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1975 Moto Guzzi 850T restoration – gearbox strip

Posted by on May 10, 2013

Hopes that life in the sealed environment of the gearbox – away from the dirty air and oil that had done all the damage to the engine – might still be hunky dory were short-lived.

The magnetic filler plug’s spiky metallic hairdo pointed to horrors within even before I’d drained the old oil.







At some point a lone roller had escaped from the torrington-type thrust bearing, and soon all the others went scuttling off after it.






A bit of detective work soon revealed what had been the undoing of the thrust bearing.The bearing itself is in three parts – the rollers and two large precision washers, called ‘runners’. In addition, the effective length of the shaft is set by the use of a shim which should be the same inner and outer diameters as the bearing runners to the distribute the loads evenly. In this box that shim was missing and in its place was a washer of dubious origin not wide enough to support the bearing properly. The dodgy washer is on the left; the factory shim on the right.


Where had all those rollers gone? Everywhere. There was swarf in every nook and cranny, and this bearing retainer plate shows the signs of Armageddon; as bits of hardened metal were mashed by the spinning gears the shrapnel must have been sent hurtling round inside the casing.





Amazingly the damage did not extend to the bearing faces of the gears and their respective inner sleeves. All escaped harm except this one.







And as if all those bits of bearing weren’t enough to be getting on with, the speedo drive seemed to have shed it’s locating ball bearing at some point and promptly eaten it. Well, that’s my guess. There was certainly no ball to be found and the drive gears looked like they’d had a good old chomp on something hard.





And finally … the shim at the front of the shift drum was missing altogether. Shimming this drum is the key to optimising the quality of your gearchange. No wonder this one was so clunky.












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