Must-do Mods for Atlas Motor

The Atlas can be a bit noisy ( piston slap , timing chain, valve gear ) , a bit oily , (wet sumping, oil burning , head leaks,  bad breathing) and vibratory (not well balanced , too heavy Commando pistons) ,Heavy to operate on its limit clutch , Could use a 5th gear overdrive ,not a close ratio box , that no one seems to make. Any thing to improve these areas and not make worse !. 

Richard.....as below may be of help.  This is an extract from a forthcoming Roadholder article dealing with the Norton Atlas. However much of the contents could apply to other models.

Tuning for speed and/or reliability;

Thanks to its successor, the Commando, having many common or easily fitted parts, the Atlas engine can be turned into a track racer or very reliable touring bike. The concern of an engine that shakes both the rider and bike to bits can be solved with a number of sensible modifications. Some of these allowing the bike to keep its original factory look.

First - head down the electronic ignition road and banish the dodgy points and advance / retard issues forever. Some of these magical Ignition kits can even be hidden inside a magneto casing or replace the alternator inside the primary cases. The difference will be easier starting, smoother idling and acceleration. Plus less vibration and better fuel consumption.

Second – get the crankshaft rebalanced. This can make a huge difference to an engine with regards to its vibration. John Hudson suggested a dry crank balance factor of 84%.

Third – change the pistons for the higher compression 8.9 to 1 Commando versions. Do not to forget to reset the ignition timing to 28*. At the same time fit a Commando 750 head. You may have to consider cylinder spigots and head bolt diameters, but this mod will add another 5 or more BHP to the motor throughout the whole of the rev range. Using a Commando or later Atlas barrel will avoid any spigot or head bolt issues.

Fourth – fit a single carb set-up. There is a choice of makes and sizes. All should improve the engine running and fuel consumption. Go for a 32mm or 34mm choke. It does not seem to matter if there is a small step in the manifold to carb joint. Apparently it helps the fuel mix with the air better.

Fifth – up the gearing. Go for a 22 tooth engine or a 20 tooth gearbox sprocket.

If all of the first five modifications are completed then, this should allow the bike to cruise at 70 mph at around 4,400 rpm. Which is well below the normal teeth rattling and finger blanching vibration point. (usually 5,000rpm)

Sixth – change the primary chain for a belt-drive conversion. This will smooth out the primary drive, end any worries about chaincase oil leaks (unless your crankshaft seal has failed) and make the clutch action much lighter. Thus preventing the very common Atlas broken clutch cable syndrome from doing its worst.

Seventh – this is optional. Dump the old Lucas rectifier and Zener diode electrical chunks, if they are still fitted. Go for a 12 volt system with an electronic regulator, which will do both jobs and be ultra reliable for the same cost as replacing the Joseph Lucas bits. At the same time spend £50 on LED bulbs for the whole bike and enjoy a battery that will stay charged from then on. You can use a Motobatt, MBTZ75, which has 6.5 Ah capacity.

There is a degree of 'rubbish' in the above.

1 Replace the alternator. It doesn't say what with or how. Replacing the alternator with another alternator will do NOTHING for starting or anything, useful except if broken, replacing it with a working will restore battery charging. There is a thought that some alternators can include electronic ignition.

7,Dumping the Zener/rectifier and substituting the reg/rect will NOT improve reliability or battery charging. The zener has been with us 70 yrs and is still very viable. Although it could do with checking properly after this time (I can do this) The reg/rects are NOT reliable yet. The fitting of a reg/rect might allow better voltage stability for LED lights though.

The Motobatt is a good way to go but get as many AHR in the battery as you can, 9 or even 11Ahr?

I rebuilt my Atlas engine last year, & as with my other Norton twins, fitted a reed valve breather to the rear of the crankcase. The same position as the '72 Commandos. This along with having the crank dynamically balanced are the best mods you can do, if you intend riding the bike hard. 

If you want an even smoother engine fit a pair of JS super light long rods & pistons. 

Going for  single carb and one of Al's voltage control black boxes would be eminently sensible - that's exactly what I have done.

However, I wouldn't do any of the other recommended actions. The standard as-left-the-factory crank gives a pretty smooth ride. The standard primary chain and gearing work fine for me. I only have Commando pistons as I couldn't get dished Altas ones - however since then I have managed to find a pair for when my hips get dodgy. I do love a decently overhauled magneto. The engine keeps going when the lights go dim.

The bike will sit on the Motorway in comfort at an indicated 80 mph or potter around country lanes at 30. Good enough for me.