Vibrations.

[Tripleking]

Did 120 mile round trip to and from a classic bike ride on my 75 GT380. She performed flawlessly, even during a two mile stretch on the expressway. I did notice a vibration below 3700 RPM and even more above 4500. It is like an on/off switch, it is there and then it isn't. It only opens under load at those engine speeds. Coasting at those RPMs produces no vibration. There are no unusual noises from the engine and I have good power from 3500 to about 7200. Also, when I come back on the throttle there is some drive line lash. I am thinking the problem is in the clutch or gears. Any thoughts?

[Craig380]

my first thought would be the drive chain being either too tight or too loose. Also check the engine mounting bolts, they can come loose ...

[Tripleking]

Might be the chain. I had a vibration before I adjusted the chain and it went away after tightened it, but that was less than 200 miles ago. Maybe too tight now. I will also check engine mounts. Thx.

[Tripleking]

Engine mounts are very right and chain is properly adjusted. I rode the bike and even though there is no vibration through te pegs between 3700 and 4500, a vibration can be felt when touching the ram air hood at all RPM. As long as engine is accelerating or under constant load. This will happen when sitting in neutral and revving the engine. However, if I run the bike up to say 6000 rpm in any gear (easier to do in the top 3) and let it coast and decelerate, there is no vibration. It is high frequency vibration. It never makes it to the bars however.

[Craig380]

What you've described there is pretty normal on the 380 - although it FEELS smooth through the footpegs, seat and bars, the engine does actually shake and buzz quite a bit if you put a hand or a foot on the generator cover or Ramair cowl.

Although a 2-stroke triple with 120-degree crank throws has perfect primary balance, you do get quite strong secondary 'rocking' forces from the motor because of the 1-2-3 firing order. These do tend to even themselves out a bit above 5,000rpm, but the rubber mounting of the motor is a necessity rather than a luxury.

If the motor isn't making any strange rattling noises, just ride and enjoy (and avoid touching a boot or glove to the engine )

[Tripleking]

What you've described there is pretty normal on the 380 - although it FEELS smooth through the footpegs, seat and bars, the engine does actually shake and buzz quite a bit if you put a hand or a foot on the generator cover or Ramair cowl.

Although a 2-stroke triple with 120-degree crank throws has perfect primary balance, you do get quite strong secondary 'rocking' forces from the motor because of the 1-2-3 firing order. These do tend to even themselves out a bit above 5,000rpm, but the rubber mounting of the motor is a necessity rather than a luxury.

If the motor isn't making any strange rattling noises, just ride and enjoy (and avoid touching a boot or glove to the engine )

No strange noises of any kind. Except for the vibration, it sounds and runs very well. My only concern was the vibration through the pegs.

[Tripleking]

After reading some older posts on this board, I am thinking that my clutch might be the source of my vibrations. I am only getting a "buzzing" vibration in the pegs, not the bars or seat. I mainly get it above 4500 and only when the power is on, never on decal. When I go on and of the throttle, I feel some slop in them drive train. It feels like play in the clutch. Could this be cable adjustment related or is it the nut on the clutch or the clutch itself? Input is welcomed and appreciated.

[Craig380]

I have had the clutch centre nut come loose on my own bike (previous owner had not bent the tab washer enough to stop the nut loosening).

As I recall, this didn't cause excessive noise or vibration, but what it DID do was allow the clutch to slip if the bike was at speed (say 60+mph) and I went over a pothole or bump in the road. The bump caused a jolt through the gearbox which moved the clutch basket, causing momentary clutch slip.

The other thing is, the 380 clutch basket has shock-absorbing springs in it, and these will surely be worn and tired after 40-plus years, which will increase driveline shunt and noise. I think the only cure for this is installing an NOS basket or a less-used one.

Removing the clutch cover is easy enough to check all these points, it's just a pain in the arse having to re-set the ignition timing when you reassemble If you do decide to have a look in there, don't forget the two screws hidden behind the points plate

[Tripleking]

It was the harmonics from the Bassani pipes and header nuts which need to be tightened. Tightened them up and vibration is barely noticeable at any rpm and is absent completely below 4500 and above 5500.

[Craig380]

Glad you got it sorted. Next time, just twist the throttle harder and you won't hear a thing over the noise from the pipes

[Tripleking]

[pearljam724]

Show me a two stoke that doesn't vibrate.

[ConnerVT]

Most barn finds don't vibrate. Until you get them running again. Or if they have a hornets nest in them.

[Tripleking]

Show me a two stoke that doesn't vibrate.

My T250 with a GT250 engine is as smooth as silk. Smother than my four stroke twins.

[tz375]

Try a Yamaha Twin. When all set up perfectly an old style TZ or TD/TR will shake your feet off the pegs and that vibration is hash.

A triple is inherently in almost perfect balance apart from rocking couples. In the real world they tend to shake a little and pipe resonance can make that worse at certain rpms. Wheels out of balance can also cause quite a shake rattle and roll at certain speeds.