Bent Swing Arm on 2008 CRF-150RB

[KangarooCourt]

This is the story;

14 year old child races Supermini 2 in Western Pennsylvania. Doesn't woods ride or take a mechanic on the back to the start grid. His maintenance is all fantastic.

They complied with the recall about the swing arm replacement and the replacement swing arm is bent on both sides. Worse yet, the drill hole where the countershaft sprocket side chain guide goes has fractured completely through.

This thing was ready to fail!

We paid for a replacement swing arm, because Honda considered this an "isolated" event?

Vin # JH2KE03C88K100337.

Anyone else have this happen?!!

[honda53]

I've heard of the replacement swingarms for the recall breaking, so you're not the only one. "Isolated events" must not be too uncommon, but i havent had problems with mine. Did he case soemthing hard or did it just happen?

[KangarooCourt]

No he didn't case anything. There's no external damage to the swing arm at all. I am an aircraft engineer as well as a pilot. The loads are consistent with sheer loads and torque, not being bashed in by anything. The structural failure is spread at the same points about six inches behind the fulcrum (swing arm axle). As you probably know the swing arm is a second order lever Fulcrum/Load/Effort. The bend is exactly at the point of maximum load on both sides. There is some packing of the aluminum along the crease bend and the inside of the swing arm has bent inward at the creases.

This is either a raw materials quality issue or a materials thickness spec' not being met. Another thing, Honda simply drilled holes in the aluminum to put the chain guide on that precedes the countershaft sprocket. There's no reinforcement around the hole and thats where it has cracked through.

I am looking for a magazine that will take the swing arm and alert consumers that can be trusted.

I will post photos tomorrow.

[G31m]

I am an aircraft engineer as well as a pilot. The loads are consistent with sheer loads

I would think an engineer would know how to spell "shear".

[KangarooCourt]

Yes you're correct! Rather unfortunate, but I can assure you, not as unfortunate as a child having a motorcycle break in half.

From Kansas I see, I hope all is well in aerospace for you!

[G31m]

Oh, and another thing; the swingarm's pivot point is not a fulcrum. The linkage attachment point might be considered as such, but not the pivot.

(There are LOTS of very different engineering disciplines in the aerospace industry, not all of them deal with materials or mechanics.)

[KangarooCourt]

Respectfully, I disagree. The fulcrum is the axis, which is the pivot point. Thanks for keeping the post alive. I am well aware of the various engineering disciplines. I'm sure everyone else is too.

[G31m]

I will have to apologize on this one, 'Roo. (I seem to have forgotten my college physics classes) You are right; if we consider the swingarm to be a lever of the second class, then, yes, the swingarm pivot is, indeed, a fulcrum.

I'm now curious, to which engineering discipline do you belong?

[KangarooCourt]

Aircraft. My work mainly dealt with long range fueling operations, field repair and modification requiring STCs. Also inspections.

Now I just fly them. I pick up planes in Kansas quite often and they do really nice work. I'm on the Citation X.

[KangarooCourt]

[KangarooCourt]

[KangarooCourt]

This is the first time I've ever used a photo bucket to upload to a message board. Anyway...the first image shows the bend and the next one shows that Preston is not over the accepted weight limits of the bike. On the inside of the right side of the swing arm, there is creasing of the aluminum. It was just about to snap. Again, the bent swing arm is the one that was replaced as part of a recall notice in January of 2009. Honda made us pay to replace it the second time to finish the season. He won his class outright. I suspect next year he'll get an RMZ-250 FI to compete in School Boy 1, I'm not sure if he'll ride red again.

We've been in quite some discussion on this board about the validity of referring to ourselves in engineering terms, but it appears to me as though the failure originated in the side wall thickness of the material utilized on the inside of the swing arm.

Edited October 28, 2009 by KangarooCourt
add content.

[BC3]

I will have to apologize on this one, 'Roo. (I seem to have forgotten my college physics classes) You are right; if we consider the swingarm to be a lever of the second class, then, yes, the swingarm pivot is, indeed, a fulcrum.

I'm now curious, to which engineering discipline do you belong?

Go to your room ??

[KangarooCourt]

Honda will not accept any responsibility for this at all. I just got off the phone with them today. The swing arm is being sent to the CPSCA in Washington for testing.

[G31m]

I'd be quite interested in what you find out...keep us posted.

Edited November 4, 2009 by G31m

[crf150rkid]

Thats kinda weird. Wish i knew all this engineering stuff. He does seem a little big for the bike ion all honesty. Im about the same size and know for sure i cant ride a 150r very well because there so small. Well atleast compared to my 250f. Hope to hear what they find while testing it.

[JLF88]

Is it a stock the rear spring ?

[KangarooCourt]

No, both rear spring and front forks were matched by Pro Action to his weight and ability. For those of you who think he's too heavy, he's not. He has a very low Body Mass Index; besides the new swing arm didn't bend and he's riding better and weighs more than he did before. It's an engineering flaw, based upon the lack of similar experiences, it might just be a fairly isolated problem.

[G31m]

It's an engineering flaw, based upon the lack of similar experiences, it might just be a fairly isolated problem.

If it was an engineering(design) flaw, all the swingarms would be bending. This leaves the isolated problem you mentioned as the only real conclusion.

By the way, I've googled "CPSCA Washington" and come up with nothing.

What is this?

[500XC]

I've actually got magazine and hop-up house evidence that while it might be an isolated problem, it's not just you.

I've got a Dirt Bike Magazine featuring a vs. test of a Supermini CR85 and a CRF150R that R&D Racing built, and while I can't remember what issue it was in (I'll look later), I do remember it saying that he noted his riders bending swing arms, and that a different link changed the ratio enough that it stopped. Apparently.