OK here goes, I have a 400ex that just recently had motor work done to it, new crank new top end. valves were in good shape so they didnt have to be replaced. heres the problem.
it sounds like the valves are tapping but this only accures when it has been ridden for about 20 or 30 moinutes. it does not happen when it is cold or durring idle. Do I need to go in and adjust the valves or do I have another problem. Im curious as to why it doesnt tap when when its just sitting there running? it seems to be tapping when its under a load after running for 20 to 30 minutes?
Does any one have any answers. I seem to get alot of good advice from this forum.

 

Is the engine just rebuilt but stock...If you did it yourself then what I would do is check the valve clearance to see if they are up to spec and make sure that everything is torqued down the stock specs also because those 2 things could cause tapping...take a look over the engine and see if you can see where anything would be rubbing or any other damage...also do you have enough oil in the engine because there may not be enough oil getting through the galley in the head and after so long once the engine is warmed up it is causing the valves to tap.

 

I had a cam put in mine, then when I went ride it it tapped also. I checked my valves twice. That was not it. I then checked my cam chain tensioner. It is on the back right side of the motor, right side below the carb. I took mine out, and and cleaned it up and put it back in. I can't remember but I do believe the manual said to put it a certain way. I could be wrong, so check the manual on the cam chain tensioner. This eliminated my tapping noise. Hope this helps.

 

yes the motor is stock. If the valves were out of adjustment wouldnt they tap no matter what?(whether hot or cold)? Oh well I have a free day tomorrow and I guess I will have to get in there and take a look. I will also check the cam tensioner too.. thanks for the help fellas.

 

Yea thats the last thing you would want is the chain flopping around in the engine due to the tensioner not working...Make sure everything is gapped right the chain is tight...guides for the chain are in..etc...check to see if you can see any scrapping or any damage that will indicate what the noise is pointed towards.

 

my 400ex does the same thing. when i start it up and hold the gas at a slow steady speed to warm it up it does the usual for a cold engine spitters for a few minutes and ocassionaly shuts off and when it shuts off it has this loud clink and the whole quad like tillts forwards when it does it. and also when its warm and like he said its under a load such as hard acceleration it has this tappin noise, kinda sounds like a "pink pink pink" sound. it has been rebuilt by the honda dealership, they said i ran it too hard and blew it up somehow? they have a rep of screwin ppl out of their warranties too though! but anywho, ya think that is my problem?