my Yamaha TZR125 is Broken, Why???

Its seized up that's for sure the fuel on a two stroke goes around the crank if the the bike was rolling in gear as the engine died it would of dragged excess fuel in to the crank if the rings had heat seized into the piston it will allow the spark to fire passed the piston which will then ignite the fuel in the crank when you tried to bump start hence the bang as it fired out the exhaust. One thing for sure it ain't gonna be cheap.

Sounds like you seized the engine up fella. Your looking at a new barrel, piston and cylinder head at least, probably new bottom end bearings and con rod too. Basically you need to locate a second hand or reconditioned engine.

Old two strokes are reknown for bein prone to that. When you get it sorted make sure you use good quality two stroke oil and top it up at least once a week. Dont use cheap stuff in your engine. Even £20 a litre oil is cheaper than a new engine.

Look on ebay, you might be able to find one. Failing that use

www.partfinder.co.uk

To be sure it has actually seized, try gently turning the kick start. If it moves freely then you got away with it. If it is stiff or rock solid then you have a seized motor

Back in the day, I had a Yamaha 100 twin.It was aircooled,and if it was driven hard it would sieze.By driven hard I mean about 60 to 65 MPH.I believe your little "Rice Rocket",is a water cooled,state of the art,modern machine,do you have over 10,000 miles yet?If you do,then you are way over your due date for a top end overhaul.They are very simple to do,hell,thats why I loved them so much,it gives you a sense of power when you know exactly what all is going on inside your machine.Anyone can tear down and replace worn piston rings if I can.Go back outside and take a good look at your cooling system,look for leaks,hell open that freakin' radiator cap and take a look inside,if it's empty,your wallet will so be too!I've been riding since 1972,and there is nothing and I mean NOTHING like the smell of a two stroke in the morning warming up,with the choke on,the neautral light flickering,while the helmit and gloves go on....If you don't have the tooles,or the manual,or the friends,then get that bike to a dealer who knows 2 strokers,call them on the phone,tell the problem, If the guy is a mechanic,make damn sure he knows about 2 strokes,be passonite-and get back into the wind!

It was definitely a heat seize which means the piston expanded and became tight in the cylinder bore .Could occur due to lack of oil,water or incorrect air/fuel mixture did you fit a performance exhaust or a high flow air filter?When a seize occurs the front edge of the piston crown can catch the exhaust port causing serious damage to both, this may be the bang you heard from the exhaust.Sorry mate but this sounds expensive.In future at the first sign of any engine trouble pull in the clutch, stop and let the engine cool for 15 minutes. two strokes don't you just love em.

Do you check the coolant and pre-mix oil level often? and should also see whether both the pumps are in working condition. it seems you've got a siezed engine or damaged piston by less or no lubricant/over heating of the engine. get it to a good mechanic, your bike needs a thorough rebuild.

Sounds like either:

a) No 2-stroke oil in the oil tank, so no oil in the fuel mixture, so no lubrication for the piston, so seized piston.

b) Incorrect fuel/air mixture or ignition timing is out, so fuel mixture burns incorrectly, so detonated (holed) piston.

Either one will cost time and money to repair.

check to see if there are ANY leaks coming from the engine. when you try to crank the engine does it have agrinding noise? did you put oil in the engine before you drove it? how long was the bike sitting before you drove it? take it into a shop Im thinking the worse here it MAY be a thrown rod. WORSE CASE SCENARIO! take it in to be checked out you never know.

sounds like the engine seized either by oil problem or water . it could be cheaper to get a new engine than to repair it

It sounds like you did some serious damage to the motor. I'm afraid you are going to have to bring it in for a motor rebuild.

Sorry.

Sounds like a siezure to me, that's what you get for buying a Yamaha. Honda, that's what you need.