i recently purchased a 2003 honda 400 ex. i got a good deal on it, so i couldnt pass it up. there is a rattle going on in the engine. we adjusted valves and got them spot on. we checked the timing chaing and it isnt completely tight but real close and didnt look worn. there was hardly any room to pull it to where we thought it would be slapping. it smokes a little when cold but it deminishes to almost none at all and pretty much goes away when riding it. there is no loss of power at all. it runs strong and no sputtering in any gear. the noise sort of comes and goes. when i rode it for a while the noise was hardly there but could slightly hear a rattle but nothing like when i start it cold. the longer i rode it the quieter it got. took it home and started cold again and it sounds the same. rattle is still there. can anybody help??????? got me and my buddy who is familiar with honda engines stumped. thank you!

 

hey i used to have a 400 ex that made the same noise. come to find out my main crank bearings were shot in the bottom end check that hope this helps

 

It maybe piston slap, It gets quieter as the engine heats and expands. The only way to check is to tear down the top end and measure the piston and cylinder and make sure they are in spec

 

yes i have been told it could be a piston slapping. but it comes and goes as it warms up it will stop for 30 secs then start for like 15 sec then do the same thing. if it were a piston slap, would it be constant? sound linda like something inside loose and rolling around or something?

 

Had a yfz that did pretty much the same thing, had a cracked piston skirt. Let us know what you find.

 

i think i may take it in a have it redone? have a couple questions?


1. how much was it to replace the crank bearings? is that a hard task to check?

2. would someone be able to meaure the specs of the piston easily, or if they are that far into it, will they just want to rebuild any way?

it smokes a bit when cold and mostly goes away, but still a hint still and alot of black soot in pipe end. figure it needs rings? dunno may be part of the problem too? if they rebuilt top end will they re ring it? notie a hint of smoke of the top end at times as well.around where pipe goes into motor. i had a few older 400 ex that smoked and such like this, but this one seems to run stronger than any of the others. if there was no noise i would prob keep rolling for a while. noise worries me. have been told by a few honda fans that i still have alot of life left, even in shape its in?