Can the primary gear on the right be used in a 1275 Cooper S engine if the bush arrowed on the right is removed?

If you mill it out to take a 1275 size bush you can.

Edit: yours both look to be small bore ones just the left one missing the bearing? The 1275 ones are noticeably thinner on the inside face and have the step

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just to be really clear... don't even THINK about running it without a bush!

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did I tell you that I won a trophy?

I have seen what happens.. it wears the shoulder on the 1275 crank down, and the teeth get damaged. The crank then needs the shoulder ground down to 1.500" and a 998/1098 gear fitted instead. Yes it works.

A friend and I had some 998 primary gears bored out last year, to fit a 1275 floating front bush. The gears are hard and tough to machine. It cost me $75 per gear for the machining.

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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.

Does your Cooper S primary gear in picture on the left have a bush installed?
So it appears my Cooper S primary gear has no non floating bush. I wonder why!

Both my photos have a 1275 gear on the left with a bush installed. If you look at the shiny face in the second photo you can tell they are different.

Both yours appear from the photos to be small bore ones. Try measuring the inner diameter excluding the bush and see what both yours are. I can measure one of each when I'm home this afternoon (unless you get the answer sooner)

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Pretty sure the one on the right is Cooper S without a bush and the one on the left is not from the measurements. So now I need a bush I guess. Are they easy to fit?

Buy the floating 1275 front bush, it slides straight in. I have used a few in my cars.
But, if it is sticking out the front at all, get it shortened carefully, but don't squash it out of shape!
The original fixed bushes have to be bored to size after fitting. PITA to fit compared to floating one.

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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.

Is this the bush I should fit? http://minisport.com.au/mini-1275-fully ... -gear-bush

Yes.

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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.

Has anyone had experience using 1275 pre A+ primary gear floating bush and if so please put up your remarks.

I'm using one too, it's fine

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did I tell you that I won a trophy?

I have built 4 motors with them, no problems except as said above when fitting, the bush is often slightly too long. It can't stick out at all, or the gear won't run against the bronze thrust washer on the crank.

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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.