Sunl90 insane vibration

Flipem · 10-03-2021, 05:41 PM

Hi guys. I have been wrenching on 50cc "Coolster" style atvs for the last couple months. I recently picked up a Sunl90 and got it running. It runs fine and has great power but the vibration at mid to high rpm is insane. This setup only uses the rear and top motor mounts, they were loose at first and I tightened them up as the motor moved sideways a lot under load. The whole quad shakes and you can hear it growling when this happens. I have read that motor mounts could be an issue but is that the case when they are tightened right up? Are these more prone to vibration than the 50ccs that use the lower mounting plate? I have lots of spare engines to swap in and try as well.

Flipem · 10-06-2021, 10:00 AM

Since apparently no one has run in to this before I will post my solution for future users. My motor mounts were all tight and not the issue. I put a different engine in and the quad is no longer shaking my fillings out. I will tear in to the old engine someday, perhaps it has a bearing out.

buzz · 12-08-2021, 04:50 PM

bad engine

Darth Racer · 12-08-2021, 07:25 PM

I had a problem like that once when I changed the crankshaft in a small generator engine. The counterbalance weights were wrong for that exact model of engine.... Maybe the previous owner changed it out. Parts can be hard to find for some of these ATVs as manufacturers when they are here today ... gone tomorrow.

You can check the connector rod bolts... maybe its starting to come loose. No clue what else it could be.

10-03-2021, 05:41 PM	#1
Flipem Join Date: Oct 2021 Location: Alberta Posts: 2	Sunl90 insane vibration Hi guys. I have been wrenching on 50cc "Coolster" style atvs for the last couple months. I recently picked up a Sunl90 and got it running. It runs fine and has great power but the vibration at mid to high rpm is insane. This setup only uses the rear and top motor mounts, they were loose at first and I tightened them up as the motor moved sideways a lot under load. The whole quad shakes and you can hear it growling when this happens. I have read that motor mounts could be an issue but is that the case when they are tightened right up? Are these more prone to vibration than the 50ccs that use the lower mounting plate? I have lots of spare engines to swap in and try as well.
	0

10-06-2021, 10:00 AM	#2
Flipem Join Date: Oct 2021 Location: Alberta Posts: 2	Since apparently no one has run in to this before I will post my solution for future users. My motor mounts were all tight and not the issue. I put a different engine in and the quad is no longer shaking my fillings out. I will tear in to the old engine someday, perhaps it has a bearing out.
	1

12-08-2021, 04:50 PM	#3
buzz Join Date: Dec 2020 Location: Dayton Pa. Posts: 857	bad engine
	0

12-08-2021, 07:25 PM	#4
Darth Racer Join Date: Apr 2016 Location: MD Posts: 558	I had a problem like that once when I changed the crankshaft in a small generator engine. The counterbalance weights were wrong for that exact model of engine.... Maybe the previous owner changed it out. Parts can be hard to find for some of these ATVs as manufacturers when they are here today ... gone tomorrow. You can check the connector rod bolts... maybe its starting to come loose. No clue what else it could be.
	0