i have a '99 scrambler 400. same thing. mine has done it since, hmmm, i can't even tell you when i exactly noticed it. i also tore mine down, checked the piston and rings, everything was good, no wear at all. i talked to alot of guys that have the 400 2 stroke and most have this sound. also guys with the tb as well.
personally i don't like it one bit. however i am not going to tear the case apart to check the counterbalance or crank bearings. i noticed mine making that noise a short while after buying it, with not many miles on it at all.
now i will mention one thing, i sent rick ritter an email on this long ago, and he mentioned something about the clutch buttons being worn. the sound is very hard to pinpoint, i thought for sure it was coming from the cylinder. he told me that he has seen the clutch bottons wear rather quickly on these. that was my guess also, if you notice, as soon as you rev it up were the clutch starts to engage, you don't here it anymore. so that is my next project on my scrambler, to do the clutch up. although a worn bearing would act the same, it would stop chattering after reving it up alittle. well, all i could say, is that i hope it isn't a bearing problem, that will be the last i deal with polaris again.
i love my scrambler, i just wish these things were built with alittle more care.
anymore input on this subject is appreciated.

bigdevil '99 scrambler w/rcr stage 1, wiseco, douglas .190's and maxxis sure traks

 

The clutch, while sitting on the Sport, is on the left side. I'm noticing the chatter on the right side, pull start side if you will. Are the buttons on the pull start side of the motor?

The chatter goes away with higher rpm. I bought this thing used and when I bought it, there was water in the counter balancer, milky white.

Bearings may be the problem, and probably is, but it doesn't sound that bad. It sounds to the likeness but not as loud as the Banshee kick start weak spring chatter. This is something I've gotta check out, for this thing could explode on the alcohol mod.

Maybe I should scrap the motor and buy a new HPD $2995 race engine. http://www.hpd-inc.com/400race.html

Not!

 

I had a horrible clanking noise on my previous 400. The bearing on the electric starter was blown to pieces. Pain in the rear to fix.

 

Talked to a few fellow Polaris draggers this weekend and they said pretty much what Dazed posted. I recently put on a new starter and the crank drain bolt was missing. I'm leaning towards bendix bearings/counter bearings. Tear down is imminent.

Jay

 

I hope i was wrong for your sake It is going to be spendy.

 

Just a quick idea. The counter balance uses reg. 10w30 engine oil. I started using mobil 1, since it only uses a few ounce each time you change it, a quart lasts a long time and is noticeably quieter. Also, if you pulled your recoil drain, and I believe you said you purchase this quad new, pulling the recoil cover for an inspection isn't that big of a deal. It will allow you to lube/inspect your starter helix, and also by pulling your flywheel, you'll be able to inspect the stator. Make sure to index mark the stator if you loosen or remove it, this is where your timing is adjusted....don't know if you know that, just want to save some grief. Good luck!![red][OL][*]99sport[*]HPD Race-mod[*]Hot Seat swingarm/steering post[*]Ricky Stator 250watt stator[*]Schultz Motorsport nerf mod[*]Titanium/carbon fiber components
[*}Jet-Mechanics love power!!!

 

My Xplorer has done that since it was new. My mechanic says some of them just do that, and not to worry about it as long as the noise doesn't suddenly change or get louder.

 

Never let water sit in the cbalance fluid or it will rust the cbalance/water pumpshaft which will take out the seals. Expensive fix for such a small part. The chattering noise on mine is VERY loud but I live w/ it. My mechanic suggested putting heavy weight oil in the cbalance fluid but it didn't help much. If someone ever finds out what the real culprit is, please let us know. My machine would actually be very quiet if it wern't for the loud chatter. The c balance is one section away from the inside recoil housing wall so that why it's sound like it's comming from there but it's something in the cblance.
Jim Maloney 98 400 Scrambler
http://y42.photos.yahoo.com/jim400scram