Cylinder shaking violently at mid rpm's..

GoldenMotor.com

borntofli

Member
Jul 27, 2012
306
0
16
tx
Ht 66, 150 miles on it..... Take off to mid cruising speed motor runs fine,,, Above this the cylinder and head shake violently... If i go from cruising and give it full throttle it will not shake as bad thru this rpm range....
Above 2/3 throttle is smooths out a little, but still fairly bad vibrating...

Could upper needle bearing be bad?? Any ideas???

Thanks as always....
 

2door

Moderator
Staff member
Sep 15, 2008
16,302
175
63
Littleton, Colorado
Start by taking a close look at your engine mounts. If the cylinder is moving enough that you can see it, something's wrong there. If you've tried to use rubber in the mounts remove it and mount the engine solidly to the frame.

Tom
 

missle3944

Member
Feb 28, 2012
51
0
6
California
I seem to have the same exact problem too!

My engine seems to rattle when I let off the throttle after accelerating. I will accelerate and then when i let off it really starts rattaling. but it only does it for like 10 or 15 seconds

any help would be nice,

thanks guys
 

borntofli

Member
Jul 27, 2012
306
0
16
tx
Its not a mounting issue...... Rock solid 3/16 steel mount.....Vibration is from unbalanced piston or something up high..... Only the top of the motor vibrates, and I mean vibrates.... You can see the cyl and head vibrating 1/8-1/4 inch in every direction.... Its not worth tearing down the bottom, new engine is cheaper than fixint that...

I'll try replacing the top bearing and see if that helps...

What else can cause such vibration in the top end.........
 

missle3944

Member
Feb 28, 2012
51
0
6
California
The problem that I'm having is that the ubolt I'm using only comes in contact with the down tube at 2 points. Would a rubber tube around the u bolt help distribute the weight?
 

crassius

Well-Known Member
Sep 30, 2012
4,032
158
63
USA
you might have a small crack in the frame that lets the motor rock a bit

you could try running a metal bar from a head bolt to the frame
 

mew905

New Member
Sep 24, 2012
647
9
0
Moose Jaw
four-stroking may also do it too... My roommate's motor fourstrokes like crazy and the vibrations are pretty intense. My motor's a bit leaner and doesnt fourstroke until 62kph, but if I let off the throttle a bit (not completely) it'll four-stroke and vibrate.