6 replies to this topic

[Snowberry C]

 IMG_9663.JPEG   92.24K   1 downloadsHi all, 

 

My first post here; I've been searching endlessly for the answer to this conundrum. Maybe someone here can help.

 

I have what I think is a 1275 Mini Cooper S engine (in my Austin 1300GT). I'm not happy about the condition of my primary gear so am trying to get a new / good second hand one.

 

BUT- it seems mine does not match any dimensions of any available gears. The issue is the size of the bore at the front (crankshaft) end of the gear. Mine is approx 44.5mm whereas all others (including listing for new 1275 gear on Minispares website, and the replacement bushes) all have a bore size of around 41.3mm.

 

The only clue I can find is a vague mention on the Minispares site of early 1275 Cooper S engines having a larger front bore primary gear. No-one else seems to acknowledge the existence of this odd, freak size.   

 

Anyone know anything about this? Anyone have a part number for my gear, or suggest a source? Otherwise the only other option would seem to be to replace the crankshaft and fit a 'normal' primary gear!

 

Thank you. 

 

[nicklouse]

Opps and some measurements

https://www.calverst...sh-replacement/

Edited by nicklouse, 25 August 2025 - 01:00 PM.

[ACDodd]

Easy fix, a custom bush can easily be made to suit.

Ac

[Snowberry C]

Opps and some measurements

https://www.calverst...sh-replacement/

Thank you nicklouse, but that just propagates the mystery though; the 2 front (crankshaft side) bore inside diameters he gives are large: 1.628" and small: 1.503". Mine is 1.746".

I can find no reference to anything like that size of front bore anywhere, except vaguely on the Minispares site. I'll give Calver's a call tomorrow & see if they can cast some light.    

[Snowberry C]

Easy fix, a custom bush can easily be made to suit.

Ac

Thank you AC- I've watched your YouTube postings and I'm aware you really know your stuff.

If I fit a new primary gear (22G1053- 1275 pre-A+) the front bore will be too small for my crankshaft diameter, so the new gear will need boring out (and sleeving with a suitable bush?). Is that feasible? Is it something you can do? Anyone doing that would presumably need my crankshaft too, to get the bore / bush sized precisely?

[Snowberry C]

Sorry chaps- I'm an idiot, schoolboy error. 

I was looking at the end of the crankshaft poking through the transfer case and noticed a glint of bronze.. the bush from the front bore of the primary gear was still on the end of the crankshaft!

 

It must have picked up on the crankshaft and spun inside the gear, or someone had fitted a floating bush in the past.

 

It now measures the same as a standard gear and isn't a freak / mythical larger bore gear! 

Thanks for your responses AC and nicklouse.   

[ACDodd]

It pays to understand what your actually measuring, the stock internal diameter of the 1275 type gear is typically 1.75 to 1.752”, a bush is then inserted to get this down to the diameter of the crank tail.

Gears can be bored, bushes can be made to any size, the usual issue is the cost.

Ac

Edited by ACDodd, 26 August 2025 - 07:47 AM.