Hey there, I have just recently removed my barrel and head to replace the base gasket on my 2003 dtr. The cylinder and piston etc are from the athena 170 kit.
On inspection i have noticed the piston has some small scratches on the reed valve side. It appears that the reed valve petals or block have been scratching the piston skirt as it moves up and down (perhaps because its larger than the stock piston + expansion due to heat?. Is this something to worry about? Will I need a new piston? I dont see how a few scratches on the skirt could affect performance or reduce the life of the engine. But what do I know? Im merely a novice when it comes to this. Oh and before you ask there are no scratches or marks on the cylinder walls or anywhere else on the piston.
In addition there appears to be a small amount of blow-by marks on the piston (see picture below) is this normal or excessive? Again, I am a novice so please enlighten me!
Hey mate, yeah sorry i thought i deleted that other post yesterday as i was having problems uploading pics. Ill delete it now and copy over your comments so others can view them too! my bad. Thanks for replying, i have had no rebore or work done on this cylinder or piston etc, however i did not fit the athena kit myself so maybe the scratcehs were caused by whoever fitted it from my local bike garage.??
So you dont think they are that bad? They really arent very deep. There are no noticable fragments or anything like that in the crank case. also what do you think about the blow-by?
Posted in the prievious post by Calum122: "I seriously doubt it to be the reeds mate. They would fracture and split long before theh put scratches on the piston.
Something is amiss here. If it were me. I wouldn't run the bike until i know what the cause is.
So the cause. I dont think its the reed petals. They just arent strongf enough to withstand a piston moving 6 thousand times per minute on it.
Have you recently had the bike rebored? Did they chamfer the ports properly.
Has the bike had engine work done. Any metal fragments in the bottom end? Did you flush it correcly.
You'd be surprised mate. Remember how quickly everything moves in an engine. The slightest wear will cause premature wear to the engine.
Best you get us some photos up here so we can have a look.
It could be down to an air leak somewhere causing unfiltered air into the engine.
Lets see what others think but there are just some ideas to keep you going."
"If you dont replace the piston you risk further damage to the bore or even worse the bottom end"
You speak about an air leak, well there was a leak in the base gasket, this is why i had the cylinder off (its still apart now). its posible dirt particles could have got sucked through the leak in teh base gasket i suppose?
Looks like it could be running too hot. Try upjetting.
Yeah well i was having problems with my carb before all this so maybe that was a cause of it running too hot. the slow jet was blocked which meant i had to keep it on the chocke for it to just sit at idle otherwise it would cut out. main jet is 260.
dont look to hot, when ever it goes over a sertain temp the crown goes/gray/white colour, thats nice and black
excess carbon build up can flake off during running and float round the engine causing the grazes on the piston but more than any thing it will be stuf thats entered the engine bypased the filter or what ever, may of had a bit of muck in the airbox and its passed thru the motor
wants new rings in it bare minimum looking at the pics, make sure the expander ring is also installed under the ring . pople some times leave them off coz its hard to get the ring in the bore when re building
