Model 12 , AJS No. 2. Gearbox puzzle.

Information relating to Matchless and AJS Models built prior to 1939
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Model 12 , AJS No. 2. Gearbox puzzle.

Postby Edward Johnson » Sun Nov 05, 2017 1:57 pm

Hello, could any member assist me with advice regarding the gearbox fitted to my 33/12 AJS 250 "Big Port". It has a marking on the topside : AJS No. 2. It appears to have 3 ratio's (original adverts for the bike state either 3 or 4) The problem is that the foot change gearlever is secured unconventionally , in that there is no splined shaft protruding from the box, instead there are teeth cut into the approx. 1" diam tube shaft, which is flush fit with the boss on the box, the gearlever should have similar teeth so that shaft and lever can mesh together , with a bolt going horizontally through the lever into a threaded boss inside the box to secure the lever. First can anyone help me obtain a correct lever or suggest a viable alternative. The gearbox is underslung from the frame by 2 vertical studs into slotted mounts(to allow chain adjustment) It looks to be an original fitment but I have viewed late 1920's bikes which appear to have a similar box. The particular bike was only produced 1933-1934 with the sloping AJS engine, after that they had the Matchless vertical engine and probably Burman gearbox's.
Another problem cropped up after riding the bike only about a mile, the exhaust valve gradually stopped opening, yet the Inlet operated correctly...any suggestions before I dismantle ? Any advice would be most appreciated as I am a Newbie to AJS/Matchless bikes.
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Re: Model 12 , AJS No. 2. Gearbox puzzle.

Postby SPRIDDLER » Sun Nov 05, 2017 3:32 pm

Welcome, Edward.
I can't help with the gear lever question - before my time, but when you said the exhaust valve 'gradually stopped opening' did you mean 'stopped closing'? The valve is opened mechanically but relies on the force of the valve spring to close it. Assuming you meant that the valve has stopped closing the most likely cause is hardened carbon/oil deposits (crust) on the valve stem. The inlet is more likely to work o.k. since there is no zorst gas passing over its stem and it is constantly cleaned by the incoming fuel/air mixture.

Later.......
Incorrect reference to s/v edited out of this reply :oops: .
Last edited by SPRIDDLER on Sun Nov 05, 2017 10:14 pm, edited 1 time in total.
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Re: Model 12 , AJS No. 2. Gearbox puzzle.

Postby Rob Harknett » Sun Nov 05, 2017 3:42 pm

http://archives.jampot.dk/book/Workshop ... dition.pdf
Edward, check out the workshop manual above, if you do not have it.
Just a little history so you can consider what your bike consist of. 1932 was the last full model year of AJS of Wolverhampton. In the troubled times during world recession sales were very low. In 1932 the model 12 was not within the range offered. Then AJS of Wolverhampton sold out to Matchless. 1933 the first AMC year for AJS, was produced from the ashes of AJS of Wolverhampton. This would have been from stock of parts, new design, and work in progress from AJS of Wolverhampton. I would guess the 1932 mod 12 had been on the drawing board, redesigned as a slopper for 1932. So you do need to look back to AJS of Wolverhampton, for your gearbox. AJS used 2 types of heavy 4 speed gearboxes. The lighter 3rd 3 speed gearbox, I am sure was used on the model 12.This was in fact a hand change gear box. There should be fitting points on your petrol tank for the hand change lever. I am sure you will see the gearbox in the above workshop manual. So you now have to try and get it back to original, or sort out what you can of the changes made to convert it to foot change. 1934 AJS did not have a Matchless engine. Spot the difference.
Ashampoo_Snap_2017.11.05_15h12m23s_001_.png

Ashampoo_Snap_2017.11.05_15h13m16s_002_.png

You could try lubricating the exhaust valve, it may only be sticking. You do need to regularly grease the valves/rockers via the nipples. Perhaps remove the ex valve nipple and try getting WD 40 or the likes in it. Also spray the valve stem. You should be able to see if the valve springs are compressed. They should not be if the valve is stuck shut. So why will the springs not compress to open valve???
They should do when the engine is turned over. If the engine turns over, but there appears to be no movement to compress the springs, to open the valve. Take the rocker box cover off and check the rocker arm nut has not come off and slipped off the spindle. They do come loose, the warning if this is happening is increased top end noise. If you do find the nut loose or off. Give it a peen to lock it on. Mixture helps to lubricate the inlet valve.
I see Neville has made a comment similar to mine except.
AJS model 12 became OHV in 1930 Neville. It was only a SV when introduced in 1928 to 29. So 33 mod 12 is OHV not SV
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Re: Model 12 , AJS No. 2. Gearbox puzzle.

Postby SPRIDDLER » Sun Nov 05, 2017 10:17 pm

Rob Harknett wrote:AJS model 12 became OHV in 1930 Neville. It was only a SV when introduced in 1928 to 29. So 33 mod 12 is OHV not SV


:oops: Thanks Rob. As I mentioned it's before my time! My earlier reply edited accordingly.
If it is a case of the valve not opening it does sound as if it's mechanical issue rather than a sticking valve not closing.
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Re: Model 12 , AJS No. 2. Gearbox puzzle.

Postby Rob Harknett » Sun Nov 05, 2017 11:15 pm

SPRIDDLER wrote:
Rob Harknett wrote:AJS model 12 became OHV in 1930 Neville. It was only a SV when introduced in 1928 to 29. So 33 mod 12 is OHV not SV


:oops: Thanks Rob. As I mentioned it's before my time! My earlier reply edited accordingly.
If it is a case of the valve not opening it does sound as if it's mechanical issue rather than a sticking valve not closing.

There's so much more to know about pre war than there is post war machines Neville. I cannot remember everything and don't try. I have a library I can always refer to.

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Re: Model 12 , AJS No. 2. Gearbox puzzle.

Postby Edward Johnson » Mon Nov 06, 2017 9:59 pm

Thanks for your advice regarding my AJS model 33/12. The engine is the "Sloper" type, OHV with exposed rockers/springs. The Exhaust valve is failing to OPEN, although the Inlet is operating normally. If I operate the kickstart, full(good) compression is there and the engine will briefly start then cut out(the cylinder obviously choked with exhaust gasses , which can not escape due to the closed valve . If I wait a minute I can restart it as before. The original fault came on gradually over a few minutes, the exhaust rocker gradually moved through less and less of an arc until it stopped moving the valve. I am of the opinion that the fault is due to possibly bent pushrod, cam follower or cam lobe trouble. The oil was changed and proved returning to tank before I set off, so I do not think it is cam lobe rapid wear. I will remove cylinder head and look further as soon as I have time. Regarding the Gearbox, I have a 1934 motorcycle magazine with an AJS advert for the bike and it shows foot change gear with hand change as an option .My bike has no signs of any hand-change mechanism ever being fitted to the tank. There are photos of my bike when it was sold previously at a Bonhams auction in 2012, which can be viewed on the Bonhams website. The original owner was stated to have been a Speedway rider, although my bike is in road trim but with no signs of it ever having had lights installed.
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Re: Model 12 , AJS No. 2. Gearbox puzzle.

Postby Rob Harknett » Mon Nov 06, 2017 11:22 pm

I do believe your bike could be an early 1933 built from parts from the Wolverhampton factory. Not fully up to the 1933 spec. It could have also been rebuilt since then with some non standard parts. You do say your bike has a 3 speed gearbox. Which I am sure would have been an earlier hand change gear box. This would have required a petrol tank for hand change lever. As you do not have this tank, the bike should have had the latest 4 speed foot change gear box. At some time in the bikes life, it has got the wrong gear box or the wrong tank. Tanks are the most difficult to find. You could check your gear box out to see if the parts agree with the parts list. If it appears there has been an attempt to make the gear box foot change, this could confirm the theory it has been done to match the tank that was available. They did usually use up old stock parts on the basic SV model. It is not uncommon to discover bikes of this era, where it would appear, Matchless made up bikes from parts left over from AJS of Wolverhampton parts.http://archives.jampot.dk/book/Spares_l ... s_list.pdf
Check out the parts list above. It is dated June 1933. It contains a list of AJS parts left in stock from 1920's to 1930. Why no 1931/32 parts. They were all used to make up bikes in 1933. That is not guess work. I was told about it by a person that worked at Plumstead and did it. There were lorries loads of stuff everything you could think of, moved from AJS to Plumstead. Even toilet paper printed AJS. Some of these bikes built, perhaps nothing like you see in sales cat's and adverts may still exist. I tried to make notes of all the stories I was told, via many visits I made to this old AMC worker. He ended up a supervisor. His wife also worked at Plumstead. At one visit the old boy gave me a book, in which he had written all his memories. Since then two authors have written and published books using info from his book. Which was hand written. It is now typed out an archived on the website. Here: http://www.jampot.com/article_read.asp?id=570
I just realised. The typed copy has none of John's illustrations. I think I had better scan the original hand written book.

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Re: Model 12 , AJS No. 2. Gearbox puzzle.

Postby Edward Johnson » Mon Nov 13, 2017 7:10 pm

Regarding the Exhaust valve staying shut problem. I removed the rocker box inspection cover and found the Exhaust pushrod mis-placed from the "pip" on the rocker arm, the pushrod was stuck against the arm , so I loosened the rocker box and both pushrod tubes, lifted it up approx. 6mm then replaced the pushrod onto its correct position. Re-secured the rocker box and tubes, re adjusted the valve clearances and carefully turned the engine over to observe correct valve operation.Greased all rocker mechanism and then Tried kick- starting but tank had dried up since last use of the bike. Will get fuel and report on starting/running later.
E.Johnson

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