Kymco 90 keeps breaking master links

[turbofiat124]

Sorry, I haven't been on here in awhile. The co-worker who gave me my daughter's 110cc ATV a couple of years ago has a problem with his daughter's Kymco 90 ATV. I have not seen it in person which might be obvious to me but not him since I like to tinker with stuff but he doesn't.

He said she's had this thing for at least three or four years and was riding the other day and the master link broke. So he brings it into work and I measured the chain and came up with a #480. I ordered two master links. He installed one and rolled the chain back onto the sprockets. Which I've done many times when the chain has jumped off.

She made a few laps and the master link broke again. So he installed the other one and within a short period of time it broke! He went back to where the chain came off and found the master link. He says the pegs pulled out of the backing plate.

I've had master links break on me but after replacing them, I've never had one fail.

1) I asked him did he tighten the chain? He said no.
2) Was there an excessive amount of slack in the chain. He says maybe 1/2" or so like it's always been
3) Is the rear end cock-eyed or have any wobble in it like the bearings in the swing arm are bad. He said no.
4) Did you install the chain clip in the correct direction. He said yes
5) Did the master link appear to match the other links. He said yes.

I can't think of what it might be. Poor quality master links? However something caused the original master link to fail after three or four years. So did it just fail from normal wear? Or is there another reason it failed and is the same reason the last two suddenly failed?

He may just have to bring it to me (I don't make house calls) and let me inspect it to see what the issue is. Worn out sprockets?

Any ideas?

[dirtbkr188]

I'd say to replace the chain and sprockets with new ones, especially if the chain is 4 years old, it certainly doesn't owe you anything.


You made a reference to a #480, are you referring to a chain size?

[FLASHLIGHTBOY]

If you google what chain foes a BAJA 90 USE.... it will say #428 chain... I do not know where you got the 480 chain from.... but it is wrong.... if the chain is new and adjusted right... 1.2 inch slack... and straight to the engine.... measure both axle spread side to side.. the sprockets look ok... then good to go....

[Weldangrind]

Switch to a 428H chain for better durability.

[turbofiat124]

Originally Posted by Weldangrind

Switch to a 428H chain for better durability.

I meant to say in my earlier post this ATV used a 428 chain. Sorry.

I took some photos of the link. It didn't actually break but the pins pulled out of the mounting plate:

Question. Aren't these pins supposed to be brazed or something. Or the heads hammered so they dont pull out? I thought about spot welding them in place to prevent this.

[dirtbkr188]

IMO, there is still something out of alignment, putting undue side stress on the chain at the weakest point - the master link.
Welding the pins doesn't solve the overall issue. It could be rear wheel bearings, a tweaked or twisted swingarm, bad swingarm bushings, all of those things will contribute to creating a "hard" or "high spot" in the chain, popping the plates.
Just my 2¢...

[bogieboy]

looks to me like chain was too tight.... popping them out of the link like that.

[JerryHawk250]

Looks like the pins were never pinned or hammered. Try a higher quality master link designed for motorcycles. https://www.amazon.com/RK-Racing-Cha...W7SZJQ2Y5X4MBT

[FLASHLIGHTBOY]

but as he said... he has try several connections... maybe cheap joints... I guess yu could buy some good qual;ity stuff... but like someone else said... something else is going on,... poor aligment.. bad bearings or ????? you have to check it all over .. do not use 1/2 links .. use good chain and better links..

[bogieboy]

i kindof doubt that its the quality of the master... i have run the cheapest masters i can find on my 200cc bike and never had one pull out... i use masters from tractor supply or from the john deere dealer i work at... not exactly rated for moto use, yet i have never busted one... thrown the clip when i let the chain get so loose that the chain falls off plenty of times, but never broke one...LOL

[Weldangrind]

Originally Posted by turbofiat124

I meant to say in my earlier post this ATV used a 428 chain. Sorry.

I'm saying switch from a 428 to a 428H. H means heavy duty.

[JerryHawk250]

Going by the pictures posted it looks like the ends of the pins are straight like they were never pinned like most of the master links I have seen just like the picture below. I'm sure there is some form of misalignment that is probable causing them to fail prematurely.