ATC90 Weird Noise

[Frankencelery]

I finally got my ATC90 assembled and running. That's the good news. I rebuilt the top end, replaced timing chain, etc, and got it started and moving. Once I got the timing right I was fairly impressed with the power for such a little thing.

The one issue I'm having is a repetative rattling noise as it gets moving. You don't hear it at all at slow speed. It shows up at about 10mph.
I thought it was a front wheel bearing at first, but that spins smooth when it's off the ground, so I don't think that's it.
Now it sounds like it's coming from the engine itself. It's hard to tell because i think the frame might be telegraphing the sound from somewhere else.
It definitely increases in frequency with speed. Pulling the shift lever up so it's coasting has little effect. It can't be something in the engine then, can it?
It's slightly worse under load.
I even shut the engine off while moving to see if I could track it down. That seems to confuse me more. The sound doesn't go away, but it sounds different.

Last, in an effort to further define the sound, it's not a random rattle like something loose, but like something rubbing or knocking. I've never heard a small engine like this with a bad crank bearing. Could it be that?

Any thoughts or ideas on this would be helpful.

[84honda200s]

could it be the drive chain?? it may be to loose . just a thought

[MTS]

Worn out drive sprocket, The chain starts to ride up on the aluminum Case's and chew's the hell out of it, Pop the cover off and see what it looks like, the whole left case+high low assembly has to come off to get at it.

[SWIGIN]

iv had sub trannys make a noise like that id open that up and look

[Frankencelery]

I replaced the chain and both sprockets, so they're both brand new. I had the sub tranny apart when I did that, and I didn't see anything. Maybe I reassembled something wrong? Chain noise is the most logical answer because it seems to increase with speed. I wonder if there's any angle in which I can see into the front sprocket area and see if anything is visible....

[darrel632]

If you figure it out let me know, I've got the same issue, only in 3rd gear. Mine has a new subtranny, new chain, new sprockets, new seals, shaft rebalanced between trans and sub trans, and it still rattles, to go with this, it will break the drive chain once in a while, only in 3rd, concidering 3rd is probably the most used gear on these units, it seems likely that I will have to tear the tranny down to find some issue with the gear assembly which is putting out a harmonic vibration, like a worn / missing shim, chipped tooth, or something else out of balance.

Good Luck

[Frankencelery]

I probably won't get to look at it now for a couple of days, but this is in every gear AND it seems to occur even in neutral. After reading other people's thoughts and your comments, I would agree that it's starting to sound like tranny or chain issues.

[DeePa]

maybe the noise of the tires on pavement?

mike

[Frankencelery]

Aww, come on DeePa. I'm not THAT new, am I?

Actually, I did get a quick look at it and noticed two things right away: first, the chain tensioner isn't holding. I've tightened it twice now and then when I check it its loose again. Second, the tensioner sprocket teeth are worn concave in one direction, which may account for the noise. I think I have another tensioner assembly to try, so I'll do that and let y'all know. (whoa...southern Iowa and saying y'all...what's up with me?)

I gotta do it before my wife gets home because she's already mad at me for spending too much time with my 3-wheelers. (yeah, but my ATC's are *always* in the mood)

[Frankencelery]

Ok, I did get a chance to replace the tensioner arm. Not only were the teeth worn, but it had a tooth missing! Woo-hoo, problem solved...I thought. But after getting that replaced and the chain to just the right tension, it still makes that !@#$!@ noise!

Still can't tell for sure where it's coming from either.

[ATCnut]

Try starting it up with the chain off. Put it in gear and run it through the gears. That should tell you if the noise is in the motor. Roll the trike down a hill with the chain off, that would tell you if the noise is in the rear end. If both of those are quiet, then it has to be the chain.

Check the allighment of the sprockets. You had the whole trike apart, You might have to loosten up the motor and wiggle it until the drive sprocket is alligned with the rear sprocket.

[84honda200s]

good thinking man. only if i were that smart. lol

[Frankencelery]

ATCNut, that's a good idea. I did sight along the chain last night with a flashlight, and didn't see anything odd, nor did it look like the sprockets were misaligned. But I'll definitely try running through the gears without the chain, and then rolling without it and see if i can narrow it down further.

[Frankencelery]

Ok, I decided to be late for work and check this out first. Who me? Obsessed? Anyway, I pulled the chain and started it and I can hear the sound when I put it into gear with no chain. It's much quieter, but that's probably because there's no load, but it's definitely the same sound. So it's tranny or sub-tranny. Sigh. I'm not sure what to look for. I'll take apart the sub tranny tonight and see if I can see anything. Maybe I'll take out the sub gears and run it through the gears again and see if it still does it. Process of elimination.

[darrel632]

Just pull the sub into neutral and see if you get the noise, bet you do, and then is it really worth ripping the whole thing apart to find??? nothing? something worn? can you find replacemnt parts, or do you have to start putting in 125 TRX trans. parts? with any luck its just the trans output shaft is out of balance from wear and it will cost you 30 or 40 bucks to rebalance / rebuild.