Burnam Clutch Advice

Information relating to Matchless and AJS Models built prior to 1939
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Burnam Clutch Advice

Postby Diana3899 » Fri Dec 29, 2017 9:21 pm

I have a 1937 model 8 AJS which I have not had for very long and have been trying to sort out problems. I seem to have it running ok now but I recently took her out on a 20 mile run and at first the clutch was ok but towards the end of the run the clutch started to drag badly such that changing gear was very difficult and finding neutral was impossible. So I decided to examine the plates before I tried to adjust it and I now need some advice.

The gearbox is stamped XCPBD17260 which may mean something to some people but I assume it is a CP box. According to my 1937 parts list the clutch should have one thick plain plate which I found at the back of the clutch basket and there should also be 4 thin and 4 friction plates but in my case there are 5 of each. It is a 4 spring clutch.
Not sure what is going on here, can anyone advise!

For information the thick plain plate is 3.5mm thick and the 5 thin plates measure 0.73 / 0.74 mm thick.

The 5 friction plates which appear to be surflex ( not sure of spelling) measure 4.3 / 4.4 mm across the friction inserts.

The push rod according to the parts list should be 11 and 9/16"long, mine measures 11 and 5/8"" long which is near enough I think!

The 4 springs measure 44.16mm.

Can anyone please explain why I might have 5 thin and 5 friction plates instead of 4 of each as per the parts list.

Also does anyone know what the free length of the springs should be and what should the minimum thickness across the friction inserts be before I need to change the friction plates.

If I do need to change the plates, where can I get new ones if that is possible?

Regards,

Diana 3899

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Re: Burnam Clutch Advice

Postby Rob Harknett » Fri Dec 29, 2017 11:23 pm

First of all. The bikes are not that fussy about parts they have and how much they are worn. They will still last years giving you the odd run out. So the owners should not be too fussy. Gear changing may be awful, perhaps changing up OK but changing down you may go down 2 and up 1 to find the gear you want. This will improve once grease gets warmed up. This can be helped by putting in an egg cup full of oil. Remember its going come out again. Drag and clutch slip. I have a mixture of well worn plates picked up at jumbles, cork and fibre lining's. Given a good clean with petrol and the shin taken off them with a bit of steel wool. Dust them with Fullers Earth powder ( or talc ) That should stop them slipping. If you have it all assembled and you have very little cable adjustment left, also the thrust rod adjuster screwed well in. Your trust rod may worn or of the wrong length. A longer or correct thrust rod will give you back that adjustment on thrust rod adjuster and cable adjuster. This allows the cable arm to lay back and give max push to open the plates. Which do not want to be bent. A mixture of old springs as found at jumbles will also be OK if correctly adjusted. So adjust the springs as stated in the book, as a starting point. Operate the clutch, you should now have a good pull on the lever to fully open the plates. Now adjust the springs until you see them open the plates evenly all round, to prevent drag. If the clutch tends to slip a little using the kick starter, tighten all equally to eliminate slip. You may still have to run the bike a few miles each outing to warm up gear box grease. Gear changing may still not be very positive. Something you may have to put up with, and ride your bike. Or keep it in the garage forever trying to find new parts or less worn parts, to get it to run like new.

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Re: Burnam Clutch Advice

Postby Rob Harknett » Fri Dec 29, 2017 11:32 pm

Burman gearbox and clutch parts. Unlike A.M. C. who changed old part numbers to new pt. no's circa 1952. Burman parts keep the same part numbers. Pre war and into the post war era. So you do not need to convert the numbers to check parts club and other dealers stock.

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Re: Burnam Clutch Advice

Postby Duncan » Sat Dec 30, 2017 2:06 pm

Diana3899 wrote:The gearbox is stamped XCPBD17260 which may mean something to some people but I assume it is a CP box. According to my 1937 parts list the clutch should have one thick plain plate which I found at the back of the clutch basket and there should also be 4 thin and 4 friction plates but in my case there are 5 of each. It is a 4 spring clutch.

Can anyone please explain why I might have 5 thin and 5 friction plates instead of 4 of each as per the parts list.


Hi, I assume that you have already discovered the "Archives" as there is a lot of information on there on Burman gearboxes: http://archives.jampot.dk/technical/Transmission/Burman/

A picture might help with identifying the gearbox, it is possible that it could have been upgraded/replaced over the years (as you note the code might reveal that), regarding the clutch it is possible that you have a later 500 clutch fitted which ran on 5 plates (for example see the 1947 parts list, page 22: http://archives.jampot.dk/book/Spares_lists/1947_Matchless_Spares_List_all_models.pdf )

You may be lucky and have a true running mainshaft, quite often they will be a little excentric, and it is possible for the primary chain to run slack and tight leading to clutch drag as can a worn clutch drum and burred tangs on plates are yours all okay?

Are the ends of the clutch pushrod also good, they can sometimes soften reducing the ammount of clutch lift you have leading to drag. A similar sympton may present its self if there is too much clearance on the pushrod actuating mechanism, as parts heat and expand the effective amount of lift could reduce leading to clutch drag.

Self levelling grease appears to work okay in Burman gearboxes but will find its way out over time as will normal grease.

As Rob states Burnam parts are generally available from the Club, AMC Classic spares, Andrew Engineering, Russel Motors and Draganfly to name the most likely few.

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Re: Burnam Clutch Advice

Postby Rob Harknett » Sat Dec 30, 2017 4:47 pm

I've got a load of worn jumble clutch parts and a rough old gearbox on my 1936/22 250 cc. Its a pig changing gears. BUT after over 30 years I've done well over 10, 000 miles 2 up on it. During that time I have only had to clean the clutch plates twice. As they slipped after a winters lay up on trying to start it. For two years I had a strange jingle noise, I thought was a loose round glass rear light lens. Then one day it threw its gear box sprocket. I then discovered what the jingle was. When I put the sprocket and nut back on, the jingle stopped.

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Re: Burnam Clutch Advice

Postby Diana3899 » Sat Dec 30, 2017 5:02 pm

Rob and Duncan,

Thanks for your response and advice, I will take it all on board and have a go at setting up the clutch.

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