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Discussion Starter #1
I have slowly been rebuilding a basket case T140D for several months.
Just getting around to putting oil in the frame this morning only to find that the large down tube has a crack at a weld right in the swing arm area. (this is about 6 " above the strainer filter and drain plug plate)
Needless to say I'm very disappointed after all this work but I'm wondering if the crack could be welded without major stripping of components. If I remove the rear wheel and the front wheel while on the center side it would allow pretty good access to the crack.

Any advice?

Charlie
 

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It is unusual for a late frame to crCk but the early ones did.

I would be reluctant to say that it will mend in situ as the frame needs to be clean for the weld to be ok.

If you google t140 frame repair you should come up with some pictures. There are some on britbike.
I think that big d cycles has some pictures of a repair?
People take the opportunity to add two bits of angle steel on either side of the swing arm to brace the frame.
You could also add a couple of captive nuts or studs so that a spin on filter can be added in the future.

t140 frame repair swing arm
http://www.triumphrat.net/classic-vintage-and-veteran/234064-repairing-oif-swinging-arm-pivot-crack.html
 

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I have been studying pictures of T140 frames on the Big D site that have been strengthened for racing by Ed Mabry - in addition to some triangulation tubes to the frame ,the only strengthening they appear to have to the swingarm mounting is to add tabs from the top of the mount to the oil tube - exactly as Meriden did to the later frames ( the T140D had this mod) --- however as your frame has cracked despite this additional strengthening you need to consider the extra strengthening shown in the link given by Dave M -- I would also agree that it would be wise not to try a repair in situ -- is the crack above or below the swing arm pivot ?-- the repair in the link assumes a crack below the pivot
 

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Since I have an OIF bike, I follow these threads closely. Seems some crack & others don't with many thousands of miles on them. What is the root cause of cracking?

On the bikes with cracked frames was the swing arm pivot binding or stiff in any way? How much force does the side plates on frame take? I understand eng plates take no force, but the plates behind the eng plates should?? Is it acceleration forces pushing the frame tube forwards, or braking pulling it back? Since the frame tube is only thick sheet metal you'd expect it should not be expected to take much force. It seems the side plates should take the brunt of the force. I really don't know though.

I look at my pivot often for oil seeps. So far it's been ok, but if there is a key component to these fractures, maybe it can be avoided?
Don
 

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FWIW I had my 650 OIF reinforced around the swing arm pivot.

NB this is a very early OIF frame.


This was done as a precaution, rather than to stop any existing leak.

I had the frame stripped and straightened and the fellow that did the work said he had done a number of similar reinforcements to OIF frames over the years.


This is how he did it.

 

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I find this a bit humorous because when I asked on this forum about reinforcing an oif in that area a few years ago I was told it was unnecessary. If my frame cracks in that area in the future, it won't be that humorous anymore.
 

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my thoughts on the cause of cracking if it occurs is that the main oil tube must be subject to flexing - the pivot bolt transmits force into the frame via the "end" plates to which the pivot bolts tightens - so its up for discussion but I believe that the engine itself plays a part in keeping the swing arm mounting rigid -- the engine plates and mountings front/rear and bottom all contribute to making the frame loop rigid and thus spreading the load put into it by the swing arm pivot -- for the frame to crack there must be a period where some of these fixings were loose -
 

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My Feb 71 frame is still not leaking or welded.I do check all nuts and bolts every ride though to be sure not too much falls off.Maybe not having any loose engine mounts has prolonged the life of mine.
Today,as it happens,a front indicator nut unscrewed even though the fixing nut had a serrated washer and loctite on the threads. !
 

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Discussion Starter #9
Thanks for your in site. My bike has been off the road for many years. I'm sure the guy I got it off was not aware there was a leak there as he had the frame stripped and repainted. He got ill and had to give the project up and that's where I came in.

The crack is on the bottom side of the swing arm towards the chain side. From the oil flow it is less than .5" long and I can't actually see the opening. Must be a tiny hairline crack right at the bottom of the weld bead.
 

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Hi,

FWIW, I flogged these pics of a repair that someone had done. Seemed like a nice strong reinforcement to me.





Always hoping I don't have to copy it. :grin2: RR
 

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I always thought this area of the frame looked weak. I didn't realize Triumph strengthened later versions. Also a stronger swing arm, correct ? What years did these changes occur ?
 

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That is why I am surprised that the OP's bike ( a D) has a crack.

there are loads of OIF bikes without cracked frames. it is very rare to hear of one, mores a late one.
The Royal Signals used to jump these and although they may have modified the bikes, I never heard of them strengthening the frame.
LF Harris made more bikes for the Royal Signals after the production shut down.
 

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When I looked at that area on my 73 and 77 Bonnie's I didn't see much difference, but I did notice that the swing arm mount looked flimsy. That mount should have been braced on both ends from the factory. I would really expect an improvement in response with it properly braced.
 

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Discussion Starter #14
Took my sump plate off tonight and cleaned inside the tube with card cleaner. Its very clean now inside and out now but still can not actually see the crack.

I think I'm going to get it Tig Welded by a local guy and hope for the best
 

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The stronger swinging arm was introduced, as far as I know, on the 1980 bikes. The 'D' was introduced a year before that I think, so may not have had this mod? I believe the 'strengthening' to the swinging arm central lug occurred at the same time. It can't add much strength but it may shift or dampen vibration which may have caused cracking. I'm only guessing about this, but my guess is based on the fact that the factory mod consists only of extending the pair of mudguard bracket tabs forward so they butt against the down tube, and welding them to it. The steel is noticeably thinner than the earlier 'stand alone' tabs, suggesting that strength per se was not the goal.

B50 frames are identical to B25 frames and TR5T frames, except for thin steel plates welded between the rear frame tubes above the swinging arm lugs. This was done to solve a problem with frames cracking in that area, due to the B50's different vibration characteristics compared to the other engines. Hence my guess re T140s.
 

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My 1979 T140D has the strengthening tabs to the frame - as John says they are not very thick
with regards to the swingarm itself - I just measured a swingarm with an underslung brake caliper at approx 32.5 mm -- My T140D (overslung caliper) measures approx 34.5 mm -- but the difference could be explained by thickness of powder coat ; if so then my T140D does not have a stronger swing arm (both these swing arms have their legs "squashed! to form the mounting or end plate to take rear wheel spindle -- i have another / later swing arm where the end plates are separate pieces welded in - this is the strengthened arm and i believe it started with the 1980 models - it is approx 38.5 mm tube
 

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Hi,

FWIW, I flogged these pics of a repair that someone had done. Seemed like a nice strong reinforcement to me.

Always hoping I don't have to copy it. :grin2: RR
Those are shots from my thread at http://www.triumphrat.net/members-restoration-and-rebuild-projects/219481-t140-cafe-project.html. T140 stock frames would be stronger around the swingarm pivot if Triumph had copied Trackmaster more exactly and stuck the pivot tube through the center of the backbone rather than tacking it to the back. Anyone who decides to reinforce the pivot tube, whether by my method or another, should also seriously consider welding in race-style reinforcing tubes, which stiffen the entire frame around that area. In case my way is too unorthodox, one of the most successful Triumph road race teams, Big D Cycles, does it like this https://bigdcycle.com/photo-gallery/.
 

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I have been studying for months every picture i can find of the Big D frames that have been strengthened ( by Ed Mabry i believe) -- apart from a few additional additional triangulating tubes the swing arm pivot itself only appears to have the same additional tab to the oil tube that the later Meriden frames had -- the swing arm itself had additional tubes added underneath --- i will be attempting a copy of these mods myself over the coming months --- some work to the steering head is also done with obvious removal of the gusset plates - the angle of the steering head may have been altered in the process but of that i am unsure
 

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The Mabry frames were de-raked (maybe to 26 degrees?) because a stock T140 is too slow steering for road racing. I assume that Mabry/Big D figures their frame bracing obviates any need for specific pivot reinforcement, at least on later frames (mine is a '73, incidentally).
 

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Same thing happened on my '73 T140, had to take the motor out to get access for cleanness and good weld. Add a reinforcement plate as well.
 
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