Hello All,
I am currently rebuilding my gearbox and have come to the point of deciding what needs replacing. So my question is how much wear in the gears is too much wear?
This also goes for the selector forks, how much is permissible?

Cheers,
Alex

It's hard to explain this in print-... but this is a start.

Selector forks had about .010-.015" clearance when new.
The bit on the gears that wears is the dog teeth, if they are rounded off find better ones. New, they have a sharp edge on the front.
Check the synchro hub outer teeth too, same deal.
The 3 springs inside each of the synchro hubs get soft with age, this prevents good synchro action even if you fit new baulk rings- so spend $30 and change them.
Replace baulk rings if less than .020" gap to the dog teeth on a gear.
Inspect the mainshaft nose for wear and pitting, if worn get a new one or PM me for a possible exchange reconditioned one.
The layshafts wear, it's rare to find one worth re-using, so replace.
Replace all the bearings in the box, including the idler gear ones, to do a proper overhaul- (note the thin needle ones inside 1st, 2nd and 3rd gear hardly wear and are usually OK to keep unless corroded).

Check the 1st motion shaft circlip for wear, if only worn on 1 side turn it over, if on both replace it.
Diff bearings are often OK to re-use, they are big and run slow so don't wear much.
Check the diff pin for wear, if worn more than a couple of thou fit a new one. Fit new planet gears too, if you can find any.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

I agree with what the good "Doc" has said but I am not impressed with the diff pins that are available and would reccommend fitting a cross/4 pin diff especially if you like to get a "little" enthusiastic when driving. The reason when under load it is spread across 4 pinion gears to the output shafts and doesnt have the wear on the "diff pins".

Anyways thats my 5cents worth

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http://www.youtube.com/watch?v=nDMkVq1jRGU

re the layshafts, there were some soft ones about recently from UK that were so soft you could file them.
IMO this is not a layshaft, it is an expensive drift.
I saw one of these turn to scrap in under 1000 KM.

To run needles directly on a shaft it must be at least RC61 hardness.
Ask you supplier how hard they are, or try to file the corner on the small end.
If the file makes any impression, they are junk.

I have found the Oz made ones from Heritage MG to be good.

_________________
DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Are you going to have it built in time for the mini muster?

Check the integrity of your linkages and gearshift while you are at it

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"Show me the Mini!"

This was the mistake I made the 1st time around which meant I had to pull the gearbox apart again almost straight away.Not impressed over some relatively cheap parts.

I also should have changed the 1st/2nd selector fork but the part got lost in the post for a couple of months and I lost patience waiting.At least its still going although a touch sloppy.

It was an interesting learning experience.I doubt I got everything right but its still going a few years latter.

Also check the laygear float - 2-6 thou is the range - lower the better. You may have to search a bit for a thicker washer to adjust. There are some NOS about in the right places

_________________
David L


My greatest fear in life is that when I die my wife will sell my Mini and tools for the price I told her I paid for them!

Could you put a shim behind the washer if you could not get a thiker washer ?

Yes you can, the thrust washer is keyed, it can't turn anyway, so the shim will be static.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Ok, I did a few quick measurements,
I have 9 thou on the lay gear so I will have to get either a shim or some new washers I guess, should the washers be equal each side or doesn't it matter much?
And I measured 51 thou on the 1st and 2nd slector fork!
I couldn't get at the 3rd and 4th selector fork yet but I can guess that will need replacing as well.
Dog teeth on the gears are rounded, it's a 3 synchro box and all three are worn so I guess I will need new ones... Can you get these new?

And also another question, were abouts do I measure the gap for the baulk rings? it looks like a lot more than 20thou to the dog teeth on the gear? Does this mean they are good?
Are there any special things to note about the 3 synchro boxes?

Only one is adjustable - the other is fixed In the 3 synchro box the large one comes in different thicknesses the small is fixed. In the 4 synchro box it is the other way round

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David L


My greatest fear in life is that when I die my wife will sell my Mini and tools for the price I told her I paid for them!

Unless it's for period correctness I wouldn't bother with 3 synchro boxes now. 4 synchro are stronger and parts are easier to get. Ratios are better spaced than all the 3 synchro ones too (except Mk1 S).
I doubt new gears (except cluster) are available for most old 3 synchro ones now.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Oh well, I have two 3 synchro boxes, no 4 synchro boxes and I have already started on this fella so I may as well finish it. Its only for an 850 anyway...

Can anyone tell me how to get the baulk ring gap to assess the wear? A picture might be best

I couted up the ratios and they seem to be early 850 so maybe not the best...
You have one of these boxes don't you wombat? Can you tell me what the ratios are like to drive with?

My 3 synchro was stuffed and needed new first gear and I had got an overhaul kit for a 4 synchro by mistake - balancing up the differences it was cheaper to get a s/h 4 synchro box and chuck the kit into it instead.

I have another 3 synchro box from a Cooper MK1 but the laygear and 2nd gear are stuffed having thrown a tooth. When and if I need to I'll spend a couple of hundred and get new gears and use it on something or do a 'quick and easy' with some second hand gears if I can get them and sell it on eBay

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David L


My greatest fear in life is that when I die my wife will sell my Mini and tools for the price I told her I paid for them!