Re-manufacturing Jack Knight 5/6 speed layshafts

[Nathan1293]

Hi All

I am going to get at least a couple of layshafts remade for my Jack Knight 6 speed. Either in the same steel material or a more modern stronger material.

If you need a new one, or want a spare let me know.

I am not doing this to make any money, it’s just an offer to help someone else if you need a new layshaft.

Cheers

Nathan

[Nathan1293]

Thanks to All Gears Services, I have a new and spare layshaft. I also have the end that runs in the terminal roller bearing.

[Peter Laidler]

Wow....., that looks like a nice bit of work. I don't expect that they told you what material it was made from out of interest.....

[Nathan1293]

They are local to me, so we had a good discussion about various options.

I could have chosen to use EN36 (hardened) as we are pretty sure the original is made from.

I decided to try an more modern steel that is similar, not quite as hard as EN36 but more elastic. I do have the metal spec just not to hand and can post it later.

The price was reasonable, they generally make a lot of old racing gearbox parts. F1 cars, and other special gear sets.

I should also add originally we hoped to repair the shaft, there was some damage on it. But grinding undersize, then using a firm to lazer weld the material oversize and grind to spec. But the shaft has a bend in it, so it more cost effective to reproduce a new shaft.

If anyone needs any parts, I would be happy to liase with them.

[Nathan1293]

The steel used is S155. This was my choice as one of the issues with en36 is the brittleness. Will see how it goes and I could always switch back to en36 if I needed to.

[r.tec]

Not a bad choice:
https://www.smithmetal.com/s155.htm
and:
https://www.smithmetal.com/pdf/steel/bar/s155.pdf

Tensile strenght of 1900...2100 MPa should be enough.

[snoopy64]

Close to old EN19, tougher but less wear resistant than case hardened EN36

[Spider]

Not for these boxes, but I use EN36A for Layshafts, it's often described as Shafting and Gear Material. I * think * from memory, the factory used EN352, which is also very good, but I don't think quite as good as EN36.

Material though is one thing, the heat treatment and tempering is the other most important part of these type of shafts.

[Peter Laidler]

Metallurgy is always the best of a good compromise I was always taught.

[Nathan1293]

Yes you are right the new layshaft will be more prone to wear, but this gearbox will need regular maintenance, and the engine also. Not least because it will likely run a 3.9:1 crown wheel and pinion, the new ones have generally have very small pinions and the teeth can fatigue and break.

If the wear is a problem then I’ll get another made in en36.

Interestingly the five speed version has slightly longer splines to drive fifth and reverse, compared to my six speed version. It is possible to see this in the photo when looking at the original shaft.

I just need a new mainshaft nut and I’ll start building it back together.