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Gearbox/clutch engagement problems

I have a 1942 BSA m20 hat i have fully rebuilt and cannot seem to get the gearbox to engage when running. I can shift through the gears when the bike is not running. I also can pull in the clutch and the gears free up. When the bike is running all I here is grinding there is no engagement of the gears when I pull on the clutch. The previous owner said that the transmission was rebuilt but i also went through it when i rebuilt the motorcycle. Is it ok to take the inspection cover off the gearbox when running as well as the primary chain cover to inspect the cause. I understand that i have gear oil in there but is there anything i could try before I rip all of it apart. It seems like everything works as it should when reading over some of the other posts when the bike is not running but i am at a loss when its running

Re: Gearbox/clutch engagement problems

Hi Barret,
While there is some fine adjustment that can be made for gear selection I would look more closely at the clutch, is the pressure plate lifting sufficiently or not lifting squarely? is the clutch operating arm set to give maximum lift when the lever at the bars is pulled in? Is the clutch push rod the correct length? It's ok to run with the outer primary case off but running with the inspection cover off will make an absolute mess. The inspection cove is really only good for checking gear engagement when stationary and even this will be difficult when the box is mounted in the frame.
If everything with the clutch checks out then inside the outer gearbox cover is the adjustable control rod, small half turn adjustments can be made to lengthen or shorten the rod. Lengthening the control rod will move the selector forks towards first and third gears thus improving their engagement, shortening the rod moves the forks towards second and forth. Improving selection in one gear may adversely affect selection in the others so take note of where you started and make small adjustments.

Just another thought, what happens if you try to kick start the bike when in gear and the clutch pulled in? This will tell you if the clutch is operating well.

Re: Gearbox/clutch engagement problems

I’ve got a similar problem with a 1943 M20 I just acquired. It has been sitting for a long time and the previous owner said the it started acting up recently. It clicks over and starts up fine. Once running, when you pull the clutch lever in and try to engage the gears, they grind and you can’t engage them. My gut tells me that the clutch plates might be stuck together from sitting. I should note that with the bike off and in gear when I pull in the clutch lever the bike rolls free. Once I let out the clutch lever it engages the engine, but it takes a second or two. Any thoughts?

email (option): pswebster1@netzero.net

Re: Gearbox/clutch engagement problems

I should also note I have a significant leak emanating from the bottom of the primary. I’m not sure if there is a connection between not being able to engage the gears and the leak.

email (option): pswebster1@netzero.net

Re: Gearbox/clutch engagement problems

Steve,
I can't imagine how a leak from the primary case could affect your gear engagement. The clutch for all intents and purpose is a dry clutch, the oil in the primary is there to lubricate the chain, cush drive and clutch bearing.

Re: Gearbox/clutch engagement problems

Hello,

A common problem with gear selection is with broken or worn out springs on the gear selector. I had this problem and tried everything, until I replaced the two tiny springs -- whereupon the gears were able to select easily. You can get at the springs by taking off the outer cover, which is a bit fiddly as there are four bolts that have nuts only on the inner side of the forward bulge. Check the selector is not badly worn at the same time.

If your clutch disengages when you kick the engine through, at stand still with the engine off, obviously, your clutch is probably doing its job.

There's quite a good thread on this already here on the site.

That said: First is often a problem for many people when starting. My advice is get the lowest engine revs you can, by using the advance/retard lever, and then roll the bike forwards a shade as you click into first. Works a like a charm. Some people choose to engage second from a standstill and then click into first.

I hope this helps.

Allan

email (option): allanmatchless@yahoo.com

Re: Gearbox/clutch engagement problems

Thank you I will check the clutch today. As for the clutch rod length I have tried adjusting the set screw and if I thread in to far the kick lever just kicks freely it with no resistance to build pressure to start. Is that telling me that the clutch is engaging properly?

Re: Gearbox/clutch engagement problems

Yes. When the clutch is engaged (no hands on the lever) you'll get resistance from the engine's compression. You should be able to kick the engine over, with no feeling of anything slipping. You'll need to use the decompression lever, of course. You'll feel the engine turn over. If you adjust the clutch set screw by turning it too far inwards the clutch will disengage, and the engine won't turn, but the clutch will slip.

Allan

email (option): allanmatchless@yahoo.com

Re: Gearbox/clutch engagement problems

Ok so I took the primary chain case off and the clutch cover to inspect the clutch. As i pull the clutch cable i see the clutch plates only expand on one corner of the clutch depending on the orientation of the clutch. The expansion is not even enough to see the plates separate (very minimal). I am going to reference the maintenance manual. But can any one tell me what I should be seeing visually when the clutch is pulled in? i ordered a rod from draganfly but i guess it could possibly not the right length or does the clutch spring need to be tighter? Anything helps. I believe the transmission is not the problem

Re: Gearbox/clutch engagement problems

Ok so I took the primary chain case off and the clutch cover to inspect the clutch. As I pull the clutch cable I see the clutch only expand on one corner of the clutch depending on the orientation of the clutch. The expansion is not even enough to see the plates separate (very minimal). I am going to reference the maintenance manual. But can any one tell me what I should be seeing visually when the clutch is pulled in? I ordered a rod from draganfly but i guess it could possibly not be the right length or does the clutch spring need to be tighter? Should i see a seperation in the clutch plates? Anything helps. I believe the transmission is not the problem

Re: Gearbox/clutch engagement problems

Yes the plates should separate evenly, sounds like you have a worn clutch spring that's not lifting squarely.
There's a great write up in the technical section of this web site on determining and solving clutch problems.

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