Join Date: Feb 2014
Location: New Hampshire
Thanked 18 Times in 17 Posts
I have replaced the top end twice due to piston knocking, at ~15k miles and ~30kmiles (at a shop), and I am preparing to do another top end rebuild myself (first time) with about ~50k miles on her. I've taken everything apart and the piston has a thick deposit of carbon on it, the cylinder has wear from knocking, the combustion side of the head is pretty toast, and the camshaft lobes are worn.
I'm no expert but all of this doesn't sound right. I believe that the knocking is from the carbon build up. The carbon is increasing the height of the piston giving it a higher compression ratio. But there shouldn't be that much build up. What I want to know is what kind of riding do you do? A lot of city riding at low RPM's can contribute to carbon building up. Also lugging the engine can do the same. I noticed that you also have an after market pipe. Do you have it tuned at all or stock map? If it running rich carbon with definitely start to form. Also how often do get up near red line and ring her out?
It just doesn't seem right to me. When I did my valve adjustment at 12,000 I looked in through the spark plug hole and my piston looked basically spotless.
2012 CBR250R Black
Racetech springs and emulators, Yamaha R6 shock, Yoshi Rearset Risers, Babyface GP Shift adapter, EBC HH Sintered Front and Rear Brake Pads, CBR600RR pegs, Mirror delete with CBR600RR block offs, Ebay Bar-end mirror, Red LED dash, The2Wheels levers, Homemade Fender Eliminator, LED Blinkers, Tank pads and grips, CBR300R seat, Spider Peak red Grips, Vortex Clip ons, DFC, Delkevic 14' Slip on, Spiegler Braided Front Brake Line,Black Rims
Soon to be mods: