Petrol Tank - rigid versus Swing Arm

Information relating to the Matchless G80 or AJS Model 18 500cc Heavyweight.
Member
Posts: 46
Joined: Tue Dec 08, 2009 2:21 am
Location: IOWA USA

Petrol Tank - rigid versus Swing Arm

Postby oldandmatchless » Sun May 19, 2019 6:31 pm

Hello:

I am working on a couple of G80 rigid frame projects. Mostly 1949 G80C, but partly bitsa. I will admit that I am not experienced with rigid models so I am needing some questions answered by those more knowledgeable. I have several petrol tanks that have the seat nose area filled in (see pictures) and I have been told that these are for the rigid models. Is that correct? If so, how does the saddle mount as the tank will cover up the saddle mount pivot hole through the frame.

Also, I am confused on the changes in rigid frames over the 1948, 1949 and 1950 years. Will a rear frame section from a 1948 not work with a 1949 or 1950 front frame section? It is my understanding that the geometry changed in 1949 for the front frame section and the wheelbase was lengthened. Is that correct?

Thank you.

Image
Image

Member
Posts: 6367
Joined: Wed Sep 01, 2004 12:00 am
Location: WEST SUSSEX UK

Re: Petrol Tank - rigid versus Swing Arm

Postby SPRIDDLER » Sun May 19, 2019 7:29 pm

The Spares Lists for each year may give you a good guide.
There are good illustrations of the basic frame arrangement (page 24) and the tank (page 36) here for 1949 for example:

http://archives.jampot.dk/book/Spares_l ... 0_G80C.pdf
I poke badgers with spoons.

Member
Posts: 46
Joined: Tue Dec 08, 2009 2:21 am
Location: IOWA USA

Re: Petrol Tank - rigid versus Swing Arm

Postby oldandmatchless » Sun May 19, 2019 7:46 pm

Thanks for the reply Spriddler.

Unfortunately, the Matchless spares books are poorly updated (illustrated) year to year. The pictures shown in the 1949 Spares list for the frame actually pictures a 1948 frame. The 1949 frame had the side stand lug in front of the foot peg mount. The one pictured shows the lug behind the foot peg mount (as was 1947 and 1948).


Also, the 1949 frame had the seat pivot lug in front of the rear tank mount whereas 1947 and 1948 had the pivot integral with the tank mount.

The spares manual simply doesn't picture the front saddle mount.

Regards,

Rick

Member
User avatar
Posts: 255
Joined: Tue Nov 29, 2005 8:51 pm
Location: Herts UK

Re: Petrol Tank - rigid versus Swing Arm

Postby Group Leader » Sun May 19, 2019 9:53 pm

oldandmatchless wrote:Hello:
I have several petrol tanks that have the seat nose area filled in (see pictures) and I have been told that these are for the rigid models. Is that correct? If so, how does the saddle mount as the tank will cover up the saddle mount pivot hole through the frame.

Firstly a disclaimer; I'm sure the knowledgable members (rather than this Newbie) will have the definitive answer and correct me (every day's a School day) if I'm wrong!

I always imagined that the seat nose area cutout was for the nose of single seat saddles (they seem to be the right shape) which tend to be on earlier machines which also tend to be rigids by virtue of their point in time. My 16MS is from 1953 so in the transition period from rigids to sprung and has the cutout although I've no idea if it's actually the original tank. My bike is fitted with the dual seat which I think was an option at the time but, of course, the seat does not "fit" into the cutout by virtue of the shape of these seats.

So, logic might suggest that tanks with cutouts were made to match single seats the majority of which would be fitted to rigids rather than sprung so the converse of your assertion. Tanks without cutouts would better match the later dual seats which became standard fitments to the later sprung bikes wouldn't they?

Or have I got the wrong end of the wrong stick (again)?

Alan
1953 AJS 16MS, 1939 BSA 250 and a 1/3 scale Sopwith Triplane but that's another story ..... :lol:

Member
Posts: 1050
Joined: Wed Oct 12, 2005 9:45 pm
Location: KENT UK

Re: Petrol Tank - rigid versus Swing Arm

Postby alanengineer » Sun May 19, 2019 10:05 pm

Any chance of pics of the tank with the filled in cut out around the cut out area. In many esteemed areas of this club, these tanks were never made!

Member
Posts: 46
Joined: Tue Dec 08, 2009 2:21 am
Location: IOWA USA

Re: Petrol Tank - rigid versus Swing Arm

Postby oldandmatchless » Mon May 20, 2019 1:16 am

Sure. Attached is a picture of the bottom. Tank is very nice condition and appears unmolested.

Also, I am attaching a picture of two 1953 Competition tanks. One has the cut out and one does not.

Image
Image

Member
Posts: 6367
Joined: Wed Sep 01, 2004 12:00 am
Location: WEST SUSSEX UK

Re: Petrol Tank - rigid versus Swing Arm

Postby SPRIDDLER » Mon May 20, 2019 7:47 am

oldandmatchless wrote:Unfortunately, the Matchless spares books are poorly updated (illustrated) year to year.

Indeed so, partly because new models were introduced after the factory shutdown in August each year and not at the beginning of calendar years so there will be cross-overs. The spares lists illustrate the change progression over time rather than the definitive design for each year.

Group Leader wrote:
oldandmatchless wrote: I always imagined that the seat nose area cutout was for the nose of single seat saddles (they seem to be the right shape) which tend to be on earlier machines which also tend to be rigids by virtue of their point in time.

My '54 has a tank cut-out and dualseat leaving an unnecessary void between them which allows engine noise through to the point that when going on a run of several hours between stops I stuffed a rag in there to reduce the annoying engine clatter and carb chatter. It's cheaper than an overhaul ;) .
I poke badgers with spoons.

Member
Posts: 1050
Joined: Wed Oct 12, 2005 9:45 pm
Location: KENT UK

Re: Petrol Tank - rigid versus Swing Arm

Postby alanengineer » Mon May 20, 2019 11:19 am

Your 'fill in' panel on the road tank looks a lot different from mine from the underneath. mine is a great thick slab of steel, probably 5/16" at its thickest, blending down to 1/8" where it meets the 'normal'part of the tank. Its goot good paint on it, so at the moment i dont want to dig any deeper.

Member
Posts: 46
Joined: Tue Dec 08, 2009 2:21 am
Location: IOWA USA

Re: Petrol Tank - rigid versus Swing Arm

Postby oldandmatchless » Mon May 20, 2019 4:37 pm

Here is a picture of the underside of my 53 Comp tank. It appears the tank was made this way. Note the part number shown. This is in the spares list as a 1952 G3LCS or G80CS.

Image
Image

Member
User avatar
Posts: 2758
Joined: Mon Jan 01, 1990 12:00 am
Location: HAMPSHIRE UK

Re: Petrol Tank - rigid versus Swing Arm

Postby ajscomboman » Mon May 20, 2019 6:03 pm

oldandmatchless wrote:Here is a picture of the underside of my 53 Comp tank. It appears the tank was made this way. Note the part number shown. This is in the spares list as a 1952 G3LCS or G80CS.

Image
Image



I don't think it is a G3LCS tank, what you have there is the G3LC rigid trials tank same as fitted to my 52.

Next

Return to G80 / Model 18

Who is online

Users browsing this forum: No registered users and 16 guests