gy6 72cc vibration By jofos (Read 1,825 times)

[jofos]

Hey folks! Hope everyone is well...

I upgraded the engine from 50 to 72cc and it has been fine... Recently I noticed an oscillating vibration when at high revs. It started weak but seems to be getting stronger and is causing me some concern. (Just got a new job and will have to ride it 45 minutes each way!)

Does anyone have any experience with this occurrence?

Thanks!

J

[sprocket]

Check your cam chain tension...

[felliott]

Could be drive belt causing it also.

[Bashan]

It's hard to say, yes, I've had those things happen. Most of them seem to come and go and mean nothing. If it's running OK you're probably good. My wife's Puma had a buzz develop that seemed to be coming from the engine. It turned out to be the front shroud had a loose fastener. If your valves are set and everything is tight wait for it to resolve or get louder, I've had both happen. If it gets louder you'll be able to isolate it.

[Alleyoop]

Yep, it could also be that the fuel ratio mixture is not set right and not running as smoothly. Also check the motor mounts as well they may be a little loose causeing to much movement. Also check your Muffler and pipe make sure they are nice and tight.
Alleyoop

[jofos]

And the winner is:

Drive belt!!!!! (ding-ding-ding-ding!) (Kudos to felliot for the right answer!)

Just wanted to follow up and say thanks...

Also, let this be a warning to anyone who has this issue:

CHECK the above before you go out, if you are having a weird vibration.

My drive belt broke into a bunch of pieces as I was riding down the road to work. Was able to fix it same day, but it was a PITA!

Thanks again for the info guys!

[Alleyoop]

Great!! Now ask yourself WHY DID THE BELT SHRED? To many miles without changing to a new belt, rollers binding, clutch binding and not opening etc..
Alleyoop

[jofos]

Thanks Alley, you are right... I thought I was in the clear, but after one day of riding it to work it started vibrating exactly the same way again.

I had an old belt (in perfect-looking condition) from when I took out the old engine and put that one on, rode it to work the next day, and it started vibrating a bit on the way home. (45 minute ride each way)

Today it went right back to the same vibration as before, oscillating in and out getting stronger the higher the revs.

Of course I became worried, and drove carefully home. I just opened up the cover where the belt is and checked the belt. It looks fine. No marks or discoloration. But the whole area is VERY hot.

I don't have an impact wrench lying around so I can't easily take off the outer parts to check inside. I took off the front part to replace the belt, looked fine to me (had to disassemble it and reassemble it.)

Other than that it runs fine... Any help?

[Alleyoop]

Mark the Variator to see how high the belt is traveling it may be you need a little longer belt.
If the belt is a little to short when your up there in speed it may want to go higher but it cannot so it is putting a lot of pressure and what it does is it creates a lot of heat.

What size belt is on there?

Here is how to mark the Variator to see how high the belt is traveling up it:
Alleyoop

[jofos]

The belt is a 669

[Alleyoop]

You can get a 681-17.7-30.
Alleyoop
www.partsforscooters.com/106-92_CVT_belt

[jofos]

I think I figured it out (with your help of course).

I was questioning why the belt would suddenly want to travel more without any changes to the mechanics. I was totally forgetting that I recently had an electrical problem and switched out the cdi to a high performance one I had as a spare (I stopped using it because it caused the scoot to "burp" when at high revs, like a miss in a car engine). I guess using that HP CDI gave it that extra boost, allowing the belt to travel more. It would increase my speed if the belt would support it, but if it could not then it would cause the belt to travel too high, cause friction, then heat, and the previous belt over-heated and broke.

Make sense?