francoblay1
The Spaniard
Last edited:
Broken swingarm!!
- Thread starter NZBigDog
- Start date
OK....So ive been trying to actually use my brain to think about this....
Are there any "frame designers" on this site???
Back in 2002, would RT have been using some sort of CAD software to design the frames? If so I wonder if it would have had "stress testing" or some sort of "loading" in the software to test the frames before they were made.
Im not a mechanic and this is my first bike ive owned so im still learning alot. I realised yesterday that this part of the swing arm actually has ALL the spring pressure applied on it (in a 'pull' motion) when the suspension works. I guess with 12 years of this pressure it just starts to crack and then breaks. I would have thought the "tab" where the shocks actually mount to would break first but im no expert.
If this IS the case...then I would think that this will actually start to happen to ALL of our BigDogs....
Anyone want to comment on this or even correct me in the thinking if im wrong...
Are there any "frame designers" on this site???
Back in 2002, would RT have been using some sort of CAD software to design the frames? If so I wonder if it would have had "stress testing" or some sort of "loading" in the software to test the frames before they were made.
Im not a mechanic and this is my first bike ive owned so im still learning alot. I realised yesterday that this part of the swing arm actually has ALL the spring pressure applied on it (in a 'pull' motion) when the suspension works. I guess with 12 years of this pressure it just starts to crack and then breaks. I would have thought the "tab" where the shocks actually mount to would break first but im no expert.
If this IS the case...then I would think that this will actually start to happen to ALL of our BigDogs....
Anyone want to comment on this or even correct me in the thinking if im wrong...
Got a response from Rolling Thunder
Hi Jason,
Sorry to hear that your swing arm snapped at the shock mount. Yes I have seen this before and first thing that you should know is that all Big Dog Frames are the sole responsibility of Big Dog Motorcycles as the designs of the frames are their proprietary design. Needless to say if you would want us to repair the issue we will if you take care of the shipping to and from our shop and in good faith we will take care of the repair at no charge.
We have built thousands of swing arms with that design and we may have had 2 or 3 issues that I have ever been aware of. Ok to explain why this may have happened is quite easy and I hope I can explain it well enough for you to understand. The shock mount does take a hit with every bump in the road, it gets used in compression and extension both and where the shock gusset meets the crossover tube (See Attachment) is a high stress area of the swing arm. That is the case anytime you have a huge gusset meeting a piece of tubing now this doesn’t mean they will all fail during regular road use but if there is an accelerator then there is a greater chance of it failing. What I mean when I say accelerator is that there is something that happened to the regular function of the swing arm that caused the cracking of the tube because it would not just crack by itself especially if it lasted 12 years. One of the other times I seen this happen it was due to the customer having a seized spherical swing arm bearing on the side that snapped and this can happen if the bearings were not properly greased and maintained at regular maintenance intervals so what that did is cause the left side to move freely and the right side was sticking as it went through its range of up and down motion. This continuously added stress and eventually caused that swing arm to fail, again this may not be your case but it can be an issue similar like maybe the shock on that side has become weaker then the other side therefore again the stressor changed and caused the swing arm to fail.
The proper repair for such an issue is to replace the complete tube because if you just weld it up there may be another chance that this swing arm will fail in the exact same area. If you have it repaired locally please make sure that the swing arm is checked for straightness because it may have lost its shape depending on how long this has been going on.
I hope that this e-mail helps explain what may have happened to your swing arm but I am always here to help so please don’t hesitate to contact me with nay other questions that you may have as it would be my pleasure to assist you.
Thanks,
Sam
Hi Jason,
Sorry to hear that your swing arm snapped at the shock mount. Yes I have seen this before and first thing that you should know is that all Big Dog Frames are the sole responsibility of Big Dog Motorcycles as the designs of the frames are their proprietary design. Needless to say if you would want us to repair the issue we will if you take care of the shipping to and from our shop and in good faith we will take care of the repair at no charge.
We have built thousands of swing arms with that design and we may have had 2 or 3 issues that I have ever been aware of. Ok to explain why this may have happened is quite easy and I hope I can explain it well enough for you to understand. The shock mount does take a hit with every bump in the road, it gets used in compression and extension both and where the shock gusset meets the crossover tube (See Attachment) is a high stress area of the swing arm. That is the case anytime you have a huge gusset meeting a piece of tubing now this doesn’t mean they will all fail during regular road use but if there is an accelerator then there is a greater chance of it failing. What I mean when I say accelerator is that there is something that happened to the regular function of the swing arm that caused the cracking of the tube because it would not just crack by itself especially if it lasted 12 years. One of the other times I seen this happen it was due to the customer having a seized spherical swing arm bearing on the side that snapped and this can happen if the bearings were not properly greased and maintained at regular maintenance intervals so what that did is cause the left side to move freely and the right side was sticking as it went through its range of up and down motion. This continuously added stress and eventually caused that swing arm to fail, again this may not be your case but it can be an issue similar like maybe the shock on that side has become weaker then the other side therefore again the stressor changed and caused the swing arm to fail.
The proper repair for such an issue is to replace the complete tube because if you just weld it up there may be another chance that this swing arm will fail in the exact same area. If you have it repaired locally please make sure that the swing arm is checked for straightness because it may have lost its shape depending on how long this has been going on.
I hope that this e-mail helps explain what may have happened to your swing arm but I am always here to help so please don’t hesitate to contact me with nay other questions that you may have as it would be my pleasure to assist you.
Thanks,
Sam
will_65466@live.com
Member
Holy crap!
bearman
Active Member
I agree that if both sides of the swingarm are not moving freely, then this part that cracked would have a twisting force put on it. I also agree that uneven shock wear could cause a twisting force on this part, but I think that it would be a much smaller force.
It could also be that one of the rubber bump stops fell off and the other is still there. Hitting this one bump stop on the one side would also put a twisting force on the swingarm.
But 12 years to failure means it’s a pretty strong part to begin with.
And a big Kudos to Rolling Thunder for their offer to repair for free (plus shipping).
It could also be that one of the rubber bump stops fell off and the other is still there. Hitting this one bump stop on the one side would also put a twisting force on the swingarm.
But 12 years to failure means it’s a pretty strong part to begin with.
And a big Kudos to Rolling Thunder for their offer to repair for free (plus shipping).
Yep, i agree, i think it is really good of them to offer to repair it after 12 years.
Just a note: both of my swingarm bushes are fine and also the bump stops are also in good condition....not sure about the shocks, not sure how i would check them.
I think it might just be put down to "wear and tear"
Yep, if you are close enough then I would send it to them....might be better than a new one because they are going to make sure it is 100%?...and itsa free repair!!:2thumbs:
Hirter6Pack
Not Quite A Guru
How about an intro Dave Z
http://www.bigdogbiker.com/forums/introductions.2/
Glad ya got that Dog fixed.
