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Gearbox mainshaft - is it bent?

Posted by ChazzyB <iframe src='https://members5.boardhost.com/classicbikemart/info/user=ChazzyB' width='330' height='300' border=0 style='border:none;'> on February 4, 2025, 3:17 pm

I have a gearbox mainshaft that may be bent. How can I check that? I don't have a lathe handy to chuck it in (did you see what I did there?). But I do have a dial gauge, so that's a start. It wobbles when installed in the gearbox. But that's in neutral when I hold the shaft to stop it turning but turn the rear wheel so the main driving/output gear through which it passes, turns.

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Re: Gearbox mainshaft - is it bent?

Posted by Nigel B <iframe src='https://members5.boardhost.com/classicbikemart/info/user=Nigel+B' width='330' height='300' border=0 style='border:none;'> on February 4, 2025, 3:28 pm, in reply to "Gearbox mainshaft - is it bent?"

Do you have a couple of vee blocks ?

Sit the shaft bearing locations in the vee blocks & rotate the shaft from there. Easier if vee blocks & a clock stand can be set on a surface plate, but lashed up on a bench would probably show up if the shaft was appreciably bent.

Nigel B.

Re: Gearbox mainshaft - is it bent?

Posted by Andy C <iframe src='https://members5.boardhost.com/classicbikemart/info/user=Andy+C' width='330' height='300' border=0 style='border:none;'> on February 4, 2025, 3:31 pm, in reply to "Gearbox mainshaft - is it bent?"

Got any V blocks ?

If so lay it in the blocks, clock it with your dial gauge, note the measurement, turn it 1/4 turn and keep repeating.

If you can take all the gears off the shaft roll it over a flat surface such a piece of plate glass - you will see if it is bent.

Put it in the chuck of your pillar drill if you have one, clock it while turning by hand. Probably too big for the chuck though !

All a bit basic but might give you an idea.

No doubt someone will come up with other ideas.

Who needs a signature anyway......

Re: Gearbox mainshaft - is it bent?

Posted by MadMike <iframe src='https://members5.boardhost.com/classicbikemart/info/user=MadMike' width='330' height='300' border=0 style='border:none;'> on February 4, 2025, 4:12 pm, in reply to "Gearbox mainshaft - is it bent?"

A couple of things from me on this one.
1. Do not try putting iy in a chuck on either a pillar drill or in a lathe. A 3 jaw chuck is merely a holding device and is nowhere near accurate enough for this job.
2. If you have friend with a lathe get him to mount the shaft between centres and then simply rotate it by hand and use your DTI to check the run out.
3. If you cannot locate a lathe then get a piece of 6mm (or thicker) float glass from a local glass merchant. the thicker the better. Alternatively borrow a surface plate if you have a friend with one. them locate the shaft on a pair of Vee blocks, remembering that both blocks must locate on identical diameters on the shaft or you will not be able to measure anything. Then again use a DTI to check the run out.

so far so good, and now things to consider.
1. The diameters will most certainly have been sized by grinding after hardening.
2. the toleences will be very tight, probably in the low 10 thousandths of an inch...NOT ten thou (0.0100, but one ten thousandth of an inch (0.0001). So it begs the question about how you will get the shaft straightened to allow the sizes to match.
3. The shaft will have been hardened and tempered before final sizing on a grinder. there is a risk that pressing the shaft to straighten it might cause it to break.
4. Check the runout as described, and I suspect that it will still be true, and then consider that the movement that you have detected mat be due to bushes wearing, or after very high mileage the shaft may have worn.

I don't know where you are located Chaz but if you could get the shaft to me I will happily check it both for straightness and size/wear. I am in Leicestershire.

Other opinions may be available but this one is always correct.

Re: Gearbox mainshaft - is it bent?

Posted by ChazzyB <iframe src='https://members5.boardhost.com/classicbikemart/info/user=ChazzyB' width='330' height='300' border=0 style='border:none;'> on February 4, 2025, 4:28 pm, in reply to "Re: Gearbox mainshaft - is it bent?"

East Suffolk, me, Mike.About 150 miles, at a guess.

The bit that continues to perplex me is why I see the shaft wobble when it's not turning, but the top gear bush through which it runs, is.

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Re: Gearbox mainshaft - is it bent?

Posted by MadMike <iframe src='https://members5.boardhost.com/classicbikemart/info/user=MadMike' width='330' height='300' border=0 style='border:none;'> on February 4, 2025, 4:41 pm, in reply to "Re: Gearbox mainshaft - is it bent?"

We could meet halfway perhaps Or perhaps DBD Brian could help. I shall ask him for you.

Other opinions may be available but this one is always correct.

Re: Gearbox mainshaft - is it bent?

Posted by dommie90 <iframe src='https://members5.boardhost.com/classicbikemart/info/user=dommie90' width='330' height='300' border=0 style='border:none;'> on February 4, 2025, 5:24 pm, in reply to "Gearbox mainshaft - is it bent?"

wave a Rainbow flag in front of it and watch its reaction, if it wobbles, its bent.

Re: Gearbox mainshaft - is it bent?

Posted by ChazzyB <iframe src='https://members5.boardhost.com/classicbikemart/info/user=ChazzyB' width='330' height='300' border=0 style='border:none;'> on February 4, 2025, 6:56 pm, in reply to "Re: Gearbox mainshaft - is it bent?"

You must have missed the re-education programmes...

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Re: Gearbox mainshaft - is it bent?

Posted by NVNL <iframe src='https://members5.boardhost.com/classicbikemart/info/user=NVNL' width='330' height='300' border=0 style='border:none;'> on February 4, 2025, 7:02 pm, in reply to "Gearbox mainshaft - is it bent?"

Far too technical for me, Carlos, I wish you well with the work.

Very happy to have succeeded in "logging on" after so many failed attempts over so many months.

R

R

Unlicensed chainsaw wielder

http://thebridgeclubfive.blogspot.co.uk/?view=flipcard

Re: Gearbox mainshaft - is it bent?

Posted by ChazzyB <iframe src='https://members5.boardhost.com/classicbikemart/info/user=ChazzyB' width='330' height='300' border=0 style='border:none;'> on February 4, 2025, 7:14 pm, in reply to "Re: Gearbox mainshaft - is it bent?"

I'm sure all will agree that it's relief to find you extant, Richard.

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Re: Gearbox mainshaft - is it bent?

Posted by DBDBrian <iframe src='https://members5.boardhost.com/classicbikemart/info/user=DBDBrian' width='330' height='300' border=0 style='border:none;'> on February 4, 2025, 8:10 pm, in reply to "Re: Gearbox mainshaft - is it bent?"

Hi Chazzy, just spoken to the MAD one. I am quite happy to be of help if I can. I live four miles south of Norwich.
I must admit I don't have a rainbow flag, but I have quite likely got something a little more accurate.
Send me a PM if you wish to proceed.

Brian
Made In England

Re: Gearbox mainshaft - is it bent?

Posted by ChazzyB <iframe src='https://members5.boardhost.com/classicbikemart/info/user=ChazzyB' width='330' height='300' border=0 style='border:none;'> on February 5, 2025, 8:22 pm, in reply to "Re: Gearbox mainshaft - is it bent?"

Crikey, I'm all of a fluster. Wow!

Let me get the merlot* out of my system (*other grape varieties may have been used) and I'll reply. ;-)

We can't be that far apart.

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Re: Gearbox mainshaft - is it bent?

Posted by ChazzyB <iframe src='https://members5.boardhost.com/classicbikemart/info/user=ChazzyB' width='330' height='300' border=0 style='border:none;'> on February 6, 2025, 5:40 pm, in reply to "Re: Gearbox mainshaft - is it bent?"

PM'd you, Brian. Thanks.

And thank you Mr Mad.

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Re: Gearbox mainshaft - is it bent?

Posted by Andy C <iframe src='https://members5.boardhost.com/classicbikemart/info/user=Andy+C' width='330' height='300' border=0 style='border:none;'> on February 4, 2025, 8:36 pm, in reply to "Re: Gearbox mainshaft - is it bent?"

Good Lord, what an unexpected surprise. Good to know you are still alive and kicking, or that at least someone knows your username and password

Who needs a signature anyway......

Re: Gearbox mainshaft - is it bent?

Posted by JERRY <iframe src='https://members5.boardhost.com/classicbikemart/info/user=JERRY' width='330' height='300' border=0 style='border:none;'> on February 4, 2025, 10:37 pm, in reply to "Re: Gearbox mainshaft - is it bent?"

Welcome back mate.

The oldest rocker in town!

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