Engine seized - Aprilia rs250

[nudedaytona]

OK thanks I'll have another go this weekend, following Xions instructions. I've got some work to catch up on, as well as prepare for an interview on monday, so hopefully I'll have enough time to do it.

If anyone wants to help out, let me know your contact details and I will get in touch (the bike is in birkenhead, north shore).

[Sketchy_Racer]

From the photos, it looks a lot like the piston on the right hand side has heat siezed, caused by a large amount of detonation meaning piston temps got far to high. What would cause the detonation? At first guess I would say it is most likely a lack of fuel. The hose to the carb blocked, of the float valve no opening. I'd almost put money on that.

Second is A very very serious air leak in the intake letting air get in and not enough fuel, causes very lean running, leading to detonation.

Third but highly unlikely, ignition timing out. but I would suspect that it would affect both cylinders if that was the case. But, while were on ignition. check you spark plug numbers. are they both the same?

-Sketchy

[Ixion]

Crankcase seals will cause lean detonation (though usually other symptoms also). Most common cause , IMLE, is a carb not securely attached, causing a leak between the carb and the manifold (loosly expressed). Ignition timing is rare in these days of solid state ignition . though it can be caused by a dud coil or CDI unit.

Water in the fuel is another possibility, though unlikely to affect only one cylinder.

[k14]

I reckon it looks like the headgasket has been leaking?? Or maybe the head has warped and caused that crap around the head surface??

EIther way, the right cylinder is stuffed and the left one is fine. Don't take the left one off, if it ain't broke, don't fix it. They are supposed to be black, it isn't a 125GP bike. Black is good. See how much a new piston is and take the cylinder into the bike shop for them to check it out. If its ok (i'm pretty sure those barrels are nikisil so you might be lucky) then you can throw a new piston in there and you'll be away laughing. Assuming it isn't a bung crank seal etc. Not sure if those bikes can suck air in with a bung crank seal. Do they have a dry clutch?? Pretty sure they don't. So one side is oil, that only leaves one crank seal as a possible culprit.

[nudedaytona]

Thanks for suggestions. When I get the cylinders out I'll have a proper look at it. I'll concentrate on the right one first. The cylinder heads were on pretty fucking tight on both cylinders.

The fuel hoses to the carbs look fine to me. Haven't taken the carbs off yet, but they seem to be attached fine. A couple of times I've had the fuel cock turned off, then forgotten about it, following which I've had trouble starting it after its stalled a minute later. I know that probably wasn't too good for it. But the last time I did that was a while ago, and I always check the position of the fuel cock now before I start it.

The air filter foam was stuffed - could that have led to too much air not enough fuel? Anyway, I've ordered a new one. Spark plugs were both the same. Anyway I've got new ones to put in because they're dirt cheap. Sorry for the lack of progress - will try again this weekend.

[Sketchy_Racer]

The air filter foam was stuffed

Bingo

Stuffed in which manner? as in blocked? or falling apart

If falling apart, you have the chance to

1 - Let too much air through, but I would think that would affect both cylinders.

2 - debri foam to easily block one of the air tracts in the carb, then not letting fuel through..

No matter what the out come, just pull apart the carbs while you are there, and clean them with compressed air..

[nudedaytona]

OK it looks like the piston in the right cylinder is broken. I've removed the cylinder and you can clearly see that on side underneath the head there is a whole chunk missing.

I've had huge problems removing this piston though. I removed one circlip, no problems. But I could not remove the circlip on the other side because the gap in the circlip is right where the hole is to put your screwdriver in, meaning I could not push it out using a screwdriver.

This shouldn't matter because I thought I'd just push out the gudgeon pin through the side where I have removed a circlip. But it won't budge. I've tried using a screwdriver and hammering with a mallet on the screwdriver handle, and that moved it a little bit, but not any more. Plus I'm worried that I might move the piston out of alignment if I keep at it like that.

I've tried using a clamp but that doesn't work either. Can anyone tell me the best way to remove the gudgeon pin. Is there a tool that would make it easier?

(There's no danger of bits dropping into crankcase because the piston is hanging downwards out of the engine).

[nudedaytona]

I've started a new thread on this http://www.kiwibiker.co.nz/forums/sh...95#post1540195