1973 Norton Commando

Discussion in 'Old's Cool' started by rudolf35, Jan 25, 2012.

  1. rudolf35

    rudolf35 Warped & Twisted Mind

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    I have a lead on a 73 850 Commando. The bike was ridden to the current owners location and the fuel drained and then it has been sitting for 12 years. The bike is kicked over (not started but just turned over) once a month so the motor spins free, not frozen. I am waiting for images but would love to know what issues, Norton specific, I might run into. I have spooled up many BMW's and other British iron but never a Norton. Any info would be of value.

    :ear
    #1
  2. Twinboy

    Twinboy Adventurer

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    I may be able to help on this one! We have had a 73 Norton for 35 years so I am very familiar with it.After sitting so long all fluids will need to be changed. 20-50 in the engine, 80/90 in the transmission,and 20-50 or ATF in the primary. The Amal carbs will at least need a good cleaning and maybe resleeving of the slides depending on mileage/condition. Check the valve clearance,adjust the points or replace with an electronic ignition ,we use a Pazon.The gas petcocks will probably need replacement along with the gas lines. Replace the tires and battery and go for a ride. 73/74 Commandos are considered the best of the series and as all Brit bikes of the era will require attention to keep running well.The Commando will surprise you with its excellent handling and gutsy mid range torque that make it a delight on the twisties.The rubber mounted motor will allow hours in the saddle without vibration fatigue. Parts are readily available and reasonably priced from multiple reputable dealers.Good luck!
    #2
  3. rudolf35

    rudolf35 Warped & Twisted Mind

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    Twinboy, those are some good pointers, slide on the carbs etc. Funny you mention 20/50 - this has been my oil in every bike I have owned since I can remember.

    The basic spool up is the same on most bikes it is the idiosyncrasies I am looking for; like on the BMW's it is the splines (real or imagined) and rear end main barring.

    What, besides the original shop manual is a good one, Clymer?

    :ear :clap
    #3
  4. Twinboy

    Twinboy Adventurer

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    Yes, the Clymer manual is decent. The main issues on the Commando are the carbs wearing and ignition.Update these along with the front brake master cylinder.These bikes will leak oil from various places but they are easily solved with careful attention and some hylomar sealant applied sparingly. The isolastic rubber mounts will need proper shimming but once set and rubber buffers freshened up they will work for a long time.Check and clean all wiring connectors and look for any suspicious rubbed wires.Our Commando still has all the original electric components except bulbs.Careful attention to solid connections and routing will pay off.Have fun.
    #4
  5. rudolf35

    rudolf35 Warped & Twisted Mind

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    Great information! I fully expect to rebuild the carbs and once up and idling see where the oil spews from - had a BSA 650 Lightning many years ago and went through the same drill.

    Good point on the isolastic rubber mounts. I am sure, unless treated, the rubber mounts should be well age rotted by now. The wiring, see what that looks like but I am sure the connectors will need cleaning and a good lube with dielectric grease.

    Your Commando has a owner that cares about it. Some PO's need to be slapped the way the bikes are treated.

    As soon as I get the images from the owner the penny might drop - hope at least.

    :clap
    #5
  6. chasbmw

    chasbmw Long timer

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    does a '73 850 have a fibreglass fuel tank? My 72 POS 750 did.

    If so it will need to be sealed before using any fuel with (much) ethanol in it.

    Charles
    #6
  7. rudolf35

    rudolf35 Warped & Twisted Mind

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    Very good point! I know that the original tank is there but as of now it has a second one mounted. I am still waiting for the pictures so I can not answer if it is glass or not. This find is very farm fresh, still has the straw on it.

    :lol3
    #7
  8. lemieuxmc

    lemieuxmc Banned

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    The single Mikuni or dual flat slide carb conversions are very popular.
    #8
  9. rudolf35

    rudolf35 Warped & Twisted Mind

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    Thank you to all for the information. This will make the "new frontier" easier to conquer.

    :evil
    #9
  10. lrutt

    lrutt SILENCE.....i kill you

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    73 is steel for the tank.

    As for carbies, if the bike has over 10k miles they are likely loose. Stay with the amals. You can actually get new ones, much improved with better floats, forged and hard anodized slides, etc. It has been proven that few conversions can produce as much power as the good old stock Amals. If your carbs are in pretty good shape, it would be worthwhile to upgrade the slides themselves to the hard anodized forged units. That is what I'm doing to all my brit bikes now. This can extend the life of your carbs greatly and is cheaper than sleaving.

    Key thing to check is the swingarm bushes. If loose, strip and replace. Do NOT try and grease them. Use the proper straight 140w gear grease in them as recommended. It won't leak out and will keep them properly lubed once rebuilt.

    You will have to check the shimming on the isolastics. Not a big deal to check and or add shims to. Hopefully you have a good shop manual and parts book.

    Remember........stock these were positive ground. Do not for get this!!! A good AGM battery is a god send on these old bikes.

    Mine is all stock, with points and amals, and never fails to start first or second kick. Many of the guys who 'improved' their nortons with electronics and mikuni's can't say the same thing.

    And lastly, it no doubt has wet sumped all the oil from the tank to the crank case. Nortons are notorius for that. Drain the crank case for sure. In normal use, if you ride it every week, you likely would not have a problem. What you DON"T want to do is assume that the oil pump will pull all the oil from the crank case and put it back in the tank. These things will drain down to the point the oil intake or feed is hi and dry. Meaning that when you start it, you are NOT pumping any oil. Not good. I always pull the tank cap off and check. If the intake screen is covered and can't be seen I'm good to go. If it's exposed, drain the crank case and put it back in the tank. Not doing that could not only ruin the motor but blow the crank seals out from excess pressure. The trick I use, that works 75% of the time to prevent wet sumping, is that when you park it, push the kickstarter down so that the pistons are at TDC. The therory is that the oil passages on the crank will be pressed tightly against the rod shells and slow down the oil bleed to the crank. It does seem to work, at least on mine.

    Remember the 850's have an oil filter down under the swingarm. A great from the factory.

    And...no doubt you will need to rebuild the master cylinder. A worthwhile mod at this time would be to sleeve down the master to provide better braking. Several places do this and it's worthwhile. Wish I would have done it on mine. Helps prevent Popeye arm.

    Gratuitous pic of my 73 850, 4800 original miles when extracted from a barn in colorado.
    [​IMG]
    #10
  11. rudolf35

    rudolf35 Warped & Twisted Mind

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    Irutt, now that is what I call good points! Had no clue as to the oil tank draining into the crank. That means when I change all the fluids I will also have to make sure to drain the crank.

    On all of my bikes I like to go stock on the motor and from what you describe that seems to be the way to go on the 850. Points, no big deal - as long as one keeps up with them. The slides, now that is a very good pointer - keep the stock bodies and go with the new hard slides. The master cylinder will need a rebuild anyway so I might as well sleeve it to get more power to the pads.

    Now all I have to do is wait on the photos and see what is in store.

    :norton
    #11
  12. Twinboy

    Twinboy Adventurer

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    73 Nortons had steel tanks new. Do you know if it is an Interstate with the 6 gal tank,large seat and bigger sidecovers. Or is it a Roadster with the 3 gallon tank and smaller seat and sidecovers. The Inerstate is great for longer trips and the Roadster feels lithe and lean on the backroads. It got up to 64 today so I was inspired to roll the Norton out and go for a ride in the mountains here in Western North Carolina.Remember that the shift pattern is up for 1st and down for 2-4,or down for faster.You have received some great pointers on how to check and fettle a Commando.Good times await you!
    #12
  13. Voltaire

    Voltaire Bored Of The Rings

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    I bought a 72 Combat last year and I'm lovin' it. Carbs were sleeved, boyer ign, trispark regualtor makes for easy starting.
    I'm saving for a Lansdowne Fork conversion next.http://www.lansdowne-engineering.co.uk/three_3.html
    Best site I have found for info is :
    http://www.accessnorton.com/

    I read all the horror stories about build quality etc........ It really comes on strong at 5000 rpm but as its 40 years old I don't thrash it ( much).

    Prices are all over the place here in NZ but demand is high as they are a nice bike to ride and very cool.
    Even the Combat is easy to kick start and you get used to the upside down R/H shifter....most of the time... apart from the odd oops back into 1st...:rofl
    #13
  14. noman

    noman Been here awhile

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    crank bearing upgrade? 7 or 8 ball, 10 ball, superblend? much discussion here and there on the intranetz.
    #14
  15. lrutt

    lrutt SILENCE.....i kill you

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    73 will have proper superblends on the crank. Only bearing of concern might be layshaft bearing in the tranny. and it will give you a subtle warning, the dancing kickstarter.
    #15
  16. norton73

    norton73 drinkin'

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    One of the best resources for Norton Manuals is the Kim CD man manuals. Shop, parts, riders, and plenty of other info is all available in one place. I print out the relevent section I need to do some work, then use the paper to wipe up the oil when i'm done.

    A search will find you a retailer that you can order from.

    Also, the INOA has a tech manual that is a good adjunct to the service manuals, plenty of experience to be found there, especially about upgrades.

    The above link is to some articles, go to Mechendise for the Tech Manual, I can't access that page from work.
    #16
  17. norton73

    norton73 drinkin'

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    Old Britts has some good info too. Scroll down to see the technical articles,
    #17
  18. Rightshiftrick

    Rightshiftrick Been here awhile

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    Also check the exhaust threads. They are notorious for stripping if you don't get them tight enough. All the little safety wire and clips won't help much if they aren't tight to begin with.
    #18
  19. lrutt

    lrutt SILENCE.....i kill you

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    Good point. I use the stock fin tabs to ensure the collars stay tight. Others safety wire. If they are good, make sure they are damn good and tight then apply the fin tabs to keep them from loosening up. And if they are stripped, well.... that's a different topic.
    #19
  20. Steve G.

    Steve G. Long timer

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    IMO, the best of the Nortons,,,,,late 750's, and all right hand shift 850's. You've been given many great pointers. I will list some of this particular machine's weaknesses, which you can look at later or right away.
    1] The upgrade to some form of electronic ignition really is a no brainer.
    2] The isolastic engine/gearbox suspension system really does work well at isolating the incredible vibration of this engine,,,,which started out as 498cc. The original rubbers will now be getting tired if original, and a perfect time to upgrade to the Mk111 850 system which allowed for quick and easy 'vernier' adjustment instead of the tiedious and time consuming old system which all Nortons had except the Mk111 electric start models.
    3] The swingarm bushings are in fact oil bushings, not grease bushings. And the system is sealed with o-rings. And they leak. So get used to it, you will have to get some 140 weight oil in there or the bushings wear out quick.
    3] Amal carbs work very well on these engines, and they look 'right' on them. I certainly can understand upgrades in this area with a single Mikuni for an example. I'm a bit of a traditionalist in the visual aspect of all my machines, and this is one upgrade I won't do, stricktly on visual. that said, Amals have a hard life bussing away on the end of those solidly mounted intake manifolds, lifespan around 10-15,000 miles, where slide/body clearances open up. This essentially causes one issue, upward creaping idle rpms whilst sitting at a stoplight. Once on the road, you won't notice a difference.
    4] A big problem with the Mk111's [Portugese bearing supplier], but also an issue with the others,,,,the gearbox layshaft bearing is under-qualified to handle the tourque of this engine package. As mentioned, the telltale sign will be the kick starter starting to shudder downwards while accelerating from a start in first gear. If not changed to the upgrade 'mini superblend' bearing, this can cause complete rear wheel lockup as the kickstarter goes down far enough to hit the exhaust.
    5] Exhaust nuts,,,,keep them tight. Tighten them while the engine is hot.
    6] As mentioned, avoid fibreglass tanks totally. Ethanol kills them. There were actually two tank options for '74, not counting the Highrider or the JPS. The standard steel Roadster tank, and the Italian made 4 1/2 imperial gallon steel Interstate tank. There is a distinct visual difference in width to the later 5 1/2 imperial gallon English made steel tank, or the huge 6 gallon plastic tank. The only drawback with any Roadster tank is range, probably 100-115 miles before reserve hits. Interstate tanks have a disadvantage in that the tank is 2 1/2" longer, forcing the rider back, while the footrests are not. This causes the rider to become a human kite at highways speeds. luckily, several manufacturers have rearsets to turn this situation around.
    7] 1973 and later Commandos will have indicators as standard. Unfortunately, the indicators are self grounded through the chrome plating on the inside by the light bulbs, and the improper grounding is somewhat common.
    8] High quality upgrade kits to the charging system are available, including eliminating the zener diode heat sink, fragile bridge recifier and single faze stator. And the magnets on the rotor will be getting tired now.


    Steve
    #20