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« Gepost op: 15 december 2020, 02:01:41 »
Heb dit nog gevonden op een Engels forum
A common issue with pre-unit gearboxes, of all makes, is that the bronze layshaft bushes wear only at 6 o'clock position due to the 2 shafts trying to get away from each other. So the bushes only wear in a single focused spot, which is why the needle rollers were such a giant leap forward.
Now the cutting of gear teeth is a precise science so as to preclude the making of noise and prevent excessive tooth wear. There are entire textbooks on the subject that are larger than the phone book for a large city. So.... when the 2 shafts migrate apart (as is common in bronze bush gearboxes) the tooth wear rapidly accelerates. Often in older boxes you'll find the gear teeth sharp on their tips, where there should be a flat spot about 1/16 inch wide. Compare your gear teeth against new parts and you'll probably see a BIG difference in shape AND overall tooth thickness.
You've got to remember that this g/b is from a time that precedes the introduction of 90W gear oil, so even under the best circumstances gear wear will be more than a modern person would "normally" expect.
Bottom line....
• Start running 90W gear oil, if you are not now doing so
• The noise most likely is from "thinned" gear teeth which will eventually break off some day
• There is no gear noise in top gear because the gears have zero load in high gear
• The damage is already done, so just run the gears until they break (could be 10 more years) and use this time to find replacement parts
• Try to find a whole, later model "TT" gearbox that had the roller layshaft bearings fitted stock
• If you decide to replace gears, then remember that it's the set making the noise, so you'll need to replace the mated set together, that is 2nd main AND 2nd layshaft
Hope this helps! :bigt: