Buzzing at high speed

TVB · Post by **TVB** » Wed Oct 02, 2013 11:58 pm

Lately my Buddy 50's been making a new noise (or maybe it's just gotten loud enough for me to notice it), and I'm wondering if anyone has any guesses what it might be.

At high speeds [insert deprecating remark about 50cc scoots here], on top of the usual purr of the engine there's a buzz. It's high, but not really high: around the frequency of a bee or fly. It shows up above 35mph (indicated), but doesn't vary in pitch with throttle or speed. When I let off the throttle – and especially if I brake – the buzz stutters, then fades away as my speed drops. That pattern suggests to me that it's related to the transmission, but I lack the expertise to guess what.

I haven't been riding any distances lately, but it sounds the same whether the bike's been going 5 yards or 5 miles. It's performing normally otherwise in terms of acceleration and top speed. Gas mileage is off a bit, but that's probably the colder weather.

Any thoughts?

charlie55 · Post by **charlie55** » Thu Oct 03, 2013 12:05 am

Does the point at which the buzzing stops altogether seem to coincide with the speed at which the clutch completely disengages (I.e., when you start to freewheel)?

lovemysan · Post by **lovemysan** » Thu Oct 03, 2013 2:11 am

How many miles on your rollers? And or belt? Check for cracked mount on airbox or exhaust?

OldGuy · Post by **OldGuy** » Thu Oct 03, 2013 2:28 am

If it isn't transmission, then it sounds like something external to the motor/transmission buzzing which has a specific oscillation frequency. For example, a mirror, exhaust shield, rack, kickstand, engine mount bolt, or other items might have a very specific frequency they'll vibrate at. And this frequency won't change with engine speed or actual scooter speed.

Such a vibration requires only a loose component and enough energy to keep it going. When you reach a certain speed your scooter may produce enough vibration amplitude to "excite" this vibration. When you slow down enough the buzzing quits because there is not enough energy to keep it going.

I suggest you carefully go over every fastener and part on the scooter that you can reach and see if you can find something that needs to be tightened.

Whatever the cause, the buzzing is probably an indication of something loose or something else that is not right. And these things tend to get worse instead of self-correct. I hope you find it!

agrogod · Post by **agrogod** » Thu Oct 03, 2013 8:51 am

Electrical parts will also make a buzzing noise as they get older, with as many miles as you probably got, and all the weird stator stories this year......

TVB · Post by **TVB** » Thu Oct 03, 2013 3:52 pm

charlie55 wrote:Does the point at which the buzzing stops altogether seem to coincide with the speed at which the clutch completely disengages (I.e., when you start to freewheel)?

Could be. I can't tell for sure when that happens.

TVB · Post by **TVB** » Thu Oct 03, 2013 3:54 pm

lovemysan wrote:How many miles on your rollers? And or belt? Check for cracked mount on airbox or exhaust?

Belt and rollers were replaced back in March, so they only have a few thousand miles on them. The exhaust is getting pretty corroded and flaky where it connects to the engine, but last I checked it was intact.

TVB · Post by **TVB** » Thu Oct 03, 2013 4:18 pm

OldGuy wrote:If it isn't transmission, then it sounds like something external to the motor/transmission buzzing which has a specific oscillation frequency.

Yeah, I've been thinking it might be some kind of resonance vibration, but haven't been able to locate anything that might be making it. It's hard to gauge the source (especially at 35mph), but it does seem to be coming from the nether regions.

TVB · Post by **TVB** » Fri Oct 04, 2013 10:06 pm

It's also doing the stutter-buzz when I drop the throttle at slower speeds, which I'm guessing points again at the transmission.

ed85379 · Post by **ed85379** » Tue Oct 08, 2013 3:04 pm

TVB wrote:
OldGuy wrote:If it isn't transmission, then it sounds like something external to the motor/transmission buzzing which has a specific oscillation frequency.
Yeah, I've been thinking it might be some kind of resonance vibration, but haven't been able to locate anything that might be making it. It's hard to gauge the source (especially at 35mph), but it does seem to be coming from the nether regions.

Put it up on the center stand and rev it up stationary. Have someone help you to make it even easier so you can track down the source. One trick is to hold a straw up to your ear. When it is pointed right at the source of the sound, it will sound a lot louder through the straw.

When my scooter was making a similar sound, it was the side bolts for my cowl-protector/rear-rack that were loosening.

TVB · Post by **TVB** » Wed Oct 09, 2013 9:08 pm

I brought it in to the shop, and he replaced the rollers and the variator, which were both showing wear that would cause vibration at speed.

Unfortunately, on the ride home, I heard most of the same buzzing. At times it seems worse.

And more unfortunately, the mechanic said the engine in general was sounding like it was going to need a rebuild. He couldn't be sure without further evaluation (he mentioned a compression test) just how much rebuilding, and I didn't have time for that (this was me on a long lunch break and already late for a meeting), so that question was left for another day. He's going to call me with some estimates of the possibilities, which might include: top end, bottom end, and (possibly just as cost effective, and to be honest the only one that I – not a gearhead – fully understand what it involves) replacing the engine.

Post by **ericalm** » Wed Oct 09, 2013 11:14 pm

Why would it need a rebuild?

MGM · Post by **MGM** » Thu Oct 10, 2013 12:07 am

I wouldn't automatically assume rebuild. My son has a Buddy 50 with about 9000 miles. Rollers, belt and brakes replaced at 7000. There are definitely noises that weren't there 2000 miles ago. More like a whine in the trans area. I've checked everything and have come to the conclusion that things change with age. I know you ride alot and take long trips. I also believe that you've done maintenance at least to recommended schedule. There is no reason to believe there is need for rebuild. Do you notice any performance degradation? The top end usually goes first on a two stroke and I believe that you can feel that coming. Just my opinion, but I'd be wary of the recommendation of rebuild based on noise alone. Compression check is a good idea.

TVB · Post by **TVB** » Thu Oct 10, 2013 1:52 am

MGM wrote:Just my opinion, but I'd be wary of the recommendation of rebuild based on noise alone. Compression check is a good idea.

He wasn't recommending it just based on the sounds. What he was recommending was a compression check and some other detective work (that I didn't have time for today), warning that some kind of rebuild might be what it called for. My bike has a bit more than 9000 miles on it (2.5 times that), and one of the sounds he heard while it was idling (he "pointed it out" to me as best as one can do with a sound) suggested to him that ... rings ... something. Sorry, but internal combustion engineering is about as interesting to me as 19th century European history, so I'm not particularly good at following it or repeating it. (And if I'd wanted to learn it, I'd've bought a Chinascoot.

)

TVB · Post by **TVB** » Fri Oct 11, 2013 9:38 pm

I left a message for the mechanic this afternoon, saying that the buzzing is still a problem. They're open Saturday morning, and maybe he'll pull a solution of out of his ... hat, but otherwise it looks like the Buddy is going to have to miss my Fall vacation. I've got a cabin on a river in the woods near Grand Traverse and Sleeping Bear Dunes for next week, and I was hoping to ride up there, and do a little color touring on the scooter. But instead I'll have to take the car. I'll probably put the bicycle in the back and do a little pedaling instead, but the extra work and shorter range takes some of the fun out of sightseeing.

TVB · Post by **TVB** » Sat Oct 19, 2013 11:49 pm

Pardon me while I go off on a tangent here ....

Part of the reason I wanted to get the scooter fixed – and pronto – was that I had a vacation planned, leaving Monday morning. Since I canceled the big ride up to the UP this past summer, I had a week of paid-time-off to use, so I rented a cabin on a river up north (Traverse City area), just to get away from the world for a while. And at this time of year, it'd be a great color-tour ride up there and back, and maybe a day trip or two. But on Saturday, I left the scooter at the shop.

OK, so I'll drive up there. Won't be as fun, but it'll be more practical. Then, the night before I left, the car wouldn't start. Not the battery: it had started without hesitation 15 minutes earlier, and now it wouldn't even murmur. It was clearly a dead starter (or possibly something electrical, like a popped fuse or something) ... and there was no way of fixing that quickly. Another day, another vehicle out of commission.

So on Monday, one of the few days of the year when I needed a vehicle to take me out of town ... both of mine were out of service. What are the odds of that? Any other week, I'd be able to make do with my bike and the bus. But not this one. Which added a $125 emergency car rental for the week, on top of the painful sums that my scooter and car would require.

Anyway. The trip was good. Weather could've been nicer, but I got out on the river in the canoe one day, and out for a long ride on the bicycle another. Relaxing. Rental car was a Toyota Yaris: I like.

The car's problem was the starter, and just like any other time in the shop, it's hundreds of dollars in labor and parts.

The scooter's problem ... I haven't talked to the mechanic since I left it with him, just voicemail. At the time, he was talking about starting with compression tests and probably rebuilding the top end, maybe having to rebuild the bottom end, at which point it might be more economical to replace the engine, and if it came to it, they have a new-old-stock 2009 Buddy 50 they could give me trade-in value and a good deal on. I told him to slow down, and authorized him to do the tests and redo the top end if needed. His last message said that was all it took. He didn't say how much, but I'm hoping it's less than the car repairs.

I hope he's right, and the engine's good to go for a while. I'm pretty sure I'll be replacing the car sooner than later (it's turning into a money pit), and really didn't want to buy a new scooter at the same time. Either way, that's about 23K miles on the Buddy without anything that I'd call "engine work" (just routine replacement of worn parts), which is pretty good, I suppose. We'll see how much more I can get out of him.

Dirvin · Post by **Dirvin** » Sun Oct 20, 2013 1:55 pm

I had a similar problem lately, after having the 70cc upgrade done to my Buddy 50. At about 45 bmph, I would hear a buzzing sound, that would disappear after releasing the throttle. When I took the bike in for a 14,000 mile tune-up, the tech found that there was a bad crankshaft seal on the variator side. He replaced that and the buzz is gone. He gave me a long technical analysis which was promptly forgotten. Bike is doing great now.

TVB · Post by **TVB** » Mon Oct 21, 2013 9:04 pm

I picked him up today, and I'm pleased to report that that damn buzzing is gone. In fact the whole tone of the engine has changed, and my nagging this-muffler's-gonna-need-replacing-soon feeling has subsided. Turns out the piston had a crack in it, which wasn't good. But what was causing the noise was some metallic debris inside it, which at certain speeds was was putting it off-balance or something. (Repeat disclaimer about my engine non-expertise.)

He didn't need to go beyond the top-end rebuild that I'd authorized, but he checked out the rest of the engine, and found that it was all within tolerances. He was a bit amazed, and credited getting this far in such good shape to me taking such good care of it. Which is nonsense, because I ride this thing in any weather from 20ºF-100ºF (as long as the streets are clear), and have been known to put 250 miles on it in a 12-hour day.

Although I like that it's much quieter, the engine isn't quite as peppy as it used to be, which I assume is due to fresh components in need of a fresh break-in. Fortunately I have several weeks of stop-and-go commuting still ahead of me this year, which should do the trick.