17 replies to this topic

[my mini rulez]

is it possible to make a 970cc cooper s engine from a 850

what other things will need to be changed??

[Guess-Works.com]

The origins of the 970 start in the 850 but Cooper put a lot of work into the block.. I believe there were some radical changes to the oil ways and also the mains, and of course being bored out to 2.78" (std 1275 bore) but because of the tappet covers that does loose some of the residual strength of the block, which is why it is not recommended to bore S blocks any more than +20 ( waits for the onslaught of profanities )

It's much easier to take a 1275 engine and short stroke it.... with a 970 you will have to remove a fair amount of metal from the top of the block to get the compression ratio up.

[Dan]

I thought the 970 came from the big bore block anyway?

The crank is a custom forging for this motor and NLA in forged form (the tool went missing years ago) but you can get much more expensive and weaker billet ones produced to order.

[miniboo]

sorry what does NLA mean? No Longer A.....

cheers

[Sprocket]

A.....vailable

[Sprocket]

Ok not intentionaly rubbing salt in any wounds that may still be healing, i would just like to clarify a few things. This is not of my mind but rather what is in print in the book 'Mini Cooper & S' authered by Nigel Edwards and published byGreenwich Editions ISBN 0-86288-180-3 used in refference along with the big yellow book

The Cooper 997 was a long stroke 848 engine(62.94 bore by 68.25mm stroke) at 62.43mm bore by 81.28mm stroke. The Cooper 998 again used the same casting as the 848 but was bored to 64.588mm by 76.2mm stroke. The Cooper 1071S was the first of the 'Big Bore' engines utilising a completely new design of block, crank and rod design, at 70.6mm bore and 68.26mm stroke. The subsequent Cooper S engine capacities saw first the 970S at 70.6mm bore and 61.91mm stroke, and lastly the 1275S at 70.6mm bore by 81.33mm stroke..


The 848 block cannot be bored to the same cylinder centers ( maybe it can bore size???) as the big bore block due to the fact that the cylinder pairs are spaced a resonable distance apart, there is a water jacket betwwen cylinders two and three, with one and two siameased as are cylinders three and four. The big bore block, all cylinders are siameased to each other and Ccoopr S blocks have been known to be bored to 74.7mm as stated by Dave Visard in the big yellow book, this being very much the limit of any big bore block and is hit and miss of success.

All that needs to be done is to remove the center core plug of an 848 block or have it sectioned and it will then become aparrent.

This is intended with respect and not to offend any one.

Hope that may clear some of the mist and is open for further discussion.

In Light and Peace

MS

[Feeble]

Why should that offend anyone..? You're just pointing out a fact!

[Oldskoolbaby]

Of all the cranks to become impossible to find, it had to be one of the best. The 970 S motor that was in my car was taken to 11000 rpm and apparently, the bottom end was pretty much stock. Id give my right arm away to have a 970S crank. If you couldnt find a suitable block, you could always resort to getting costom made Arrow rods or the like to bring the piston up to the top of the block.









EDIT:

Just spotted a 970 S motor on Ebay. Definatly going to have a flutter on that!

[Sprocket]

And there is a crank with standard journals on ebay too

http://cgi.ebay.co.u...1QQcmdZViewItem

And check the price on a half engine. Now that shows how rare it is

http://cgi.ebay.co.u...me=STRK:MEWA:IT

Production numbers just to put things in perspective

970S = 972

1071S = 4017

1275S Mk1 = aprox 14,000, Mk2 = 7000, Mk3 = 19,500

[Jammy]

I always thought the 1071 was the harder engine to find?

[Oldskoolbaby]

Just had another look at the Short motor which is on Ebay and it says that the cranks been reground +60. Its making me think twice about bidding on it.

If I get a 970 S crank on its own, fit S Rods to them, could I use a normal S block? I know it will need skimming but will it be to the point where the block isnt thick enough to cope?

[miniboo]

the block has been rebored +60 and the mains on the crank +30 and+20 big ends

[Sprocket]

Just had another look at the Short motor which is on Ebay and it says that the cranks been reground +60. Its making me think twice about bidding on it.

If I get a 970 S crank on its own, fit S Rods to them, could I use a normal S block? I know it will need skimming but will it be to the point where the block isnt thick enough to cope?

All original (id recon on the Mk1s being the ones in question) S engines were machined from the same block. The deck of the block was fairly thick and machined to suit the stroke of the crank, hence why the 970 uses slightly longer rods as the surface may not have been that thick that they needed longer rods (maybe not the only reson for going for longer rods, I know)

So, yes you can use a 1275 S ( again I recon only the earlier ones) block and machine it down enough for the 970 rods and crank to fit. Dont forget that you may well be able to gain a little more hight if you choose your piston carefully, IE tall piston compression hieght, meaning you have to machine that little but less off the block

[Oldskoolbaby]

So if I bought the crank on its own, will it be very hard to find a set of 970 S rods at the aurojumbles?

[Sprocket]

??

It'll be easier to find the rods rather than the crank. The cranks wear out and its been a good fourty years since they were new, hence why the one on ebay at the mo with standard/standard journals is a unusual