M20 clutch push rod

[Mike Farmer]

 

Is the M20 clutch push rod the same for both gearboxes.

Mike

[Pete C]

I think that as long as you haven't fitted a different clutch it should be the same. Not 100% sure tho

Pete

[Mike Farmer]

Thank you.

Mike

[JulianS]

BSA listed a number of different pushrod lengths for the M20. On parts bulletin from 1956. See second image.

[Pete C]

AFAIK they changed from the single spring clutch to 6 spring after the war - which might expalin some of the differences.
Except to the AA who kept the single spring.
I usually just get a 13 inch length of 1/4 inch  silver steel and work out how long it needs to be and then cut and harden the ends. Dirt cheap and it will fit.
You can also make the rod in 2 parts and add a ball bearing to the middle to cut down on wear.

[Mike Farmer]

 

Thanks yet again Julian for help and advice.

Thanks Pete now a question. What method are you using to harden the ends. Heat or acid or?

I've heard of the centre ball bearing but never really considered it. I don't think my old M20 is going to do enuf miles to bother,  but still quite interesting.

Mike

[Pete C]

Hi Mike

This is the methof I use and the text is stolen from the WM20 website, authored by Ian Wright...just in case he comes after me for copyright!!

I harden both ends. Particularly if you use the ball bearing in the middle route as the ball will splay out "soft" rods and make them a bugger to remove from the tunnel in the mainshaft.

Pete

The pushrod  should be made from 'silver steel' and have the ends hardened. Silver Steel is a flame hardening high carbon steel and it is easy to make alterations to a pushrod made of this material if required.
First you will need to soften one end.
Heat the end to red and allow it to cool naturally in the air. This will soften or 'normalise' it.
Once cold shorten the rod to the desired length..but take care. Small reductions in length make a lot of difference. When you are happy the rod is correct and the clutch adjustment is correct with the rod fitted, remove it and heat the end you have altered to red, quenching it immediately in cold water.
This will re harden the end.
Then clean the end off with some emery cloth until you have a bright finish.
You will now have to 'temper' the end. (this softens it slightly and makes it less brittle.)
Place the end into a fairly gentle flame and allow it to slowly heat up. You will see the steel gradually change colour as it heats, first to a very pale yellow, then a darker yellow...then brown. This is an indicator of the changing temperature of the steel.
Allow it to go pale yellow and just as it starts to darken quench it very quickly in cold water. The rod is then ready to use.
If you go too far and the rod goes brown simply heat it to red, quench it again, clean it off and have another go. Lubricate the rod well with some light oil before refitting

[Mike Farmer]

 

Thanks again, that's brill. My main thoughts were what colour guide to go forallow the heat to permeate the metal

[Mike Farmer]

Sorry. Pressed tooooo soon. that should read, fine that's standard procedure but I was hoping you had something seriously simple up your sleeve. Now I know what colour guide to use to allow the correct heat/hardness level.
I guess that we are there now.

Appreciated

Mike

[Mike Farmer]

 

Just as a matter of interest, I haven't ever done this since I was taught it in metalwork classes at school. That was a few several years back. And I never ever used the knowledge afterward. Now here we are ?8 years later. who'd a thought it.

Have fun all

Mike