Dad
08-09-2009, 07:30 PM
I thought I would share my experience with replacing a piston in my Son's 2005 YZ125. A brief lesson, for any young riders and mechanics would have to include 'how we get experience right after we needed it'. Riding in a muddy field with no rear fender, leads to no air. This is where you need to stop, take it apart and clean the air box. Do not use a screw driver and chip some of the dirt out the next day, tear the filter and go riding. The engine may run for a few days before coughing up gray matter, but it will die. This one had 40 lbs. of compression at best. The next lesson involves taking the engine apart and actually keeping track of where things are, because someday you will need this stuff to put it back together. A really good idea is to put as many bolts back in the hole they were removed from as possible, and, cover all the ports, including both ends of the exhaust pipe.
After all the painstaking care of cleaning, measuring, oiling and assembly, you want this puppy to run great.
After starting the engine, we found poor throttle response and low exhaust flow. Then the "stuff" started flying out of the muffler. I pulled the packed side and it was wet from being outside, uncapped, in the rain. We started it back up without the muffler and still had low flow. Off came the expansion pipe, which was plugged almost solid.
It will probably have to be cut, cleaned and welded, but a borrowed pipe proved having a mouse in the muffler is no fairy tale.
Be good!
Dad
p.s., I would like to thank the guys again (see no spark YZ125) that encouraged me to put this basket case back together, you were right, it was easy!
After all the painstaking care of cleaning, measuring, oiling and assembly, you want this puppy to run great.
After starting the engine, we found poor throttle response and low exhaust flow. Then the "stuff" started flying out of the muffler. I pulled the packed side and it was wet from being outside, uncapped, in the rain. We started it back up without the muffler and still had low flow. Off came the expansion pipe, which was plugged almost solid.
It will probably have to be cut, cleaned and welded, but a borrowed pipe proved having a mouse in the muffler is no fairy tale.
Be good!
Dad
p.s., I would like to thank the guys again (see no spark YZ125) that encouraged me to put this basket case back together, you were right, it was easy!