loud noise on honda trx 400

rpeace9803 · #1 03-16-2011, 03:57 AM

ok new to site here but i have a 2003 400ex with 440 big bore kit,450r carb,hmf full exhaust blah blah blah..

Anyways I got the 450R carb put on and somewhat jetted still a little sluggish at WOT. rode it for about an hour or so and was just about and and went to slow down to get on the road and heard a crazy loud rattle! sounded like valve rattle but was INSTANT! anyway. got online did some searching and seen it was either valves or timing chain wore out or tensioner bad..We set the valves put it back together and still same thing! replaced timing chain and tensioner checked out ok was functioning properly..started it up and RATTLE RATTLE RATTLE!!

I have NO clue what this and my buddies dad who is our wrench is stumped as well

Have a XC race this weekend so trying to figure this out ASAP!

at low speeds and idle is when it does it when actually getting on it it doesnt seem to do it really.

Here 2 help · #2 03-16-2011, 01:05 PM

Sorry - your problem probably needs "hands-on" to figure it out. My guess is it might be a scored piston or a bad crank. Slightly sluggish at WOT might indicate a lean condition. although it could also be a rich condition; a tuner could tell by riding it, but not by description (at least without more detail). The description "somewhat jetted still a little sluggish at WOT. rode it for about an hour or so" indicates you provided ample time to have done serious damage due to spark knock or pre-ignition.

One last thing - I worked in a Kaw shop during the early 70's. We had a series of bikes that got a piece of casting flash lodged in the teeth of the clutch gear. Sounded just like a rod knocking. Kaw never figured out where the flash came from. We replaced one crank (even though the old one checked good) and found the noise was still there. Finally we found the debris between two teeth of the clutch gear. Just knocked it out with a hammer and a screwdriver th fix the problem. It's possible that your problem might be something similar (but maybe not). This is what makes wrenching FUN!

rpeace9803 · #3 03-16-2011, 08:41 PM

i could see it doing ample damage if i rode it the whole time making this noise but as soon as i heard it for first time i only rode it another minute or 2 to get it back to the house. it did it at low speed and idle but when i would actually get on it and put a load on it it would go away and i still have good power so it wasnt like i lost power at any time. and yeah i love wrenching but not when i work all week and have a race sunday haha

90vfradam · #4 03-17-2011, 02:36 AM

Check the decompression valve assembly , I had one let go and it rattled like crazy...

rpeace9803 · #5 03-17-2011, 01:05 PM

90vfradam yeah the decompressor is all we could this it could be now. When had the cam out we checked it and it seemed to have a little play to it. One way still worked like it should tho just seemed to have some slop to it all. Is it hard to get all that off? Also will it affect much if I take it off?

90vfradam · #6 03-17-2011, 01:24 PM

I know with some cam modifications it is removed, it is worth a try to see if that is what make the rattling

Here 2 help · #7 03-17-2011, 02:02 PM

Yes - check or remove the decompressor to see if the noise goes away.

I work on other peoples machines all week long and ride on Sunday. I only get one day a month to work on mine, but it has to be done.

rpeace9803 · #8 03-17-2011, 09:49 PM

How can I know checkin it if it is working properly and is ok? I just shook it and wiggled components with my fingers to check for play. Is it hard to remove? Will I need a press or can I do it without

Here 2 help · #9 03-18-2011, 12:38 PM

To remove the compression release, the cam gear boss needs to be pressed off and back on. It appears Wiseco recommends the removal of the compression release when installing their 440 kit.