So this is why compression is Low 90 psi, interesting how wear is on exhaust port side, Piston has welded to the rings anybody else had this happen, Obviosly going for rebore and piston kit etc.6500miles  apparently that is about the time for first rebore according to Local Yam centre

yeah although the pic is only a thumbnail it does look a bit ragged, 90psi though, not great but not the worst either

6500mls, yammy dealer is talking crap. More like 14k. My TDR did that b4 it blew.

I have heard of 350's doing 20k before trouble. Used responsibly and with quality oils.

 

Well this little DT has not been looked after very well by previous owner,so hardly suprising, just hoping after rebuild that she will start as that was original problem, classic case of no PPM ( planed preventive maintenance ) being carried out .

Will be a good bike in the end but bought a pup as they say oh well deep sigh.

Been there, everybody has bought a lemon at least once.

 its a common enough happening for 2 strokes and looks pretty much like yours, ignoring the vertical lines you can see the actual damage on the piston wall at approximately 4 equidistant spots on the piston..

Look here for a deeper explanation... http://www.off-road.com/dirtbike/tech/dirt-bike-tech-twostroke-seizure-52428.html

Edited November 28, 20159 yr by Cynic

A good link Cynic thanks, I am wondering if the wear took place on the exhaust port side of piston because the power valve was not working when I got it, it was in the closed position permanently I am thinking this could have caused the overheating of the piston in that area as the exhaust gases could not get away at higher revs like they should.

 

6500mls, yammy dealer is talking crap. More like 14k. My TDR did that b4 it blew.

I have heard of 350's doing 20k before trouble. Used responsibly and with quality oils.

 

Agreed, My uncle Rob had a 350LC YPVS  that had done over 42k, ragged to the limit constantly and never missed a beat with the original, 2 strokes are stronger than people give them credit for. Although it did eat itself alive at the end of its life. 14 seems close to the truth.

 

I think a rebore wouldn't go a'miss on that barrel  

 

yep re-bore and new piston etc definitely on the to do list.