Not a shimmy, not a shake. What is it?

Brly · May 28, 2011

Soooo, The Norton ('74 850) runs awesome. Got my paint back last night and spent this morning putting the final touches on everything. Starts first kick. Took it for a quick spin down the dirt road, then set the timing with a light. Runs great. I've had it out twice today for short runs and it has performed perfectly, except......

There is no shaking at all (other than normal vibration) and no shimmies, had it up to around 60 mph I would say. At pretty much any speed over 15 mph, it feels like there is a bump on one of the tires, almost like a "chugging" sensation but the engine is running smoothly. I couldn't find anything that would make the symptom go away. At no point was it overbearing or uncomfortable, but it was definitely there and is not normal. All I've done so far is to tighten up the chain (more because it needed it than a solution to the problem). While on the center stand, spinning the front or back tire produces a nice smooth spin of both tire and rim.

I put brand new MKIII isolastics on and I'm using the stock headsteady. I will check the gap on the iso's.

Ideas? Possible causes?

Let me know what other info you need.

Thanks,
Ben

rvich · May 28, 2011

A spot on the tire where the bead didn't seat properly and is causing a flat spot on the tire?

Just a guess based on personal experience.

Russ

daveh · May 28, 2011

Hi Ben — Russ could be right. In case it isn't that, how old are the tyres? You sure they have not deformed? It would hardly be an unbalanced front wheel because you say it happens at slow speed. How about your final drive chain — has a link seized or are there any teeth missing or broken on either sprocket? The chain could have a tight spot and you can see this if you rotate the wheel. Check the tension while sitting on the bike or otherwise compressing the rear suspension.

Brly · May 28, 2011

Going out to check these things very soon. The tires are brand new Avon Roadriders. Have to check to see about the beads being seated. The drive chain is brand new also, masterlink installed correctly. I did not change the sprockets but all the teeth are there. The chain runs smoothly.

Keep the ideas coming. I'm going out to investigate right now.

Love this forum!

Ben

AussieCombat · May 28, 2011

Yes Dave that sounds also possible. A stretched chain, possibly too tight.
Sprockets can wear out of shape.
AC.

comnoz · May 28, 2011

If you have rimlocks installed make sure the tire is under the lock and not on top of it. Let the air out and see if you can push the rimlock in to make sure it installed correctly. Also check to make sure you can push the valve stem in while the air is out. They can get caught and do bad things as well. Jim

Brly · May 28, 2011

Thanks guys! It got dark before I got a chance to check out the tire beads. But I did find that my primary chain was pretty tight and my drive chain was also a little tight. They are set correctly now. I'll have to wait until tomorrow to check out the tire issue. If it is just a mis-set bead, can I let the air out and reinflate until I get it right? Or is there more to it than that? Never had an issue with tires, so I don't know much about them.

Thanks again,

Ben

Edit: Jim - rimlocks? I'm pretty sure I just have stock wheels. Enlighten me please.

comnoz · May 28, 2011

Rimlocks came stock on Commandos. You can tell if they are still there by looking for the stud that looks like a valve stem 180 degrees away from the real valve stem. They are not needed unless you are drag racing or running very low tire pressures so most have been discarded long ago as they make installing a tire a little more challenging. Jim

Hobot · May 28, 2011

Don't know if it applies in your case but I once had a thumping that turned out to be a combo of too stiff an O-ring chain and too slack tension which allowing it to ride on top of the teeth to jerk swing arm up against the shocks.

I've had a rear tire leak down w/o rim lock on and almost killed me when the tire came off the rim over 50 mph. Only powerful dragsters with wide sticky tire can spin rear tire in its rim so not really its purpose on street Commandos. I now struggle with rim lock on rear for that rare event that can be too damn memorable.

rvich · May 28, 2011

I put Avons on my bike. The tire would not seat correctly due to some rust on the inside of the rim that the sticky rubber just would not slide over. Looking at it, you wouldn't have thought it would be that big a deal but I had to take the tire and rim band off and clean it well with a wire brush before I could get it to set right. When I rode the bike before getting figured out the flat spot created was most noticable at about 30 MPH. There is a tiny raised stripe on the sidewall of the tire that should be about 1/16-inch away from the edge of the rim all around. It makes it easy to spot if it disappears below the edge of the rim.
I would try deflating, lubing the rim well and inflating first but it didn't do it for me. If you find a spot where the bead has not popped out all the way, mark it , deflate the tire and push it away from the rim and look to see if there is a nice crusty spot on the inside of the rim there.

Russ

Hobot · May 29, 2011

uGH it took me 5 or 6 tires, [stopped wanting to count] to get 130 on a WM3 rim w/o the bead indicator line obviously way out bounds. It took sun hot, soapy water spray plus kicking, shoving horizontal wheel to get mostly centered then over 60 lb to finally get it to pop-seat pretty much dead on all around. On this brute the slam bamming on ground didn't do much but beat me down.

Sure hope this instant case is as simple as a tire out of round or not squarely seated, one is an annoyance the other is dangerous. I did not feel a thing on unseated bead, till it tied to pass me and then the survival fight was on with 2nd,3d,4th --- instant reactions being to bail off - it was so hard effort scary lucky.

Theze Cdo's might be simply the most mysteriously complex craft ever conceived.

Carbonfibre · May 29, 2011

If all else fails check the wheel balance, even though issues here seem to affect bikes at much higher speeds.

splatt · May 29, 2011

Back brake not centralised ?

Torontonian · May 29, 2011

It could be a "Shake, Rattle and Roll" and then U could make music. But seriously inspect the tires and then OVERINFLATE ! Then bring air pressure way down again to say 30 lbs. Inspect again tires. I'm sure you parked the bike for the long winter on the centerstand to avoid settling/flat spots ,right ?

comnoz · May 29, 2011

hobot said:
Don't know if it applies in your case but I once had a thumping that turned out to be a combo of too stiff an O-ring chain and too slack tension which allowing it to ride on top of the teeth to jerk swing arm up against the shocks.

I've had a rear tire leak down w/o rim lock on and almost killed me when the tire came off the rim over 50 mph. Only powerful dragsters with wide sticky tire can spin rear tire in its rim so not really its purpose on street Commandos. I now struggle with rim lock on rear for that rare event that can be too damn memorable.

I hate to tell you this but if the tire deflates at speed it will come off the rim even with a single rimlock in place. Ask me how I know. Maybe it would stay on with three rimlocks. Jim

Brly · May 29, 2011

The tires are brand new, put on about 2 weeks ago by a dealership near my apartment. Checked the tires. Rear tire is good. Front tire has about a 10 inch section on both sides of the rim that the bead is not set. I followed the suggestions here; deflated, sanded any rust I could (pretty clean actually), greased the crap out of 'em and inflated, no dice. Did that about 6 times. Beat the crap out of the tire with a hammer, etc, etc. Couldn't make it happen. Of course everyone is closed today and tomorrow for the holiday. SO, I'm gonna truck it out to my apartment and have it remounted Tuesday by the people that didn't do it right the first time.

This is extremely frustrating as the rest of the bike is 100% ready to go. Also frustrating because I can't fix it.

Big thanks to everyone for your help. I'll have pictures of the completed project up soon.

Ben

Hobot · May 29, 2011

Been there done that Ben as a bunch of others have and will continue too. Part of the Commando maturing process to me, like learning to fast in yoga routines for self discipline and stilling ones restless mind and desire to ride with the wind...

Torontonian · May 29, 2011

Brly , just got back in 1 : a.m. with wife on back after amazing drive back from dinner party. After thinking about your predicament , I pre - overinflated to 32 lbs. and life is good. Awesome drive home. New shocks. High test gas ,twistin' er .

Brly · May 31, 2011

Boy what a weekend. I couldn't ride the Norton because of the front tire issue, which will be taken care of today. So I talked my brother into hauling it out to my apartment for me. So we got it all loaded up and ready to go, had my car packed with all my tool boxes and tons of other stuff. Got down the road about 10 miles and stopped to get a drink and check the load. All was good so we went in to get a soda and my brother says "Hey, is that your car that's smoking?" .......Yes. Popped the hood and theres oil on the case. It probably would've made it, but it was an hour and half ride, I had my girlfriend with me and my brother still had another two hour ride ahead of him once he dropped my stuff off. Luckily I was able to borrow my Mom's car for the week.

Anyway, the whole reason for this post is pictures.

And before anyone says anything; I know, its another black and gold roadster. I picked out a black with tiny tiny metal flake in it. I like it.

Thanks everyone for all the help through this build. I will be doing upgrades like belt drive and suspension in the future so I'll be back for more help.
Ben

daveh · May 31, 2011

Looks a really nice, tidy Roadster!

Not a shimmy, not a shake. What is it?

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