Your axle isn't perfectly smooth or round! You can be almost CERTAIN that the holes through the bearings are PERFECTLY 'round' so it MUST be the axle! It wil have burrs, dents, rust or even be BENT. You can clear come of these simply by using Emeray paper/cloth. You axle will be a complete pig's ear if you need to hammer the bearing into place.
By the way... the 'hangers' are the bits welded to the chassis. The bearing is the bit within the 'carrier' or 'cassette' which bolt TO the hangers.
I wrote this ages ago: it will only help if your axle IS in good condition:-
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**** AXLE MOUNTING FOR THE BEWILDERED ****
This is not THE definitive method; it's just MY method!
All changes have implications. However, I would argue that the smooth running of the axle is minor compared to the many other changes you should make. If you’ve done all the other changes correctly, continue by improving your axle mounting technique.
The axle has to fit in the chassis with EXTREME accuracy; kart manufactures do not build chassis very accurately AT ALL! That’s the reason for the oversized holes in the axle hangers, so that we can adjust the axle into the best position.
Ignoring the fact that the axle MUST be
be straight
be parallel (and perpendicular) to other parts of the chassis
have good bearings;
..the following procedure has served me well over thousands of years!
1) With axle out of the chassis, clean (with emery cloth) the axle and then oil it. New axles will have ‘burrs’ along the length and old axles will have rust, dents and ridges.
2) Loosely construct the axle in the chassis with NO grub screws fitted and all the bearing bolts loose
3) Bring all the bearing bolts to ‘finger tight’ and check the axle still spins freely AND moves WITHIN the bearings along the line of the axle (left and right). This ensures that the axle is STARTING in the right place.
4) Now tighten each bearing bolt by a small amount (1, 2 or 3 ‘flats’, depending on your taste and time available) in a ‘patterned’ manner (eg, [3 bearing axle] top left, bottom right, top centre, top right, bottom left, bottom centre)
5) Check that the axle still rotates perfectly AND STILL SLIDES FREELY along the axle length (left and right)
6) Continue until all the bearing bolts are tight. If the axle ‘tightens’ at any stage of the bolt tightening phase, loosen each bolt by the required amount, and try again.
7) Check that the axle protrudes the same amount from the right and the left hands sides of the kart.
8) Now align the bearing collars (places where we insert the grub screws) so that the grub screw holes are aligned with each other ALONG the axle. The reason for this is that the axle must have some ‘float’ within the bearing to allow you to move it through the bearing in the first place, so, when you finally tighten the grub screws, you will move the axle in the same direction within each of the bearings. If the holes are out of alignment, you will accidentally be moving the axle in different directions (‘forward and backward’ or ‘up and down’) within each bearing and thus it will no longer be able to spin as freely.
9) Lightly tighten all the grub screws so that they will mark their position into the axle. I repeatedly tighten and loosen each one so it makes a good mark. Now (with a felt pen) mark the axle alongside each grub screw so that you can easily find your ‘new’ marks when we move the axle in the next phase. BE CERTAIN that you have not moved the axle AT ALL along the axle line (left or right) during this phase
10) Now loosen all the grub screws and move the axle, left or right, within the bearings so that the grub screw marks can be seen ‘outside’ the bearings. 'Dot' the ABSOLUTE centre of the grub screw marks with a dot punch (if you are thinking of using a nail or screw driver at this stage, just give up and sell the kart!) and very lightly ‘dimple’ the axle with a drill wide enough to let the nose of the grub screw descend into it. DO NOT MAKE THIS TOO DEEP! Those with 50mm axles be particularly careful!
11) Now re-align the axle left and right so that the holes line up with the dimples. This is where the felt tip mark will save hours!
12) Tighten the grub screws in the sort of order given above CHECKING THE AXLES SPIN FOR EACH GRUB SCREW!
13) That’s it!
Three bearing axles are more difficult as there is more to go wrong! You can argue that, ‘if 4 grub screws hold an axle in a 2 bearing chassis, why do I need 6 in a 3 bearing axle?’. Don’t ask me! I have (on dire occasions) omitted the dimples from the centre bearing on a 3 bearing chassis. I have also REMOVED the centre bearing grub screws altogether as that bearing is mainly used for longitudinal and vertical support (‘front to back’ and ‘up and down’ support) [as the disk is usually near this bearing] and the outer bearings can carry the horizontal (‘left and right’) retention. However, if you can make all three fit perfectly, DO IT!
Ian
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