed. 2, Oil junction block with larger diameter oil passages. 3, Oil feed drilling in the timing side of the crankcase increased to a size of 5/16 inch. 4, Six start oil pump and worm drive, and larger diameter oil feed outlet from the oil pump. 5, Positive feed to the rocker-taken from the blanking plug on the timing cover. Plain rocker spindles used to restrict the oil feed to the rockers.
Each conrod had a 1/16 diameter hole drilled at an angle of 15 degrees piercing the con rod bearing shell, allowing the oil from the journals to centrifuge to both cylinder bores for supplementary lubrication. Con rods with this modification are assembles with the oil holes pointing away from the centre of the crankshaft. A later Commando type spin on oil filter can also be fitted to get better filtered oil. This is a car type oil filter, and it is available as a fitting kit from many suppliers. A magnetic drain plug can also be fitted to the oil tank and gearbox, as retailed by RGM Motors. The earlier copper pipe can fracture, and the later Commando's used a rubber tubing to supply oil to the rockers. This type of rocker feed is also made to fit the Atlas motor.
The later 5/16 head bolts were heat treated and should be torqued to 25 ft lbs. Best of all use the 3/8 Commando bolts and make the modifications to the earlier head and barrel if need be.
With the later oil pump modifications it is very important to use the later oil control rings. The later Commando pistons used a better Apex oil control ring. This was also first used in the De-Haviland Gypsy Queen inverted engines, back in 1962 or so.
The new Atlas or later head is 25359,and the rockers were also changed in the later cylinder heads.
Inlet rocker left 25330, inlet rocker right 25332, exhaust rocker left 25334, exhaust rocker right 25336. The rockers in the later cylinder heads were also changed as previously listed.
Use a Commando oil pump and gears, as this oil pump has the feed gears, and scavange gears the same size. The later Mark 3 Commando's uses bolts to fasten the oil pump to the crankcase, but the earlier models used studs and nuts. Well thats all folks. I should get my own web site 8-)
User avatar
John Donne
Posts: 303
Joined: Wed Oct 29, 2003 12:00 am
Location: SURREY UK

Re: Atlas Engine, Alternator and other improvements.

Post by John Donne »

Another very good editon to the Atlas motor to improve the engines oiling system is to add the Norvil supplied sump drain plug, as this incorporates a magnetic drain plug into the main unit. The Norvil part number is 067221A. 8-)
Verbatim
Posts: 18
Joined: Fri May 02, 2014 3:13 pm
Location: London, UK

Re: Atlas Engine, Alternator and other improvements.

Post by Verbatim »

John thank you, you are an amazing source of info. I'm glad it's all in one place here!
Get a copy of Paul Dunstals Tuning book, and American published INOA Tec Digest, as this will be a huge help to you. 8-)
I will order these soon and look forward to receiving them, (then perhaps I can stop badgering you :D )

Much appreciated!
User avatar
cf160
Posts: 522
Joined: Sun Jul 30, 2006 7:24 am
Location: Ottawa, CANADA
Contact:

Re: Atlas Engine, Alternator and other improvements.

Post by cf160 »

Dear J. Bol:
After reading the instructions from our 17th Century Poet member, I am curious if you have thought about the total cost of the rebuild actions he has suggested? I would love to hear your realistic estimate .
David Potter (cf160)
David J.Potter
Verbatim
Posts: 18
Joined: Fri May 02, 2014 3:13 pm
Location: London, UK

Re: Atlas Engine, Alternator and other improvements.

Post by Verbatim »

cf160 wrote:Dear J. Bol:
After reading the instructions from our 17th Century Poet member, I am curious if you have thought about the total cost of the rebuild actions he has suggested? I would love to hear your realistic estimate .
David Potter (cf160)
I will probably budget £8000 (probably an overestimate tbh) for the whole bike + all the work and that would probably mean not buying a Nourish crank, this will probably include a Suzuki 4ls drum brake also. Other than painting etc. I will probably do all the work myself, I zinc plate at home, other than that all stainless etc. Head work I outsource etc. etc.

I have decided against trying to buy a bike in parts as it is a hell of a lot of work to source parts as I have discovered with the Honda I'm rebuilding, I will be looking to buy a complete one from the states eventually unless I find one in the UK (much cheaper to import anyhow).

I would want to modify the G15, put an older bigger tank on it and lower the front forks to mention a few.

That said I am incredibly tempted to buy a BSA A10 Road rocket instead :D , and much easier to find. Just would love the Atlas powerunit.
Locked