A beautiful morning and I had thoughts of calling Greg Harding to see if his usual Sunday ride was open - my TLR is still in pieces but the Montesa has been fine - so I wheeled it out of the shed and kicked her over - slightly reluctant but she has hardly been touched in two months. The engine kicked and away she went, so I thought I just better check everything before loading on the trailer and my optimism was crushed to see the front spar of the frame was about an inch disconnected from the base. A fairly clean snap of the joint where the pipe joins the base but what I am not sure of - is the frame welded in a stressed structure or has my frame bent, because I struggle to bring the two parts together in order to weld it. The frame doesn't look bent so it appears the stress is deliberate but wow there is a lot of pressure required to bring it together
Broken Cota frame
Moderator: Moderators
Re: Broken Cota frame
Spanish TS frames are generally not made out of very good tube, and welding often isnt that great either. The last of the Bultacos, which had lower frame tubes removed commonly used to snap the top tubes. Anyone riding an old Spanish bike should keep an eye on the frame, as its easier to repair a crack than an actual break.
Repairing that break is pretty simple, but you will need to clean all the paint off the repair area, and temporarily weld something onto the down tube, which you can use to clamp onto and pull the tube back into position. If you dont want to weld something on the down tube, it might be worth trying 2 ratchet straps, going round lower fork yoke at the top, and front engine mount bolt at bottom
The actual welding needs to be done by someone who knows what they are doing, but as it would only take about 5 minutes to do, if you have it all clamped up properly, shouldnt cost much if you need to pay someone.
Repairing that break is pretty simple, but you will need to clean all the paint off the repair area, and temporarily weld something onto the down tube, which you can use to clamp onto and pull the tube back into position. If you dont want to weld something on the down tube, it might be worth trying 2 ratchet straps, going round lower fork yoke at the top, and front engine mount bolt at bottom
The actual welding needs to be done by someone who knows what they are doing, but as it would only take about 5 minutes to do, if you have it all clamped up properly, shouldnt cost much if you need to pay someone.
-
- Champion
- Posts: 4062
- Joined: Thu Jun 05, 2003 7:01 pm
- Bike: Many Twinshocks
- Club: CQTC Inc, RTC Inc
- Location: Gladstone, Queensland
Re: Broken Cota frame
Here is a possible scenario
The frame may have developed internal stresses from being moved out of shape over time by use (riding rocky sections, MX jumps or from hitting the lower frame rails on solid objects), and there may also have been some internal stresses left over from when it was manufactured. Those internal stress were relieved when the failure occurred, by the bottom end of the tube moving forwards, causing the positional mismatch at the break.
If the bike had been ridden with that break, I suspect that the frame backbone would have bent like a banana. Good that you saw it in time
The frame may have developed internal stresses from being moved out of shape over time by use (riding rocky sections, MX jumps or from hitting the lower frame rails on solid objects), and there may also have been some internal stresses left over from when it was manufactured. Those internal stress were relieved when the failure occurred, by the bottom end of the tube moving forwards, causing the positional mismatch at the break.
If the bike had been ridden with that break, I suspect that the frame backbone would have bent like a banana. Good that you saw it in time
relax, nothing is under control
-
- Expert participant
- Posts: 209
- Joined: Tue Dec 28, 2010 10:44 pm
- Bike: Ty250,Ht5.
- Club: Bath Classic
- Location: Near Bath,SW UK.
Re: Broken Cota frame
If you are not worried about originality it may be worth adding some extra bracing to that area,or you could use a bracing sleeve inside the original tube.You can move this into place using a small hole or two in the existing tube and using a scriber or similar to lever it into place,if that makes sense,weld over the hole after which also holds the sleeve in place.I have recently used this method on the front spaceframe on an E - Type Jag which meant I could do an effective repair without completely stripping the front end.(Cant believe how thin the original tube was...)
Re: Broken Cota frame
Jon V8 wrote:If you are not worried about originality it may be worth adding some extra bracing to that area,or you could use a bracing sleeve inside the original tube.You can move this into place using a small hole or two in the existing tube and using a scriber or similar to lever it into place,if that makes sense,weld over the hole after which also holds the sleeve in place.I have recently used this method on the front spaceframe on an E - Type Jag which meant I could do an effective repair without completely stripping the front end.(Cant believe how thin the original tube was...)
I was about to say the same, apart fixing the Jag part. I once used a bicycle gooseneck bolt with the angled nut to pull the tubes in to place with 2 well placed holes and bit of steel bar as a big washer, but you can use some threaded rod to anchor it at the back frame tubes.
Re: Broken Cota frame
FM350 wrote: it might be worth trying 2 ratchet straps
I tried that and then a wire with turn buckle but no where near enough pull. So I rigged up a fence strainer which is a lever that climbs a chain and using this I can just get it together but I can't hold it and weld it at the same time
That's why I was wondering if the were assembled in a pre-stressed way or should I be looking a lot closer for a bent frame.
Re: Broken Cota frame
No Spanish frames made out of cheap ERW tube were not pre-stressed in any way whatever. Your top tube might be bent a little, and this will mean the repair is going to be more difficult but still possible. If you get a couple of these: http://www.demon-tweeks.co.uk/Product.d ... &%20Plates
and then weld bolts on the side of the down tube to fit the eyes over, and make a fitting to bolt onto the front engine mount which you can drill to accept the threaded rod, then after applying heat to top tube (if its bent to any extent), pulling the tubes back together is just a matter of tightening the nuts on the eye bolts.
and then weld bolts on the side of the down tube to fit the eyes over, and make a fitting to bolt onto the front engine mount which you can drill to accept the threaded rod, then after applying heat to top tube (if its bent to any extent), pulling the tubes back together is just a matter of tightening the nuts on the eye bolts.
Re: Broken Cota frame
FM350 wrote: Your top tube might be bent a little.
There is a hairline crack where the down tube joins the steering head on one side only. But running a straight edge on the top and the down tube I can see no discernible bend. Anyway I guess I'll have a go with the bolt - unless anyone else has better ideas.
-
- TA Supporter
- Posts: 152
- Joined: Wed Jan 14, 2009 10:46 pm
- Bike: Bultaco's
- Club: denman
- Location: armidale. nsw
Re: Broken Cota frame
G'day Andrew,
I think your model Cota frame is chromoly so maybe should be TIG welded, what about putting a straight edge along the backbone to see if its bent there
I think your model Cota frame is chromoly so maybe should be TIG welded, what about putting a straight edge along the backbone to see if its bent there
Re: Broken Cota frame
brownie wrote: what about putting a straight edge along the backbone to see if its bent there
Well spotted Ross the left hand tube shows a couple of millimetres clear under the straight edge - right side appears flat. Now I have no idea what to do
Return to “Twinshock & Classic Trials”
Who is online
Users browsing this forum: Bing [Bot], Greg Harding and 39 guests