Piston Slap?

[hkeller]

Greetings. Just joined; intro is in the proper section.

After adjusting the chain, loosening the throttle stop screw, loosening the brake adjustment and lubing everything, this mini-bike is pulling my 9 year old around just fine, even hills. Although, that wasn't the case right out of the box (see intro).

I have one concern, when he is running at full throttle (after he's gotten up to speed) the bike makes a banging noise. It is a pretty loud slapping or popping, which sounds a lot like piston slap. I just changed the oil (after about 10 hours of riding) and it was full of metalic flakes, but no chunks (although they wouldn't make through the small drain hole even if they were in the engine). Anyone have any thoghts on this? I know it could be chain slap, but is sounds more internal, like a hammering in the motor, and it is timed with the exhaust note.

Is this common? Anything to worry about? I still have 60 plus days of warranty.

Thanks in advance for your help.

 

[Oldschool]

Change the oil.

I would not run a new engie more than a few hours tops with out an oil change to get the metal out. New engines will have a lot of metal in the oil as they break in so its best to cghange it very often at first ( I usualy do 3 changes before the first 2 hours ). Change oil every 20-30 hours there after depending on use.

As for the noise I can 't help you...

Make a video post it on YouTube so we can see and her it.

 

[cxbra]

Banging at full throttle?? Sounds like its misfiring or running lean. When I was running my bike too lean, it would backfire (pop and tick), but when I gave her some more fuel (air/fuel mix screw) she was 100% in the turn of a screw.

 

[Strigoi]

how much play is in the chain? it's common for them to hit the chain guard even when set up properly.

 

[hkeller]

I loosened the chain some. I'd say there is probably an inch of play. I am hoping that is it; just the chain hitting the guard. But, it just sounds more internal.

I don't get any popping or backfire. The little engine runs pretty well. However, this sound did not appear until I backed out the trottle stop screw a few turns.

 

[Strigoi]

you want to have 1/2"-3/4" of play. pull the chain guard and ride it, that will tell you if that's the issue. that's quick/easy so i'd do it just to get it out of the way.

 

[cxbra]

I loosened the chain some. I'd say there is probably an inch of play. I am hoping that is it; just the chain hitting the guard. But, it just sounds more internal.

I don't get any popping or backfire. The little engine runs pretty well. However, this sound did not appear until I backed out the trottle stop screw a few turns.

Sorry man, I must not have read your full 1st post. Im positive that its chain-slap. Its a very high-pitch (for metal) CLING-CLING-CLING sound. The part that kept making contact for me was the very front of the chainguard. You can inspect, if the chainguard has paint missing on the underside, then chainslap is your noise. You can easily move the chainguard up in any position you need, and it actually has a little bit of space so you can loosen the chainguard and raise it up as high as it can go. Also, its better to run the chain snug (1/2 inch play), I've had mine pop off while jumping off curbs (not that your daughter will be doing that :smile and that wasnt too fun.

The clutch springs can make noise also, but thats only at the engagement point.

 

[Strigoi]

I've had mine pop off while jumping off curbs (not that your daughter will be doing that :smile and that wasnt too fun.

the chain can also lock up the rear wheel when that happens. that's when it gets dangerous.

 

[Modding_out]

the chain can also lock up the rear wheel when that happens. that's when it gets dangerous.

Tell me about it:doah:......The most common way is for the baja bikes chain to get caught on the studs on the back side of the sprocket :censure: and that just can't be good for the chain :doah:

 

[hkeller]

Good idea, I'll try it with the guards off. However, it is not the ding, ding, ding noise cxbra describes. It is more like a hammering or deep knocking. It sounds like rod knock, but I can't imagine how that could be in a one cylinder engine and have it still run.

 

[cxbra]

Have you oiled the clutch bushing? If not, it can seize up randomly and make the bike buck. I have heard a thumping before (like a duunk-dunk hammering sound) and I couldnt find out what it was. I oiled the clutch bushing and it never bucked or knocked again.

 

[125ccCrazy]

Good idea, I'll try it with the guards off. However, it is not the ding, ding, ding noise cxbra describes. It is more like a hammering or deep knocking. It sounds like rod knock, but I can't imagine how that could be in a one cylinder engine and have it still run.

You probably notice the noise more as he gets further away right? if so thats a pretty common noise from these type of engines, usually it's the rod hammering on the crank from my experience... since there are no rod bearings it's just the rod against the journal and being the qaulity on these chinese engines is pretty low the rod may have excess tolerence or even low torque on the rod bolts...