Vintage Mazda Rotary RX-2, RX-3, RX-4, REPU, etc....

12B question

Old 02-13-2019, 04:09 AM
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Mia
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Default 12B question

early 12a's used twin distributors. the first rotary with a single distributor was the 12b, used in late model RX-2's and RX-3's.
after this why did mazda drop the 12b model code and go back to using the 12a model code, using a single distributor, instead of keeping the 12b for later models?
also what is the advantage of a single vs twin distributor? less parts and better timing?
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Old 02-16-2019, 05:52 AM
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Default Re: 12B question

There is no such thing as a 12b they are all stamped and called a 12A Twin distributor and single distributor.
The 12A single distributor was an improved motor with steel 3mm apex seals instead of 6mm carbon apex seals and many other changes to improve reliability and fuel consumption
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Old 02-16-2019, 06:44 AM
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Mia
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Default Re: 12B question

Originally Posted by WJMRTY View Post
There is no such thing as a 12b they are all stamped and called a 12A Twin distributor and single distributor.
The 12A single distributor was an improved motor with steel 3mm apex seals instead of 6mm carbon apex seals and many other changes to improve reliability and fuel consumption
Quick search:

"The 12B was a short lived engine that was produced for the Mazda RX-2, and the RX-3. It had increased reliability from previous series, and it introduced a single distributor. This was the beginning of the single distributor rotary engines: the earlier 12A and 10A were both twin distributor Wankels. The improved 12B was quietly introduced in 1974.Applications:
  • 19741978 Mazda RX-2
  • 19741978 Mazda RX-3"
"The Series II RX-3 came to Australia in March 1974 powered by the new 12A single distributor (12B)."

RX-2:
1146 cc Wankel 12A rotary (S122A)
1146 cc Wankel 12B rotary (CB12)

RX-3:
982 cc 10A-0866 Wankel
1146 cc 12A Wankel
1146 cc 12B Wankel

Not saying you're wrong. So I'm comparing with what I've found online with what you've said above, and guessing that the 12B was still stamped with "12A" on the rotor housings since it was just an improved version of the engine?

Last edited by Mia; 02-16-2019 at 07:55 AM.
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Old 02-17-2019, 04:18 AM
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Default Re: 12B question

Yes it was called a 12B by some people But was never called a 12B by Mazda or any Mazda dealers or marked as a 12B. Only marked and sold as a 12A
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Old 02-17-2019, 10:40 AM
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Mia
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Default Re: 12B question

Thanks.
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Old 05-18-2019, 08:52 AM
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Default Re: 12B question

Originally Posted by Mia View Post
early 12a's used twin distributors. the first rotary with a single distributor was the 12b, used in late model RX-2's and RX-3's.
after this why did mazda drop the 12b model code and go back to using the 12a model code, using a single distributor, instead of keeping the 12b for later models?
also what is the advantage of a single vs twin distributor? less parts and better timing?



To answer your question, yes there was a 12B engine built but never advertise. Reason for this is Mazda had spent thousands of dollar advertising the "12A" and felt they may lose customer or confuse them launching another "12B" motor. That's why they never went thru with the name change. In 1974 they release the 13B advertising it as a bigger motor. Hope this answer your question.
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