AJS & Matchless Owners Club

Anyone know the thickess of the fibre spacer originally fitted between the carburettor and the cylinder head on the 350 cc Lightweight?

The one that came with mine a long time ago was 5/16" thick with a rubber ring seal in one side. It is too damaged now to be reused & may not have been the type fitted by the factory, anyway. The trade/Russells/etc. seem to offer a 3/4" thick spacer nowadays but I don't remember this on the Lightweights & wonder if this thick spacer is acftually for a Heavyweight model? What do you know?

Rod

I don't know what was original on a G5 but the spacer on my G2CSR measures about 11/16". I'm not saying this would be the same as yours but just showing that some lightweights had thick spacers.

I would have thought the bore size more important. Certainly not a 1" bore on 1 1/8" bore carb.
010676 1" bore. 3/4" thick. Old pt. no. 41-G3L-E167
010677 1 1/8" bore 3/4" thick. Old pt. no. 37-G3C- E167
015875 1 1/8" bore 3/4" thick
021252 1 5/32" bore 3/4" thick
021346 1 1/16" bore 3/4" thick
024308 32 m.m. bore
I did not know all that I just checked it out. Quite easy really. In this instant I checked 1954 parts list old to new conversion book. I'll leave you to check your own bikes parts list, in which you should discover the correct spacer pt. no. for your bike. Then order by the part number.
Not sure if the lightweight pt. no. appears on that list. Note from 1937 G3C all appear to be 3/4 thick. Janet measures her lightweight spacer as about 11/16" thick. I would say that's about right for what started life as a 3/4" thick spacer, having undergone some cleaning and shrinkage. However BORE size is the important factor. ( Assuming you do of cause have the correct carb fitted, to take the correct spacer )

5/16" to 3/8" is about right from what I can remember. It's certainly not bigger than that and is thinner than the one used on the 250 and heavyweights.

The Spares List Nos for Carb Spacers on the LWT 350 cc is 041014 with an ‘O' ring & 044003 without one. No information on thickness, of course, is to be found in the Spares List. Finding out the bore size not the problem as the cylinder head inlet & carb flanges measure 1 & 5/8” on my bike at least.

The reason I'm bothered to find out the original thickness of the spacer is because it determines how long the studs in the cylinder head for mounting the carb have to be. Changing these (old) studs is more of a hassle than swapping a spacer.

Neither of the Part Nos in the Factory Spares List are available from JAMPOT or listed by Andrew Eng. Russells supply only the ¾” thick one. I enquired with Autocycle recently who said the spacer with the ‘O' ring hasn't been seen for 20 years. Surrey Cycles do carb spacer but in metric sizes only so the fit is not so good on old British bikes & some additional machining, etc. may be necessary to alter the bore, etc.

I've just had a thought about another approach & went out to excavate deep under the rubbish heap corner of the garage where I came up with two old scrap 350 cc LWT heads. On both these, the carb studs look unmolested & original and on both heads the studs stand 1” proud of the carb flange. Allowing 5/8” for the thickness of the flange on the carb plus a 5/16 nut & heavy washer leaves 3/8” for a spacer with a paper gasket on each side of it . So I'm guessing is that the spacer originally fitted by the factory to these heads at least was about 5/16” thick. But don't take my word for it!

I happen to have an old “new stock” 11/32” thick spacer (without an ‘O' ring) with the correct bore bought years ago and will fit that now. Unfortunately, to do so I will have to change the carb studs in the head which were fitted to take the ¾” spacer. Hi-Ho!

Thanks, Janet & Ron.

Rod

Thanks to you too, Rob, for confirming that.

Rod

Bore size can be found on Amal parts lists. One ref. is for 1962/63 AJS mod 16 & 8 carb type 389/68 bore size 1 1/8" That may not be the year of your bike. My 250 lightweights appear to measure same as Janet's at 11/16" thick ( assume that's 3/4" )

Rob Harknett wrote:Bore size can be found on Amal parts lists. One ref. is for 1962/63 AJS mod 16 & 8 carb type 389/68 bore size 1 1/2" That may not be the year of your bike. My 250 lightweights appear to measure same as Janet's at 11/16" thick ( assume that's 3/4" )

Bore size of what? A 389 carb has a bore of 1 1/8" to 1 3/16" depending on what model it has to fit but never ever 1 1/2". The bore of the head is usually the same as the carb but occasionally the head can be larger and the spacer is then tapered to suit.

Sorry, I gave the wrong size for the inlet on in the cylinder head on my G5. It's 1 & 1/8" not the 1 & 5/8" in my question. Apologies.

Correct carb studs now fitted!

Rod

ajscomboman wrote:

Rob Harknett wrote:Bore size can be found on Amal parts lists. One ref. is for 1962/63 AJS mod 16 & 8 carb type 389/68 bore size 1 1/2" That may not be the year of your bike. My 250 lightweights appear to measure same as Janet's at 11/16" thick ( assume that's 3/4" )

Bore size of what? A 389 carb has a bore of 1 1/8" to 1 3/16" depending on what model it has to fit but never ever 1 1/2". The bore of the head is usually the same as the carb but occasionally the head can be larger and the spacer is then tapered to suit.

Well spotted Rob 1 1/2" should read 1 1/8" for the 389/68 carb. I have made a correction. Fractions are difficult to read on some of the old archive scans. When had loan of a huge Amal literature collection, taking three weeks to scan, I never scanned items already in the archives. As I promised the return of the loaned collection asap. I will check my own collection to see if I have the original mid 60's item that is almost unreadable and replace it with a good scan..