Tank mounting crack

Jed · Nov 22, 2014

I am going to repaint my tank & sidecovers (candy red) but when I took the tank off I noticed petrol leaking from around both front mounting points through a hairline crack which I will get braised
There was no sign of a leak before that so maybe the rubbers stopped it from leaking
Seems I may have tightened the bolts too much prior to that to stop the tank jumping around as the tank hit the top triple clamp and chipped it. I had no rear bracket at that time so that no doubt did not help and the space between the tank and triple clamp is less than quarter of an inch
The PO had put 3 quarter inch rubbers between the tank & the frame which seem too thick as the stock rubbers don't look that thick and the manual is pretty vague on this saying whatever the owner thinks is best
If anyone knows the best spacing for the rubbers for a MK3 interstate tank I would appreciate their opinion

Cheers
jed

Rohan · Nov 22, 2014

Your pic shows the foam/rubber pad in the U of the tank is missing.
This stops the tank itself rubbing on the frame spine/backbone.
With it refitted, you may need less rubber packers ?

Steel welding may be better than brazing ?,
since once its brazed it can only ever be brazed again.
And you need real strength in the tank mounting area,
lotta weight on those mounting points.

concours · Nov 22, 2014

The spacers are "as needed to suit" that is, when the spacing up off the frame, away from the neck looks good, that's it. Due to manufacturing variation, it may be a bit more or less.

Jed · Nov 22, 2014

thanks for that I'll look into steel welding and am getting all new rubbers & pads when it goes back on. I'd really hate the new paint job to get knocked about

Cheers
Jed

concours · Nov 22, 2014

HARD & FAST rule.... LAST thing after all prep, (sandblasting, sanding, etc.) is pressure test the tank before paint.

comnoz · Nov 22, 2014

I always get rid of the stud in the tank and replace it with an muffler mounting rubber. That eliminates the cracking problem permanently. Jim

Jed · Nov 22, 2014

Thanks again
I was going to pressure test the tank but the muffler mounting rubber is something I did not think of but will definitely consider. I'm not sure how to use it to make the best for this application

Jed

comnoz · Nov 22, 2014

Jed said:
Thanks again
I was going to pressure test the tank but the muffler mounting rubber is something I did not think of but will definitely consider. I'm not sure how to use it to make the best for this application

Jed

I normally use about a 1/8 inch rubber washer between the muffler mount and the tank and another between the mount and the frame.
Then I just use a fender washer and nylock nut to mount it to the frame.
Without the long stud sticking out of the tank there is no leverage to flex the tank bottom and cause a crack. That is a normal problem on any steel tank and especially a big steel tank like an interstate. Jim

kerinorton · Nov 23, 2014

The originals had nyloc nuts on those stud's so you didn't need to tighten them too tight. The big round holes on the frame brackets also allow you to shift the position away from the stem as needed. Steel welding is the only way. Just fill the tank with water and that will stop it blowing apart on you. Don plenty of those jobs.
Dereck

Jed · Nov 23, 2014

Thanks Comnoz

A muffler mounting rubber like the ones on the oil tank?
I modified these on mine as they tended to break and replaced them with a spring between the threads (from the original mount) instead of rubber
The ones for the tank may be bigger (like the head steady) and so not as delicate?

Kerinorton mentioned the nylock nut which I had the suspicion may have caused the crack as the torque require to undo it was more than would otherwise be necessary (the bastards were tight until the end)
I was thinking about using two nuts to secure it but was a little concerned about how fiddly that may be
Anyway more to mull over
Thanks a lot
Jed

Time Warp · Nov 23, 2014

No the bigger muffler ones like at the stock head steady.
The roadster tank has inserts for the studs, not flush like that, hate to say it but the Indian Interstate tank has even larger compensating discs at the mount locations.
Has that tank been modded in a past life perhaps, given the extra capacity it would need sturdy mountings.

Jed · Nov 23, 2014

As far as I can tell the tank is original
It has been painted over in a fairly good attempt but was not taken back to bare metal as the candy apple colour is still underneath which I guess was the factory job. The paint is susceptible to metho and petrol dulls the sheen as it has not had a clear coat
The tank has been marked by a leaking master cylinder at some stage. It may have other damage that necessitated the new paint job but that will be found out once I strip the paint back
I'm pretty sure the tank has been on the bike since new from appearance but then I don't know how long they have been made in India
It's as good as any (shape and construction wise) I've seen
I have some old steady mounts from the rebuild so will try them for thread size. I guess if they are UNF and not metric that will point towards Brit made
Thank you for the heads up

Jed

olChris · Nov 23, 2014

I would suggest that the majority of the fuel and tank weight are supported by the foams in tunnel under tank and the bolts are "merely" locators with opposing support rubbers to foams, with a bit of torque on nuts . Eg, So that the tank and fuel is supported predominatley by centre tube foams and any "lift", by going over whoops, is secured by the mounting points in question to hold down the tank.. IMO, finger tight wingnuts with rubber washers would be sufficient.... No need for excessive tightening of nuts.., Wonder what the manual says?????????

Jed · Nov 23, 2014

Point taken on over tightening but the "whoops" can deliver g forces outside normal intended use. Some of the roads here are a bit of a worry at times - after lulling you into a false sense of security you hit the moguls. Like most places I imagine

Another thing I am trying to decide is whether to replace the side cover decals with ELECTRIC START or just use the ones from the MK2 which I prefer
I find it amusing all the other changes on the MK3 were not listed there as well albeit in smaller print. it seems like such a strange thing to display

Jed

Jed · Nov 23, 2014

Steel welding is the only way. Just fill the tank with water and that will stop it blowing apart on you. Don plenty of those jobs.
Dereck[/quote]

Just to clarify
are you saying the tank needs to have water in it while it is being welded or just thoroughly soaked and rinsed prior?

Jed

worntorn · Nov 23, 2014

Electric start was a big deal on a Commando. A bit like seeing Anne Murray singing and dancing in high heels first time.

Glen

comnoz · Nov 23, 2014

Jed said:
Steel welding is the only way. Just fill the tank with water and that will stop it blowing apart on you. Don plenty of those jobs.
Dereck

Just to clarify
are you saying the tank needs to have water in it while it is being welded or just thoroughly soaked and rinsed prior?

Jed[/quote]

I would never attempt to weld a tank filled with water. It is not a safe way to do it. Purge it with argon or another inert gas instead. Jim

Matchless · Nov 23, 2014

This happened to my Interstate tank. It is caused by omitting the rubber pads on the spine. This means all the weight of over five gallons of petrol is taken by the mounting studs.
I fixed it by removing the threaded inserts & turning up a pair of top hat threaded bushes, with a head dia. large enough to cover the crack. Then I brazed these on to the tank. This gives a much stronger repair than welding, as capillary action means the braze flows under as well as around the top hat. This will reduce the possibility of the repair cracking again, which welding will not.
I also use exhaust mounts like Jim as they stop any vibes getting to the tank, which the stupid original setup doesn't because the studs can, if you are not careful, contact the frame brackets.
Martyn.

Biscuit · Nov 23, 2014

If you are merely looking for personal opinions as to displaying proudly "ELECTRIC START" mine is don't. I lost that decal years ago on my MK3 thinking that's really nothing to brag about.

mschmitz57 · Nov 23, 2014

Jed said:
Steel welding is the only way. Just fill the tank with water and that will stop it blowing apart on you. Don plenty of those jobs.
Dereck

Just to clarify
are you saying the tank needs to have water in it while it is being welded or just thoroughly soaked and rinsed prior?

Jed[/quote]

I had my alloy Atlas tank repaired at Framecrafters in Union Illinois while I watched. No water was used.
I had washed the tank out with lots of water and detergent beforehand and thought it was pretty clean.
When I got to Framecrafters, Randy carefully sniffed the tank, than took it to his outdoor welding area and set it on the ground.
He took an acetylene torch and slowly waved it around the gas filler then he directed the torch flame into the tank.
The vapor slowly ignited and shot a plume of exhaust out the top like Old Faithful. Quite impressive, and surprising to me thinking it was clean. "Now it's safe to weld" he said. Not sure what he'd done if it still had gas puddles in it.

I also did Caswell 2 part epoxy afterwards. Belt + suspenders.

Tank mounting crack

Jed

Rohan

concours

Jed

concours

comnoz

Jed

comnoz

kerinorton

Jed

Time Warp

.......back to the 70's.

Jed

olChris

Jed

Jed

worntorn

comnoz

Matchless

Biscuit

mschmitz57

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