I'd say you can't really tell anything except that it's shagged!
The barrel has to come off anyway, so why not lift it to get a true idea of what's happened? You can take the head & barrel off as a single unit to (possibly - if the head's not damaged) save the cost of a head gasket. _________________ Andy.
NSR-WORLD.COM
Please keep all responses to Forum posts on the Forum so that others may benefit.
Please DO NOT PM me for technical advice. My time is precious, and you will probably receive a faster response on the Forum anyway.
With a chip like that taken out of the crown, I am thinking there will be an issue with the cylinder and/or head. The savings for a new head gasket is nothing compared to what it will cost to replace/repair the piston and possible the cylinder.
Pull the head, and get a better idea of what is up. Of course before you pull the head of cylinder, drain the coolant!
StephenRC45 scrapped a cylinder recently; it had lost a rather large chunk of the wall above the RC Valves! The chucks of metal appeared to go straight out the exhaust without damaging much else! Of course the piston/rings/cylinder were buggered, but it just goes to show!
In retrospect though, when I wrote my last post I was thinking about a recent rebuild I did that just needed pistons/rings etc., so just pulled the head/barrles complete to save time. The head on this one will almost certainly need to be popped as the cylinder is most likely in need of a replate.
Whatever... back to the original point of my post - just pull the barrel! You'll have to to find out what is really wrong with it! _________________ Andy.
NSR-WORLD.COM
Please keep all responses to Forum posts on the Forum so that others may benefit.
Please DO NOT PM me for technical advice. My time is precious, and you will probably receive a faster response on the Forum anyway.
I never did find all the bits! I shook a whole load of ring out of the exhaust but never did find the bits of cylinder.
They might of gone streight out the exhaust on the way home mind as i didnt hang around. I wasnt/still arnt a very happy bunny about the whole thing and these things keep going down in my estimations.
Still like all good sports man i will try yet again, but by god if it happens again! _________________ If I have to take the carbs off once more...
A piston coming apart like that "CAN" be caused by an intake air leak on that cylinder.
if your seizing top ends over and over again, then make sure you do a proper leak down test on that cylinder giving you trouble. Make sure the head and base aren't leaking. Also check the cases, as well as the Reed cage seal, and the intake boots. Even a small leak will kill power, and lean that cylinder out potentially causing another top end to go bad.
Your engine should be able to hold 6-7 PSI for a good 3 minutes.
Also, if your missing "parts" best to pull the engine out of the frame, and fluch the cases. You can do that with the crank still in place. Flush with cleaner, and then blow everything out with air. Of course the best way to do it is to fully tear it down, but who really wants to do that.
This is the first time ive had a top cylinder go wrong. This is also the first time ive had a prob with a 250. Its normaly the 300 that kicks me.
I ended up taking the crank out and flushing the cases. The piston didnt fail i dont think. What has happened is both sides of the barrel above each exhaust port have broken up. Taking out about 10mm square. You can now see light above the power valve even with them lifted to the open pos. _________________ If I have to take the carbs off once more...
the point of my post was that you have a underlying problem. we all know that pistons scrap and a replate is going to be needed and poss a head repair. but you also need to look at why it happanen or you could have it go all over again. power jets do like to block on 21s
You cannot post new topics in this forum You cannot reply to topics in this forum You cannot edit your posts in this forum You cannot delete your posts in this forum You cannot vote in polls in this forum You cannot attach files in this forum You cannot download files in this forum
here is a pic of my piston 
