So, wanting to build a 1071cc based cooper s motor, and will be wanting to modify a 1275 block to suit the crank as i haven't been able to find a 1071 s block anywhere! (if you have one under your bed, pm me now!! )

How uch do I need to deck the block (in general, will do final measurements etc with it all assembled) to go from 1275 to 1071cc?

Thanks,

Matt

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68 Deluxe.... it's shiny..... I like shiny!!

I would do a trial assembly to check the piston to deck height and go from there.

Will do that, but before I get the block, i need to know how much damage can there be to the deck before it is no good to me. So anyone have a rough idea?

Would it be the same as the difference in the stroke or is it more complicated?

Did the 1071 and 1275 use the same pistons?

Cheers

matt

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68 Deluxe.... it's shiny..... I like shiny!!

The amount you need to remove is the difference in stroke between a 1275 and 1071 crank about 1/4 of an inch.
But you can only use a cooper s block, as a later 1275 block has not got enough deck thickness and will become too soft and head gaskets will fail.
If you have a south african 1071 crank the piston were different than 1275 ones the compression height is bigger to suit. I built a 1071 engine and had new pistons made to suit but I think JP pisons make some to suit now. Otherwise you need longer rods to suit which is probably better as the compression height is quite large and this tends to rock the piston in the bore.

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4efte powered Clubman
supercharged 998 race car

The difference in block height is the stroke difference /2
ie the crank throw difference.
I make it 6.53mm. (81.33-68.26)/2
This assumes standard 1275/1071 Cooper S rods and pistons.

It was the 970S that had a 1/8" longer rod.

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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.

So standard S pistons are OK? will be going flat top to bring the compression up.

Excellent, and thanks for the calculations. With a deck thickness of 625thou (5/8") as opposed to 450thou(1100s) the S block is definately the one to find for the job!! Besides I have a cooper s head AEG163, cooper s rods, and the 1071 cooper s EN40B crank, a genuine S block just feels right!


Matt


Thanks Guys

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68 Deluxe.... it's shiny..... I like shiny!!