Any history on this part, there is nothing on google!!

You won’t really find Aussie part numbers on google

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I'll check that part number tomorrow.

Is it stamped on the part itself?

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ex-NSW Police 1970 MK II Cooper S
VMCI #43

That is correct.

At 64 teeth, Australian made, my bet would be Morris Mini Minor (850), Mini Deluxe or Mini K. (17/64T, 3.765:1)
John Smidt would know...

Edit
Could also be Morris 1100. Or (maybe) Moke?
15/64T, 4.26:1

Edit 2
Measure the diameter accurately and I can confirm which ratio it's for.

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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 have the engineering drawing for this part which is a modified version of the UK crown wheel part #22A303. It was introduced into production in August 1964.

I can't find any reference in Mini, Moke or Morris 1100 parts books, price lists or other technical documents to either the UK or Australian part number, which is very abnormal. It doesn't ring a bell with John Smidt either.

So at the moment it's a mystery.

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ex-NSW Police 1970 MK II Cooper S
VMCI #43

Diameter is 165mm or 6.5".

that's a bit odd... might make a good door stop?

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did I tell you that I won a trophy?

"drmini" Any news for me!

Could it be Austin 1800?

My 3.765 850 crown wheel measured 6.5", has
17/64 teeth.
If it was out of a Morris 1100 15/64T it would be bigger diameter.

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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 have a Morris 1100 15/64 diff but can’t access right now, will be swapping out for 3.4 shortly so can check size and if it has a part # then (couple of weeks)

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1966 Mini Deluxe - “Gabby” 34 years under restoration and counting...
1970 MGBGT
1959 MGA

So the 15/64 crown wheel out of the morris 1100 gbox i have is a 22G370. So still not sure what you have is out of

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1966 Mini Deluxe - “Gabby” 34 years under restoration and counting...
1970 MGBGT
1959 MGA

All of the crown wheels listed in Pub1011m all start with 22a or 22g, there isn't actually a 15/64. Perhaps they were a special order? You'd want pretty big wheels and ear muffs for anything over 80

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1966 Mini Deluxe - “Gabby” 34 years under restoration and counting...
1970 MGBGT
1959 MGA

BMC used a 15/64 ratio in some products and 15/62 in others. With 12" (M1100) and 13" (Moke) wheels.
Both fit a Mini box but yeah they're a bit short gearing.

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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.