ASK THE MXPERTS: WHAT CAUSES PITTING AROUND THE TOP OF A TWO-STROKE CYLINDER

ROLL UP YOUR SLEEVES

Dear MXperts,

I have a 2015 YZ125, and I figured it was time for a new top end. When I took the cylinder off, there was heavy pitting on the top of the cylinder’s edge. I showed the cylinder to a service rep at my Yamaha dealer, and he said he had never seen anything like it. He said I could get a sleeve put in. What would you advise?

The pitting around your cylinder is caused by detonation, more commonly known as pinging. This can be caused by low-octane fuel or poor jetting. It is not advisable to run that cylinder, since the ragged edges of the cylinder will create a hot spot that will continue to eat the cylinder away. We don’t recommend putting a sleeve in the cylinder, although that might be a last resort. Instead, go to Millenium at www.mt-llc.com or call (920) 893-5595 and find out what they can do. We sent our 2007 YZ250 cylinder to them for replating, and it came back looking like new for $250.