Atlas chain upgrade

I incorporated some easy mods into/onto my Atlas and changed it instantly from a teeth rattling, fuel guzzling embarrassment into a fast, economical and comfortable touring bike, which took me all round Europe for 13 years.

I fitted Commando 8.9 to 1 pistons and reset the timing to 28*. This gave me extra power throughout the rev range. Later I added a Commando head, electronic ignition and the timing went forward again to 30*.

Off came the twin carbs and instead a big 32mm single Concentric was bolted on. Despite the bigger main jet, I gained a 30% improvement in mpg at the same high 65 to 70 mph cruising speed. The bonuses were no balancing carbs every month and loads of smooth bottom end pull.

Next addition was to swop the magneto for an electronic set-up using a twin output coil that sat just behind the headstock. Now I like mags because you are always free from the need for a battery. But.....the trade-off gave me easy timing adjustment, reliable starting, plugs that never had to be cleaned or changed (each year) and a much better ignition advance curve that stopped the engine knocking when accelerating hard.

To complement the above changes, I went for a belt drive with a 2 to 1 engine to clutch sprocket (drum) ratio. Plus I added a Commando 42 tooth rear sprocket. These changes upped the overall gearing and now dropped thepreviousengine revs needed for 70 mph. Well below the bone shaking level required before. The extra poke the engine was now pushing out at lower and medium revs meant that .......never again was there any need to exceed 5000 rpm. Excellent News!!!!

Tha same as you to start with.

Gearbox - 19 Rear - 42

When the rear sprocket wore out, after just 15,000 miles, because it was a cheap copy I went back to a 43 tooth item. But I then raised the gearbox up to 20 tooth/teeth to compensate and keep the chain length the same. This altered the overall ratio slightly but obviously not enough to make a signifcant or noticeable difference. My calculator shows either a 0.011 or 0.024 change compared to a standard 19 & 43 set-up. So a gain or loss of about 1.1 or 2.4 around 100mph. I don't think I lost any sleep over it.

Previously gary_currier wrote:

What gearbox sprocket did you use ? At the moment I have 19 tooth with a 42 tooth rear.

gary

Previously phil_hannam wrote:

I incorporated some easy mods into/onto my Atlas and changed it instantly from a teeth rattling, fuel guzzling embarrassment into a fast, economical and comfortable touring bike, which took me all round Europe for 13 years.

I fitted Commando 8.9 to 1 pistons and reset the timing to 28*. This gave me extra power throughout the rev range. Later I added a Commando head, electronic ignition and the timing went forward again to 30*.

Off came the twin carbs and instead a big 32mm single Concentric was bolted on. Despite the bigger main jet, I gained a 30% improvement in mpg at the same high 65 to 70 mph cruising speed. The bonuses were no balancing carbs every month and loads of smooth bottom end pull.

Next addition was to swop the magneto for an electronic set-up using a twin output coil that sat just behind the headstock. Now I like mags because you are always free from the need for a battery. But.....the trade-off gave me easy timing adjustment, reliable starting, plugs that never had to be cleaned or changed (each year) and a much better ignition advance curve that stopped the engine knocking when accelerating hard.

To complement the above changes, I went for a belt drive with a 2 to 1 engine to clutch sprocket (drum) ratio. Plus I added a Commando 42 tooth rear sprocket. These changes upped the overall gearing and now dropped thepreviousengine revs needed for 70 mph. Well below the bone shaking level required before. The extra poke the engine was now pushing out at lower and medium revs meant that .......never again was there any need to exceed 5000 rpm. Excellent News!!!!

Hi Phil

In the process of rebuilding an Atlas and want to change to a belt drive - please advise what make and model you fitted - what about clutch also looking for a decent after market unit

Going to go for a Trispark Electronic ignition when I get to that stage

Also looking for exploded spares part drawings etc - basically have a basket case with hundreds of bits and pieces

cheetrs Tony_maple

Did you consider this combined generator electronic ignition unit - thinking of going this way on my own belt-drive Dommie. (I get to lose the distributor, coil, alternator and battery) 50W should be plenty with a led rear lamp, but at how many rpm? Maybe a tiny gel battery would help.

Advising people as to which Belt Drive Conversion to go for is not easy. I like the idea of the Norvil kit because it uses lots of standard Commando chunks and is now easy to fit. It was also one of the cheapest on the market. Other owners have promoted the RGM conversion as good value for the money. Tony Hayward's gear is very popular. The Bob Newby and some American kits are excellent but tend to hit the wallet hard. Mick Hemmings and Norman White are both worth talking to. Try and talk to other owners who have done the deed!!!

The Electrex generators are brilliant if you are into daytime running only. My own Atlas really needed 100 watts to cope with Continental touring. Remember, at cruising and town speeds, you are not getting the full Monty from any generator. 80% of power output at best.

Ride with a 55W headlight plus 25W of other running/stopping lights and you are draining the battery in stop go traffic. Throw in some coils (30 to 40W) and you are on a hiding to nothing if you are sensibly running with lights blazing.

Phil - I was assuming that as this is a development of a spark only kit that the sparkical part was entirely separate from the 50W dc output, leaving virtually 80% x 50W for the headlight - if you use a led rear light. Do you know if that is the case or not? They could certainly be an expensive mistake if the 50W has to supply everything.

The attached schematic suggests that the power output is indeed separate, but the bad news is that you only get 50W a/c (not great for leds, don't imagine that horns will like that too much either), less than 50W with the losses of a dc regulator - maybe 45W?

50W ac will not be enough for powering your headlight. Do you want a daytime only restriction? On grounds of safety, I do almost all my riding with the headlight on. From a car, an unlit motorcycle can be hard to see, and bear in mind the large number of elderly drivers out there whose eyesight isn't what it once was. You have been warned!

Previously phil_hannam wrote:

Thanks Phil will keep looking around a long way off until get to this stage

Tony

Advising people as to which Belt Drive Conversion to go for is not easy. I like the idea of the Norvil kit because it uses lots of standard Commando chunks and is now easy to fit. It was also one of the cheapest on the market. Other owners have promoted the RGM conversion as good value for the money. Tony Hayward's gear is very popular. The Bob Newby and some American kits are excellent but tend to hit the wallet hard. Mick Hemmings and Norman White are both worth talking to. Try and talk to other owners who have done the deed!!!

The Electrex generators are brilliant if you are into daytime running only. My own Atlas really needed 100 watts to cope with Continental touring. Remember, at cruising and town speeds, you are not getting the full Monty from any generator. 80% of power output at best.

Ride with a 55W headlight plus 25W of other running/stopping lights and you are draining the battery in stop go traffic. Throw in some coils (30 to 40W) and you are on a hiding to nothing if you are sensibly running with lights blazing.