3rd gear noisy

[Alex kettle]

Good luck Slymo. I’m just rebuilding a spare box that I bought so will see if this suffers the same fate. Interesting to see if polishing the pinion teeth helps any.

[berger]

I built a std box last year out of loads of bits I had and there was no whine in 3rd , I was really pleased but I think I heard it coming back on the last run out in october  

[stev60]

My 51 A7 has the third gear whine, on the stand its just noticeable but of course louder under load, at least I know what gear im in. Just done up a spare box, got it off Dragonfly, had  new kickstart quad , replaced bearings and bushes,everything else looks good, would be interesting how it sounds but with the drama involved in changing boxes Ill put up with it whining. The oil I use is pennzoil 50 for motor bikes it has a high zinc content use the same in the motor, Ive noticed on the change if your light with your foot it clicks through with no noise , push a bit harder and there is a definite clunk 

[Slymo]

I've also decided to polish the mainshaft in the lathe with a stone. There is a rather uneven surface on the mainshaft which I think tends to strip out the sleeve gear bush further adding to the noisy meshing of the constant mesh gear. I tried it on a spare mainshaft ai have that has suffered minor water damage and it came up really well. What I will need to find is an undersized bush for the sleeve gear to compensate. Got to get a friends OIF Bonnie sorted first as there isn't room in the shed for such games.

[Slymo]

All done now. I have to say polishing the mainshaft with a carborundum stone is the business. Held in the lathe between two centre's and checked with a micrometer for eveness across its length.  I finished by polishing it with 1500 wet and dry. Looked like a new item on completion. As mentioned elsewhere the box is now quieter by a substantial margin.