New to me 850 MK3 and a couple of questions

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raleypc

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I recently picked up a very nice 850 MK3 that had belonged to a friend for 20 years. I really enjoy riding it. The top gear roll on performance is addicting. The electric starter works great along with everything else. I have owned a 650SS for over 40 years myself but always wanted to try a Commando. The transition above 3000 rpm is quite amazing. I worked for years reducing the vibs on my 650SS (lightest std size HBH pistons, dynamic balance, different balance factors, etc.) but no comparison to the Commando over 60 MPH. The featherbed frame does feel just a bit more solid...at least so far. Here are a couple of questions.

1. Current tires are some older Avon AM26 100/90 x 19 Roadriders. The front has about 60% tread left and the rear about 20%. The previous owner provided a new pair of Dunlop K81s in 4.10 x 19. I have heard mixed reviews about K81's although the original testers back in the day thought they were great. Should I go ahead and mount the K-81s or wait until after the first of the year when the rumor mill says Avon Roadrider MK2s might be available in 100/90 x 19 again?

2. I do have a bit of the low speed (40 mph) Commando wobble. Okay with both hands on the bars but it would be nice to minimize this. I do have one leaking fork seal so I plan to rebuild the forks (PO provided an AN kit), replace the tires, verify alignment, adjust the isolastics, and maybe add a steering damper. Is this a reasonable plan? Any other suggestions?
 
I have K81s on my Mk3 and Avon Roadriders on my CB750K6. I was going off the Dunlops, they didn't seem as good as the Avons, until I like for like replaced the Commando's worn rear (front still plenty of life). The new tyre made heck of a difference. My conclusion is both brands give plenty of confidence and performance for spirited road riding. I also feel the Dunlop looks better for the Norton, if that is important.

That said, neither are as good as modern tubeless like the Road 6s on my modern bike. That's a heck of a tyre, takes abuse, handles and lasts.
 
raleypc said:
I recently picked up a very nice 850 MK3 that had belonged to a friend for 20 years. I really enjoy riding it. The top gear roll on performance is addicting. The electric starter works great along with everything else. I have owned a 650SS for over 40 years myself but always wanted to try a Commando. The transition above 3000 rpm is quite amazing. I worked for years reducing the vibs on my 650SS (lightest std size HBH pistons, dynamic balance, different balance factors, etc.) but no comparison to the Commando over 60 MPH. The featherbed frame does feel just a bit more solid...at least so far. Here are a couple of questions.

1. Current tires are some older Avon AM26 100/90 x 19 Roadriders. The front has about 60% tread left and the rear about 20%. The previous owner provided a new pair of Dunlop K81s in 4.10 x 19. I have heard mixed reviews about K81's although the original testers back in the day thought they were great. Should I go ahead and mount the K-81s or wait until after the first of the year when the rumor mill says Avon Roadrider MK2s might be available in 100/90 x 19 again?

2. I do have a bit of the low speed (40 mph) Commando wobble. Okay with both hands on the bars but it would be nice to minimize this. I do have one leaking fork seal so I plan to rebuild the forks (PO provided an AN kit), replace the tires, verify alignment, adjust the isolastics, and maybe add a steering damper. Is this a reasonable plan? Any other suggestions?
Click to expand...
Call me about the wobble - too hard to explain here. And/or, read the section starting at September 18, 2024 here: https://gregmarsh.com/MC/Norton/Combat240721.aspx

That bike was looking for a rider to kill! If the rear brake didn't get you, the high-speed wobble would if you didn't know how to stop one! Little wobble below 50 mph, full stop to stop at 70 mph. A steering damper only masks the problem - fix the problem, not the symptom!

I posted today that the Roadriders won't be available in the US until mid-2026. Dunlop K81s were the tire back then. However, roads have changed - if you're into dirt roads and reasonable cornering - they are great. For hard cornering, not as great. I don't know how true, but Dunlop doesn't like people using old tires even if never mounted so look at the date code and the Dunlop site.
 
IMHO, the Avon AM26 offers noticeably superior handling compared with the Dunlop K81 and the bike sits about 1/2” lower.
Nothing compares to the featherbed frame. The 650cc motor will vibrate, but nothing like the 750cc Atlas. Having owned 3
Commandos and a 650ss, I have never experienced any sort of wobble and if I did I would seek to fix the problem. A damper is just
masking it.
 
Mart UK said:
I have K81s on my Mk3 and Avon Roadriders on my CB750K6. I was going off the Dunlops, they didn't seem as good as the Avons, until I like for like replaced the Commando's worn rear (front still plenty of life). The new tyre made heck of a difference. My conclusion is both brands give plenty of confidence and performance for spirited road riding. I also feel the Dunlop looks better for the Norton, if that is important.

That said, neither are as good as modern tubeless like the Road 6s on my modern bike. That's a heck of a tyre, takes abuse, handles and lasts.
Click to expand...
Thanks for the feedback on the K-81's. I think I will give them a try. I like the looks as well. They fill out the fenders nicely compared to the Avons.
 
lazyeye6 said:
IMHO, the Avon AM26 offers noticeably superior handling compared with the Dunlop K81 and the bike sits about 1/2” lower.
Nothing compares to the featherbed frame. The 650cc motor will vibrate, but nothing like the 750cc Atlas. Having owned 3
Commandos and a 650ss, I have never experienced any sort of wobble and if I did I would seek to fix the problem. A damper is just
masking it.
Click to expand...
Thanks. I have AM26s on my 650SS and they do handle great. Quite a step up the Avon Speedmaster and GP that I had on the bike. I hoping new rubber might cure the wobble on the 850.
 
marshg246 said:
Call me about the wobble - too hard to explain here. And/or, read the section starting at September 18, 2024 here: https://gregmarsh.com/MC/Norton/Combat240721.aspx

That bike was looking for a rider to kill! If the rear brake didn't get you, the high-speed wobble would if you didn't know how to stop one! Little wobble below 50 mph, full stop to stop at 70 mph. A steering damper only masks the problem - fix the problem, not the symptom!

I posted today that the Roadriders won't be available in the US until mid-2026. Dunlop K81s were the tire back then. However, roads have changed - if you're into dirt roads and reasonable cornering - they are great. For hard cornering, not as great. I don't know how true, but Dunlop doesn't like people using old tires even if never mounted so look at the date code and the Dunlop site.
Click to expand...
Thanks Greg! Interesting issue with the tweaked yokes. Maybe some NT quality control problems in 75? I will check mine when I rebuild the forks. Thanks for the heads up on the Roadriders. I don't think my current rubber will last until mid-26 so I am going with the K-81's for now.
 
Wobble is gone! Added an AN steering damper which cured 80% of it. Replaced the worn Avon Road Riders with new TT100's and that took care of the rest. Really solid handling now. It seems like a lot of 70's bikes had that tendency. I had a few BMW's of that era and would head shake a bit around 40 mph if you let go of the bars. My Moto Guzzi Eldorado has a bit of that as well.
 

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