How can you tell if a motorcycle engine is blown?

Question

i have a 03 yz250f. i was riding when i didnt know i had a leak in the coolant and when it happened it kinda just bogged down but kept running until i came to a stop. I have comprestion but my decopresion leaver wont do anything. Anybody know what could be wrong

Answer 1

if you want to be lazy remove headpipe and intake and take a look at your piston though these 'windows'while moving it up and down via kickstarter

if you see any scrapes or scratches do a top end

Answer 2

doesn't all japp crapp blow?

Answer 3

Its shot.

So's your English.

Answer 4

Check the oil, for coolant.

Usually, the head gasket goes first, and you get coolant in the oil, or blow your radiator up like a bull frog, along with oil in the coolant.

Its an equal employment act for mechanics

Answer 5

From the details you gave,it seems like a typical seizure.It has overheated and either the piston,rings or both have smeared against the cylinder.Pour a drop of oil in through plug hole to see if compression rises,and you will know for certain.

Answer 6

Best way to tell is by doing a compression test.

Answer 7

You may have a broken or stuck cable for the decompression device.

Pull the spark plug out and turn it over, smell test, comp test and pop the head off to see if you have shavings from the piston on top or scoring on the walls.

Answer 8

A truly "blown" engine is pretty unmistakable...the crank breaks, usually into more than one piece, and while you're trying to stop the still-turning engine sounds like it's got a piece of metal loose inside, which it does.  People on the sidewalk turn to look, and children either point and laugh, or run the other way.

"bogged down" and "kept running" tells me that it didn't 'blow", but like the others , I'm thinking the head gasket blew out.  If you have compression, maybe it's not even that.  No head gasket should mean zero compression.  

It's too new a bike for the cooling liquid to have gotten into the engine, but the two happening together would make me

look at that possibility.

Answer 9

Doug,I believe you will have to pull the top end.Usually when this happens the aluminum from the piston rubs off on the cylinder.That is what happens on a piston seizure.Have a Yamaha Tech. fix it for you.They have to remove all of the aluminum off of the cylinder walls.Their may be crank damage as well.