520 "O" Ring Chain

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Dec 5, 2003
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I REALLY want to convert to the 520 O-Ring chain. Has anybody done it and what's required. I know CNW does it along with a trans rebuild but I've already got my transmission rebuilt and ready to put back in. Cleaning oil and chain lube off the swing arm and wheel are not my favorite activities :x .

Thanks, Scooter
o ring chain

the conversion is simple. order an early dominator frount sprocket. if you have a lathe or any good machine shop you will need to cut .125 off the outside ( left side ) on the rear sprocket brake drum. or clubman racing sells both sprockets I think.

bill who has done a couple of conversions :D
Thanks Bill;
Doesn't sound too difficult so I'm surprised if there isn't a "kit" already out there for this.
Also I'm surprised that nobody has developed a lighter weight rear sprocket. The one on my MK III must weigh 5 lbs. and when the sprocket wears you've got to replace the entire peice. I think there's a real opportunity here for an enterprising machinist.

Chopper gauges

I was admiring the gauge set up on your chopper project. It appears to have a machined plate mounted to the triple trees with Autometer gauges. They are probably electronic. How does the speedometer operate?
they are indeed the autometer pro cycle guages. the speedometer works off the rear sprocket. I used a HD speedo sensor ( hall effect ) I made a bracket that centers off the rear axel, runs forward ahead of the sprocket than over it with the sensor facing the teeth as the reluctor. the insterment bracket is custom milled from two pieces of flat stock than welded togather. it fits under the fork nuts like the stock mounts. after those pictures was taken I put a blue and green LED just under the gauges with them counter sunk and a dark lens over them to tone them down one is high beam and the other one is for lights on I also added a LED charge indicator made by kurkurian. a very nice piece. I am NOT a chopper guy myself. I am doing this for a guy near me and as a test of what I can do and sofar I think it will be a nice old school chopper.

Bill, If I understand this correctly, The senser is facing the teeth, between the high and low side of the chain forward of the sprocket. The sprocket teeth are breaking the signal, thus sending the signal. Is this correct??
Now accurate is it?
michael you are correct in the way it faces. the speedo is infinantly calibratable. the directions say to get on a road with marker posts. stop at a post and set it in calabrate mode, ride 2 miles, stop and lock it and it is set. if you want to run one on a brit bike I dont think it will work because of the positive ground. the chopper has been changed to negative ground so we can run ANY electrical parts we want. I am using a sparks alt. kit and a suzuki regulator. the rita will run with either polarity by changing 2 wires.

Back on to the 520 chain. I have done this with both Nortons and like it. I have heard after useing the Atlas front sprockets that it's better to machine down the Commando one's because of higher stength. It's ben a while so I can't recall any size difference. Also I belive that the front sprocket is heat treated to some degree and were it is still machineable I wonder if taking off the case from the Commando sprocket would negate any advantage of using the higher strength sprocket. Be sure that the machinist knows that chains like about .010 clearance on the sprockets, so .240 not .250 for thickness. norbsa
Thanks Bill,
Yes I was thinking about it. I have a Combat that someone has done some real nice work on. They bored the stock triple trees and installed 36mm tubes and lowers with a Brembo caliper, 13" floating rotor and 18" Excel. Very nice.
It currently has no gauges. I wanted to go the Autometer electronic route for the clean cableless look. I HAD NOT considered the positive ground, so thanks for the reminder.

I have done this on my bike and am pretty happy. I got new front/rear sprockets from Clubman Racing. Actually, the front didn't arrive for awhile, so I turned down my stock one on the lathe and that worked well. You will likely encounter chainguard clearance issues. I just took mine off.

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Thanks Guys;

This is one I'll have to get the Machinist to do since Clubman Racing only has the rear sprocket for the pre '75 drum brake models.
I'll probably turn down both sprockets after a trial installation to make sure there won't be alignment problems. The joy of throwing the chain lube can away will easily offset the extra work.

I did weigh the old rear wheel sprocket and believe it or not its 6 lbs. not the 5 I guessed, anyone know where I can get some titanium?

Thanks again, Scooter
dont throw out the chain lube, you will still need it just a LOT less often.

I dont see where there would be any diffrence in atlas or commando sprockets in strenght outher than one is .125 narrower. I have not tryed to cut a counter shaft sprocket on the lathe because you can buy one that is the right size for the 520 chain up to 21 teeth. but if it is case hardend I would think that it is NOT .125 deep and it might be easer to use a tool post grinder than a cutter bit.

ps I looked at your bike and saw that you have an 810 cylinder on it. what luck have you had with headgaskets? I had one MANY years ago and could not keep a headgasket on it.

Bill, it's a DMR racing jug from Left Coast Racing. and it's been off and on four times to get it working. It's a .020 over 750 so still under 750 cc not that Iam a racer. I could go into a three page story on this thing but the only way to get one to work is to make two inch tourque plates and use stock head and base bolts at tourque speck and than hone it to final size. You got to really want one if you know what I mean. norbsa
Scooter62, You just take all the stock off the side facing outwards. This is true for useing the Atlas as it is with a the Commando rear sproket or both Commando sprockets. When I did mine I set it up on a surface plate at work and compared were the extra stock was. This way provides a litte more room for the chain guard that is a good thing and behind the primary case also a good thing. I guess Triumph guys like it off the inside for fatter tires. norbsa
Hey Chris,
I just took a look at your pics. Really nice bike! Nice clean improvements that keep the classic Commando look.
I really like the dual Brembo front brakes. Did you do that yourself? What did you use for a front hub? It's so much cleaner than the clunky Lockheed or Grimeca single disc adapter.
How did you add the lug to the left leg?

Thanks for the compliments. The brake setup is a kit from Norman White. It prices comparably with Norvil kits. Norman turns the hubs himself as well as all the spacers and rotors. The kit comes with a left slider that matches the right one and the whole setup is very clean. I added a fancy pants Brembo GP Radial master cylinder up top and the thing stops beautifully. The whole thing looks quite good as well. In retrospect, I think one of the advantages to a Norvil kit would be the availability of replacement Brembo rotors, where my rotors are more custom.

Next up, my Wilcox tank has just arrived and gotta get that painted as the finale to this long project......

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My compliments on your machine. Very nice.
Is that the Wilcox tank in the picture? Is that an 18 or 19 front wheel
Inquiring mind you know.
Yup, that's the Wilcox tank. I had a modern style flush mount cap welded in and the knee indents are more pronounced, giving a little more retro cafe feel. It is yet to be painted, the image shows my photoshop mockup of a two tone paint scheme.

When I got the front brake kit from the UK I decided it was finally time to have Buchanan's build me some new wheels around 18" Excel alloy rims 110 front 120 rear.

Hmm..... I think that sums it up for now.....

-Chris in Chitown
O-ring Chain

About the chain...
I have done about 4 o-ring chain conversions in the past. I made a set of arbors and machined the sprockets myself with a carbide insert tool. The transmisions sprockets seem to be through hardened but turn quite easily with carbide. I actually machined 1/16" of either side to maintain the chain centreline. If you have a good set of sprockets I will turn them for you if you want.
I have put over 6000 miles on my '72 Combat with the 520 chain. I have lubed it about 4 times and haven't had to adjust it since I installed it.
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