I recently bought a 1995 JT320.

It is in good clean condition and was not expensive so I wasnt that bothered that it had a bit of a top end rattle. The worst outcome (I thought) would be a rebore, new piston, and rings.

I did not know that it has a plated barrel, and re-plating piston and rings would cost nearly as much as I paid for the bike.

The bike has now been ridden for about 4 or 5 hours and the noise has NOT got any worse.

I will try to describe in detail and hope someone can tell me what the problem is.......

1. The noise is coming from the top end

2. It is NOT piston slap

3. It only gets very slightly louder when it warms up

4. It is like a regular tapping that speeds up with the revs

5. It does not change when it is under load accelerating or decelerating

6. It is less noticeable at higher revs (this could be because the exhaust noise is masking it)

7. The bike has loads of power

8. It takes LOTS more effort to kick start it than my TXT 270 (so I assume it has good compression)

I am hoping that someone will tell me it just needs a small end bearing, but I won't strip it down untill I have got some advice from this forum !

Edited March 31, 200917 yr by bhg

Small end wear usually causes a noticeable "tinkling" sound. Piston Slap is usually more a definite metallic tapping sound especially on bigger bore machines, also can often be noticed when just easing the piston over tdc with the kickstart by hand.

Best to take a look.

Wayne...

Thanks for your advice Wayne

I have had worn barrel problems with smaller 2strokes in the past, but this sounds different to me.

On those bikes the rattle was worse when ticking-over really slow, and more erratic, this is more regular.

The other bikes were air-cooled, maybe that is why it sounds different (no fins to amplify/change the sound)

What do you think?

bhg

are you sure it is top end?

lean it 45 degrees to left, then to right. does it change?

I have a 2000 200 that has nasty noise. top end rebuilds, new mains, not solved it. come to find out the crank moves left and right in the bearings. The helical gear pushes one way on compression, then load reversed when cylnder fires and it walks the other way.

Tore down, used high temp red loctite on one side. lasted about a month, let lose, noise is back.

Nothing excessively worn, just terrible noise and embarassing. And it will wear the crank journal eventually.

Now I have .014 inch of axial play. Next step is R&R and add some shims from Grainger between main bearing and crank shoulder.

kcj