AJS 18CS Trials bike

Information relating to the Matchless G80 or AJS Model 18 500cc Heavyweight.
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dave16mct
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Re: AJS 18CS Trials bike

Post by dave16mct »

My 18CS engine is only 117 numbers after yours. Your frame number seems right for the year. Your rear frame should be in one piece, that is with no seperate bottom rails. The rear frame sweeps around and under the engine to join the front down tube. Definately a scambler, way too heavy for trials. Photo's would be nice.
Cheers Dave.
fullchoke
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Re: AJS 18CS Trials bike

Post by fullchoke »

I'm reasonably sure it was used for trials. These pictures aren't the greatest. I have no lighting in the building it is in, so I have to get close, so a full bike picture isn't possible and focusing is a problem in poor light, but I hope it shows the basics well enough. I took the tank off to get at the engine and forgot to picture it but it is original without any dents, and rather small. The rear sprocket seems large like it is set for slow going, but I haven't counted the teeth yet. The seat looks too thin for anything but trials. The gearbox # is M1173. Hopefully that helps identify it, along with the pictures. The magneto says Lucas Competition, I don't know for sure if that means it's special, but I thought it might. If the frame ID needs more pictures, I can get something more specific. Appreciate the help!

Thanks

https://imgur.com/a/osqXPKc
fullchoke
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Re: AJS 18CS Trials bike

Post by fullchoke »

I also noticed that the carb is a 389/12 and only 1 1/8, not the 1 3/16 listed in the brochure. If it was original would it be more likely to have a smaller carb on a Trials bike? I know when we modified our bikes for the dirt, we wouldn't have gone to the extreme of changing our carb, jetting yes, carb itself no. If anything we would have gone bigger, not smaller. We were always looking for more power, not throttle response. What do you guys think, could you get a 18cs set up for trials, and shipped to the US from the Competition Dept? It probably would have been special ordered, if they did special orders.

Thanks
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Cjay59_LAPSED
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Re: AJS 18CS Trials bike

Post by Cjay59_LAPSED »

The engine number is 57/18/2597CS. That's 1957/ model 18 (500) / No2597 Competition Spring. (Not rigid).

The frame number is 7528C. From September 1956 the frame numbers started from 7350, September 1957 from 7592.

The No's start in September at the Earl's Court Show each year, so a 1957 model would go on display in September 1956.

From November 1955 18C (Trials) production was stopped.

From September 1956 you have the 16MC,16C which are Trials, the 16MCS, 16CS and the 18CS which are Scrambles, all the engine numbers for that year started from 7350.

So yours could be a 1957 350 Trials frame with a 1957 500 Scrambles engine, but the gearbox from 1956 to 1965 for the 18CS model was an AMC Trials. The main difference to look for on the Trials frame is a shorter wheel base introduced in 1956.

I think yours is a 1957 model 18CS, take a look at the frame comparisons..

Wheelbase, Scrambler 55.2 inch, Trials 53 inch. 1946 to 1955.
Wheelbase. Scrambler 55.2 inch, Trials 54 inch. 1956 on...
Last edited by Cjay59_LAPSED on Mon Sep 13, 2021 6:30 pm, edited 1 time in total.
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Cjay59_LAPSED
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Re: AJS 18CS Trials bike

Post by Cjay59_LAPSED »

AJS Frame
AJS Frame.jpg
AJS Scrambler 500 18CS 1957
Scrambler 500 1957.jpg
AJS Trials 350 16MC 1957
Trials 350 1957.jpg
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fullchoke
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Re: AJS 18CS Trials bike

Post by fullchoke »

Thank you CJAY very much for that information.

I measured the wheelbase and it is 55". From your information, it looks like I should figure that my bike started life as a Scrambler. If someone wanted a 500cc AJS Trials bike, this was their only option....convert a Scrambler. Someone else told me that Don Morley's book on Classic British Trials recommended not to build a Trials bike from a Model 18sc, that the long wheelbase, and low ground clearance, rendered them uncompetitive, let alone the extra weight. Apparently people were doing it, because they wanted the extra power of 150cc over the 350.

Unless something else comes up, I'm going to consider my 18sc a scrambler modified privately into a Trials bike.

The transmissions ratios listed in the brochure are different between the 18sc and 16mc. Was this done with the chain case sprockets?
I counted 52 teeth on the rear wheel sprocket. The transmission is stamped M1173. I don't know what to make of that.

Thanks again
fullchoke
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Re: AJS 18CS Trials bike

Post by fullchoke »

I typed my response before I saw your last post, or my post had to be approved before I could see yours.

Am I seeing things wrong? My frame looks different if the scrambler frame has a loop going across the top of the fender at the shock absorber and under the seat. I see the large difference between the 500 scrambler and the 350 Trials.

Anyway I'm a little confused now. Is my frame not a scrambler frame? What about the numbers on the frame? Do you think they have been faked? I guess that is possible if it is done before 1964. But for what reason? The person that bought it in 1964 didn't think it was valuable as they sold it for $400 in 1980. From 1980 until I bought it at an estate auction it was tucked in storage gathering dust, never ridden.

Thanks for your help!
fullchoke
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Re: AJS 18CS Trials bike

Post by fullchoke »

If anyone posts before my last post gets approved, I won't be able to see it.

I have looked for pictures of other 1957 18sc scramblers and what I have noticed is that the loop or brace that runs across the fender appears to be bolted on. It's missing on mine. So is the chain guard. One place said that the 1957 scrambler frame was a 1 year only frame. If anyone thinks they can help if they had pictures, I'm happy to take whatever is needed. Please let me know.

Thanks
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clive
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Re: AJS 18CS Trials bike

Post by clive »

You seem very active on the website. Why not join the club and your posts will appear immediately.
clive
if it ain't broke don't fix
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clive
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Re: AJS 18CS Trials bike

Post by clive »

Eamonn wrote: Thu Sep 09, 2021 12:26 am Membership details can be found at www.jampot.com - look under the club heading for Membership.
clive
if it ain't broke don't fix
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