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A recent strip down to change the bearings revealed a crack in the drive side swing arm in the section between the bearing and the weld at the chain stay section. For sentimental reasons I'd really like to keep this bike on the go, but unfortunately it can't be a money no object project. So any suggestions for repair? So far I have thought of:
1. Direct replacement- I've spoken to orange who no longer have any, and googling suggests a history of swing arm failure, so unlikely that I will find one
2. Repair - any recommendations? Also, how likely is it to be successful? I still want it to be a rider, not a showpiece and it's a fairly critical area
3. Resin and carbon fibre bodge over the top of the damaged area and hope...
4. Custom replacement from a frame builder - the original is still in one piece and square to be able to make a jig from, possibly remake in steel to avoid cracking issues in future - less worried about a little extra weight or an exact match as long as it is functional - although likely to be the most costly. Any ideas of ballpark figures?
I guess putting a pic or two up might help.
Working on it - not the most technologically successful!
Is it made from Shimano crank arms?
Use postimage.org
from that site, just upload pic then use the "forum hotlink" copy/paste tab.... and paste on here.
Make sure you replace it with solid tubing
https://ibb.co/k8PX97
https://ibb.co/cWmC97
https://ibb.co/iwTs97x
Sorry, that didn't quite work - iPad running at a snails pace. Off out, will try again later 😂
Cost wise, look for a second hand frame as a replacement. That's a high stress area. Orange Five would do.
As you say, Orange had issues with this swing arm and the early rockers - I had two rockers and a swing arm on my 2009, replaced with updated 2010, but the swingarm was nicked from another HQ bike as they had no more, and that was in 2012.
still the best bike I have ever owned.
Mark it, see if it’s spreading. If it isn’t keep riding. It’s not like a 2010 frame owes you much. I sold my st4 for £250 about 4 yrs ago.
as an aside, a 26” transition bandit is very similar in geometry and ride if you can find one.
That's dead imho.
How about turning it into a lamp, or something?
I'd cut out the crack, weld the gap back up and add a gusset to move the stress concentration away from that radius. Depending on the material it might benefit from post weld heat treatment, but that may not be the be all if the gusset reduces the stress in that area sufficiently.
Whether repair makes sense or not depends on if you're paying for the work or not. Got any welder mates? If it's free or at least cheap then you've nothing to lose really.
Thanks for all the replies folks.
New frame is a final resort - I'm not bike less without this one and the sentimental reasons mean I'll probably put it on the long term list if I can't afford a repair now.
Speaking to a few welder mates most haven't been particularly confident of a long lasting repair - it's an odd shape with a stress point in a piece of billet. Admittedly none are used to working on bikes so are worrying about design stresses. The more obvious design suggestion would be to put a gusset over the whole of that milled out section to create a box section profile, would have to do some measuring up to confirm if there was clearance to do that, although going 1x might help in that department.
Any suggestions for alu frame repairers I could talk to? Argos have been mentioned, know of a few folks who work in steel.
Not the news you're after but I think that's goosed. The crack's already permeated along most of the width of the swingarm and that area is already a natural stress riser. I wouldn't ride that as when chainstays go it's sudden and i've seen a couple of hefty crashes arise as a result.
Milling the crack out will still leave a large stress riser, in an area that's just cracked without a large groove added. A gusset might help but I'm doubtful it'll reduce much stress away from that area and be difficult to implement given it's on the bend. Welding would be a bad idea as without heat treatment the residual stresses will outweigh any benefit imo, as well as being a tricky area to weld alu with the thin cross section there.
Second hand st4 or five might be the best option there sadly,
patch it with carbon fibre ...job done you won't have any more issues
Im surprised there's any of those ST4s lasted this long.
It was on swingarm number 2 already, this one lasted 6 years though.