My 14 yr old son saved all his money from snow blowing and lawn mowing to buy used 2005 CRF 150 2 weeks ago. Road it a few days and it quit. I wasn't with him but he said he was downshifting from 4 to 3 and heard a pop and then it just quit. I know just enough to find my way around but by no means am I a mechanic or expert.
I pulled the upper crank shaft cover and the left engine/stator. The crank chain had fallen off. I thought it might be an easy fix so removed the top crank shaft gear and repositione the chain back on lower and upper gear and put it all back together but it won't start and it fell back off. Any idea what may have caused the chain to initially fall off?
My son was crushed. So I decided to pull the engine and learn more. I pull the cylinder head and the valves are covered with carbon? The piston is pitted and covered with carbon too. Does this indicate anythig specific? At this point I'm thinking about replacing the valves and piston since I've got it torn apart. The rod feel very sturdy and there is no visible wear/damage inside the cylinder.
Back to the crank chain: it's not very flexible and a few of the links are almost "seized" up if that make sense? Again, just curious as to why this is? Simply the age of the bike??
Luckily Except for some damage to the 2 long chain tensioners, there doesn't appear to be any damage caused from the chain falling off.
Does anyone have some good suggestions or thoughts on this? I'm hoping once I replace crank chain and tensioners and adjust the chain so it is snug AND replacing piston, rings, valves and springs she will start up. But I would be grateful to anyone that has some additional advice. Don't want this to happen again! Need to get my son back on the bike. Thank you.