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More on early crownwheel bearing degradation due to excess shim thickness:
The history of this FD is unkown, purchased by a forum member off eBay. There was oil leaking at the hub seal but no other indications of FD failure.
Findings:
Existing shim was 0.8mm (of all the drives I've rebuilt, I've removed many 0.7, 0.8m and even the occasional 1.0mm shim. I've never had my measurements call for more than a 0.7mm shim.)
In this case, the new bearing called for 0.50mm shim thickness. That suggests that this FD had 0.3mm excess preload.
The original bearing seemed fine, but past experience told me to cut it open. Sure enough, wear of the outer race groove was clearly evident. I used a pencil to drag the pencil lead across the edge of the groove in a couple of different places to show how the groove is worn to a sharp edge in some areas, but much smoother in other areas. The sharp edged area shaves the pencil lead, the smoother area just leaves a normal pencil tracing across the edge of the groove.
I speculate that this wallowing out of the bearing race results in just enough axial runout of the wheel to cause a weeping of lube at the seal, but otherwise is unnoticed. The bearing turns smoothly and there are no shiney flakes of metal on the drain plug. I suspect that there may have been increasing grey fuzz on the drain plug but that history is not available to me.
The history of this FD is unkown, purchased by a forum member off eBay. There was oil leaking at the hub seal but no other indications of FD failure.
Findings:
Existing shim was 0.8mm (of all the drives I've rebuilt, I've removed many 0.7, 0.8m and even the occasional 1.0mm shim. I've never had my measurements call for more than a 0.7mm shim.)
In this case, the new bearing called for 0.50mm shim thickness. That suggests that this FD had 0.3mm excess preload.
The original bearing seemed fine, but past experience told me to cut it open. Sure enough, wear of the outer race groove was clearly evident. I used a pencil to drag the pencil lead across the edge of the groove in a couple of different places to show how the groove is worn to a sharp edge in some areas, but much smoother in other areas. The sharp edged area shaves the pencil lead, the smoother area just leaves a normal pencil tracing across the edge of the groove.
I speculate that this wallowing out of the bearing race results in just enough axial runout of the wheel to cause a weeping of lube at the seal, but otherwise is unnoticed. The bearing turns smoothly and there are no shiney flakes of metal on the drain plug. I suspect that there may have been increasing grey fuzz on the drain plug but that history is not available to me.
