Petrol tank dimensions wanted

[Dixter]

A friend gave me an old, well preserved, circa 1940s, AMC petrol tank, that apparently someone had modified in the past. I'm planning to restore this tank and need to replace the 'collar' the Piecrust cap closes upon.

I have ordered the correct petrol tank cap, 35-G3-T130, and anticipate little difficulty in fabricating the part and welding to the tank. However, it would be helpful if someone could take a few measurements with a vernier, dial, or digital caliper, and help fill in the blanks. Dimensions can be in metric or Imperial units, avoiding bushels, cubits, and chain/lightyears, please. Recognizing part to part variation in parts made a few decades ago, measurements from several kind souls would be appreciated.

Here is the info I seek.

collar.jpg

Clarification: A = Outside Diameter, B = Overall height, C = OD measured at the 'bulge', D = material thickness for rolling the collar.

Dimension E, (top edge to centerline of the bulge will be difficult, but a rough measurement will be helpful.

Dimension F, equally challenging to measure, this relates to the size of the roller that was used to roll this bulge. Perhaps an estimate of the end radius of the roller would be helpful.

Here is what I'm starting with.

Old opening.jpg

Thanks to all in advance. Every safety element will be taken into account. I'm a capable machinist, and welder, well acquainted with the hazards imposed in this work, and at 72, still have all digits, both eyes, and crappy hearing. I promise to be extra careful.

Ciao,
Dick Casey

[SPRIDDLER]

at 72, still have all digits, both eyes, and crappy hearing.

I'm 72 as well so understand the deterioration process.
I'll drop round to a pal at the weekend who has a '46 tank (not sure which cap though) and endeavour to take some measurements and take a photo or two.

[Rob Harknett]

I am just a bit puzzled. Are you saying this is actually a 40's tank that has had the cap fitting altered. Strange some one should do this unless they wanted to fit it on a later machine. They would probably then need to alter the tank fittings to suit the frame. Do you only have the tank, not a complete bike? The WD bike used the same cap on both tanks. The cap was used from 1935 to about 1946. Pre 1940 AJS differed. It had a similar oil tank cap, Same fitting but plain flat top , not pie crust. The AJS petrol tank had push on and turn fitting flat top cap. I assume the tank you have is 1941 on, with no instrument panel.
I could measure my prewar AJS oil tank only, which did accept the internal expanding type cap.

[Dixter]

Hi Rob, I'm puzzled as well. The friend who gave me the tank has a very nice collection of old bikes, a prewar Velocette MAC, a 39 G3L, a pre war AJS and all in outstanding shape. He is a perfectionist at restorations. He did not recall from where or when he acquired the tank, but it was decades ago.

I do not have a complete bike, a '46 rigid frame, a '46 G80L engine, and a basement full of old AMC stuff collected over the last 50 years. The tank fits the frame perfectly and comparing the indentations on the underside, this tank matches all aspects of an AMC tank from the 40s. I have nothing earlier for comparisons. And no, no instrument panel in the tank. Below is a full top image. I can only add, the closure mechanism on the top of this tank is well made. If some previous owner made this part, he should be contacted for make future docking collars for the International Space Station.

I looked up parts as best I could scanning everything I could in Christian's archives. Unfortunately, I found no illustrated spares list from the 30s. I did note the petrol tank cap was AF-30, but was unable to find anything combing Google. Looking at the sales brochures, owner's manuals, and press reports from the 30s / 40s I could not get a clear picture of a petrol cap, or when it might have changed to the pie crust version. Frankly, I was almost astounded that someone had not seen this tank opening before. I entered this process firmly believing this to be an original AMC part. I hold the knowledge assembled here in very high esteem.

From the limited info I have, I would think most of the dimensional info from the oil tank would relate to the petrol tank. the notable exception would be Dimension B, Overall Height, in my crude hand drawing.

I'd be beholding to you or anyone else if I could get some measurements..

Ciao,
Dick Casey

IMG_6409.jpg

[39speedtwin]

I suggest that you look on EBay or other auction sites for the collar, the plain bayonet type are available probably from India.

[39speedtwin]

On EBay UK this appears to be the correct neck.

222423689674

[Rob Harknett]

If this tank fits circa 1941 / early post war frame AJS or Matchless, it would have the internal expanding pie crust cap the same as the oil tank. I thought dimensions from one of my pre war AJS oil tanks would be OK as they have the same cap fitting. However as pointed out the high dimension cannot be discovered from an oil tank. All this based on the understanding the fitting seen on the tank has been altered by a PO. There was a prewar AJS tank 37 /40 like this tank with bayonet type push on and turn cap and no instrument panel. This tank fitted to comp machines only. However the frame fitting may be different. There are no illustrated parts list AJS or Matchless from 1934/1940 Apart from 1935 AJS . This book is an instruction/parts list book. Faked copies were being sold of the instruction section only. So recheck the archives, there is a complete copy to be found that has the illustrated parts lists section that followed instructions. ( Illustrations are only for a 250 )

[Dixter]

Speedtwin: Thank you, those collars on eBay may be exactly the ticket. Good call!


Thanks Rob, Following up on your recent post, I went looking at pre war machines in The Club's collection, and chose 1935 as an entry point. Bingo, three pages into the 1935 Matchless sales brochure is a spiffy looking Model 35 / D80 500 cc machine.

Of note here is the petrol cap has no discernible collar. The underside of the cap is almost flush with the top of the tank. I grabbed a screen print, but I'm on my iPad and can not figure out how to add an image to this post, but will submit the image later.

Chasing the part in Christian's archives, I found an illustrated owners manual/spares list. Part of the text is too blurry for me, but two illustrations are numbered. P43 and 12361. Additionally, the spares list shows two available thicknesses on the rubber washers, leading me to believe, this is not the later cap which can be cinched down to adjust for wear.

I'm feeling re energized. Thanks for the direction.

Ciao,
Dick

[39speedtwin]

Dick, the neck on EBay takes a standard bayonet cap, not the internal expanding type. I all depends on how original you want the bike to be, if it's a Bitza it probably will not matter. Regards Dudley

[Rob Harknett]

Just noticed the tank has screw holes for a screw on badge. That also helps date it.