new 1970 roadster

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Aug 26, 2005
Hi all - I am new to the forum (first post)....

Just purchased a 1970 roadster in good condition, with the exception of what appears to be some piston slap noise that I intend to address this winter.

What are some of the aspects (good & bad) of the 1970 model I should be aware of?

Note I have been a biker for over (dare I say it), 37 years, have owned Kawasaki, Suzuki, Honda, Harley, KTM, BMW, and worked on British bikes in the 70's but this is my first Norton!

I havn't yet obtained the parts & service manual, also will the advice/direction in this be current based on what has been learned about this bike over the years?

Many Tks & have a great day!

You will want to get a hold of the INOA Tech Digest ( and the NOC Commando Service Notes ( as well as a Clymer, and of course the original partsbook and manual. Most of the 1970 parts are available from BSA-Regal (aka Andover Norton) broken link removed but are not listed on the exploded diagrams found on their site - use the part # and search function.

I'd say the swing arm pivot is a definately a weak point. Take a gander at my site to see what I've done. My bike is still a work in progress :cry:

Good luck!
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Thank's for the info & the great links!!!!!!!!!!!! Lots of good study material!

Any comments out there re my question if the 1970 commando has a any particular Plus's or minus's?
Greetings Biker-man!!

If the engine / bike is still original (i.e. not been apart or modified), it will have the following traits:

1. No Superblend bearings, which is not the end of the world for this engine.

2. Full Slotted oil groove pistons, which will crack over time and allow the piston skirt to break off. You say you have some piston slap, may be time to address that and have a look at your pistons.

3. No oil filter, when running detergent oils, a filter is crucial.

4. Timed crank case breather, not the most efficient method of crank case ventilation. A supplementary breather can be added to the intake rocker cover or the rear of the timing chest. Simply tee the two together and run them through a power brake booster check valve, then to the oil tank. This will reduce engine leaks, substantially!

5. Questionable / no intake valve seals, will allow some oil to be drawn down the intake valve guides, may cause the engine to smoke.

6. Worn Amal carb slides, a very common problem, causes erratic idling. Check out

7. Worn ignition advance mechanism. A Boyer rectifies this.

8. Fibreglass gas tank - prone to leaking with the use of modern fuels, there's a few things you can do: find a steel tank, buy a new aluminum tank ( ), or have your tank sealed. Do a search on this website for sealing materials, some work better than others.

None of the above are going to cause immediate catastrophic engine failure, but if you plan to keep the bike and ride it regularily / vigorously, these are things that should be considered.

As far as the remainder of the bike, the '70 roadster is a very rideable bike with few known unique bad qualities.

As you have no doubt discovered, you have British Cycle Supply nearby in Wolfville, NS, so parts are readily available.


Since Derek covered the basic engine stuff pretty nicely, I'll take a stab at the rest. (BTW, I asked the same question about a year and a half ago when I purchased my '71. There should be a long list in the archives somewhere.)

I'll try to summarize the handling and braking stuff as I've read it:

Brakes - Drum brake performace kit (Norvil?) and nice, sticky shoes (think Vintage Brake still is doing the Fedoro linings).

Isolastic suspension - the MkIII's iso's make for a nice upgrade in terms of their ease of adjustment. Requires some machining and its not a one-day job. Just making sure the old ones are serviceable and shimming to the appropriate specs should hold you over until you get the teardown-bug.

Headsteady - lots of opinions and very little agreement except that the stock stamped unit isn't the best. I purchased a Dave Taylor unit from Clubman Racing, but haven't ridden it so I can't vouch for it. Norvil makes one, Old Britts makes another... you get the picture.

Swing-Arm - the single locating cotter is an issue that was rectified with the MkIII's. There's a fix in the Norton Tech Digest. Might be a good time to oevrhaul the pivot anyway.

Forks - I like gaiters over wipers. They offer better protection from rocks with reducing some of the stiction in the forks. 1970, eh? I think it still has the old style hydraulic dampers, so a "coventry" kit for the damper is probably in order. Progressive-brand springs - some like 'em, some think they're too soft in the initial travel. Get a fork overhaul kit with "leak proof" seals, new bushings, etc.

Shocks - Ikon and Prorgessive make nice replacements. The Progressive's have a larger body and need a spacer and a longer bolt for the bottom of the shock. I machined some PTFE impregnated polyurethane bushings to replace the rubber ones for better swing-arm locating.

Did I miss anything?
Great list!

I think the only thing I would add, not resticted to the 1970, but a must-do nonetheless is the Layshaft bush/bearing in the gear box! Lots of info on that in the mentioned references.

Thanks again for all the great information & comments!

I have more questions & will comment on your points for you to futher consider.

I intend to tear down the top end this winter to inspect for suspected piston slap, replace pistons etc. I was told the engine now has 20 th oversize pistons. Is the fact this model doesn't have superblend bearing an issue? While I am working on the engine should I consider updating the bearings even if they are OK? I know I may end up with pistons quite a bit larger then orginal (30 th??).

The bike does have an oil filter added on.

Re: the suggestion "A supplementary breather can be added to the intake rocker cover or the rear of the timing chest. Simply tee the two together and run them through a power brake booster check valve, then to the oil tank." This sounds like a great suggestion! Is there a more detailed description of this somewhere as if this will help the oil leak problem I am definately interested.

The last run I had on the bike (over 100 miles) with some fast running, I had quite a bit of oil comimg from the primary case side, I know it was engine oil as the primary & transmission oil hadn't changed that much, but the engine oil had dropped... I have't yet figured out when it all came from. Where does the tank overflow end up?

I was told the head just had valve guilds & seals put in. By your comment are you indicating the stock engine didn't have any?

Not sure about the status of the carb slides but the engine has been idling fairly well (sometimes a bit fast but quickly settles down). Something to look at this winter I suppose.

All appears well with the timing & gas tank... I do like the idea of keeping it as stock as possible, BUT I also want a very good running bike (is close to that now with the exception of 2 or 3 kicks to start at times). I haven't however gone over the plugs, points, timing etc yet.

I will definately look at the brakes suggestion as they certainly don't compare with my RT!

Re: the isolastics they are orginal were shimmed by the previous owner & appear to be working great.. I was intending to leave this alone unless it is strongly recomended to change the system. comments?

Not sure what the problem with the head steady is. Is it weak? hard to install? other???

Re: the swing-arm "single locating cotter" I am not familiar enough with how this is put together to quite understand what you are concerned with.
I have gotten the parts & service manuals but have't found the tech Digest yet maybe then I will better understand>>> Is the tech digest available online?

Also I am not familar with the ""coventry" kit for the (fork) damper". I will have to study this a bit. Any suggestions for location of more info? I do know when I work the forks up & down there is a fairly loud clicking sound, so I intend to dismantle them this winter to inspect. I was told that they were completely rebuilt.

The rear shocks are new...

The transmission was rebuilt so I can inquire about the "Layshaft bush/bearing" . I was told that new bushings were installed during the rebuild so it's likely done.

Thank you again for your help & comments!!!

My goal is to have a great looking & running, very close to stock 1970 Norton.
If the bike lives consistently over 5000 rpm, then consider replacing the bearings, NOW! If not, then I'd only replace them when I had reason to split the cases. The issue is with crank flex. At high rpm the crank flexes and destroys the bearing races and often the crank and cases.

If you believe you have engine oil entering the primary case, it's probably getting by the crank seal. This can be replaced by removing the primary drive and with the engine in the frame. However, there may be a secondary reason for the oil in the primary. There could be excessive crankcase pressure (insufficient crankcase breathing), and/or the bike had wet sumped and you did not allow sufficient time for the pump to completely scavenge the sump before "turning up the wick".

By the way, if engine oil was entering the primary, the level in the primary should have exceeded the height of the "sight hole".
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