Throbbing sound

[Pitts2112]

No, not that kind.  Sorry to disappoint.

Got a question about the Bandit 1200S.

I just took my new-to-me 2001 Bandit out for the first run this afternoon.  It handled great but I noticed the engine runs a little rough.  More importantly, though, I noticed a distinct throbbing sound after the bike warmed up a bit.  The frequency was related to tire speed, not engine speed, because I tried various engine speeds and the sound only changed with the speedometer., but I'm not sure what it is.  

Knowns:
1.  Neither tire was at correct pressure but were not more than 5 psi high or low.  I know that's a lot but it's what I had to work with.
2.  Before I took it out, I tightened the chain as it was way too loose. I put 11 quarter-turns on the adjustment screws before I had the 1/2" or so free play.  When I got back after the 10 mile run, the chain was very tight and all the free play was  out of the chain.

Is it normal for a chain to tighten up after it warms up or did I just not cinch up the axle nut enough?

Any input greatly appreciated!

Cheers

[Cvergi01]

did the bike surge with steady throttle?

is there another description for "throbbing"

grinding?
crunching?
howling?
whining?

throbbing makes me think of a heartbeat

[zeebandit]

Did you adjust the chain when the bike was on the center stand or side stand? The chain should be adjusted when the bike is on the side stand.

[sammyseaman]

Set the proper slack back in chain, make sure everything is tight then ride to see if the sound is still there.

[BuckeyeRider]

Any input greatly appreciated!

Cheers

After you adjust your chain again, go for a ride and once you start to hear/feel the throbbing noise -- reach out and grab your windscreen and see if that changes the noise. If that doesn't do it, push on each side of the fairing a little.

I had a 1200s and the damn fairing and windscreen constantly hummed/buzzed/throbbed. It's a known "thing" with them. I tried a few things that helped (tighened down the bolts a little tighter, replaced the windscreen, added some bits of rubber to the fairing mounts) but it still buzzed away the day I sold it.


I do miss the torque on that thing, but not the buzzing.

[sammyseaman]

After you adjust your chain again, go for a ride and once you start to hear/feel the throbbing noise -- reach out and grab your windscreen and see if that changes the noise. If that doesn't do it, push on each side of the fairing a little.

I had a 1200s and the damn fairing and windscreen constantly hummed/buzzed/throbbed. It's a known "thing" with them. I tried a few things that helped (tighened down the bolts a little tighter, replaced the windscreen, added some bits of rubber to the fairing mounts) but it still buzzed away the day I sold it.


I do miss the torque on that thing, but not the buzzing.

Hmmm... mine never did that but that is interesting. Those kinds of wierd noises drive me nuts.

[Blunder]

No, it's not normal for the chain to tighten up. It's possible your chain has a tight spot. You can tell when the slack changes as you roll the rear wheel a little while the bike is on the centerstand. It's not unusual and not necessarily something to freak out over unless really bad. If it's impossible to keep 1/2" to 1" of slack throughout the length of the chain, then you probably need a new one. It could be the source of your mystery throb, though I imagine it's more of a thrum.

How old is the chain? Has it been cleaned and lubed lately?

I had the fairing buzz, too. I tore up a perfectly good book of matches to make some inserts for where the windshield and fairing come together at the outer edges. A touch of black Sharpie and it's good to go. Bandit mods are cheap.

[Pitts2112]

Adjust the chain while on the SIDESTAND, eh?  Well, because that's a bit counterintuitive, I did it on the centerstand.  I'll have another go tomorrow on the sidestand.  I did adjust it on the centerstand, though, and then put it on the sidestand to check the chain tension while the bike was on the suspension.

The throb is a bit like a heartbeat, in that it's regular and consistent as long as the bike is in motion.  It's not a buzz.  Not a wrenching or graunching but sounds like a low frequency vibration and it definitely fluctuates with the speed of the bike.  If you've ever had a wheel bearing on a car start to go, this sound is similar to that.

Is it possible that I tightened the axle nut too much or not enough?

I THINK this chain only has about 1700 miles on it, but I'll have to check back with the previous owner.

I'll back off on the chain tension with the bike on the sidestand and properly inflate the tires, then see what happens then.  Watch this space!

Thanks for the input everyone!

[Blunder]

You'd think checking chain slack while the bike is on the centerstand would make sense, but truly the results are false.

When the bike is on the centerstand there is no weight on the rear wheel; it's at full extension. What is desirable is enough slack in the chain that it can accommodate the full range of movement of the swingarm. If you have 1/2" of slack when the swingarm is at full extension, as the arm moves to 'level' it might be too tight.

Do you follow this line of reasoning?

Ideally, the swingarm pivot point would be the same as the countershaft axis, but this is hardly ever true. Given this fact, the slack in the chain differs as the swingarm moves during the normal function of a bike's going down the road. That's why it's indicated we check chain slack while the bike is on the sidestand. The suspension is weighted and is somewhere near the midpoint of swingarm motion.

If you want to get all anal about it, have someone near you own weight sit on the bike, holding it upright, and check the slack that way. Fortunately, modern chains that are regularly cleaned and lubed are robust and the sidestand only method will suffice.

Again, I want you to check if the chain is old or neglected. Irregularities in stretching are normal, but there are limits.

[Pitts2112]

Thanks, Blunder.  That explanation makes sense.

Frenchaman, I'm definitely going to give the tires a closer once-over.

I'm taking it in for the state inspection today or tomorrow so I'll have an expert look over these couple of things.  Being a former Harley owner, these chain thingys are all new to me.  

[APEowner]

As others have pointed out the chain is tighter when the bike is on the side stand and there's typically one spot that's tighter than the others.  As you've noticed it's a lot easier to adjust the chain on the center stand than on the side stand.  The technique I was taught when I was a Yamaha tech in an earlier life was to adjust it on the center stand and check it on the side stand.

Rotate the wheel until you find the tight spot on the chain.  Adjust so that you have about 1/2" of slack at the tight spot and the wheel is straight  (If you're feeling particularly anal or your think you have an alignment issue use one of the string techniques to check alignment).  Rotate the wheel again while checking slack to make sure that you don't have more than an inch of slack anywhere and stop again on the tight spot.  Make a chalk mark on the tire aligned with the swing arm or something so that you can find the tight spot again.  Take the bike off the center stand and roll it till you get the mark lined up and check slack again.  The first couple of time you do this you might want to have someone sit on the bike while you check slack so you get a feel for how it changes with chassis height on your bike.

[Pitts2112]

Seems like nothing to worry about.

I just took it to get the state inspection sticker.  Asked the mechanic to check tire pressures, chain tension and explore the throbbing sound.  Tire pressures are now correct, he said chain tension looked fine, had no mechanical explanation for the sound.

On the way out, another guy that had been in the shop and overheard me talking to the mechanic stopped me in the car park and said it was probably just road noise from tires that had been ridden hard on the track.  He used to teach track days somewhere in Georgia and he said that's not unusual and it's nothing to worry about.  

Just finished putting another 50 miles on it and she was fine in all respects.  I'm chalking it up to unfamiliarity with a new bike.

Thanks for the inputs, guys, especially on chain maintenance.  I'll know better next time I decide to check the tension.

Cheers!

[Blunder]

Get new tires.

Tires that have been used on the track are probably shagged out. A decent set of road tires will do you well. Michelin PR2s fit nicely on B12s.

[Giaka]

Chains develop tight sections and that leads to a throbbing sound. Put the bike on the center stand then put it in neutral. Slowly spin the back tire four full rotations and check the chain slack while doing so. Does it get tighter at some point? If it does you are done troubleshooting. If not, then its probably the tires.

[CLAY]

Get new tires.

Tires that have been used on the track are probably shagged out. A decent set of road tires will do you well. Michelin PR2s fit nicely on B12s.

+1.  I have had PR's and PR2's- I love the PR2's.  

[Pitts2112]

I have found a tight spot on the chain.  Is that indicative of a problem or is it a routine trait of every chain?

[APEowner]

I have found a tight spot on the chain.  Is that indicative of a problem or is it a routine trait of every chain?

In my experience (which is now 20 years out of date!) most chain/sprocket sets have a tight spot.  Even brand new.

[Pitts2112]

I finally figured it out!!!!

The throbbing sound was caused by the chain, the drive sprocket or the rear sprocket or some combination thereof.  All three were completely cream crackered so I replaced them all today.  What a difference a tight chain and new sprockets can make!

[Cvergi01]

+1    Been there