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Discussion Starter · #1 ·
Hi all, just wondered if any of you who own a 1971/72 Bonnie, Tiger or trophy: do your tanks have a tie strap under the front of the tank to steady the 2 halves as the later T140Es have? The 1971 parts book does not list or illustrate this at all, but in 1979 or 81 parts books it is there, p/n 83-4395 or 83-4118 (UK tank version).

Did T120s and 650s in general not have this part ever? Even with bigger tanks?

cheers, Pat
 

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Hi Dr Pat, So far as I can tell 71 OIF 650 tank didn't have the cross brace bottom front. At some point the '72 tank got the brace. I don't know if all later '72 got it or just certain shapes. The '72 tank still had the raised center top seam covered with chrome trim. There may be supplements to '72 parts books that list this tank, strap.

1972 was a year of many changes on both bike & motor. Frames, intake manifolds, rocker boxes, gas tank, exhaust & more. The part #s for some of these are not as easy to find as I would like. Some of the parts are very hard to find.

Here is example of a later '72 tank.
1972 Triumph T120R T 120 T120V Bonneville 650 TR6 T120 *2297 GAS TANK | eBay

1973 on all the smaller sport tanks I've seen have the front lower cross brace. All have a smooth top, no chrome strip.

What year strap started on bread bin tank I don't know. Period photos show mid to later high frame, push over pipe motors with bread bin tank that has strap at bottom front. The 71& 72 tanks had raised top center seam. Top seam was eliminated for 1973 bread bin tank as well.

I think Stuart is very knowledgeable on this subject. Waiting for the correct info from him. I only have a little bit of personal experience from friends bikes.
Don
 

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Hi Pat,
I think Stuart is very knowledgeable on this subject.
Don is too kind; I'd say, "In the realm of the blind, the one-eyed man is king" at best ... :)

Aiui, '71 tank steel was specified thinner, not a problem on 'dry' frame tanks because they still used the same front mounting as pre-'71; however, as OIF tanks pushed over the rubber 'horseshoes' over the OIF top tube, the 'horseshoes' imparted sideways stress on the two halves of the tank, which'd be exacerbated by a tank bag; certainly some tanks cracked at the front weld. :(

The strap appears to have been an attempt to stop the OIF tanks cracking by stopping the two tank halves being pushed apart by anything? So afaik, '71 didn't have the strap but certainly @rambo Geoff and/or @Happyfeet Robert can confirm; while the strap isn't in the Triumph '72 650 parts book, it is in the BSA '72 650 book (albeit allegedly just for the breadbin), Don's Ebay link might be an original late '72 tank and the '73 Triumph book illustrates/lists only the US-market tank but with the strap.

So, if your bike's tank has the holes for the strap bolts, imho fit the strap; otoh, if your bike's tank doesn't have the holes for the strap bolts, you might want to consider laying hands on a tank that'll take a strap?

When/if fitting the strap, be aware the listed parts/spec. are piss-poor - both BSA and Triumph spec'd bolts to screw into the tank, when Meriden had changed from bolts to studs from '70 to try and stop the paddlers at the shallow end of the gene pool screwing replacement bolts through the bottoms of tanks ... 😖 If I was fitting an OIF tank strap, I'd open out the strap holes to 3/8" ID and use 21-1883 Studs, four 82-5228 Rubber spacers around the strap on the studs, 82-3814 Cup washer and 5/16"UNF locknut on each stud.

Top seam was eliminated for 1973
Afaict, this is true of all tanks, OIF and 'dry' frame; seems the press tools were changed then?

Hth.

Regards,
 

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None of my 71 spare fuel tanks have a strap across the bottom. When they split, it is generally the seam right behind the headstock. Most will have been weld repaired at that point. I have found the USA large tank is very prone to splitting and the UK type usually survives. All the 72 type seamed tanks i have seen have the brace underneath.
The ones i have that were repaired have not split open after welding.
Certainly, a braced tank will be of benefit if you have an expensive paint job. Unbraced is much more likely to split.
Other leak area is around the central tube at the bottom. Many i see are bodged with resin etc
 

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Hi Stuart, My thoughts on the strap is it should not be rubber mounted as this will allow flexing. I think the point of the strap is to lock the front sides solidly together to stop/reduce flexing.

I have observed on many tanks now the bushing for the bolts are deeper than the weld seam. So strap doesn’t set flat on the bushings, but is resting on one or both weld seams. So when you tighten bolts it both bends the strap & flexes the bottom of tank around bushing. Some 1/8”. I’ve not seen this fracture tank, but I use spacer washers such between bushing & strap such strap clears weld seam.

You are most correct about bolt length. It must be thoughtfully chosen. Not so long as it bottoms in bushing, but long enough to have enough threads to get a good hold. This is not hard to do. The bushing is pretty deep.

Simply trial fit bolt by hand until it bottoms. Measure gap between bushing & bolt head. Compare this to thickness of strap plus all washers. Plus 1/8 or more extra.

Not bottoming bolts is super important, but it’s not rocket science. Just trial fit the bolt & look at it. That simple.
Yet we see tank damage from too long of bolts too often.

On a side note I’ve observed a fair amount of rust in the bolt hole. Have struggled removing some. I personally smear thick coat of water proof wheel bearing grease on them. Doesn’t make them come loose & you can still feel the torque. Anti sieze works too but be careful of the torque can make it hard to feel. Same with the Center mount bolt. It will rust & very hard to remove.
Don
 

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Hi Don,
strap
should not be rubber mounted as this will allow flexing.
Uh-uh, 'fraid you've misunderstood. Far from suggesting the strap is rubber-mounted, my suggestion mounts the strap to the tank more rigidly (and more safely) than the spec'd parts.

The 21-1883 Studs are 3/8" OD between the 5/16"-24 threads, I've suggested opening out the 5/16" ID holes in the strap to 3/8" ID. The shorter stud threads are screwed into the holes in the tank, the strap is to prevent these moving further apart; how will that happen with the 3/8" OD of each stud in a 3/8" ID hole in the strap?

Otoh, the spec'd 14-0113 is described as "Bolt"; it isn't anything of the sort, it's only 5/8"UH so it's a (fully-threaded) setscrew, that means thread in the strap hole, which is considerably less than the nominal 5/16" OD. This excessive clearance allows the tank halves to spread apart 'til each "Bolt" thread contacts the outside of the strap hole. (n)

I have observed on many tanks now the bushing for the bolts are deeper than the weld seam. So strap doesn’t set flat on the bushings, but is resting on one or both weld seams.
Precisely. (n)

As the part numbers I've listed indicate, all the parts are off-the-shelf. Two 82-5228 Rubber spacers' thickness plus the strap thickness is what the Studs' 3/8" OD length is made for. Nevertheless, one 82-5228 Rubber spacer on each stud between strap and tank will ensure the strap cannot foul any seam at the lower edge of the tank (nor scratch the tank paint). (y)

I use spacer washers such between bushing & strap such strap clears weld seam.
... I rest my case ... :cool:

Also, the parts I've listed are fail-safe if anything comes loose:-

. If a "Bolt" (e.g. 14-0113) falls out, that end of the strap is loose, the sides of the tank aren't tied together 'til the rider notices the fastener is missing, then there is a temptation to screw in any available bolt, which has the potential to pierce the bottom of the tank. (n)

. Otoh, the 82-5228 Rubber spacers are a tight fit on the Stud, preventing it unscrewing. Even if the locknut, Cup washer and one Rubber spacer falls off a Stud, the strap cannot come off the Stud, the other Rubber spacer keeps the Stud in place, the two halves of the tank still cannot spread apart. (y)

Hth.

Regards,
 

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Re tank straps they were introduced during the 1972 model year.

The UK Breadbox tank Second edition used the 83-4118 tie strap (same as shown in the 72 BSA book previously mentioned). The 83-4118 strap was used until the end on the UK tanks. The late 71/early 72 breadbox tanks did not have the tie strap. The 71 early 72 UK tank uses a part # 83-2881 which would have been followed by a color code while the later 72 tank with a tie strap & chromed badges would have been 83-4638 (T120) or 83-4639 (TR6).

The late 72 US tanks would have used 83-4395 tie strap. and again this was used until the end on US tanks. All 71/72 tanks had the center ridge with the multipiece chromed strips The 71 and early 72 large US style tanks were part #83-2996 followed by a color code. (I have an early 72 large TR6 tank with out tie strap provisions.) Sometime after the 72 model year started two new part numbers were issued to replace 83-2996 these were 83-4629 (T120R) & 83-4631 (TR6R/TR6C) I do not know for a fact but I suspect these tanks may have used a tie strap. Two additional tanks were i introduced in 1972 as Slimline's They were 83-4636 (T120R) & 83-4637 (TR6R/TR6C).

Regardless all the 71/72 tanks without the tie straps are subject to fatigue cracks due to vibration. Failure to use the strap on later models WILL also result in cracking and fuel leakage. Also the center mounting bolt/nut should NOT be cranked down on the rubber bush. This should be a snug fit as on the rubber of a shock absorber mount.

On tanks without the tie strap provision I have always advocated the attachment of two nuts so a strap may be fitted..

K 😷
 

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Discussion Starter · #9 ·
Thank you Don, Stuart, Robert, Rambo and Kadutz, this detailed info is very much appreciated. I only picked up my 71 TR6R on Friday to go with the 81 electro I managed to score just before Christmas (some rearrangements going on in my shed - I am sick to my back teeth of twin carb wrangling!!! Some problem children are up for adoption!!)

The 71 is a real nice one which has had a lot off care and work, but I was surprised to see no strap (unable to view it in the metal before I bought it). The holes are there, but on close inspection the damage has already been done as the paint bubble demonstrated, and the neck has a leak as I now find this morning with a few more litres in it after a run around yesterday, so the whole question is moot. Damn!! Anyway, when I get it repaired, if that's possible, it will have the strap from here on.

The thought that the steel was thinner is interesting Stuart; of course at 50 years in I have no idea whether the machine started life with this tank....BUT, the holes are there for the strap.

Thanks again everyone, and for detailed p/ns!! cheers Pat
 

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Hi
Harris sourced cheap thin metal, seamed tanks for the 95-97 Devon Bonneville. These are about half the weight of a Meriden tank. To stand the strap clear of the seams he employed hard plastic spacers between the strap and tank.

regards
Peg.
 

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Sorry bout the leak not fun and it is dangerous.

For what its worth I have friend that bought a 78 T140 about 1990. His tank had a fatigue crack he fixed it by soldering it using the same type solder you would use to solder gutters with. That repair is still holding His tank cracked as the previous owner had the center bolt cranked down.

Lost a fellow club member when his BSA tank blew up (leaking petcock). Leaking petrol is NOT a good thing;

K 😷
 

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71 with US slimline tank.Has strap across bottom.

I had leak at base of mounting tube, took it to a radiator repairer, they pressure tested and sealed it up using solder or lead type process.

I’d then refurbished tank by stripping those stupid paint liners inside, etching/de-rusting inside, and fully respraying. paint job was quickly wrecked by high octane fuel spilling out a cheap repro fuel cap after my original went flying off on a highway and was never seen again…
 

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Discussion Starter · #13 ·
Ah noooo!! What a prick of a thing to happen mate!! Interesting strategy trying radiator repairers! I'm gonna get it fixed if it proves viable (hard to tell how the tank is, it's just a simple gloss black (haha) which is good). Just a bit of a process: welding; stripping; painting, and no-one in my town up to the job. Bugger as only had the bike 3 days, but I agree with Kadutz: not willing to ride a mobile fireball - thanks for the thoughts - cheers Pat
 

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Hi Pat,
the damage has already been done
when I get it repaired, if that's possible, it will have the strap from here on.
Before having the tank repaired, ascertain whether the two threads for the strap fasteners are parallel? Two long 5/16"UNF bolts or studs, one screwed gently into each thread, eye'll tell whether they're parallel.

If they're parallel, or can be made parallel before welding/soldering/brazing, my studs idea will work if required.

However, if they can't be made parallel, you'll need to use bolts to secure the strap; consider making them a better fit in the strap holes than the standard "Bolts" (setscrews)?

Ways I'd consider "making them a better fit":-

. Shouldered bolts - Before Triumph used the aforementioned shouldered studs into '70 dry-frame tanks, they used shouldered bolts - the 3/8" OD through the Rubber spacers and frame mounting strip, 5/16" thread into the tank. Unfortunately, these Triumph bolts off-the-shelf have Cycle thread, which won't fit into an OIF tank. :( I'd be able to get similar turned from hex. bar with UNF thread but, if you're struggling with having the tank repaired, such machining could be an issue too?

. Using actual 5/16"UNF bolts so there is an unthreaded part though the strap holes, so they're a closer fit in the standard strap holes. Such bolts will be longer than you'll need, but hacksawing or Dremel-ing 'em to the correct length and spinning them in an electric drill so you can clean up the cut ends with files wouldn't be difficult?

Imho, I'd continue to use Rubber spacers at least between strap and tank. Similar to a description by @TR7RVMan Don in one of his posts, tank threads not parallel, when you tighten the strap bolts into the tank, the strap will bend.

Hth.

Regards,
 

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Discussion Starter · #15 ·
Thanks Stuart, I have the tank off today, very easy and in nice enough nick EXCEPT for the leak. Petcocks and everything tight, but no good if it's coming out the front...!! Also the stud holes are there and I see they are threaded, so I'll clean them up gently and see how they look with a bolt or stud in them. I do recall those shouldered studs, weren't they on some seamless tank Tridents too? My one way back was a 73 T150V, I don't ever recall tank leaks it was good in that regard. When it comes back I'll certainly put some buffer between strap and tank - the hard plastic spacers Peg mentions from Harrisses sound good, but at the very least a copper washer would be OK, and a spring washer on the underside of the strap. Anyway, in the meantime the saga of repair must be started, it has to go to 2 other towns north of me....
 

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Hi, I pay attention to this stuff. If bolts are properly tightened the tank strap doesn’t seem to work/fret at all. I specifically look got this. Easy to see if it’s been working

Factory strap one end has hole clearanced for 5/16 bolt. The other end is slotted.

I’not had a lot of these tanks off. Maybe 12 or 15. If you properly tighten bolts it holds perfectly. Even with hex against slot no lock wash or anything. I’ve seen a few vibrate out. The owners under tightened almost ever bolt on bike. Fenders, exhaust brackets everywhere!
Best practices says, you never have hex against slot. You use flat washer on slots. Split type lock washers work really well over the flat washer.

Triumph didn’t worry about flat washer too much. Certainly did not use them on from rear fender bracket or air box bolts.

The set up on my bike is one side 2 flat washers against tank, strap, flat washer, split lock washer. Bolt. The other side is same except only 1 flat washer against tank. My original bolts were long enough to have good amount of thread in bushing. Again never let bolt bottom in bushing. Been like that for 33k miles.

I ride with quite a few guys with these later tanks. All are strapped. None have cracked. Not one. We kick this stuff around.
Several have developed rust pin holes and or seeped at filler neck seem. Rust is another subject.
One fractured at center bolt. Way over tightened with no spacer.

All you need to do is have a strap across & the bolts tight.

The Factory strap is 3/4” wide. .105” thick. Either buy one from a vendor or make one from 3/4x1/8 metal from hardware store.

Verify your threads. Some owners have retro fitted home made bushings. Factory is 5/16-24.

The Devon (Harris) tanks I have no idea. I’ve never even seen one of these bikes in person.
Don
 

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Hi Pat,
recall those shouldered studs, weren't they on some seamless tank Tridents too?
(y) T150 frame was a development of the 650 dry frame and kept the same tank mounting (on the If It Ain't Broke, Don't Fix It principle? :sneaky:). What became the T160 was initially developed at Meriden after the OIF was in production; perhaps interesting to consider it never had the OIF tank mounting ... and BSA managed to use the single-bolt tank mounting for years pre-OIF without needing "tank straps" ... :whistle:

The stud part number I posted earlier are dry-frame Triumph twin, T150's are a little longer and the Rubber spacer between tank and frame bracket is thicker than the twins' 82-5228.

When it comes back I'll certainly put some buffer between strap and tank - the hard plastic spacers Peg mentions from Harrisses sound good, but at the very least a copper washer would be OK, and a spring washer on the underside of the strap.
Risking labouring points in earlier posts:-

. Rubber won't scratch the tank paint, unlike copper, and possibly hard plastic; 82-5228 were fitted originally by Meriden for longer on more bikes than made by Harris, might be easier to obtain in Oz?

. While spring washers under bolt heads work often if not always, Rubber spacers compressed impart greater friction to all other parts and, if you can use the shouldered studs, they were fitted with self-locking nuts as standard.

Factory strap one end has hole clearanced for 5/16 bolt. The other end is slotted.
God forbid they could get two holes the same distance apart consistently ... Curious they managed four holes the same distance apart consistently for tank racks ...

Best practices says, you never have hex against slot. You use flat washer on slots. Split type lock washers work really well over the flat washer.
(y)

Triumph didn’t worry about flat washer too much.
Their primary concern was cost - how much they could make a bike for vs. how much they could sell it for. Otoh, our primary concern is longevity ... and doing it better?

Hth.

Regards,
 

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FWIW my 71 BSA breadbox does have the strap --- but it's not necessarily the original tank. And it needs welding ;-)

I had a friend who had a '72 Bonnie, and he left the strap off for some reason that escapes me, commenting that he heard the tank split without it, and he was going to test that. He was right, it did split, and destroyed a very expensive custom paint job.
 

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As my bike came without the strap I’ve been collecting the parts to fit it.
However it seems the design of the strap I’ve bought has been “improved” with slots both ends.

 

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Hi all, just wondered if any of you who own a 1971/72 Bonnie, Tiger or trophy: do your tanks have a tie strap under the front of the tank to steady the 2 halves as the later T140Es have? The 1971 parts book does not list or illustrate this at all, but in 1979 or 81 parts books it is there, p/n 83-4395 or 83-4118 (UK tank version).

Did T120s and 650s in general not have this part ever? Even with bigger tanks?

cheers, Pat
My 1972 OIF has the strap.
 
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