A tin can in my XR400?

[Kawidude]

I recently bought a '97 XR40 and I've got four rides on it so far. I have done no modifications to the motor yet. About a week ago, I was finishing a ride and I noticed a strange sound coming from the bike. All I can is that it sounded like there was a tin can flopping around somewhere on the bike. It seemed to happen on bumpy terrain the most.

My first thought was that the exhaust was loose somewhere. I checked it out thoroughly when I got home and everything was snug. I found nothing externally on the motor that was loose.

I went out for another ride yesterday and the sound seems to have gotten a little worse. I stopped the bike and got off while it was running. It didn't make the sound while idling, but when I gassed it, it rattled again as the rpm's dropped. I put my ear close to the motor and it sounded like it was something internal. I also checked the oil (the engine was warm) and the level was fine. I'm pretty stumped as to what I should start looking for.

Has anyone had a similar experience before? I'm trying to figure out what's wrong, bu not sure where to start. Valves, gears, worse? Thanks in advance for any help you can provide.

 

[Trailryder42]

Hey Dude,
I had the same kind of sound coming from mine also. It turned out to be the plastic ring that the front brake line runs thru, rattling inside that metal keeper that's bolted to the upper left triple clamp.

 

[Kawidude]

Hmmm...it definitely sounded like it was something inside the engine, but I will go check that front brake ring right now just to be sure that's not part of the problem. Thanks for the tip.

 

[snaggleXR4]

Hey,
Loose cam chain and/or valves can rattle around. I'm pretty sure the 400's have automatic cam chain tensioner, but the valves are your problem. They need to be adjusted at least once a year. More often, is always better. The sound should be coming out of the top of the cylinder, if it is indeed valves. I have an old beat up '96 400, that runs like a champ. I can't think of anything else that could be rattling other than just various body parts that have worked themselves loose. Give a complete and thourough inspection of body parts, if they are all good, look at the valves next. Good luck.

 

[DualSportr]

I can't think of anything else that could be rattling

Anything can rattle, given enough time and clearance.

If it's not the brake line stay, you can pinpoint it better by trying a few things:

1. does it happen only when the bike is moving?
2. when you pull in the clutch, does the sound go away?
3. when you rev the engine, does the sound speed up also?

Stuff like that can help narrow down the options.

 

[Kawidude]

DualSportr-

The sound happens whether the bike is moving or standing still. If I remember correctly, when I pull in the clutch, the sound lessens but it's still there a little. The best way for me to hear it is when I'm not moving and revving the engine. The sound presents itself when the rpm's are on their way back down after a rev.

I had a friend look at it this past weekend. I started it for about 5 seconds and he told me to shut it off. He was convinced that it was the cam chain that needed to be tightened. I know where to make the adjustment (tucked in under the header on the right side) but I don't have the service manual yet. Does anyone know if that phillips head screw is just a dust cap? What should I expect to see when I remove that screw? I was told there should be a nut in there that I should tighten until snug and then back out a 1/4 turn. Does this sound right? Thanks again for the help.

 

[smb_racing]

does the engine still have good compression?
It could be piston slap depending on how many hours are on the top end.

 

[DualSportr]

I agree with SMB, I'm leaning towards piston slap.

It may be the cam chain, but the adjuster is automatic, so if it is the cam chain, you'll need to replace it (and probably the tensioners also, since they'll be worn).

Either way, you'll have to tear the top end apart. But before you do that, I'd adjust the valves just to make sure that's not the culprit. Then do a compression test - if it's a sloppy piston, the compression will definitely be down.

If you do end up tearing into it, also check the valves (get new ones and do a valve grind). Also check the small end of the rod for galling and/or pin tip.

 

[SpeedyManiac]

I would guess camchain and/or valves. That's what my bike sounded like when it was loose.

 

[klymr]

Hi Kawidude-

I too own a 97 XR400. I too experienced an annoying rattling noise last year. After much searching and tightening I found a rock trapped on my skidplate!

I hope you find something as simple as this and nothing major.

good luck.

Klymr

 

[Kawidude]

Thanks klymr-

I was hoping it would be something easy to find, but it hasn't been yet. I think I'll double-check my skidplate today to be sure. A better description of the sound would be to say it sounds like there is a small rock in the headpipe...but it's a sealed exhaust system so I don't know how that would even be possible.

I'll check everything over once more, then I'll check the valves tonight. I'm hoping I'll have the sound gone before my harescramble this weekend.

 

[tristan18au]

dont worry

its normal i had the hole top end rebuilt on my 1998 XR250 cam chain valves ect and it still rattles and runs great!

dont worry!:cool:

 

[Kawidude]

Well, I checked the valve clearance yesterday and they were all perfect. I'm taking it to a shop on Tuesday just to make sure there isn't something major wrong with it. Looks like I'll miss my harescramble on Saturday:(

 

[Dr.billZ]

How about a loose skidplate mounting bolt.

 

[Kawidude]

Dr. BillZ-
Nope, that was one of the first things I checked. It actually started doing it before I bought and placed the skidplate on the bike. I wish it was that easy. It's sounding more and more like there is a rock in the exhaust somewhere. I'll see if I can find some time to rip it off tonight just to be sure.

I re-tightened all of my skidplate bolts again just to be sure!