Author Topic: Kick start spring help splitting engine case  (Read 456 times)

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BalideyUK

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Kick start spring help splitting engine case
« on: 26 May, 2024, 12:21:50 »
Hi all,
I have a 1939 BSA B21 De Luxe 250cc that is new to me.
Kick start spring is broken and I have a replacement.
I followed the manual I have as best I could, getting to this point in the photo, but I can't get the inner case apart.
I have tried gently chapping it off from the left side but no movement.
I have kept the gearshift mechanism in place as the manual suggests and the screws holding this inner case are removed.
A friend who ran Bantams suggests applying some heat and continue chapping from the other side.
Is this correct, or is there a trick I am missing?

Thanks in advance for any help.
1939 B21 De Luxe

militaryron

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Re: Kick start spring help splitting engine case
« Reply #1 on: 26 May, 2024, 14:10:04 »
You need to remove the gear change mechanism, especially that nut on the end of the selector shaft. That actually looks like a later M20 gearbox.  I have the work sheets for the M20 box, which ought to be studied before assembling. Ron
« Last Edit: 26 May, 2024, 14:44:43 by militaryron »

BalideyUK

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Re: Kick start spring help splitting engine case
« Reply #2 on: 26 May, 2024, 20:20:06 »
Thanks, when I get to the workshop I'll try with that nut off.
1939 B21 De Luxe

militaryron

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Re: Kick start spring help splitting engine case
« Reply #3 on: 26 May, 2024, 20:45:24 »
Let me know if you want a copy of the M20 service sheets

BalideyUK

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Re: Kick start spring help splitting engine case
« Reply #4 on: 28 May, 2024, 23:03:01 »
Got the case apart. There was a third bolt hiding behind the linkage!

militaryron, yes please, if you could share the service sheets that would be a great help, thanks.
Can you attach them to a message or do you need me to send you my email address?

regards, Steve
1939 B21 De Luxe

militaryron

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Re: Kick start spring help splitting engine case
« Reply #5 on: 30 May, 2024, 05:08:38 »
I sent a PM with my email address. Ron

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Re: Kick start spring help splitting engine case
« Reply #6 on: 02 June, 2024, 22:55:45 »
Funny enough I've just had to replace my kick starter return spring.   

I found it quite tricky getting the 1/2 turn of pre-load on re-assembly.  It needed a suitable tool for the screw driver slot and another pair of hands.    We managed to use a bit of plate and some Molegrips.  If I have to do it again I'll make a proper tool from bar material with a suitable "blade" on the end with a centering spigot and a hole for a Tommy Bar at the other end.

It seems to me that the design of the spring/quadrant gear is very poor; the coils get displaced as it rotates as the tang/end of the spring is only partially retained in/against the quadrant gear and the part of the spring that actually takes the load bears on a sharp corner on the gear.    The broken spring shows extensive wear on numerous coils.   I wonder were all that metal went?  Oh, I know, in the gear box.    Still it's a bit late to query the manufacturer I suppose!

Alan