Atlas barrel interchangeability

Previously wrote:

Hi, My memory is hazy on what fits what, as I have not had a Norton for 40 years, and am trying to build an Atlas out of what I can find, hopefully before the Grim Reaper gets me first. The Frame is 1967, crankcases 1967, barrels possibly. What is the height of the barrel flange to head? Is it the same on spigot barrels? I have barrels at plus 0.040, but not sure whether plus 0.060 is safe, and looks very thin around the base neck for sleeving. The other problem is matching a head to barrel. I have a later 25319 head that needs welding and flatting, also an early 23166 head that is good, but would need an insert ring. How does one fit the ring, if available? Lots of small bits missing, and seems difficult to find everything. I cannot believe the prices paid these days for old bikes. I bought four in 1971 for £10, and an aquaintance bought four Vincents in 1971 for £10. Will the Combat camshaft and followers fit in the Atlas OK, and go with commando pistons, as Atlas ones seem extinct? Any help much appreciated, chaps. Best regards, Paul

Hello Yes I can remember buying a BSA RGS for 25 quid back then , well your seam to be in a bit of pickle well 1967 barrel had No spigot on them they were machined off by then so this solves that problem the best thing is to go to Standard by the way of new sleeve , and if you fit commando pistons then you need to get the crankshaft balanced right . or the hole bike will shake its self to bits , balancing the crank is money well spent you need the rods and piston and crank all balancing up. the combat cam will fit but it may need some mods doing .if were me I go For The SS cam . and lower compression of around 8:9:1 . ethernol does not like high compression engines . its got no anti-knock in it , like 4 star Did ! Yours Anna J

You can get away without the insert ring while using the good head. Purists will be aghast, but having done it, the annulus just gradually fills with carbon anyway. The downside of insert rings is that they can (see other threads on this forum) come adrift and cause a lot of damage. You may not need to balance the crank - I got away with fitting Commando pistons, as that's all I could get, without re-balancing. The vibrations levels are still acceptable, no better or worse than before. I didn't re-balance as that would have meant taking my daily commuting transport off the road for far too long. I wouldn't recommend a Combat camshaft - in any case, only the very earliest Commando camshafts would fit an Atlas. If you are being sensible, any Dominator camshaft would do - even the trusty old QR. If you get stuck for a camshaft, let me know. Gordon.

Anna, whist I do not dispute that you know a lot about Nortons, you do not seem to know a lot about fuel. The sole reason of adding ethanol is to increase the anti-knock properties of petrol,as an alternative to lead. In the early post war years (and right up to the early 60's) Cleveland "Discol", and National "Benzine" fuels contained approximately 10% alcohol, and were unleaded. In those days, I ran a '53 Dominator which thrived on these fuels (when I could not get "Avgas!). John.

John, I disagree that providing "Anti knock" properties is the sole reason ethanol is added to petrol. Ethanol is added in the USA by law, and this law was passed largely in order to provide a market for ethanol for agribusiness like Archer Daniels Midland. The US government even subsidises ethanol for addition to petrol.

Modern folklore has it that using ethanol reduces the amount of carbon dioxide in the atmosphere. This is untrue if you consider the carbon dioxide generated when making the ethanol. Like everything else, money and special interests are to blame.

I disagree with you, John. The reason ethanol is added to the gas in the US was to reduce the emissions (NO) and thus reduce the smog levels.

ADM saw an opportunity and jumped on it with a little help from their local congressmen.

Sorry all, I stick by my guns! The return of ethanol (alcohol) to fuel may well be for the "Political" reasons above. However, it was originally used as an anti-knock additive. Not many will remember the early post-war speedway racing bikes, these ran on pure alcohol, with ridiculously high compression ratios (by modern standards). Also, alcohol burns much cooler (a major factor with these engines, racing in a stadium). I am not suggesting pure ethanol for road use, for a start, fuel consumption would be much higher. John.

All alcohols are not ethanol. Speedway engines ran, and still do run, on methanol (CH3OH), not ethanol (C2H5OH). A lot more power is made from methanol than petrol, but a much larger volume is used. 14:1 compression is quite normal for a speedway engine. I had a speedway bike with a J.A.P. engine which ran on methanol, and it needed a two float chamber carb to feed it. Methanol does run cooler, but since a speedway race is only 1 mile plus getting out of and back to the paddock, I don't think overheating was much of a concern.

I do remember Cleveland Discol (DIStillers COmpany Limited) petrol. Most fuels back then used tetraethyl lead as an anti-knock ingredient, but that was phased out for environmental reasons. I don't know if Discol was leaded, but I suspect it was. Lead also helped with valve seat preservation.

Ethanol in petrol has ruined a lot of fibreglass tanks, like the one which came on my Commando S Type! Be rid of it, for goodness sake.

Your barrel can be bored out to plus 0.060" but you may end up with very thin cylinder walls at the bottom of your barrel whichwill probablybreak up. The top lip of the spigot will almost certainly fall off with a plus 0.060" rebore. It is best to get rid of it anyway, fit the insert rings and use the later chunkier head gasket.

The steel insert ringhad part number 25494 but Aluminium versions were available at one time as well. I think these are better.

The early Atlas heads had 5/16" bolts each side of the plug with barrel threads to match. This is one way of identifying early heads and barrels.What sizes are yours? 25319 indicates a later head using the 3/8" head bolts but you can keep the thinner5/16" if the barrel is an early type.

My 1965 Atlas kept blowing head gaskets, thanks to the replacement higher compression Commando pistons I had to fit. In the end I had the spigots skimmed off and those four 5/16" holes re-threaded to 3/8". The cylinder head was drilled out to take 3/8" bolts and I fitted Aluminium insert rings inside the chambers. All this allowed me to use the later head gasket and torque it down more tightly.

I had my crankshaft rebalanced with the Commando pistons andthis made a huge difference to reducing the vibes. The higher compression pistons, electronic ignition and a single carb also helped increase the bottom end power. I was then able to up the gearbox sprocket to 20 teeth whichinturn allowed 70mph cruising, well below the hand numbing revs previously needed.

Lower compression pistons are available still from various sources but do check out the quality if possible.