gn250 piston + valves

[Squiggles]

Broke a valve on the gn the other day, it munted the piston pretty good.... cant afford too much so i need a budget fix, am wondering if i can get away with not replacing the piston.... $50 for one in what id say was reasonable condition off trademe...

cant believe it'll be $65 for a single valve though (exhaust side)

what do you all think? will i get away with it?

[Macktheknife]

In a word..... no.

[PSk]

How did this happen?

And yeah that piston is toast. I imagine the combustion chamber in the cylinder head looks pretty sad too?

I'd also be checking that the other valves have not become bent as the piece of valve was mashed.

Last thing you want to do is just chuck a new valve and piston in there, and find something else goes wrong, so might as well do it properly!

Best
Pete

[**R1**]

Thats fkd mate, did the valve fall in2 the cyliner and bounce around? if so you will need to check it aint cracked the head and that the valve stem hasn't punched a hole in the head, did it damage the cylinder?

[Squiggles]

bottom part of the valve broke off, bounced around but didnt appear to do any damage, it was the stem of the valve that f**ked the piston... cylinder seems fine... heres a couple of pics of the head

[Sketchy_Racer]

meh find a valve and see if it still runs with that shitty piston if it dont then replace it.....

Iv had a XL100 running with two straightened valves (done with a hammer) and a piston much worse than that!!

[TonyB]

Whats the engine number Squiggles? I can supply piston kits for GS-125/GN-125X/DR-125 so it seems a little odd that I can't supply GN250 piston kits etc. I'll ask my supplier but they will need the engine number.

EDIT: I wouldn't use that piston again. For a start one of the valve recesses looks like it now has a ridge of metal running through it. If you try and run the engine you'll probably do even more damage.

[Squiggles]

engine no: J403-102522

[classic zed]

when you put it back together its worth re-seating the other valves too, it ensures you have a good seal and the head is off anyway, if you need the valves dressing up I have the machine for it. As for the piston ..... chuck it, by the looks of the damage you might well find small cracks or bulges under the crown. Check the head very carefully and in particular the valve guide for the one that broke off, sometimes they bend slightly before they break, and when hit by the piston cause the guide to crack.