Whine in Second Gear

1975 MKIII

About four years ago I rebuilt my gearbox. I replaced everything except the gear sets, they were all in good shape. I shimmed the lay shaft to .006". I now have about 10k on the rebuild and I am getting a whine in second gear while I accelerate and down shift. It seems quite while cruising at a steady throttle. I suspect the 2nd gear bush might be on the way out. I changed the gear box oil and found bronze material in the old fluid. It did not seem like a lot, but it was there. I re-filled with Red Line light weight (blue) shockproof and the noise was less pronounced. I know it is impossible to say what is going on without taking it apart but I was wondering if anyone has had this happen to them. I will be taking the box apart soon to see for sure. Which leads me to my second question.
On my list of things " to do" is to change my front sprocket. I want to go with a 21 instead of a 20 tooth. I have a good set of the older 2nd gears, 18/24 non-grooved that I am considering installing. I was thinking this would be a better combination than the 18/23 gears when used with a 21 tooth front sprocket. I am curious to see if anyone else has tried this? I would appreciate any input.

Thanks,
Pete

21T will strain the gearbox even further, no real problem, but you may find that will need to refurbish it more often. As for your current problem, sounds like a worn gear rather than a worn bush.

I broke a tooth off 2nd gear in a MKIII gearbox. I was told at the time that 2nd is a weak link in that particular box and probably should be replaced BEFORE it takes a dump. Be sure to replace both the driven and the drive gear.

There's a constant whine coming from my '73 850. It seems to go away when my wife isn't on the back seat. Coincidence?

A few years ago my high mileage Mk3 850 began to whine in second, after a complete rebuild it whines in third. Is it a slightly bent selector rubbing ? In any case it doesn't jump out of gear and changes easy so what the heck!

Dave

Engine failure = Oh my wallet hurts
Gearbox failure = Oh my arse hurts

If it does not sound right, work correctly, then fix it, it is a lot less painful!!

eskasteve said:

There's a constant whine coming from my '73 850. It seems to go away when my wife isn't on the back seat. Coincidence?

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:lol: I bought three monoposta rides and I think she figured out the problem :shock:

OK,
Follow up on original post.

Worn fork on 2nd gear
Worn/damaged dogs on 2nd lay (probably a result of worn fork)
Worn gear faces on 2nd lay and main
Slightly worn bush on 3rd lay

I am going to install an early 2nd gear set because I will soon be putting in a 21 tooth front sprocket. Hopefully this will keep the acceleration in second similar to what it is now, plus I have them. Save some $$$ and do what I was planning on anyway. New seals, selector fork, 3rd bush and fork spindle.

Does anyone know what the faces of the selector forks measure ? I compared the worn one to two other used ones I have but I don't know what a new one is suppose to be.

Rusty bucket said:

eskasteve said:

There's a constant whine coming from my '73 850. It seems to go away when my wife isn't on the back seat. Coincidence?[/quote

:lol: I bought three monoposta rides and I think she figured out the problem :shock:

Click to expand...

+1 I also put a single seat on and did get rid of that whine. Funny, it mysteriously appears on my Gold Wing every once in a while.

Danno said:

I broke a tooth off 2nd gear in a MKIII gearbox. I was told at the time that 2nd is a weak link in that particular box and probably should be replaced BEFORE it takes a dump. Be sure to replace both the driven and the drive gear.

Click to expand...

Click to expand...

I don't know enough to say the gear is weak, but I know that with the original gear set I would always (when riding quickly) get a tire chirp when downshifting from second to first, I think the spacing was too far apart. That probably puts an extra load on the teeth.

Thank for the input,

Pete