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Discussion Starter #1 (Edited)
hey has any one experienced this? This the second set that i have had the problem with. Once on the zx9 and now on the zx10. Both bikes have about
8k-12k miles on them before failure. The zx9 i figgured it was because of chain breaking while doing burn-outs and while agressive street riding. The ZX10 has had abiut 30 trips down the track and some serious twisty street miles. (8k-10k). I regularly clean bike after every ride and inspect things, and clean bike up, oil chain, ect, just general mantaince. On both bikes only chain side had a problem. Brak sides ok.:dontknow::dontknow:
Both bikes no issue while riding, after sitting on jack stands for a few days noticed cracked extension. I check ovr bikes after every ride..Like to keep them clean :dontknow::dontknow: any ideas???
 

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Dont mess wit White Ninja
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You get what you pay for~(there off ebay right)! If your really looking to use the bike, buy a swing arm! Other than that, raise her back up and use the bike.

Good luck man, sorry to hear about your problem!

ps this is about the 10th person I've heard of breaking extensions
 

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Cheap parts. I don't like weld-on arms, looking at the design of that one, wonder how many crap parts like that caused an innocent rider to crash..
 

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Discussion Starter #4 (Edited)
Hmm..Not an ebay knock off, was purchased from exotic cycles, but then again there probally made more for drag racing, than carving up the curves, I like the extended look, and do some 1/4 mile runs at the strip, and a lot of twisy back roads. A fulll swing arm not in the budget rite now. Plus i had a few track days planned and bolt ons make it easy to change back and forth. Just wondering if any ones else had same issues. Plus i've put about 8k-10k miles on theses in the last 8-10 months.
 

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Dont mess wit White Ninja
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Like I said above, your like the 10th person I've heard that has broke a set of these.

It is what it is, buy another set and call it that, if it happens again, it happens. I bet those extensions aren't doing anything for you if your hitting corners! And why not just run swb at the strip! Sounds like you need to just put her back to stock, hit a few track days and call it that!
 

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Oh wow, didn't notice they were bolt on's, the design makes more sense now...Didn't mean to sound like I'm bashing you or anything...I get the cool factor of being able to take them off and on, but I get the idea if you buy them, you take the risk of something like this...
 

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Those extensions fit inside the arm like shit man. There's all kinds of gaps that surely allow the ext to rock up and down and the thin design where they are supposed to tightly fit in the arm adds to the liklihood of failure.
I got over a year now on my myrtle west extensions. I drag race and rip the back roads though Im no knee dragger. My links fit in my arm with mallet taps and are equal thickness all the way back. Also are solid billet except the drilled hole for the adjustment bolt. My extensions are weldable and Myrtle West offers to do the welding if you send the arm to them. Honestly, your links look like POS. I've hit potholes that I thought surely damaged some part of my bike and my extensions never shifted because they can't cause there's no room for movement and are eveN dovetailed into the arm''s axle slot.
 

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hey has any one experienced this? This the second set that i have had the problem with. Once on the zx9 and now on the zx10. Both bikes have about
8k-12k miles on them before failure. The zx9 i figgured it was because of chain breaking while doing burn-outs and while agressive street riding. The ZX10 has had abiut 30 trips down the track and some serious twisty street miles. (8k-10k). I regularly clean bike after every ride and inspect things, and clean bike up, oil chain, ect, just general mantaince. On both bikes only chain side had a problem. Brak sides ok.:dontknow::dontknow:
Both bikes no issue while riding, after sitting on jack stands for a few days noticed cracked extension. I check ovr bikes after every ride..Like to keep them clean :dontknow::dontknow: any ideas???
sorry to hear about this but those extensions you got are the Yana Shinki (crap) your lucky you got 8-10k out of them without breaking on you. do a search alot of people have had problems with there extensions. if you go back to extensions i highly recomend myrtle west, exotic cycle or roaring toyz.
 

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Shorty's Performance
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Give them a call and complain about it!! I had the same set on my 14 and never had a problem I dont know.
 

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Discussion Starter #10 (Edited)
Yeah i know lots of people that have the same extension's that i've used, from drag racers to just the bling crowd that haven't had the problem i've had. After futher inspection and measuring against a friends set from roaring toyz and another set form allthings chrome. Design and fit of extesions are fine. Olny thing I can conclude is that since i also do alot of agressive street riding more stress is put on the drive side. Brake side has extra support by the brake hanger bracket. Drive side doesn't, Needs a longer support bar on the inside to help minimize flex. Probally why I've only seen problem on drive side.
Gonna try another set/style till i can get arm made the way i like.
 

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<- mechanical engineer about to go into mechanical-engineering mode.

The other thing is that the drive side sees considerably higher stress because of the chain-pull force. I think this would be a much more significant factor than the brake hanger. The failure happened away from the area where it is bolted into the stock arm, so I wouldn't think the way it's attached to the arm is a factor. (No question that a slight press-fit is better, though.)

Is there a step in the backside at the spot where the crack started? If so, I betcha that step is where the crack began. The step is a stress-concentrator. A radius at that location, instead of a step, would make a LARGE difference to the fatigue strength.

What gearing were you using and how far back did you have the axle mounted?

There are a few things you can do to cut down stress on these.

First, you can use the stock-size front sprocket and do all the ratio-changing with the rear sprocket (I always recommend this anyway). It means there is less chain-pull force. The chain-pull force is by far greater than the force pushing the bike ahead because of the mechanical disadvantage of the rear sprocket diameter to the rear wheel itself. Anything you can do to reduce the chain-pull will reduce stress on everything involved in the drivetrain.

Second, don't run the axle any further back than necessary. Putting it further back puts more leverage (stress) on that spot where the piece broke.

AFAICT all of these are made from ordinary 6061-T6 billet aluminum and the material itself is the same no matter who does the machining or whose brand name is on the outside. But ... if you are looking for replacements and can get the dimensions, a slightly thicker section will help.

If you street-ride with this bike also ... I haven't seen a whole lot of drag-racing long arms that look like they have adequate torsional rigidity, nowhere near what the stock swingarm has. No doubt they're fine for going in a straight line, but if the arm doesn't have enough torsional rigidity, it could cause some handling problems. The stock swingarm has very large cross-sections up front that make it very stiff in torsion while still allowing a little bit of side-to-side flex.
 

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Discussion Starter #12
I ran -1/+2 gearing on both bikes. Usually run about 6" out. and adjust back as chain stretches. On brake side, brake mount added extra support between swing arm and extension. On chain side the is a small gap with no support where extension cracked:dontknow:

Brake side:[

Chain side with crack:


Other set broke in same area:


Extensions are slotted to fit in swing arm, very tight fit:dontknow:
 

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Dang, you can find complete racing arms for a little over what those sorry extensions sell for.
 

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Discussion Starter #14
QUOTE=fernman;1619091]Dang, you can find complete racing arms for a little over what those sorry extensions sell for.[/QUOTE]

Not really, most extensions set now run around 250.00 a set, Modifying stock swing arm is in the area of 500-1000 bucks, Complete swing arms run around 800-1500 depending on what extras you have added:hello: Thats just stock wheel sizes, get into a 240 or larger wheel 2k-4k .

If i was just drag racing, or just doing some high speed runs, and mellow twistys, probally wouldn't have an issue:dontknow: But after getting suspension dialed in, ride height set so as to not bottom out, handles pretty good actually. Can run pretty close to a swb in most twistys roads. I ride pretty hard sometimes, can acyually get knee down:eek:ccasion1 . probally trying to do too much with one set up..:thumbsup::dontknow:

here is a pick of complete bike
.
 

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Actually C&S Customs will extend your stock arm for about $375. 2 sets of extensions, you said $250 a piece, sounds like an easy answer to me.
 

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C&s
 

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Discussion Starter #17
mit be the way to go... gotta pick up a used arm, to get work done. i'm in westrn calli so down time is a issue, well not in the last few weeks anyway...LOL
 

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I have been making extensions since 1993. First thing is to ask what Billet are they using? Also the inside corners should have a radius. If it in not you will have a failure in that area.


 

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Discussion Starter #19
I have been making extensions since 1993. First thing is to ask what Billet are they using? Also the inside corners should have a radius. If it in not you will have a failure in that area.


all the manufactures that i've looked at seem to use the same billet material, think it's t6061:dontknow: I took the extension to a race/tuner drag racer i know. They have used the same or similar extension on there race bikes and customer bikes. He says he's never seen one break like this. He has national titles and some seriously high horsepower bikes, and has been drag racing for many years.
 

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Another thing to look for is in this pic. How thin is the area from the Tang to the Pocket. You can see in this pic it is pretty thin. They make use the Same Billet material but they doesnt mean much it they are made incorrectly


 
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