Top end noise

[jaysun]

I have a 1999 400 ex with a noise coming from the top end. It sounds like something loose or a vibrating noise in the top end of the engine. Does not lack any power. Only smokes a little bit. Went to pull the cylinder head cover off and one bolt broke off so I stopped.
Bought it for $500 bucks so I don't mind investing alittle into it if the wife will let me... Anyone have any ideas, and how can I open this up without breaking more bolts??

[blastereatin250]

your valves are in need of an adjustment. All you have to do is take off the gas tank. There are no bolts to break except the front ones that hold the gas tank on. The smoke is probably the valve seals.

[greg_gorrell]

ok well if the smoke is blue then it wounds to me like your seals are a bit bad since it is your vavles knocking. it could also be your piston rings. but if the smoke is black or another color then it could be one of a few other things. but in my opinion i would tear your top end off and put some new studs in along with a piston/rings, valve seals. while you are doing that hone your cylinder and make sure your valves are still good. if you have any questions on how to do that just ask but i would reccomend you get a service manual. but make sure your valves are adjusted right when you get with it but for $500 man you got a nice deal if it isnt in too bad of shape and if i was you i wouldnt mind putting a little money into the top end, getting the fourwheeler that cheap and all.

[tater_kamik]

do not run it! take top end off including the jug and inspect the valves, top of the piston, and rings! on the 400's you can take it apart with the motor in the frame. if its the valves you may have already damaged something, no metter what it is it cant be good but it is probably easy to fix.

[tater_kamik]

you can also use that as an excuse to build an 440 :D

[jaysun]

I bought it with this engine noise. Its in good shape, but I think the original owner neglected standard maint. I brought it to a local ATV shop and he had it for two months and only adjusted the valves. Then he gave me the run around and I pulled it out of his shop. Now I have a buddy working on it who has owned a 400ex and is a machanic. He feels pretty confident in finding out what the problem is. The only thing that freaked us out is we went to take the cylinder cover off, and the first bolt snapped off. Will I have to buy a new cylinder head if more of these break when taking this off?? We have stopped right now while I try to figure out how much a new one will be. The Honda pricing is scaring me into running it till it blows. I just would feel better to fix it right before it cost anymore!!

Thanks for the help so far. Has anyone else had problems taking the top end apart??

[tater_kamik]

i donw see why you would have too unless something is damaged, worest case scenario, ebay! bolts i would buy new since taking them in and out of the cylinder causes the threads to stretch and weaken, plus since they are breaking i would play it safe and buy all new.