It runs but I've got a rattle noise...

[two85atc250r's]

Well guys, it fired right up the 3rd time I kicked it, but..... I have some sort of rattling sound at low RPM's that I can't figure out. It used to make the same noise before I rebuilt it and I thought it would go away. Is it normal for a 250R to do this? I know this may sound weird but it almost doesn't sound like it is coming from deep inside the motor but something right on the outside. Almost like it is up front behind the radiators or something. I know that may sound dumb. That is just the best way I can describe where I think the sound is coming from. I replaced the main bearings and all the others checked out OK so I have no idea. It runs freakin great and pulls like it has never pulled before. Great power throughout the powerband so.... any idea what I might be dealing with here without hearing it for yourself? I don't want to have to crack it open again, I will let it be before I do that. Has anyone else experienced a sound like this on their R?
Many thanks to Aceman, Wilkin, and 86 Quad, without you guys I wouldn't have ever been able to do this. I am just so happy it fired right off. I just hope this is nothing serious. Please help if you have any idea...

i know mine makes a sound somthing like that but its not really loud an if im riding i cant hear it just when its sitting an running if i rev it you cant hear it tho.

[two85atc250r's]

Yeah thats exactly the way mine is. You can't hear it at all if you rev it. You give it just a little throttle and it sounds as smooth as can be. It is not very loud when it is idling, I almost didn't even notice until I listened close. So you think this is no big deal? Where do you think it might be coming from? Thanks for letting me know someone else has experienced this, that makes me feel alot better.

[pimpt250r]

its your counter balencer --they make a little noise but not much

[peeping TOM]

i'd say its u top end , doub't its your counter balance . nothing to worry about usually , till u get real piston slap.do the heat cycle,s .. don't listen to ppl saying {{ ride it like u stole }} for the break in. every 250r has top end noise.. u should hear 330,s top end noise...

[wilkin250r]

This is one of my favorite tools. I got mine from my local Kragen store for like $2.99

http://media.sourcingmap.com/uxcell/images/item/n/07c/ux_a07090700ux0033_ux_n.jpg

It's basically a stethoscope for engine diagnostics. It lets you know where sounds are coming from.

Now, I've only used it on my car, to tell if that annoying sound is coming from my water-pump, my alternator, or engine block. I don't know if you'll be able to pin-point the exact location inside your engine, because it's all pretty close in there, sound will travel pretty well.

But I bet if you pulled the stator cover side off, and put that bugger right on your counter-balance bearing holder (also holds the pulse generator) while the engine is running, you'll be able to confirm or eliminate that as the source of your noise. Same with the water pump, if the water pump was the source of the noise, this tool would tell you.

[LT250RMan]

Have you checked to see if all of the engine mounts are nice and tight ?

[atvmxr]

both my Rs do this, i asked the question years ago and was told its normal and not worry about it...

[gandgracing]

I had a lower pipe spring that rattled like crazy. Put some black tape around it and it stopped

[250r__Ice]

Thats the normal R rattle. All of mine have it.

[two85atc250r's]

Well I rode all day today and the thing runs like its on fire. The rattle is hardly noticable except at low RPMs and it's definately not affecting performance, I can hardly hold on to the thing when it hits the powerband. I can't get it to idle yet but overall I am extremely happy with it. Even my first guess at jetting seems pretty close. It tries to sputter just a little at the very top of the powerband so I might just be a little too rich but thats ok for now till it gets good and broke in. Thanks guys for letting me know the rattle is a common thing. I'm not gonna worry about it anymore.

[LONG-ROD]

Could be a number of things, alot of kick starters rattle and pipe mounts, anything that is not tight on any two stroke will rattle and make noise, just go threw it and check every thing!!!!

[86 Quad R]

as mentioned. its typical top end rattle. some are louder than others. i built three in the last month and they all had rebuilt counter balancers and all make the noise. if all is fresh. its just the reciprocating noise of the 2 stroke top end. when you start to hear a lil clap/clacking sound mixed with it then its piston slap.

btw what piston did you go with and what was the finished tolerance between piston and bore?