Nsr 125 grinding noise when put in gear advice needed

[Rory123]

Last time I was out on the Nsr I changed the gear oil then drove it about 40 mins to and fromon the motorway I noticed it was low on oil when I got there so I topped it up on the way back I came up to a roundabout put it into 2nd made a loud bang then refused to go into any gear after a few days after aggressively moving the gear selector up and down with my hand I got it to go into other gears so I started it put it in gear and it made a grinding noise similar to what a car gearbox would make took the engine apart to find some slightly damaged gears (a pair of gears have a visible groove on the edge of the teeth) and selector fork and one of the trans bearings felt gritty enough, Im trying to think what was making the grinding noise though. By the way I'd say this failure was caused by a lack of lubrication, some gears look black, I'm just wondering how far I need to go to get it working properly again I'm thinking of just getting the pair of gears that got hot along with the selector fork, all the dogs and slots are perfect just wear on the actual gears I will replace the bearings as well any suggestions appreciated. I don't think it was a seal failure that caused a lack of oil I think I might not have put enough in it all seals will be replaced anyway
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womanizer

[stinkwheel]

Check the shafts on a proper (engineering standard) straight edge or spin them up with a dial guage to check for runout. If a bit of metal tried to go between the teeth, it exerts a rediculous amount of force. Happened to one of my bikes last year where a dog broke off then got between two gears, it split the gearbox case in half broke the layshaft and bent the mainshaft.

Inspect the bearing seats in the cases for signs of cracks.

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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
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