Tank mounting difference for dual frame

Information relating to the Matchless G80 or AJS Model 18 500cc Heavyweight.
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schrottschlecker
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Tank mounting difference for dual frame

Post by schrottschlecker »

Hello,

I want to restore a tank for my Model 18S with dual frame. I have the tank that was originally on the bike when I bought it. It has 3 attachment points, 2 in the front and 1 in the rear center. I have a second tank that has the same size, but has 2 mounting points in the front and 2 welded-on brackets in the rear (without thread). This second tank is in better condition. What can I do to make it fit my frame? Is there a bracket that can be attached to match the center mounting without welding? How is the tank normally attached, when there is no thread in the rear ?

Thanks for your advice.

Christian
tanks_u.jpg
tanks.jpg
4point.jpg
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dave16mct
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Re: Tank mounting difference for dual frame

Post by dave16mct »

Hi Christian,
the tank with the rear mounting holes is for a 1959 twin. You can use it on your duplex frame if you put some foam rubber under it. The weight of the fuel and the seat will hold it in place (like mine) If you need it more secure you can weld 2 hooks to it at the rear( like the 61 twins had) and use a rubber ring to hold it down.
Dave.
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Rob Harknett
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Re: Tank mounting difference for dual frame

Post by Rob Harknett »

I substituted rubber ring with cable tie to secure it. Carry a spare in case you need to cut it off while out anytime.
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robcurrie
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Re: Tank mounting difference for dual frame

Post by robcurrie »

I found that the rubber ring perished and broke within a couple of months of fitting it, so I made up my own ring using bungee cord (from a tie-down), crimping the ends together with a short piece of steel tube.
When the rubber ring broke, I lost the rubber block that fits between the frame top tube and tank, so I made up a block using half rounds of rubber water hose bonded together. The piece that sits on the tube was left longer so that I could secure the block to the frame with tie straps.

Rob C
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Rob Harknett
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Re: Tank mounting difference for dual frame

Post by Rob Harknett »

robcurrie wrote:I found that the rubber ring perished and broke within a couple of months of fitting it, so I made up my own ring using bungee cord (from a tie-down), crimping the ends together with a short piece of steel tube.
When the rubber ring broke, I lost the rubber block that fits between the frame top tube and tank, so I made up a block using half rounds of rubber water hose bonded together. The piece that sits on the tube was left longer so that I could secure the block to the frame with tie straps.

Rob C
You can find handy rubber rings by taking apart the old vacuum cleaner before dumping it.
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robcurrie
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Re: Tank mounting difference for dual frame

Post by robcurrie »

Great idea Rob H, though I know my old Kirby uses a band.

Rob C
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griffin
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Re: Tank mounting difference for dual frame

Post by griffin »

Rob Harknett wrote:
robcurrie wrote:I found that the rubber ring perished and broke within a couple of months of fitting it, so I made up my own ring using bungee cord (from a tie-down), crimping the ends together with a short piece of steel tube.
When the rubber ring broke, I lost the rubber block that fits between the frame top tube and tank, so I made up a block using half rounds of rubber water hose bonded together. The piece that sits on the tube was left longer so that I could secure the block to the frame with tie straps.

Rob C
You can find handy rubber rings by taking apart the old vacuum cleaner before dumping it.
Or an old inner tube cut into strips
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Rob Harknett
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Re: Tank mounting difference for dual frame

Post by Rob Harknett »

Thick rings in vacuum cleaners. I found one spot on dia. & thickness to seal the gap between SR 1 mag and inner timing cover on my 55 G3LS. I cut it & fitted it without removing anything. Cut at the bottom, stops muck getting in. If water seeps in it can drain through the cut. Unlike the nice new tin chain case rubbers that stop oil leaks. Doing more harm by also stopping water that gets in, drain out. Which will ruin a chain, clutch and bearings, during a winter lay up
John Jarrett
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Re: Tank mounting difference for dual frame

Post by John Jarrett »

I don't think the 59 tank you have with the two rear attachment points will fit on a Duplex Frame. While it is the same shape as the later tank, the internal dimension at front is designed for a single downtube frame so it will be too narrow for the Duplex frame.
Your pictures don't show that part of the two tanks well, but I suggest you compare them to see the difference in the dimension at the front underside.
Regards,
John
schrottschlecker
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Re: Tank mounting difference for dual frame

Post by schrottschlecker »

John Jarrett wrote:I don't think the 59 tank you have with the two rear attachment points will fit on a Duplex Frame. While it is the same shape as the later tank, the internal dimension at front is designed for a single downtube frame so it will be too narrow for the Duplex frame.
Your pictures don't show that part of the two tanks well, but I suggest you compare them to see the difference in the dimension at the front underside.
Regards,
John
Hello and thanks to all,

John, you are right: the tank is too narrow at the front so I cannot use it.

Best Regards,

Christian
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