Commando 850 Mk.3

Hi Simon,

I'll list the faults I had when I bought my Mk3, one previous owner 17,500 miles, standard apart from silencers. (some of the faults apply to all Commando's).

Electric start is next to useless.

Camshafts can have a short life. 15,000 miles or less.

Standard Amal carbs wear out in less than 10,000 miles.

Front brake does little to slow the bike.

Rear wheel is severely mis-aligned to frame and front wheel.

Horn is in an almost inaccessible position (for maintenance).

Forks bottom out on full compression and the same on full extension.

Clutch plates become contaminated with gearbox oil and create drag and slip.

RH4 cylinder heads prone to porosity (oil leaks) and cracks by inlet guides.

Footrests are too far forward. (In my opinion)

Exhaust pipe finned collars come loose and damage the cyl. head threads.

Gearbox layshaft bearing has short life. (not sure of mileage).

Wheel rims are too narrow for the tyres.

Mis-aligned gearbox main shaft to crank drive shaft.

Poor sealing for swing-arm spindle - lets the oil out and water in. Rusts the spindle and wears the bushes.

Non-ergonomic switch gear.

Don't think I've forgotten anything. I've fixed all the above apart from the electric start, but have a view to fixing that for the future. Once you've corrected all the above they are fantastic bikes, capable of travelling all over the place with out problems - and at speed, 80mph cruise for example. The handling is superb once the problems are fixed.

Fork gaiters prolong seal life. Early Commando's came with the reverse cone silencers, later ones with the 'black cap' silencers. Reverse cones sound great. Discs changed from right to left - folklore has it in an attempt to solve handling problems - didn't work because the rear wheel is so far out of alignment. The JPS had a small tank, but not off a Roadster.

Hope this hasn't put you off,

Regards,

Simon.

Can't add much to that! Apart from I too own and enjoy Norton's ultimate 'Bendy.'

Though will say that at 6' I find the riding position (and switchgear) fine. With good nuts and threads and the proper tool I've never had exhaust problems with 850 or 750 engines, and neither were lock wired or used the bent washers.

I fitted a belt drive because the gearbox does wear quickly, hopefully this will make life a little easier for it! And yes, budget for braking upgrades!

But it's all curable with plenty of money!

Re: John Player? Do you mean the twin headlight cafe racer? Although there are adverts with a Mk3 in this guise, I believe all sold were based on the previous (Mk2a) model. Some people refer to the Red/White banded Mk3 Roadster as a 'John Player' model, this paint scheme wasn't an interstate option...

Previously charles_claxton wrote:

Can't add much to that! Apart from I too own and enjoy Norton's ultimate 'Bendy.'

Though will say that at 6' I find the riding position (and switchgear) fine. With good nuts and threads and the proper tool I've never had exhaust problems with 850 or 750 engines, and neither were lock wired or used the bent washers.

Hi Charles,

I've heard the 'bendy' tag before. The handling does feel like that through bumpy bends with all the frame and rear wheel problems - cure is to get it fixed. I'm 6' too, and now have the footrests vertically inline with the riders seat.

Problem with the steel exhaust collars is the greater expansion of the aluminium. I have a pair of bronze collars which, having a similar coefficient of expansion to aluminium, give no problems,

Regards,

Simon.

Being an owner of both Mk3 and Mk 1a 850 Commandos forover 30 years,can completely agree with the abovelist of faults and issues.

Exhaust collars on mineare secured with the locking ring and tabs you turn over into the cylinder fins.

Recently changed original Amal carbs on the Mk1a at 17,000 miles for a pair of Amal Premiers which cured the slow running unreliability prompting constant fiddling with throttle stop and air screws that I'd lived with for too long - let's see how long this reliable carburation with the twin Premiers lasts.

Upgraded front bakes on both bikes withRGM 12 inch on the Mk3 and Norvil 12 inch on the Mk1a -not much to choose between these kitsas they both use sameLockheed AP Racing caliper ,except Norvil kit rather more expensive- well worththe big expensewith very much improved braking on both bikes. Haven't bothered with the master cylinder re-sleeveupgrade- just a refurb of original unit with new seals , etc. Rear brake on Mk1a is a drum and works well enough ,as does the standard rear Norton-Lockeed disc brake on the Mk3.

Changed ignition on the Mk3 to Boyer but kept the Mk1a on original points. While the Boyer system never needs attention and starting is first or second kick , still prefer the engine running characteristics of the original points system which gives crisper throttle response when timing is correct -and which needs checking and adjustment at least every 3,000 miles. Always timed it using the standard factory degree plate mounted inside primary drive cover.

Handlebar switchgear on Mk3 is rather more ergonomic than Mk1a which requies a double jointed thumb to operate the right side mounted up and downindicator switch.

Electric starter on Mk3 has had the 4 brush upgrade although I never use it asbike starts so easily on the kickstart.

Access to clutch for cleaning plates , etc ,is very much easier on Mk1a as primary drive cover is secured with just a single central bolt and sealed with a large rubber O ring rather than Mk3 which has numerous screws and a paper gasket.

Run both on original triplex primary chains which have been changed once on both bikes - at 17,000 miles on Mk1a and 22,000 miles on Mk3.

Always used TT100's on both bikes.

Overall , both great bikes even in modern traffic conditions but ifIhad to choose between themitwould be the Mk1a due to its much simpler primary drive without electric starter drive train , etc , and easy access to clutch. (Mk1a and Mk2abikes are almost identical).

The triplex primary drive chain is the most over engineered part of the bike and whilst running in an oil bath should last for massive mileages. (Norton Rotaries with oil bath rear chain drive will get in excess of 185,000 miles out of a chain) I forked out for a new triplex for my last rebuild and comparing it with it's predecessor I should have saved myself the expense. A duplex Mercedes timing chain is a good mod and will save some rotating weight in the overweight primary drive system, particularly if using bronze clutch plates. The "chain man" can get them apparently.

Fantastic useable bikes capable of touring and great for long distance. They all essentially share the same frame so unless your a rivet counter any combination of tanks / side panels / seats that you fancy is good. Enjoy your Commando no matter which model you buy. I prefer my 850 mk1 to my mk3 but only because of simplicity. They are both equally as good.

Gino

The Mk3 solved some niggles with the earlier bikes and it does have the strongest crankcases. However, there were quite a number of changes and the model received no development between its introduction early in 1975 and the end of production (mid 1976 with a batch later). In the manner of the industry at the time, this means that they inevitably introduced some new problems too !

All the 850s are equally usable and can be similarly updated but if you value an electric start (now or in the future) and a left-foot gear change then the Mk3 is probably the best starting point.

If I could turn the clock back thirty-odd years then I'd probably choose a Mk2 as they seem 'purer' and closer to the original concept, but at the time, Mk3s were cheaper...

A good example of either is better than a bad one of the other.

I restored a MKIII a few years ago and a friend of mine bought it, so I still see the bike often. 3 things improved the reliability and usability of this bike, a Tri-Spark ignition, a good powered gel battery and a new set of carbs.

Carbs are a wear and tear item like a chain or tyres, there's nothing wrong with Amal concentric carbs, but when they get to 40 years old and people moan about the bike not running right and blame the carbs... well what do you expect..? Treat yourself and the bike to a new set, they're the same price as a set of tyres and transform the bike.

I left the original starter motor on it and with the new gel battery it starts on the button without any problem, the problem with the original motor was the battery technology 40 years ago. The Tri-Spark uses very little current (unlike some electronic ignitions) and starts first time. The other modification I would do to any Commando is up gear it. I've had my 750 for 34 years and I have a 23 tooth gearbox sprocket on it. It's the best thing I've done and it pulls it no problem with a better top speed and a more relaxed engine. My mates 850 MKIII has a 24 on it as he uses the bike to ride to Penzance in Cornwall regularly (about 500 mile round trip). I'm almost regretting selling the MKIII now, as the prices have shot up and now I'm watching my older mates contemplate fitting electric starters to there other Commandos because of aching knees etc.

Previously david_evans wrote:

The triplex primary drive chain is the most over engineered part of the bike and whilst running in an oil bath should last for massive mileages. (Norton Rotaries with oil bath rear chain drive will get in excess of 185,000 miles out of a chain) I forked out for a new triplex for my last rebuild and comparing it with it's predecessor I should have saved myself the expense. A duplex Mercedes timing chain is a good mod and will save some rotating weight in the overweight primary drive system, particularly if using bronze clutch plates. The "chain man" can get them apparently.

Indeed- after I'd already fitted new replacement triplex primary chains on both my 850's ,discovered they never actuallyneeded changing with apparently no noticable wear at all. Original chains still hanging in the garage as usable spares for the future.

Previously james_fanning wrote:

discovered they never actuallyneeded changing with apparently no noticable wear at all. Original chains still hanging in the garage as usable spares for the future.

No, they do wear enough to stretch James, about 11,000 - 15,000 miles a time? I'm sure I am on my third or fourth at 44,000. When they have stretched/worn the hydraulic tensioner on a Mk3 struggles to push the slack side and you hear it start to clack. Perhaps if you could then adjust the gearbox back a tad they would be useable a lot longer.

Previously norman_lorton wrote:

No, they do wear enough to stretch James, about 11,000 - 15,000 miles a time? I'm sure I am on my third or fourth at 44,000.....

With that rate of wear first you need to check that the gearbox mainshaft and crank drive shaft are parallel in the plan and end views. Second, check that the clutch chainwheel sprocket and crank drive sprocket are aligned correctly.

Must be at least 30,000 miles since I last changed the primary chain and it is still fine.

Previously simon_ratcliff wrote:

Must be at least 30,000 miles since I last changed the primary chain and it is still fine.

You don't ride fast enough to wear it out

Hi Simon

For what it's worth,I've had a go on two different mk3s and found them both lacking in the normal arm wrenching grunt you get from a mk2 850 or even a 750. I really had to rev them in the gears to get them going! Maybe they weren't in the best of condition,dunno?!

Chris

hi simon. I cant add any technical advice as I am too a relative new-comer to owning a commando. I bought my commando having no experience of even having a kickstart before, never mind carb tickling, all my previous bikes were kawasaki's and bmw's. having said that I absolutely love riding the bike, of course ive had issues and tantrums, but never regret buying it and the help I have had from members of this owners club has been fantastic. good luck