400EX motor problems

[free_rider20]

Well, ive had the quad for almost 3 years and have rode the hell out of it since day 1 and the only things i have done to it are typical wear and tear, oil, ect. BTW, this is a 400EX, all stock. Today I was riding in 5th gear and it lost all power and rolled to a stop. When I tried starting it after it stopped, it smoked for a couple seconds. It is getting spark. The piston is moving up and down. I believe the piston is coming up and completely closing off the spark plug hole. Can some of you help me out as far as what may be wrong. I was thinking that the wrist pin may have broke?

Thanks for any help you can give.

PS, I dont know a lot about engines and their internals so correct me on anything if im wrong.

[K_Fulk]

Did it make ant kind of unusualy noise, I think you should know if it was hitting your plug. May be some dirt in the carb or something too?

[velocityatv]

had a friend I was ridding with once loose the spark plug. The damn thing just unthreaded itself and shot out.

[jokerman_28]

i had a yamaha phazer loosen a plug and it shot right through the plastic engine shroud.

but for the 400ex. it could be as simple as a new spark plug or if that doesnt work check your compression. the rings may have burned up.

[free_rider20]

Ok, the plug is still fine. When it smoked on me it was black smoke. So do you think it could be a clogged carb? It makes a clicking sound when I turn it over.

[NTPracing22]

black smoke is burning oil if im not mistaken, if that's correct then your rings burned up

[free_rider20]

Isnt oil blue smoke? and black is fuel?

[04EXdude]

Don't know what the clicking sound could be but black smoke could mean its too rich. Have you checked/cleaned your air filter? Maybe check the float and jets for dirt?

[nakomis0]

Sounds like you need a new piston and rings.

[free_rider20]

How hard of a job would it be for me to replace the piston and rings. I would need to replace all the gaskets as well, correct? If that is what is wrong, what brand would you reccomend. For me, durability is far more important than power. Could I gain more power pretty easily by replacing smething else while I have it broke down?

[free_rider20]

Ok, The engine has no compression so I am assuming that it is the piston. I ordered a service manual today to help me with the job. Any tips on anything that I will be doing?

[440ex2001]

You had no compression at all Or was it just low? It should have some compression unless there is a hug hole in the piston. Hook up the compression gauge and remember to open the thottle. If it does need a new piston and rings make sure you have someone some one with a mechanical background help you out. Also check the sleeve for nicks then out of round and taper. All the specs will be in your manual.

[tigerdog]

sounds like piston probs to me.

you should have a machine shop check the cylender.
the measurements are complex and very precise they will have all the right tools. and its what they do every day so its second nature to them.

aside from removing the cylender , re timing the cam is the hadest part but that should be explained in the manual very clearly so not a problem.
but if you really have no compression you have to tear it down to fix it.
and black smoke is to much fuel.