Hello All,

I have a question regarding a gearbox please…

I have just rebuilt my WM20 gearbox:
A NOS mainshaft, new bearings, new sliding dog clutches, NOS gear dog assembly and new bushings all around.

Looking from the inspection window, the mesh is deep and perfect,
No end float to the shafts or dog and all looks real nice, But even when I closed the inner cover with a gap
Of about 0.5mm, In order to compensate for having no gasket or sealant,
Still, the gearbox is tight.
I mean, I can turn it over with a sprocket on, but it is far from an effortless action, and not for the faint handed…

Can I just install it like this and expect it to get softer, or should it be smooth effortless mechanism when installed?...

Thanks,,
Noam Zehavi,

email (option): noam10"at"gmail.com

Hi Noam, Just remove all those nice NOS parts and put back your worn parts again,

I found when replacing the big bearing for a sealed one that the big washers which are on both sides of the bearing can touch the bearing seal and tighten the box when they are not totally flat.

This is only noticed when the rearchain sprocket is tightend up with the nut.

So if you loosen the nut and the box is turning better this is probably the problem.

Good luck, Michiel

NOAM - i don't know the m20 gearbox, but do make sure it changes and feels nice and free - BEFORE you fit it.

The stage just before 'freeing off' is seizing up!

Thanks for your reply guys.

Yes, I guess that the worn parts would free things up,
But my goal was to build a gear with as much NOS parts as I can get,
In order to have a good and reliable one...)-:

I think that the main reason for the tightness are the new bushings.
The mainshaft big bearing is a sealed type, but has a flat rubber seal,
And the sprocket is only tighten loosely by hand.

Every shaft moves freely by itself, and even as assembly without the cover,
But when putting the inner cover in, things start to get tighter.

I guess there is no chance to install it a bit stiff and wait for it to loose up?...


Thanks,
Noam.

email (option): noam10"at"gmail.com

No it will lock up and you will be testing the abraision resistance of your trousers.

Stiff boxes are generally due to miss alignment of one of the shafts.
Remove all of the gears from the two shafts and put them back in the box.
Chances are you will find the layshaft stiff to turn because the bushes are not aligned with each other

email (option): bsansw1@tpg.com.au

Thanks Trevor.

I will try that today.

Cheers,
Noam.

email (option): noam10"at"gmail.com

Noam from what you describe, it sounds to me like you haven't got enough end float.

I watched Ian when he rebuilt one of my boxes. He put each shaft in turn into the box and put the cover on with a dry gasket and a couple of screws and measured the end float (from memory it's about 5 thou, but would have to check). Some machining took place on his lathe to obtain the correct end float. I seem to remember he added a shim to one shaft to reduce the end float and took a bit off one bush to create some end float on the other shaft (all very tedious stuff). and when everything was correct the cover was replaced with a smear of silicon on the gasket.

I rebuilt my last box myself and noted that the after-market gasket was very thick and gave too much end float. Les at Russell's sent me an original gasket which was very thin About 7 thou from memory.......So even an incorrect gasket can disrupt your rebuild of these awkward boxes. Ron

email (option): ronpier@talk21.com

Thank you Ron.

I am just getting ready to go to the shop now.
I will to check that all of the bushings and bearings are
Really all the way in, again, and test the shafts one at a time.

Yesterday, there was no end float at all, even with a nice gap
Between the gearbox body and the cover, due to either a tightness
Of the new bushings, or not being parallel...

It would be a shame to use the worn out parts again
And replace only the bearings...

I will try all and update.

Thanks again,
Noam.

email (option): noam10"at"gmail.com

Thanks Michiel

Actually, the guy from the shop told me the same.
He is very "Old school". he can build and fix engines and gears,
But knows nothing about tolerances or data, only what works.

He is in his early 80's, now, I believe.
He told me that
"The life of these gearboxes is endless.
3 wheeled BSA loaders carrying more than half a ton of paper or fabric
Used to do it for years, and the gearbox survived.
There is no justification to change any part in the box
Only bearings, maybe..."

Noam.

email (option): noam10"at"gmail.com