I decided to look a little closer at the spherical bearing and front suspension today. I had an odd incident with one of the shock absorbers too...
The front suspension system relies on the spherical bearing to provide a transmission path for all the suspension forces into the front shock in its axial plane, and all the braking forces in the bikes frame in its radial plane, all whilst maintaining enough movement to allow steering to take place, and the suspension to move. That's a huge amount to ask from one little bearing...
The bearing lives in a machined recess in the lower wishbone, the recess is shown here with the bike upside down. Note the flange against which the bearing rests, and through which the suspension forces are transmitted;
The bearing that lives in there should be a plain spherical bearing type PBA10, that looks like this;
What I found in my bike though, was a tiny bit different...
This is an odd bearing indeed. Its a compound bearing, one inside the other. The two parts on the extreme left and right are the parts that Whyte provide to connect the fork to the inner element of the spherical bearing. The bolt goes through the middle and clamps it all together. In the middle is the spherical plain bearing, as expected, but with a far larger centre bore. The pieces either side of that are inner race halves of a normal angular contact single row ball bearing. The balls should live between the groove that these parts make when joined together, and a matching groove that lives inside the spherical part of the main bearing... So what we have is a high speed - low load ball bearing sat in the middle of a low speed - high load bearing.
Yep, I'm scratching my head too... The high speed capability isn't required. Possible reasons for fitting it would be to reduce friction when steering, but it comes at the expense of an even more fragile bearing that fails in an even more spectacular manner than the type I was expecting to find. There were a number of balls I didn't find in there, so at least a few have escaped. The amount of clearance the failure of this as yet unknown bearing type generates when it fails is spectacular, the bike would be utterly unrideable.
So what sort of bearing is it? According the the dust seals I salvaged from the greasy mess inside the bearing cover boot, its a;
6800RSA From PEEL in China. Except it isn't. The 6800series bearing in peels catalog looks rather different to this one.
Un petit mystery, n'est-ce pas?
Whilst I had the suspension in bits I took a look at the other bearings as well. The upper wishbone, which is pretty much kept out if the filth, spray, mud and muck, was buttery smooth in operation. No issues there at all. The 2 Bearings in the lower wishbone have had a harder life though, as they are very notchy, feeling like they are full of sand...
The last thing I did, since everything was in bits anyway, was pull the shocks so I could give the air cans a clean. Its a simple task, that I've done dozens of times before without issue. The PRST-4 is fitted with two identical Fox Float R shocks. The rear one was fine. Vent the air, cycle the shock, vent the air again, unscrew air can, clean out filth. Easy...
The front shock was much the same. Vent, cycle, vent, unscrew. The can came away easy enough, and then the bastard
exploded... :shock:
After the ringing in my ears had subsided, I had ended up with a perplexed expression, and my face, shirt, and my patio doors covered, and I do mean
covered in shock oil... I never realised that there was so much oil in that tiny little damper. It would appear that the damper rod has sheared away from the piston and my maintenance was just the excuse it was looking for to make a break for freedom.
Take from that whatever safety tips you wish...
