A regular newbie question is about the assembly or reassembly of the rear axle.
There's itpro's guide, which among other things tells you the order of tightening up the hangers, pinch bolts and grub screws to get an axle turning freely, but how do you know how free the axle should be?
A turn by an educated hand will often show when the axle turns easily, but how does one get the educated hand?
This afternoon, reassembling the axle with a friendly engineer, he showed me a simple way of telling not only whether you have the axle turning as freely as possible, but also helps diagnose exactly where any problems may lie. No apologies to those of you who know, but the method was taken directly from the Boxford manual for setting lathe spindles after pre-loading the cone bearings.
What you need is a length of string and some small weights (we used a handful of nails, not having calibrated gram weights to hand). You wrap the string round the axle a few times with the kart on a stand, then hang a few weights on the end then let the weights hang freely from the axle.
The axle will start to rotate, lowering the weights to the ground.
All you have to do is note how many weights are needed, then fiddle with the alignment until the number of weights is at a minimum. keep a record of the weights and you will always know whether your axle is turning as freely as it has done.
It was interesting to note just how tightening up the bolts and screws affects the alignment and prevents the axle from turning freely. It demonstrates how little force is needed to affect the working of the chassis. You can even see how tightening one bolt more or less than its neighbours will distort the alignment, I had to use a 1/1000 inch shim (0.00254 mm) between the hanger and the bearing carrier to get the best alignment.
And, without the brake disc installed, I found that I could get rotation using 4 50x3mm bright lost head nails, (at 360 to the kilo they weigh 2.7 grams) that's a moment of 277.77 gram mm (25 mm * 11.111gr).
The next bit is to fit the hardware to the axle (brake disc, pump pulley,sprocket carrier and see what figures I get then.
Is it useful? Well if you are a newbie and don't know how free your rear axle should be, then this is a starting point. For regular setups it has to be better than spinning the axle and counting till it stops and it can detect misalignments after an incident or simply after track use very, very sensitively.
And it is almost free!
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How free is your axle? by 'SimonS' << You are here!
