[pennafxu]

Ok,
@StuartMac I’m confused because these are definitely bolts held in place with body filler. looking back at how the rack attached, the attachment was via a nut into the countersunk area as you stated. There is no female threaded boss on the tank surface. If you look at the 3 other studded areas as I continued removing paint/filler, they are now smooth… What about all the brazing?

 

[pennafxu]

Fwiw and depending on the rack mounting threads into the tank, you don't have to use the manky 'studs' (sawn-off bolts) and nuts ...

Standard tank mounting threads were 1/4"-26 (1/4" Cycle); if that's what's in your bike's tank, the standard screws for the rack are 82-2936 - long chromed screws with a slotted raised countersunk head, the countersinks fit in the corresponding countersinks in the tops of the rack's vertical tubes. On this side of The Pond, I think the screws are even available in stainless(?).

Even if whoever did the work on your bike's tank used 1/4"-28 (1/4"UNF), shouldn't be difficult to get four similar screws (in stainless?)?

I think this might be the same resolution with different ways of getting there.

 

[pennafxu]

Standard rack mounting threads were 1/4"-26 (1/4" Cycle); if that's what's in your bike's tank, the standard screws for the rack are 82-2936 - long chromed screws with a slotted raised countersunk head, the countersinks fit in the corresponding countersinks in the tops of the rack's vertical tubes. On this side of The Pond, I think the screws are even available in stainless(?).

How long are these? as I'm going to use weldable nutserts and follow your advice...

 

[StuartMac]

Hi Whisky,

tanks that took racks as standard had four 1/4"-26 inserts in the top of the tank.

confused because these are definitely bolts held in place with body filler.
There is no female threaded boss on the tank surface.

The tank you're working with is '71 or '72 OIF - dry-frame tanks don't fit OIF, '71 were the first OIF, '73 the tank maker changed the press tooling and '73-on tanks don't have the top front-to-back seam.

However, Triumph stopped supplying tank racks to the US several years earlier, aiui as a result of being sued successfully by a rider who slid up the tank during a crash and damaged his dangly bits ... 😫

My concern with TIG-welding bolts or studs to the tank was, if you changed your mind about the rack, removing it would leave the four bolts/studs sticking up, or a paint job'd be damaged removing them. Otoh, any 1/4" inserts, Triumph made a rubber mushroom-headed plug to fit, or 1/4"-28 inserts, grub screws can be fitted?

Standard rack mounting threads

How long are these?

The T100 tank I have, they're 5/8" deep.

Hth.

Regards,

 

[pennafxu]

The tank you're working with is '71 or '72 OIF - dry-frame tanks don't fit OIF, '71 were the first OIF, '73 the tank maker changed the press tooling and '73-on tanks don't have the top front-to-back seam.

Don't or Won't?

However, Triumph stopped supplying tank racks to the US several years earlier, aiui as a result of being sued successfully by a rider who slid up the tank during a crash and damaged his dangly bits ... 😫

Why would you leave your jewels out like that? Silly Rabbit, tricks are for kids...

My concern with TIG-welding bolts or studs to the tank was, if you changed your mind about the rack, removing it would leave the four bolts/studs sticking up, or a paint job'd be damaged removing them. Otoh, any 1/4" inserts, Triumph made a rubber mushroom-headed plug to fit, or 1/4"-28 inserts, grub screws can be fitted?

How do the inserts work? Also I have 2 other tanks to fool around with I guess...

The T100 tank I have, they're 5/8" deep.

Thanks... Also how much off the backbone does the tank sit?

 

[pennafxu]

I think these might just work...

 

[StuartMac]

Hi Whisky,

The tank you're working with is '71 or '72 OIF - dry-frame tanks don't fit OIF, '71 were the first OIF, '73 the tank maker changed the press tooling and '73-on tanks don't have the top front-to-back seam.

Don't or Won't?

Assuming you mean "fit", as you've removed the tank from your bike, parts book for your bike, "GAS TANKS AND TWINSEAT" pages, I'm guessing you have at least most of parts #4 to #9; you know they passed through the vertical tube through the tank; the head of part #4 "Centre fixing bolt" fits in the slotted lug on top of the frame backbone?

Dry frame and tank mounting are completely different.

Front mounting:-

... tank is essentially secured to the frame brackets with a stepped bolt or stud on each side; however, each stud or bolt passes through a cupped washer similar to the rear mounting one, a 1/4"-thick rubber washer between each cupped washer and frame bracket, another 1/4"-thick rubber washer between frame bracket and tank, the latter washers have a spigot that fits in the frame bracket hole to isolate the bolt/stud laterally from the frame bracket.

Rear mounting:-

... again, bolt is stepped, lower large-diameter rubber has a spigot on both ends, to locate it in the frame lug and through the tank's rear bracket, large diameter rubber washer under the cupped washer spaces the cupped washer off the top of the the tank's rear bracket.

How do the inserts work?

They're inside the tank, tops flush with the top of the tank, the one on the left has a rubber plug in it.

Thought: the inserts listed in your post #203, they're closed at one end? Risking stating the obvious, the standard Triumph ones are, because they're inside the tank.

how much off the backbone does the tank sit?

Parts book "GAS TANKS AND TWINSEAT" pages again, the OIF tank is spaced off the top frame tube primarily by the two horseshoe-shaped part #3 "Mounting rubbers". If your bike doesn't have the part #3 "Mounting rubbers", when you get them, check the part #6 "Distance tube" on your bike prevents tightening the nut squashing the part #3 rubbers too much?

"Tie strap"
Parts book "GAS TANKS AND TWINSEAT" pages part #10 - another thing that'd date your tank to '71 or '72 is the absence or presence respectively of two 5/16"-24 inserts in the bottom of the tank at the front, one on each side. '72-on had them for parts #10, #11, #12 and #27 - Triumph didn't allow for all the potential vertical forces (tightening the mounting, fuel, tank bag, etc.), used too-thin steel for OIF tanks, the forces spread the sides of some tanks, causing cracks in the front at the top; parts #10, #11, #12 and #27 prevent the "spread".

If your tank does have the inserts, be aware another mistake made was a protruding seam on each side - if the "Tie strap" contacts a seam, vibration can potentially crack the tank there ... Imho, the aforementioned dry-frame stepped front mounting studs and rubber spacer washers would isolate the "Tie strap" from the tank?

View attachment 795948

Minor thought: I believe Triumph used "raised countersunk head" screws - i.e. slightly domed top rather than a completely-flat top - so whoever was un/screwing them didn't have to have a driver exactly the same width as the screw-head, the corners of a wider driver wouldn't gouge the chrome at the top of the rack verticals?

Hth.

Regards,

 

[pennafxu]

Hi Whisky,

Assuming you mean "fit", as you've removed the tank from your bike, parts book for your bike, "GAS TANKS AND TWINSEAT" pages, I'm guessing you have at least most of parts #4 to #9; you know they passed through the vertical tube through the tank; the head of part #4 "Centre fixing bolt" fits in the slotted lug on top of the frame backbone?

Dry frame and tank mounting are completely different.

Front mounting:-
View attachment 795997

View attachment 795998

... tank is essentially secured to the frame brackets with a stepped bolt or stud on each side; however, each stud or bolt passes through a cupped washer similar to the rear mounting one, a 1/4"-thick rubber washer between each cupped washer and frame bracket, another 1/4"-thick rubber washer between frame bracket and tank, the latter washers have a spigot that fits in the frame bracket hole to isolate the bolt/stud laterally from the frame bracket.

Rear mounting:- View attachment 795999

... again, bolt is stepped, lower large-diameter rubber has a spigot on both ends, to locate it in the frame lug and through the tank's rear bracket, large diameter rubber washer under the cupped washer spaces the cupped washer off the top of the the tank's rear bracket.


View attachment 796008

They're inside the tank, tops flush with the top of the tank, the one on the left has a rubber plug in it.

Thought: the inserts listed in your post #203, they're closed at one end? Risking stating the obvious, the standard Triumph ones are, because they're inside the tank.


Parts book "GAS TANKS AND TWINSEAT" pages again, the OIF tank is spaced off the top frame tube primarily by the two horseshoe-shaped part #3 "Mounting rubbers". If your bike doesn't have the part #3 "Mounting rubbers", when you get them, check the part #6 "Distance tube" on your bike prevents tightening the nut squashing the part #3 rubbers too much?

"Tie strap"
Parts book "GAS TANKS AND TWINSEAT" pages part #10 - another thing that'd date your tank to '71 or '72 is the absence or presence respectively of two 5/16"-24 inserts in the bottom of the tank at the front, one on each side. '72-on had them for parts #10, #11, #12 and #27 - Triumph didn't allow for all the potential vertical forces (tightening the mounting, fuel, tank bag, etc.), used too-thin steel for OIF tanks, the forces spread the sides of some tanks, causing cracks in the front at the top; parts #10, #11, #12 and #27 prevent the "spread".

If your tank does have the inserts, be aware another mistake made was a protruding seam on each side - if the "Tie strap" contacts a seam, vibration can potentially crack the tank there ... Imho, the aforementioned dry-frame stepped front mounting studs and rubber spacer washers would isolate the "Tie strap" from the tank?


Minor thought: I believe Triumph used "raised countersunk head" screws - i.e. slightly domed top rather than a completely-flat top - so whoever was un/screwing them didn't have to have a driver exactly the same width as the screw-head, the corners of a wider driver wouldn't gouge the chrome at the top of the rack verticals?

Hth.

Regards,

Helped greatly!

 

[pennafxu]

Significant progress made today on the tank...

 

[pennafxu]

It appears that there were multiple poor attempts to fix this tank... This was a pin hole that opened up to 1/4"... It has various different areas of issue.

 

[pennafxu]

On to the frame... Numbers matching. Will work on some dent fixing, hole repair, and bung welding tomorrow as I'm exhausted. This tank is holier than the Bishop of Canterbury!

 

[StuartMac]

Hi Whisky,

View attachment 796810 View attachment 796812 View attachment 796813 View attachment 796817

It occurs to me that the cracks and pinholes might be connected ...:-

. In my post #207, I mentioned the reason for the "Tie strap" on the underside of '72-on OIF tanks at the front was BSA/Triumph used too-thin steel for the tanks, failing to allow for all potential forces on the tank in use. The cracks in your photos. could be as a result of just using the tank rack, the bolts/studs the PO attached simply transferred the stresses and strains of using the rack to steel too thin for them? 'Dry frame' tanks, especially ones Meriden made with tank rack mountings, were made of more-substantial steel.

. Only one of the cracks in the tank has been repaired? If yes, I wonder if the PO fixed that, another one opened up and he put the tank aside, that was all years ago and the pinholes have opened up because of poor subsequent storage?

Hth.

Regards,

 

[pennafxu]

Hi Whisky,

It occurs to me that the cracks and pinholes might be connected ...:-

. In my post #207, I mentioned the reason for the "Tie strap" on the underside of '72-on OIF tanks at the front was BSA/Triumph used too-thin steel for the tanks, failing to allow for all potential forces on the tank in use. The cracks in your photos. could be as a result of just using the tank rack, the bolts/studs the PO attached simply transferred the stresses and strains of using the rack to steel too thin for them? 'Dry frame' tanks, especially ones Meriden made with tank rack mountings, were made of more-substantial steel.

. Only one of the cracks in the tank has been repaired? If yes, I wonder if the PO fixed that, another one opened up and he put the tank aside, that was all years ago and the pinholes have opened up because of poor subsequent storage?

Hth.

Regards,

When you say connected, do you mean the metal is so thin that it has pitted out like a bad body panel on a car? If so should I be replacing the "panel" or spot filling the holes. I can also use lead body filler, or even braze with silicon bronze. I will be de-rusting the inside and sealing it also. I have about 10-15hrs in this tank and don't wish to give up on it... I will need to pressure test and fix as needed. What is this tank strap?

 

[StuartMac]

Hi,

you mean the metal is so thin that it has pitted out like a bad body panel on a car?

Ime, rusting on sheet steel, the thinner the sheet, the quicker a rust bubble will turn into a pinhole.

Decades ago, when T160 tanks were still cheap, I bought a spare. It needed a respray so I stored it 'til I could afford that. Unfortunately, I stored it in a lockup garage, where the top became first dusty and then got condensation on it. Little rust spots started in the damp dust, I wasn't worried because i was going to have it resprayed. Before I had it resprayed, I had it pressure-tested, pressure blew out all the little rust bubbles = dozens of tiny pinholes across the top of the tank. 😖 I'm just wondering if the pinholes you're finding have a similar cause?

should I be replacing the "panel" or spot filling the holes.

'Fraid not my decision. Fwiw, guy who pressure-tested my tank said it be cheaper for me if he cut out the area with the pinholes and made a new panel. Unfortunately, he's since stopped working but, were I to go that route, I'd prefer to have a completely-different shape top on the base, but then the guy who made that might say it's better to have a completely-new tank ...

tank strap?

"Tie strap"
parts book for your bike, "GAS TANKS AND TWINSEAT" pages
part #10 - another thing that'd date your tank to '71 or '72 is the absence or presence respectively of two 5/16"-24 inserts in the bottom of the tank at the front, one on each side. '72-on had them for parts #10, #11, #12 and #27 - Triumph didn't allow for all the potential vertical forces (tightening the mounting, fuel, tank bag, etc.), used too-thin steel for OIF tanks, the forces spread the sides of some tanks, causing cracks in the front at the top; parts #10, #11, #12 and #27 prevent the "spread".

Hth?

Regards,

 

[pennafxu]

Started to repair the dents... Unfortunately I will need to go another route... More to follow

 

[pennafxu]

Got the parts ready for re-assembly. Need final polishing/paint/lubrication etc...