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New to me. 1970 750 Roadster

Classic Norton Commando Motorcycles.

Re: New to me. 1970 750 Roadster

Postby o0norton0o » Sat Sep 02, 2017 8:38 am

There's a few subtle differences in '70 commandos which were changed in later production years, so the flaws associated with early bikes are largely ignored in the forum by late model owners which makes those differences, and in some cases flaws, less well known to we '70 owners.

LIke:
'70 commandos have 27 degree yoke angle where later bikes have 28 degree
'70 commandos have less offset on their fork tubes from the yoke pivot than later bikes, which gives our bikes a little more trail
'70 commandos have the marginally effective camshaft timed breather, later models eliminated it in favor of various other configurations.
'70 commandos have a different center and side stands
'70 commandos have a single bolt swingarm tube which can cause sloppy handling, later bikes have dual wedge bolts that eliminate this potential handling issue.

so,... change your main jets out to 220's. I've tried 240's and they were too rich. I couldn't get the bike to go past the low 80 mph's. With the 220's I could hit 100mph if I wanted to do that. (but I don't) Now you know about the swingarm tube flaw, so if any handling issues develop, you know where to look. Ditch the key fob so it doesn't ruin the purple sidecover...

* Maybe think about adding a reed breather to your crankcase. Jim schmit makes one that mounts on the existing timed breather port, which would be the simplest way to add a reed valve to your bike. The sump plug breather that Jim comstock fabricates doesn't fit our '70 commandos because of the location of a tubular frame member on our '70 frames... Another glitch for the '70 model year.

As far as handling goes, my bike handles great now that I fixed the swingarm tube. I'm pretty thankful for the info I learned here that helped me fix that problem, because I rode my bike with it's snake-dance motion for decades before learning what actually was the cause of the problem.

Good luck with MR. Purple
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Re: New to me. 1970 750 Roadster

Postby speedrattle » Sat Sep 02, 2017 10:47 am

i've already put the key fob back in the tool box to hold the spare keys, and i've a bid out on a centerstand on eBay.

i'll have to look into the breather. i run open tubes on my other stuff:

Image Image

there's no vacuum produced with open tubes, but then there's no possibility of failure, either.

i'll order the 220 jets. my books specify 180, 200, or 220, depending on what sort of machine you're running, but it's easy enough to see what works just by putting them in, and i know it's not rich.

can you think of any other differences between the earlier commandos and the later ones?
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Re: New to me. 1970 750 Roadster

Postby DogT » Sat Sep 02, 2017 7:05 pm

Oil tank is central, not off to the side. Electrical system is different, the key only turns off the rear brake lamp and the ignition.

I'm not sure the JS breather would do much good with the timed breather in place, it really needs to be removed, or a totally new breather installed. I've read that some live with the timed breather with good results. My results are lots of oil leakage through the air filter, I fixed that with a catch bottle, but not simple. Keep the oil level in the tank towards the low level. The front mudguard and stays are too small/short for anything larger than a 310-19 tyre. I'm not sure the later bikes had the amp gauge in the headlamp shell. Early bikes had no turn signals.

I got my swingarm fixed a long time ago with something similar to the Kiegler mod, but no clamps, just bolts at the ends and a new oversized SS rod. The early head steady was prone to breaking, I replaced mine with a home made Keith HS. The way I ride, I really can't tell much of a difference. The engine spring off the head steady will help with the idle shakes. Hemmings vernier iso adjustments are good.

My bike seems to like 240 main jet and 0.106 needle, 25 pilot. Nr 3 throttle and middle notch on the needle position.
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Re: New to me. 1970 750 Roadster

Postby o0norton0o » Sat Sep 02, 2017 7:33 pm

There's a few more differenced that I'm aware of, and maybe a few I'm not aware of too.

The 70 commando headsteady is primitive. it was replaced by the "box" style headsteady on later models. (I use a comstock headsteady which is better than any stock commando headsteady)

The 70 commando rear wheel is bolted directly to the sprocket/brake drum. Later models had a crude cush drive mechanism in order to take some of the shock load off the drivetrain.

The 70 commando had 12 volt coils, Later models got better spark out of two 6 volt coils. (I use a single dyna coil with dual leads and a boyer ignition)

The 70 commando has a drum front brake (mine was changed to a late model disc 40 years ago)

The 70 commando has a weaker swingarm. later model swingarms have reinforcement gussets welded where the arms meet the crossmember.

I'm sure there are more differences that I've forgotten about. For the most part I've done all the handling upgrades which are the swingarm tube modification, a better headsteady, koni shocks, progressive fork springs. I haven't done the landsdown fork dampers upgrade, but those are being manufactured again by madass and it's on my list to do someday.

I've also done a timing side reed breather modification because it helps to reduce oil leakage. Unfortunately our 70 commandos can't use Jim Comstock's sump plug breather because the 70 frame has a crossmember that blocks the use of his breather. Recently Jim Schmit introduced a reed breather that bolts on to a 70's crankcase at the camshaft port, so there's that simple bolt on option if you don't want to modify by drilling stuff.

HTH...

edited to add... All good stuff dog posted above me while I was typing...
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Re: New to me. 1970 750 Roadster

Postby speedrattle » Tue Sep 05, 2017 10:37 am

got this on eBay yesterday:

Image

price nearly doubled in the last two seconds because another norton guy tried to snipe it. but he waited just a bit too long and the auction ended before he could match my bid.

sorry if that was any of you. but these things are genuinely hard to find, used or new, and i was glad to get it.

220 mains are coming from MAP.

i need to look at the headsteady on the bike. the parts manuals versions don't look nearly as sophisticated as the comstock one. i'm interested in looking into the handling, although it's already good. i live within reasonable distance of the mid-ohio racetrack, and i've been thinking of joining the club racing group. i think a firm-handling norton would be interesting to take to the track days there. tightening up the front and rear would really be all i would be interested in changing, except for seating position. i like the rest of this machine as it is.
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Re: New to me. 1970 750 Roadster

Postby cjandme » Tue Sep 05, 2017 12:22 pm

speedrattle wrote:......i need to look at the headsteady on the bike. the parts manuals versions don't look nearly as sophisticated as the comstock one. i'm interested in looking into the handling, although it's already good. i live within reasonable distance of the mid-ohio racetrack, and i've been thinking of joining the club racing group. i think a firm-handling norton would be interesting to take to the track days there. tightening up the front and rear would really be all i would be interested in changing, except for seating position. i like the rest of this machine as it is.

Well, I would pony up the dough and get the comstock head-steady, it really is beautifully made, and it utilizes the existing mounting hole in the frame bracing tube under the gas tank, unlike some of the others out there that use a clamp around that tube, (I've read here from other members that they had rubbing issues between their tank and the clamp). Regardless of which one you go with, the main thing is for the headsteady to keep the engine in the verticle plane while allowing it to bounce up and down as it is want to do being a 360 degree parallel twin and all. As the older style ones wore out, they allowed the engine/rear drive to cant over to one side, adversely affecting the bikes handling.
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Re: New to me. 1970 750 Roadster

Postby DogT » Tue Sep 05, 2017 1:34 pm

RGM used to carry those early center stands. That's where I got mine.
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Re: New to me. 1970 750 Roadster

Postby speedrattle » Tue Sep 05, 2017 2:42 pm

cjandme wrote:Well, I would pony up the dough and get the comstock head-steady, it really is beautifully made, and it utilizes the existing mounting hole in the frame bracing tube under the gas tank, unlike some of the others out there that use a clamp around that tube, (I've read here from other members that they had rubbing issues between their tank and the clamp). Regardless of which one you go with, the main thing is for the headsteady to keep the engine in the verticle plane while allowing it to bounce up and down as it is want to do being a 360 degree parallel twin and all. As the older style ones wore out, they allowed the engine/rear drive to cant over to one side, adversely affecting the bikes handling.


beautiful is hardly expressive enough:

Image

i'm a machine junkie, and this is pretty stuff
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Re: New to me. 1970 750 Roadster

Postby speedrattle » Tue Sep 05, 2017 2:42 pm

DogT wrote:RGM used to carry those early center stands. That's where I got mine.


now that i bought one, there are two more for sale.
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Re: New to me. 1970 750 Roadster

Postby speedrattle » Wed Sep 13, 2017 2:32 pm

okay, got the 68-70 1/2 stand, and the correct spring for it (06-0588):


Image

but where does the top of the spring hook into?

there's a hole up in the center stand mounting plate on the right side, but i'm buggered if i can figure out how to get the spring to hook into it:

Image

it's in the right place, but there's no room to swing the hook on the spring into the hole. if i clip some of the spring off so the curved section is shorter than the diameter of the hole, then i can just twist the hook over and in. is that the correct work-around, or does the spring hook onto something else up there?
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Re: New to me. 1970 750 Roadster

Postby Bob Z. » Wed Sep 13, 2017 2:45 pm

I just checked mine and you are on the right track.
The spring top fits into the hole shown and runs down on the inside of the frame stand mount plates.
I see the issue of getting the spring hook into the hole!

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Re: New to me. 1970 750 Roadster

Postby speedrattle » Thu Sep 14, 2017 6:19 am

i'm guessing then i just need to grind a bit off the spring to let it rotate in. easy fix.
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Re: New to me. 1970 750 Roadster

Postby speedrattle » Thu Sep 14, 2017 1:51 pm

that's all it took

Image

the spring hook was just a bit long-- linked into the hole as you described it went in just fine, bob.

nothing else to do on this except better fork seals sometime and ride it while the weather holds.
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Re: New to me. 1970 750 Roadster

Postby speedrattle » Fri Sep 15, 2017 5:22 pm

well, i tried the 220 main jets in these carbs, no go. too rich on full throttle, motorboats and accelerates sluggishly, then improves if i roll back to the needles,

my 1970 repair manual says that the motor used "180s with restricted mufflers," 210s with modified megaphone," and 220s with early megaphonemufflers."

i have peashooter mufflers, so i'm gong to stick the 200s back in and see how that works.
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Re: New to me. 1970 750 Roadster

Postby o0norton0o » Fri Sep 15, 2017 8:35 pm

Kevin, Sorry about the 220 recommendation. Now that I think of it, I have dunstall decibel mufflers on my commando, which are less restrictive than pea shooters. I just forgot that aspect effects jet sizing... My mistake, I'm sorry about that.

The bike's lookin' good. Have you noticed that the centerstand is just barely long enough? I usually throw a piece of 1/4" plywood on the ground where it's parked.
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