Seized Crank

[mini]

My son came back in a van last night, he said his 1981 PX125 had seized , but said it had been running a bit rough and then stalled at at junction, then as he was kickstarting it, was when it seized . .... I couldnt understand how that could happen, anyway i have stripped the head barrel and piston off and although there was some suspicious tiny bits of metal in the barrel and on top of piston, the piston wasnt stuck in barrel, but the crank wont move at all???/ anyone any thoughts at all? please?

[rab]

 did it have 2 stroke in is it pre mix or auto lube you will have to split the casings to investigate. the right hand case is the easy side so id start with that one and you can leave the engine in to do it. if there is bits of metal then something has gone some were. drain the oil if only a tiny bit comes out then lack of oil has more than likely caused it. if you get oil out that will also more than likely be full of metal bits. until you split the casings only guesses can be given as it could be several different things at this stage.as a starting point the crank bearings could be shot. what ever has faild has thrown the bits into the crank seizing it. the fact it stopped at low revs could have saved you a fortune and a certain crash. if you split the casings take pictures step by step get them on here and you will get all the help and advice you need. check the barrel for any score marks check the rings have not got any tiny piece missing check the piston for score marks aswell . if you need it i have a complete 125px head barrel and piston you can have cheep as ill never use it

[sbwnik]

That's an odd one, but with swarf in the cylinder I'd be checking the big end bearing and the that piston rings haven't smashed.

[sime66]

Just a thought,
Couple of years back a mate lost his (metal) crank seal, it came loose, got chewed up, and wedged up side of crank...............?

- Just checked; it was big end shim, not seal.

[vespasco]

Its possible those tiny bits of metal could have lodged themselves between the crank web and cases, seizing the crank.
Possibly the bearings could be shot but unlikely if youve ben using the correct amount of oil.
Was there any damage to the piston rings?
Could something have got fed into the carb by mistake? Like a washer or something.

[bsr65]

Probably not this, but years ago I had a flywheel side bearing work it's way out the casing and heat weld it's self on to the crank, I felt it dragging coming up to a circle, then it locked up on the circle. Ive never heard of this happening to anyone else but you never know.

[mini]

Thanks to everyone who has replied.... the bottom piston ring does show signs of damage (only looked quickly last night after taking engine out) I will look more tonight, but neither of the rings are broken... It seems that it will have to be a engine split and see what it looks like, I was hoping to avoid but that is unlikely now..anyone else got any thoughts and they are appreciated... thanks chaps

[mickymidas]

might be worth checking out the flywheel side bearing race.....low level of 2stroke oil mix causes engine to overheat , race expands & slides off crank through seal, causing bearing to slip on the p**s and seize crank .