Engine is making thrashing noise at mid to high RPM


Local time
12:58 AM
Apr 9, 2008
Richmond, NH
Hi -

Love my 80cc center mount, have about 600 miles on it now. Have gotten into the habit of tightening engine bolts, carb bolts, chain, gas tank bolts. And oiling chain, greasing left drive sprocket and bearing in clutch pin, etc.

Has been pretty stable for a month but today, on my 16 mile ride to work, the engine started making a thrashing noise at higher RPMS. First I noted my exhaust was loose (I have a LARGE hose clamp that holds it to the frame, so I tightened it). I don't think it is the power part of the engine, as it sounds fine at low RPM.

When I got to work I went over it. The spark plug it tight, I adjusted the clutch after looking at the clutch pads - seems to be a lot left on them. Could use a little grease on the primary gears, but they look wet, not dry. I checked the head bolts, and tightened the chain. It doesn't look like the clutch is hitting the cover or anything, there are no marks.

Everything LOOKS fine. After my adjustments, I took it out for a ride, and again at higher engine speed I hear a thrashing that wasn't there before. It came on suddenly this morning, by the way.

One stupid thing it might be is the chain guard might be vibrating, but it sounds like it is coming from the clutch area. I am planning to grease the clutch and drive gear this evening, and will put my hand on the chain guard on my way home to see if this quiets it.

Anyone have any suggestions on what I should check ? I am wondering if I have a problem with a bearing on the piston or crankshaft. How hard is it to replace these - is there a thread somewhere ?

Any help would be appreciated

Last edited:
To finish this out - it was lack of grease (!)

Sounded so bad, I guess I expected the worst. I see a lot of posts about engine noise at higher RPM. If it is like mine, the noise sounds like the engine is going to fall apart.

A blob of grease on the primary gears (right side), and some in the clutch pin and ball bearing hole (right side) seems to have fixed it.

Someone told me these 2 cycle center mounts eat grease, and since I did this same grease routine maybe 4 weeks ago, I believe him. At that time I had a squeak in what I first thought was the rear wheel bearings, but later found out it was the clutch assembly. Started to tear it apart, until (duh) the grease suggestion that fixed this problem.

Grease it !

Where is the pin and bearing hole you're referring to - I have a squeak, too - directly related to walking the bike while holding in the clutch. I'll lube today - but I was afraid of getting grease on the clutch pads...can you possibly show a picture of where/how you lubed?

Marktur- if you pull off the cover that houses your clutch lever and cam arm (rear cover on left side, three screws), you'll find the 1" (or so) pushrod that the cam arm contacts sticking out of the hole at the center of the drive gear. Just pull it out, wipe it off, put grease on it (and a little into the hole because there's a ball in there too), and that makes the squeak go away. Just don't get carried away. :) I also make sure to lube the cam arm. If you've never taken the cover off, don't worry. It's pretty self-explanatory once you get in there. Hope this helps.