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Ossa MAR alloy tank.

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Im doing up a '74  Ossa 250 MAR and ordered a the replacement alloy tank for it. When the tank arrived it looked great but its too narrow  by 10 mm at the front where it goes over over the rubber mounts. I can modify the dowls and rubber mounts on the  frame with a grinder and shoehorn the tank on  but would much prefer get the correct tank..

 

Any advice????

Jim

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You may well have the correct tank, but the buck that was used to make the tank may be out, where did you get it from? Is that 10mm each side or overall? If this is the case then you only need 5mm clearance to be obtained either side. Have you contacted the supplier of the tank, they may be able to offer advice or suggest a fix as this won’t be a one off. You could try gently persuading the tank guides (for the rubber blocks) to move inwards by pressing against the area with a flat piece of plywood, a 2mm inset leaves 3mm to find. Try the tank on the frame with no rubbers and see what you have. I dare say if you could have been a fly on the factory ceiling ar Ossa, when the assemblers fitted the tank I suspect that there would have been a fair bit of pushing going on the achieve a fit. Overtime the tank would have given anyway what with the riders legs pushing up against the tank. Have you measured the old tank and have you checked to see if there is any depressions around the tank slider mounts? Have you got the correct tank rubbers? Lube the slide mounts with silicone and the rubbers and try to gently persuade the tank on, shaving a little (1-2 mm) off the heads of the rubbers may also win you a little extra clearance. I hope you find a satisfactory fix 🙂

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New tank or used?

New, Miller used to do a replacement but I guess they're long gone and in Spain, Ossacels sell an alloy tank which is a copy of the UK tank. I don't know of anyone who has bought one of those so haven't heard any reports about quality of fit etc. You can 'open out' the original UK tanks so I guess you could do the same with one of these. Years ago I closed up the gap on my tank which was too wide simply by leaning hard on it with it on the floor (down facing side protected)

If it's a used original UK tank it could have been through all sorts of adventures but same as above, you can just open it out which is better than altering the frame lugs and rubbers

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I have seen an excellent new tank, made in France or Germany I think.  Modern materials (seems to resist ethanol) and super replica of a Mk 1 tank.  Presumably they do Mk 11s also. Somebody on here must have details I'm sure.

Edited by 2stroke4stroke

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MK1 and MK2 were fitted with the same fibreglass tank from the factory, just a different style of green stripe. There are several places that sell repro glass tanks. UK bikes from '73/74 had the original tanks replaced with a UK made alloy tank

I forgot that Classic Trial in France also make a UK style alloy tank but it's pretty expensive at over £500

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On 9/12/2018 at 4:54 PM, section swept said:

You may well have the correct tank, but the buck that was used to make the tank may be out, where did you get it from? Is that 10mm each side or overall? If this is the case then you only need 5mm clearance to be obtained either side. Have you contacted the supplier of the tank, they may be able to offer advice or suggest a fix as this won’t be a one off. You could try gently persuading the tank guides (for the rubber blocks) to move inwards by pressing against the area with a flat piece of plywood, a 2mm inset leaves 3mm to find. Try the tank on the frame with no rubbers and see what you have. I dare say if you could have been a fly on the factory ceiling ar Ossa, when the assemblers fitted the tank I suspect that there would have been a fair bit of pushing going on the achieve a fit. Overtime the tank would have given anyway what with the riders legs pushing up against the tank. Have you measured the old tank and have you checked to see if there is any depressions around the tank slider mounts? Have you got the correct tank rubbers? Lube the slide mounts with silicone and the rubbers and try to gently persuade the tank on, shaving a little (1-2 mm) off the heads of the rubbers may also win you a little extra clearance. I hope you find a satisfactory fix 🙂

 

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Thanks for the advise lads but I got it fixed. I took a chance and spread the Tank using 2 pieces of wood and A couple of tyre levers. Still slightly narrower than orriganal but fits snugly on mounting rubbers now.

20180914_161903.jpg

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Good to hear that worked.

someone was building alloy OSSA Phantom tanks awhile ago. But I can’t find it anymore.  If anyone knows a source please let me know.

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Not sure which tank you purchased or from what vendor.

Simply a FWIW, my buddy purchased an aluminum tank for his MAR.  While it looked great, with use he found the tank had a couple of small leaks along the welded edges.

The guy we use for welding is aerospace certified.  He spent some time welding the tank and would smooth the edge back as it was with no bead of weld showing.  Try as he might, the seam would open slighly in another spot.  Point being, it appears the edge is a very thin joint after being sanded smooth.

Ultimately, I asked our welder to do a nice functional but pleasing to the eye bead around every seam. Once polished the tank looks fine.

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