Buzz vibration under load

[dnt13]

2000 GL1500 SE ~ 40,000 km
I have a buzzing sound and vibration that seems to be coming from the engine area when the motor is lugged and working hard Eg: accelerating in a gear too high or when climbing a hill. It’s not a metallic sound - almost sounds like vibrating plastic and it buzzes the footpegs. The noise and vibration go away with increased speed and/or gearing down so the engine is not overloaded. Anybody else experience this? Not sure I had this before I changed to hi output alternator. I removed the new alt to check rotation and it spins freely. Yes, I replaced the rubber alt drive dampers. Thinking maybe I should check timing belt tension? I replaced the belts about 15,000 km ago but they shouldn’t stretch, correct? Someone said it’s possibly a U-joint problem but vibration is only under load and on acceleration and there’s only 40,000 km on it! After speeding up a bit or gearing down everything is completely smooth. Decelerating from speed is also completely smooth - no vibration whatsoever. Thoughts before I dive in without knowing what I should be looking for?
Dennis

[DenverWinger]

Hi Dennis,
I kinda think you are looking for a problem where there isn't one. If you are lugging the engine, you are most likely just feeling the individual power pulses from each cylinder as the engine slowly turns. I would expect this on heavy throttle at low RPM.

[Erdeniz Umman]

When you feel the vibration, you can pull in the clutch to isolate the problem whether it is caused by engine or drive system.

[CrystalPistol]

2000 GL1500 SE ~ 40,000 km
I have a buzzing sound and vibration that seems to be coming from the engine area when the motor is lugged and working hard Eg: accelerating in a gear too high or when climbing a hill. It’s not a metallic sound - almost sounds like vibrating plastic and it buzzes the footpegs. The noise and vibration go away with increased speed and/or gearing down so the engine is not overloaded. Anybody else experience this? Not sure I had this before I changed to hi output alternator. I removed the new alt to check rotation and it spins freely. Yes, I replaced the rubber alt drive dampers. Thinking maybe I should check timing belt tension? I replaced the belts about 15,000 km ago but they shouldn’t stretch, correct? Someone said it’s possibly a U-joint problem but vibration is only under load and on acceleration and there’s only 40,000 km on it! After speeding up a bit or gearing down everything is completely smooth. Decelerating from speed is also completely smooth - no vibration whatsoever. Thoughts before I dive in without knowing what I should be looking for?
Dennis

Well, there you go. A solution looking for a problem? It's a 6 x 250cc cylinder engine of 4 stroke type with but three power pulses each revolution. The obvious cure you desire is to yank that engine out, split it open, mill out all the guts … and install a big electric motor to cure it … and haul batteries in the trailer.

You're killing it knowingly lugging it.

The 1500s have 5,500 rpm redlines, they are tuned to make power lower down than the 1200s were, but 3,000 or 4,000 ain't hurting it. The 1200s are even worse when abused by lugging under load in a higher gear, but they are 4 x 300CC cylinders & only have 2 power pulses per revolution. Any load, it was happiest at 2,500 or 3,000 rpm and above. 7,500 rpm redline. Luxury car makers used V-12 & V-16s back in the earlier days of the automobile when low rpm power was vogue, to smooth the power delivery. They knew how to build big 4 or 6 cylinder engines cheaper with fewer parts, but they would throb like a ship's engine.

[eastkytriker]

2000 GL1500 SE ~ 40,000 km
I have a buzzing sound and vibration that seems to be coming from the engine area when the motor is lugged and working hard Eg: accelerating in a gear too high or when climbing a hill. It’s not a metallic sound - almost sounds like vibrating plastic and it buzzes the footpegs. The noise and vibration go away with increased speed and/or gearing down so the engine is not overloaded. Anybody else experience this? Not sure I had this before I changed to hi output alternator. I removed the new alt to check rotation and it spins freely. Yes, I replaced the rubber alt drive dampers. Thinking maybe I should check timing belt tension? I replaced the belts about 15,000 km ago but they shouldn’t stretch, correct? Someone said it’s possibly a U-joint problem but vibration is only under load and on acceleration and there’s only 40,000 km on it! After speeding up a bit or gearing down everything is completely smooth. Decelerating from speed is also completely smooth - no vibration whatsoever. Thoughts before I dive in without knowing what I should be looking for?
Dennis

My 1500 has the same problem. It started when I replaced the Alternator with then high output one (From China i'm sure) I also replaced the rubber dampers. Getting the OEM rebuilt to put back in service hopefully it will cure the vibration.

[thebruce]

I agree with CrystalPistol.

If it makes funny noises lugging it, don't do that. Stay in the sweet spot.

Mmmm... sweet spot.

Not helping anything by making it to 5th before at least 80km/h (roundabout 50mph).

[CrystalPistol]

I agree with CrystalPistol.

If it makes funny noises lugging it, don't do that. Stay in the sweet spot.

Mmmm... sweet spot.

Not helping anything by making it to 5th before at least 80km/h (roundabout 50mph).

Yep,a vibration resulting from an alternator is not going to smooth out at higher RPMs. Man uses the word "lugging" and he even writes "The noise and vibration go away with increased speed and/or gearing down so the engine is not overloaded", he described the cause. Ain't the alternator neither.