Honda 350 Jumped Timming

[86'250sx]

Hey guys I'm working on a buddy's bike and the timming chain jumped, the one intake valve hit the piston broke off and did some damage. what now? the piston looks like I'll be able to use it but I'm not sure about the head. the threads for the spark plug got screwed up and theres some pretty deep marks. Should I just sand down the burs and what not or does it need a new head? I'm also assuming the timming chain needs replaced cause it was fairly loose. can the timming chain be replaced without tearing the engine right apart? thanks for any help. Sorry about the picture It's the only one i can get for now untill I get some batteries.

[fabiodriven]

Yucky...

I would say you may need a new head, but these guys will chime in and tell you what your options are.

All I can tell you for sure is that you do have to tear down the motor to replace the chain. Good luck.

[bcredneck]

carfully grind the burs down get a new valve and use a heily coil to fix the spark plug hole you should be ok you probly didnt tighten the chain ive done that before

[Dirtcrasher]

It has an automatic chain tensioner :rolleyes:

Are you sure it jumped time? Could it have lost a valve into the combustion chamber?

[86'250sx]

I'm thinking that it didnt jump timming cause it was only the one valve. the thing is I couldn't check the timming cause the motor wouldn't turn to tdc. I ground the burs and sharp edges off the head and piston today and I think it'll be fine. just had to run a thread chaser through the spark plug hole. Could the one valve just stuck open for some reason? I have to fix the bike as cheap as I can for the guy. Is it fine to just put in a new valve and gasket set?

[SWIGIN]

One new valve is better then running that beat up piston. The head is fine to use if it aint cracked but I'd REALLY study that piston.

[86'250sx]

The piston only had a couple small marks cause the valve was sitting flat on top of the piston. The little bit of stem that was sticking up did a pretty good number on the head though. Piston looked ok to me. I think the valve got bent and then it broke off when he was trying to start it thankfully it wasnt running when it completely let go. If it was my bike I would get it bored over put in a new piston, timming chain, and a new head aswell. buddy doesnt have the money though.

[WilliamJ]

Valve seats don't look so good - hard to tell for sure but you need to inspect them very closely. It won't run well if there is even a small indentation across one of the seats. And if there is a leak, if its an exhaust it'll burn the valve where the leak is. You can cut them clean again with a decent seat cutters.

How much good spark plug thread was there? If the plug was hit hard enough the whole thread could be weakened, so an insert or a Helicoil may be the way to go, otherwise the plug will pop out fairly soon.

Beware the piston. If there are any tiny cracks in it they will enlarge and one day not too far away, the piston will break up and the rod will make a bid for freedom through the side of the cylinder.

One valve guide looks oddly shiny so needs a close inspection.

[86'250sx]

The seats are ok, a good lapping and it'll seal up fine. It's hard to tell much from the picture. The spark plug threads only got screwed up a little on the one side. It wasn't much damage just enough to make the plug not want to seat easily. I have looked it over a few times already and I don't see any cracks or anything that worries me but I'll give it another once over today. I just have one other question for you guys how do I tell if the timming chain is too stretched? thanks for all the help so far.