AXLE TWIST LINE UP KING PINS

[Dennis Nicholas]

Another silly question.  Bearing in mind Big 7 axle with big 7 radius arms with forked ends fitting above and below axle and bolt through arms/axle (better to resist twisting)
Rods put in axle eyes seen to not line up with each other looking along the axle top.  Obviously a slight twist in the axle.
Looking along from offside, if nearside rod top is slightly backwards from top of offside rod there seems to be 4 possibilities.

1. N/S is in correct position and offside eye twisted slightly forward.
2. O/S in correct position and N/S eye twisted slightly backwards.
3. N/S twisted partly back  AND 4. O/S twisted slightly forward.
It would be easy to hold one end of axle and twist on other end till all lined up but that leads to possibility of both ends being twisted the wrong way compared to where they should be.  

How on earth do you decide where twist is?   

Some thoughts......middle of axle clamped in vice and check top and bottom ridges (i.e. vice jaws) are held vertical and measure incline of each pin in axle eyes then bend each end till pins vertical?    etc.

Dennis

[Ian Williams]

With a big seven axle first check the radius arm fork hole are in line as you would the king pins, if that is all good you can be sure the twist is not in the centre of the axle. if the twist is in the centre just align the KP's if not then check the caster on both sides this will determine which side needs tweaking in which direction

[Dennis Nicholas]

With a big seven axle first check the radius arm fork hole are in line as you would the king pins, if that is all good you can be sure the twist is not in the centre of the axle. if the twist is in the centre just align the KP's if not then check the caster on both sides this will determine which side needs tweaking in which direction

Thanks Ian.   Didn't think of checking radius fork holes.  I am presuming you are thinking of with arms fixed to cross member.
All is still disassembled so will probably be a while before can partial assemble to do checks.


Further musing......if when assembled it is found that a wedge is required between spring and chassis to align radius arms to cross shaft pivot joint (and give correct caster),  as spoken of in various A7 books, what would be the favourite method to achieve what I would think would be a fairly thin wedge?.......will probably use an alloy (hard) block.  File?  Sander belt?     ??    ??

Dennis

[Ian Williams]

I would check alignment if the mountings and eyes on the bench, only if you establish the twist is at the end i,e between radius arm and KP would I do trial assembly to verify the castor prior to further rectification work. With a standard set up a wedge may not be required as the nose piece should already be at the correct angle, however with a special you need to ensure everything goes together without strain while maintaining the desired castor, this may require wedges, as well as other adjustments and  alterations to the radius arms and mountings.

[Dennis Nicholas]

Thanks Ian
Just for clarification and recap it is a standard A7 long wheelbase chassis with big 7 axle (now a Nippy special because of engine/gearbox change to BMC A+) and Morris Minor derived hydraulic breaks. Otherwise looks just like a standard Nippy.

Dennis