[Jl1975]

Hi, I'm a new member but have been using this sit for a while. My son has a 2012 crf250r. The other day he was riding, being a dummy, with his buddies. They were revving hitting rev limiter. His bike made a grinding sound, then started sounding rough. When I took the head cover off, everything looked normal, but his timing was off. I set the timing, and the bike started no problem. After a few minutes of riding it happened again. Why is this happening? Any advise is appreciated. Thanks

[JimDirt]

Welcome to the site !!

I am thinking it is the Timing Chain Tensioner that broke ... What you need to do is remove the 2 bolts holding it to the cylinder and pull it out , I am guessing you will find it is over extended and tipped sideways and most likely broken/cracked and the retaining clip is either broken or missing , or worse that part fell into the engine (hopefully not) and that is the grinding you are hearing , where it has got mangled into the flywheel , in which case you will need to pull the flywheel cover , by laying the bike on the clutch it's side putting your bars/grip on the lift stand , then remove the cover and try to rotate the flywheel back and forth

If the sound is coming from there and you can feel it rubbing then you will need to get a flywheel puller (the correct one for the bike) and remove the flywheel to access the damage , but I am guessing you will find the Tensioner is toast , and hopefully that is it , and will need to be replaced ... , but there have been cases where the stator bolts have worked loose as well , and caused the same symptoms , the fact that it is out of time leads me to believe it is timing chain related/Tensioner ..... if it did do any damage to the chain , now would be a good time to replace the timing chain as well (for that you would need a Flywheel Puller)