Gearbox and clutch questions

[malcolm.johnson]

I am piecing together a BA gearbox and clutch to fit a 47 Sq4, from boxes containing the dismantled giblets of a couple + Burman gearboxes and clutches. Am I correct in thinking, that the lower of the two mainshafts pictured is the one to use and what might the shorter shaft fit?
Amongst the clutch parts there are 7 short and only 1 long of the spring cups and a set of 5 springs as pictured.

My instinct says I should be using long cups and springs for a 7 plate clutch, with short cups and shorter springs for a 5 plate version? What is the correct spring and cup dimensions, as Draganfly only seem to list 1 option to use for both clutches( spring 3405-54 and cup 3410-31). The springs present seem too long fitted to be fitted into the shorter cups. Do I need to get a set of shorter springs or longer cups? Thank you.

[will_curry]

The square 4 mainshaft is longer than the rest but by how much I don't know. I have one somewhere
but it will be a day or two before I get a chance to even look.

The clutch springs and cups were the same for both 2- and 3-plate clutches. There were only two
sorts of springs used. The normal set for clutches with cork plates and a heavier set for 'fabric'
plates. Your 4 should have cork plates and so the regular springs and a very pleasant clutch to use it
is too. The Draganfly springs are heavier than the originals and can make the clutch unnecessarily
hard. The 'fabric' plates need the heavier spring but they grip much more harshly than the cork plates.

Again, when I get the chance I'll dig some springs and cups out and measure them.

[paul.jameson]

The Square Four mainshaft is 3/16" longer than the singles one, from memory. Check that the splines on the clutch end are the same length. Longer clutch splines came in in 1948 and mixing pre and post 1948 gears and shafts is a recipe for disaster. The short clutch spring cups are correct. The longer ones must be from an inferior make.

[malcolm.johnson]

Thanks Paul, that is what I need to know. So the shorter shaft is from a single. You seem to infer then, that the springs like the longer cup I have are also from an inferior make, as when installed in the shorter cups, they poke out a long way! As for the main shaft, I am fairly confident it suits the 1947 casings and the gears look good too, so once the main bearing is fitted I will do a preliminary build and see what it all looks like. It is twice the work with a basket case!

[malcolm.johnson]

Our treasurer has kindly fixed me up with a set of correct springs and cups. Just for reference, my shorter cups are correct but the long springs although similar to look at are a much heavier version, being 1.75 inch long with 8 coils of 2.0mm dia. wire, whereas the correct spring is 1.625 inch long with 8 coils of 1.7mm dia. wire. I imagine that my original springs must be the heavy version described above by Will Curry. Is anyone doing clutch plate re-corking nowadays, or is it bonded plates only?

[JohnnyBeckett]

HI i have been looking for cork clutch plates but all i can find is bonded plates i don't know if peter at club spares do cork clutch plates or if they are bonded i must ask him wen i see him i know they list them if you get cork plates can you put a post up

[will_curry]

Gearbox spares provided me with three a while ago.

I'd found this on the forum just before but never tried it:

"Try Mike Chenery (who has taken over the business from Bob Metson)
Tel & fax: 01428 707538 email: clutchcorkcarvery@btinternet.com"

I avoid bonded plates like the plague - technically superior though they may be they seem to
need their own plain plates and springs and the combination is much thinner than the original so you
need more of them. A friend of mine got into terrible trouble with a BSA 6-spring clutch on a B31
with then.

[paul.jameson]

Bonded plates are far heavier than the original plates so have far more inertia. The Burman gearbox is noted for needing the gearchange to take place slowly. With bonded plates it needs to take place very, very slowly.

[nevhunter]

I second what Paul has said there. Cork is very much the "best" idea with lighter springs required and a better action (feel)Don't have any more spring pressure that is required to get a non slipping situation PLUS a small margin. A dry cork clutch is good for all but perhaps straight competition where you are doing full power starts with a CR box. Nev