Tank refurbed

S

smlav

Senior member
Location
Shropshire UK
I had my GTL tank worked on which was weeping at the front seams. I'd forgotten that it did this from new in '78, but I recently found the letters I had with Slaters trying to get a replacement tank. The weep was not bad enough to drip, but if you rubbed fingers along underside of front seam they came up smelling of fuel. I did 40k miles with it like that, but as part of my restore I want to try and address this.

So the recent repair involved cutting out the bottom, sand blasting it, welding up the weak seams, and welding the bottom back on. Then the tank had a double application sealant applied internally. All looks good and I'm hopeful the result will be tight.

However, the welder neglected to repair the front bracket which had failed at one of its two welds - I suspect it came from the factory like that. The two front brackets which sit on the frame stubs are welded to the tank in two places, top and bottom of bracket, and the lower weld on one bracket either failed or was never fully attached.

So my questions are :-

i. I bought new protectors which go onto the frame mounts where the brackets on the tank slot over. These new ones seem like a harder plastic than the original soft rubber. Anyone know if I should seek soft rubber?

ii. I could get the tank bracket repaired with a spot weld. But I'm worried the heat would cause a problem to the internal sealant. Would I be better just putting a piece of rubber under the bracket, inside the gap where the bracket should attach to tank. That should protect the bracket/tank from vibrations.

The leaflet in the photo's is the sealant which was used, and there's a before and after of the underside of the tank.
thanks for any thoughts,
Sean
 

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Sean,

While you're at it, you might want to reconsider the front mounts. Ex-factory, they come more-or-less horizontal, allowing the tank to slide backwards, only to be restrained by the seat or the rear rubber band, if it's still strong enough.

I had much the same issues as you with my GTL tank. While the leaks were repaired, I removed the front mounts and re-positioned them at an angle that would positively hold the tank in the forward position, worked a treat, no more slippin' and slidin'.

Front mount rubbers should be rather soft rubber, I have a few NOS available.

Pretty strange that it's mostly the GTL tanks suffering from fractures and failed welds. The front portion is identical to the SF1-2-3 tank, just the rear end is a bit shorter.

piet
 
Sorry, just re-read your post... internal coating already applied, welding will most certainly ruin it.
 
Thanks Piet,

My thoughts were not to weld unless I want to reline the tank. As long as I can protect the bracket with enough vibration absorption I think it’s worth a shot. I bought a GT tank and learned the hard way that the GTL tank is a one off, same as seat*. I bought a new rear strap which seems okay, and new rear tank rubbers which seem okay. It’s just the front ones which seem a bit plasticy and that front area seems to be the weak area. I’m tempted to put a very soft rubber strip under the front of the tank.

I have a small crack in the back of frame under the seat which I’ll be taking to a welder, I’ll see if he can alter the front mounts as you suggest. Got any photo’s of the mod?

Are you willing to sell a couple of the soft front rubbers?

Cheers
Sean
 
Paul Marx said:
Now you know why you should never use tank resins.
Phosphoric acid based products protect from rust very well.
Paul
Click to expand...
Well if the tank had been sealed when it was constructed I’d likely not have a problem. I only had the sealer added as a secondary protection, the welding up of the seams is the primary protection. The tank was leak tested after welding and before sealing, but that’s not the same as being fuel if fuel for ages. The coating used gets excellent reports (real ones from people I know rather than internet noise) from folk who have it in tanks for a few years. I’ve known plenty of people who have done the home brewed nuts and bolts then sealant only for it to fail. This tank has been given the works, just frustrating that the welder missed the bracket before tank was sealed. H I’m going to go with Piet’s advice and not get the bracket welded, and improve the support and vibe insulation.

Sean
 
smlav said:
Well if the tank had been sealed when it was constructed I’d likely not have a problem. I only had the sealer added as a secondary protection, the welding up of the seams is the primary protection. The tank was leak tested after welding and before sealing, but that’s not the same as being fuel if fuel for ages. The coating used gets excellent reports (real ones from people I know rather than internet noise) from folk who have it in tanks for a few years. I’ve known plenty of people who have done the home brewed nuts and bolts then sealant only for it to fail. This tank has been given the works, just frustrating that the welder missed the bracket before tank was sealed. H I’m going to go with Piet’s advice and not get the bracket welded, and improve the support and vibe insulation.

Sean
Click to expand...
You could try somewhere that supplies/ makes alloy tanks, they tend to have a rubber bridge piece that goes on top tubes. You should be able to get it to sit without rocking by chockining it up- I use cable ties at rear of tank to keep it pushed forward onto the front mounts.
Interesting that yours had a slight weep making the seam wet- I thought I had a drip from the seam but it was fuel that had come out of filler cap under hard braking had run along seam and was dripping onto hot exhaust! I was taking a picture of the bike and could hear the fuel spitting as it fried off- anyway yours should be fine with some bespoke rubbers keeping it place.
 
sfcpiet said:
Sean,

While you're at it, you might want to reconsider the front mounts. Ex-factory, they come more-or-less horizontal, allowing the tank to slide backwards, only to be restrained by the seat or the rear rubber band, if it's still strong enough.

I had much the same issues as you with my GTL tank. While the leaks were repaired, I removed the front mounts and re-positioned them at an angle that would positively hold the tank in the forward position, worked a treat, no more slippin' and slidin'.
piet
Click to expand...
Lee and I have had angled front brackets for about 40 years. Dead simple fix to an eternal Laverda problem.

Hooksey, can you show Piet's post to Shane so he can pass this little gem on to that other guy i won't name!! ... fuk, me, the shit I got trying to get this simple fix done to Walky's tank before it's beautiful paint job. I'm still seething from it. anyone would think I was suggesting removing the cradle from a triple frame! On top of that, Walky's been getting the third degree after letting same unnamed guy know we're replacing his flimsy lower rear engine mounts with proper 5mm ones!! Some crap about 'factory knows best'!!
 
Definitely recommend a chunk of strategically placed rubber under the tunnel - on a full tank there's a lot of weight on those front mounts. Shame you missed the opportunity to repair the brackets while the welding was being done. Unlucky timing ...
 
piranha-bro2 said:
Definitely recommend a chunk of strategically placed rubber under the tunnel - on a full tank there's a lot of weight on those front mounts. Shame you missed the opportunity to repair the brackets while the welding was being done. Unlucky timing ...
Click to expand...
Yes, I like that idea, additional support with a lump of rubber. I’d given instructions to the tank repairer to weld the bracket, but they missed it out and I am where I am.
 
The bracket has been loose like that since new without failing completely from what I understand. I would apply some top quality liquid metal like JB Weld to help it not get any worse.
 
The good news is I found two of the softer rubber front mounts in my box of bits, much softer than the plastic ones I bought recently, from motalia I think.

And whilst using the GT tank to mess around with spacing I noticed that the weld attaching the brackets to the tank is significantly more substantial than my GTL tank. I wonder if this is the cause of GTL tanks suffering this issue as mentioned by Piet. Here’s a pic of GT tank bracket weld,


IMG_6569.jpg
 
smlav said:
Well if the tank had been sealed when it was constructed I’d likely not have a problem. I only had the sealer added as a secondary protection, the welding up of the seams is the primary protection. The tank was leak tested after welding and before sealing, but that’s not the same as being fuel if fuel for ages. The coating used gets excellent reports (real ones from people I know rather than internet noise) from folk who have it in tanks for a few years. I’ve known plenty of people who have done the home brewed nuts and bolts then sealant only for it to fail. This tank has been given the works, just frustrating that the welder missed the bracket before tank was sealed. H I’m going to go with Piet’s advice and not get the bracket welded, and improve the support and vibe insulation.

Sean
Click to expand...
Now you know where you're going when you get the slightest ding in that tank, plus a paint job.
Electrolysis +phosphoric acid is the way to do it.
Paul
 
Paul Marx said:
Now you know where you're going when you get the slightest ding in that tank, plus a paint job.
Electrolysis +phosphoric acid is the way to do it.
Paul
Click to expand...

Electrolysis and acid not going to fix the weepy seam. I’m not over fussed by ding in tank, this bike going to be a long way from sparkly. I might, even spray it with smooth Hamerite myself if the local paint shop price is too steep, I just want it to hold petrol long term.
 
Sean,

Sure, I can sell you the front mount rubbers, drop me a line with your personal details via PM and we'll work it from there. I have new rears in stock schould you need them, as well as the rubber band. Unfortunately, the quality of todays repro rubber bits is quite shitty, be prepared to renew the rubber band every other season, latest!

The front mount was not the problem causing the leaks on my tank. In the front bottom corners, the sheet that comprises the tank base is folded and creased along the seam weld, mine had multiple fractures in these folds. No amount of soldering was able to stop the weep, didn't want to completely ruin the paint by welding. Sourced a second tank, same happened within 3 years. So I re-furbished the original tank as described, had it lined to be on the safe side and all has been well for the past 6-7 years.

The SF-type tanks have very similar folds and creases, but I can't remember ever having to deal with leaks in this area. The stupidly angled front mounts have been troublesome from the beginning of time though...

piet
 
Those folded seams secure the fuel cap stub too. I silver soldered my SF tank there when I had the bottom cut out, it used to seep there, enough to always be stained around the join.
 
I had the outside of one side front seam silver soldered back in the 80s, which helped but didn’t cure. That’s what led to me getting done from the inside. Fingers crossed.
 
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