AJS & Matchless Owners Club

Hello all, Im new to then group and need your assistance to identify valves and valve guides for a 55 ajs model 18cs.

I have these part numbers

013989 exhaust valve

013988 inlet valve

017019 inlet guide

021185 exhaust guide

are these correct for his machine?

if so I'll place an order!..

if not can anyone please correct?

many thanks in advance

dave in So Cal

Go to: http://archives.jampot.dk & download the spares list to compare part numbers. There are many other books & articles of interest, too. If more help is needed send a PM for quicker response. I am a little north of your in rural Moorpark, Ventura County. Cheers, Don.

The AJS parts list will tell you the correct valves, for the bike. There is another consideration, has the bike still got its correct head?? I think this is a prime consideration, as you will need valves to fit the head you have.

well interesting point....here's the deal on the head.

The intake valve has a head diameter of 2 inches. All the parts books on this site , all and Roy Beacon Books and every document I can find in print or on the web , I can se no reference of any larger intake valve size. The books all call for valves that say "500" , part # 01-3988 head diam at 1.690.

Did AJS /matchless ever make a different head with a larger intake valve? Its a 1955 18CS...alloy head and barrel, pushrod tubes on the outside, hairpin springs , it all looks normal, I just cant find any reference to an intake valve that size. The exhaust valve on the bikes head is as per the book 1.690.
Certainly this is not a factory "one off" cylinder head , there's gotta be someone else out there that has the same year CS bike with the same 2 inch intake valve.

I attached a photo so you can see the size relationship....

so thank you so any insights , info , secret part numbers etc


best

Dave

Bigvalve head, very BSA!! make valve timing super critical and the valve cutout is close to the plug hole. That looks like a PO modification for sport, very nice ,set up should go like stink!!

Note on the 55 head there are 3( if my memory is correct ) small fins between the push rod tubes.
On a later head all fins go over the push rob tubes.
I think you will find all model alloy heads have a larger dia. inlet valve head than the exhaust, My 55 G3/LS has.
Maybe early and later heads used the same valves, but its worth making sure before you buy.

I do not have data for the 1955 CS heads. The 1956 CS had 1-11/16in head diameter for both inlet & exhaust but different material, of course. For 1957 CS had 1-7/8 in inlet & 1-11/16 exhaust. My 1963 CS has 1-3/4in inlet & 1-7/8in exh, but I do not know if that is original. I have seen several 2in inlet valves but they are all in modified heads, some with original size ports, but usually enlarged. The CS valves are scarce so my engineer welds hard-face on good used valves & cuts them to size. That should work with using touring valves as a base. Cheers, Don.

This has been opened up by a previous owner. You will find that a 2' valve will not be available from AMC sources. Easiest way is to use Chev blanks (available with 3/8 stem) and get a machinist who knows his stuff (is Ed Crowell still around Don ?) to cut collet recesses and grind the ends to suit. I use exhaust valve blanks for inlet and exhaust, and get them from a Chev race shop, which I seem to remember are more common than Walmarts.
You may also find this is the cheapest way too.
If you are going to race the engine, convert to 5/16 stems with matching guides, use Very high quality blanks and convert to coil springs using twin valve springs and collets. This is what I did and never floated or dropped a valve.
Also- ensure you plasticine the piston crown on assy to ensure piston /valve clearances are OK. A 2' valve is a lot larger than standard and it's use would not be noticable unless other mods ie cams, piston and porting were carried out. I used 1 7/8" and was happy with the result and this was a short stroke engine ie 86 bore, not the 82.5 you have.
If it is for road use, find a road head, drill the 4 mount holes to 1/2" and use that.
My opinions only
Marty