Matchless AJS Fuel Tank Mounts

[ELPS]

Hi. Was wondering if someone may know if the main motorcycle chassis manufactured for the 1949 Matchless G80 and the equivalent AJS 500 were the same regards to mounting points? Also were the fuel tanks the same between Matchless and AJS for that year?
I recently had my fuel tank mounting holes welded up to bring the threads back to 5/16 BSC and I have now noticed that a previous owner has filed out the front chassis lugs wider to fit this tank. Rear mounting lugs are untouched. Plus the other night I found out through the dating service that my chassis number model is 49/18 (1949 AJS 500) but the engine in it is a 49/G80. So now I'm starting to wonder what I have here. A bits and pieces Matchless or a bits and pieces AJS. Thanks

[Janet]

The AJS & Matchless frames have the same part number.
The tanks have different numbers which perhaps is because the AJS of that date had transfers on and not badges. However, where the tanks attach to the frame must be the same or they wouldn't fit.

[Rob Harknett]

I am sure a bare tank would had been supplied painted. So AJS & Matchless would need a different pt. no. As AJS had gold painted pinstripes, Matchless Silver and red.

Factory records will confirm if a frame started life as an AJS or Matchless. I would not be too concerned as long as the frame is the correct year for the engine. I have a 55/G3LS with a twin frame. So used the twin head steady lug to bolt a tax disc holder, so it was not left empty.

Frame tank mounting lugs have quite large holes, to accommodate the metal tube within the large top rubber. Even then there is considerable play which assists in fitting the tank. I usually fit all parts loosely. Then shuffle the tank about until all the fittings find themselves in a vertical position. If your front mounts have been opened up quite large. I would suggest you check the reason for doing this is not because the bike has had a front end shunt, damaging the front down tube. Do not fully tighten the bolts compressing rubbers stopping them from doing their job. The bolts do have holes in the heads , which MUST be wired on to the lug. If bolts are over tightened, the rubbers will not suppress vibration, perhaps also cause tanks to split. In the effort to tighten bolts using old perished or wrong size rubbers, tank threads could get stripped, when the bolts bottom out.

[clive]

its possible someone has pressurised the tank in order to find a leak, because of the structure of the tank this can result in it flexing outwards. Not sure that a front end shunt would result in the need to open the holes outwards. I could see the logic that you might need to increase the forward length if the top tube had somehow compressed but not the width outwards of the holes. Not sure how damage to the front down tube would affect the tank mounting either. Perhaps you could explain Rob?

[ELPS]

Thanks Janet Rob and Clive. The holes havent been filed to a larger diameter but have been filed to widen the spacing so the bolts would line up with the tank threads. It was all a bit of a mess with large UNC bolts with one rubber originally holding the tank down so I purchased all the original bolts spacers and rubbers from AMOC and had the tank threads welded to get it all correct. I havent drilled and threaded the tank as yet but with the tank sitting on the bike it appears I would have to drill close to the inside edge of the welded on tank mounts, nowhere near the dimples in the fuel tanks base.

So if the frames are the same then I wonder if the tank I have is correct? It has screw on 'M' badges and knee pads but I wonder if there are fuel tanks from later or earlier models with different front bolt spacing? If not, I can only suspect the maybe front frame lugs may have been rewelded to the frame at some stage and got shortened in the process.
Wondering if anyone may have a frame that they could take some measurements from for the distance between the lug holes? Also fuel tank mounting thread spacing?

[Rob Harknett]

Looking at the 1949 sales cat. you see ridged and S/A models, ridged with black tank S/A with red chrome, both appear to have screw on Winged M chrome badges. I would not had thought the frame and tank mountings would be different between the model of that same year
( comp tanks smaller capacity. )

[clive]

I cannot offer to measure the distance between the frame lugs on a 49 G80 as I sold mine some time ago. However whilst it was in my possession it went through the fitting of a number of different tanks from a number of years including one with the wrong cutaway for the valve lifter. All however fitted happily in the front lugholes although sometimes with very litle clearance but I never needed to file anything.

[Janet]

I would not had thought the frame and tank mountings would be different between the model of that same year

I wouldn't have thought that the frame and tank mountings would be different for frames with the same part number but as I wasn't born then, I can only surmise.

[Rob Harknett]

You would not expect any difference in parts with the same part number Janet.
One reason I suggested checking for damage, in particular a front end shunt. This could twist as well as push back the front down tube.
The frame has been dated, so the tank may be wrong, if there is no damage or alterations , something must be wrong with the parts matching.
There is not anything funny going on like in late 1930's. A person had the correct frame and the correct tank. But the tank fixing points no where near lined up with the frame fixing points. Why? the tank did not fit on the front frame lug/bracket. There was another bracket that fitted on the frame front lug, on to which the tank fitted.

[G15 Roy]

The frame has been dated.

I think you will find this has only been dated by using the online system where the person enters the frame number they have this is not 100% as no photo has been seen of the number.