I have  bad knocking at all revs but louder at low revs, sounds like the piston is going up and down sideways,its has already had one new piston in it's life.

 

Any one got any other ideas , or have I answered my own.

 

And has any one tried the new exchange recon  barrel and piston from (<mention of this company is not permitted on Trials Central. Please delete this post>) 

Is the main bearings ok?see if you can get any movement on the fflywheel

Pistons tend to rattle rather than knock,does it go well or is it down on power.If the flywheel weight is loose it sounds like major engine work is needed,worth taking the ignition cover off to check

Thanks for you reply's , I a little confused as I have been told you can buy over sized piston, dose any one know about them , and has anyone fitted one ?

My 04 knocked fairly bad especially on over run. I thought it was the piston or little end.

I noticed my head gasket was in the wrong position (tab not to the front) I corrected that and decoked the top of the piston and head its quiet now and has more power.

 

Edited July 16, 201511 yr by richfr

My 03 rattled a lot which did not affect the running but offended my mechanical sensibilites.  I had "someone" listen to it and he told me that it needed a rebore with oversize piston.  I won't mention names, to avoid embarrassment, but if anyone should have known better it was this person.  The 03 has a plated bore. 

 

I don't know which company can't be mentioned on here but I sent a new piston and the barrel to one that advertises widely (and which may play tennis with a very strong arm) and the result was an excellent job.

 

Having said all that I don't think your knock will be the bore but engine noises can be hard to describe in words.  Can we post audio files on here?  Though recordings always seem to make a twostroke sound like two rats fighting in a dustbin anyway.

is this company allowed to be mentioned?

 

http://www.roadanddirtperformancebikeparts.co.uk/CYLINDER-NICKEL-PLATING.html

In regards to bore and pistons, it's correct that the bore is plated with a chrome like coating and as such, can't be rebored, but when worn is replated.

 

Again, it's correct there are oversize pistons available, but they are only microns bigger than the last, not millimeters!

(they are usually marked up A, B, C & D)

 

The idea is (check handbook) to check after X hours use and when required replace the piston with the next one up until it's gone too far and it needs a replate and you start again from A.

 

In reality, they get worn out way past the largest piston before anyone does any checking so a replate is needed.

 

I have never bought an exchange barrel and piston, but supplied a new piston to the replating company (Langcourts) and had the plating matched to that particular piston.

 

As you are unsure of what is rattling, I would advise having someone confirm the problem before attempting a "shot in the dark" repair as it can all start getting very expensive.

Maybe start with the piston and bore being measured properly, while the barrel is off asked them to check the mains and big end.