Cooper S rods and 970 S
Turbo Mini Forums

I am now in posession of a set of Cooper S rods.

I intend to buid a 970 S screamer, but the 970 used a slightly longer rod.

My question is, will it realy matter much buy using the 1275/ 1071 rods which are 1/8th inch shorter than the 970 rods and machine the extra off the block.

I have a cooper S 1275 block which will require 3/8th inch machining off to bring it down to the 970/1071 deck hight, not an issue, theres 11/16th inch thick deck so there should be enought to take another 1/8th off that again.

The pistons im picking up tomorrow are flat tops and im led to beleive have quite a high compression hight so that may reduce this last 1/8th by about a 1/16th.

So, any issues running 1275 rods in a 970.

Long shot question I know considering the 970 is rare as hens teeth.

I have milled of 7 mm on my allegro block to get the pistons up for my 1071 crank. that is working okay, but an S block is a different beast, and the answeres I got when I asked questions about milling 7 mm of a block was, its okay as long as its not an S block, or at least an S block was not ideal to use for this, as its not as stiff as the others.

also are this for the 16V? if so you cant really do this as there will be no meat left for the head studs.

Edited by miniminor63 on 27th Aug, 2006.

the 1275 s block are really taller at the head face ( 970/1071/1275 were all built on the same casting) than the 1275 gt's to a+ ones.
I would really consider the longer rod as it will help the piston to pass the tdc more smoothly

agree FAB, but as the s blocks are very often thin flange and have tappet covers, they are a bit softer to start with, I guess that may be the reason.

Edited by miniminor63 on 28th Aug, 2006.

dont worry about the head studs, i have a trick up my sleave

I had thought there may be some issues with rod angles, but will it make that much difference in reality.

Ok then, Whats the chance of bushing the little ends for fully floating pins but off setting them. Any one done this?

Presuming the Allegro block is Closed tappet chest?

Yes there are people out there skimming blocks to get the SA 1071 cranks to fit almost any non S big bore block. I was under the impression that the open tappet chest Cooper S block had the 'thickest' deck and like i said mine measured 11/16th. I need to keep the deck as thick as possible for the 16v but also want to run 970 at +30 to keep the cc in class A. 970 rods are just as rare as the cranks, you need the crank but not necisiaraly the rods?????we are talking 3.17mm difference. The deck after all the maching would be alsmost 5mm.

What is the deck thickness of an Allegro block before machining????

I'm going to measure an A + block for comparison.

Also, I sense some negative vibes

Edited by Sprocket on 27th Aug, 2006.

i like the idea, really do. Infact i want to do a similar thing depending on finances etc, already have a 970 block though.

I've done the whole bushing rods thing, but didnt offset - maybe i should have The rods/angle doesnt make much difference, fair enough if it was gonne be revved upto insane rpmw and held there for prolonged periods i can see the rods starting to make a difference, but in your application its not so important.

Offsetting the little ends/bushing the little ends for smaller pins is a whole bunch of arse if im honest. I had a real ballache getting mine done to any decent std and remember the rods maynot be straight from the start!!!! i know my minispares rods wernt! There are also very few places to get it done, MED would have done it if they wernt a bunch of tarts, but again they wouldnt have been straight, not going by the way the chap in charge said he'd have had them done!

I'll get my m8 to measure the deck on my 970 block, its still in other hands at the moment. I'll report back.

Edited by andeh on 27th Aug, 2006.

I've seen the future and tbh its Pie

isn't there a bike rod that fits and is a bit longer? I think it was covered on minimania a while back.

OK i have worked it out

using the same rod and piston but changing the stroke from 81.33 to 61.91 there is a difference in deck hight of a nats fanny under 10mm.

Also i think the rod angles are way better than the 1275 anyway. Im not quite understanding this 'helping the piston travel through TDC' business.

I have measured it again the deck thickness is 17mm so removing 9.5mm gives 7.5mm deck. An A+ block has a deck thickness of 12mm, so pretty much imossible to get the full chunk for 970, obviously the 1071 is achievable but the deck thickness is reduced to 5.5mm

Going off that information, machining 9.5mm off the cooper s block gives the same deck thickness of an A+ block machined for SA1071

Bollox, like most things, i'll just have to do it. No real reason why it souldnt work


Oh and Andeh, thanks mate

Edited by Sprocket on 27th Aug, 2006.

"Also i think the rod angles are way better than the 1275 anyway. Im not quite understanding this 'helping the piston travel through TDC' business. "

Only thing I can think of is if the rods are shorter,when the piston is mid stroke the rod will be at a lesser angle to the horizontal

Metro turbo weekend driver,Mini turbo in the making again!

yes but due to the difference in crank throw of 9.5mm. Also the piston will sit further up the bore at BDC.

Edited by Sprocket on 27th Aug, 2006.

sorry, not my meaning to sound negative! really not. About the allegro block, this is without tappet holes yes, and is thick flange, which most of the s blocks arent. My information is from Mark forster, and Rich at MS north, which are picking up 1071 cranks from SA from time to time. I have also talked about Jai about it. but as you say, you still have a fairly good deck height. A+ blocks are generally not used for this as they are very thin. I think (but dont quote me on it) my deck is about 7 mm thick now, so it must have been around 14 mm then.

If you feel like, please share your headstud trick as I would really like to use my SA crank in my 16V engine

Edited by miniminor63 on 28th Aug, 2006.

no worries MM63.

As for trade secrets, I may let it out of the bag when K1100mini forum is up and running

I can't wait for the forum to start!!!! Been lapping my valves in today and trying to get the cylinder head finished so i can get the dry build sorted.

The 970 rod is basically the std 1275 cooper(S) rod , but with the little end hole was not machined in the same spot as the 1275 rod, it was simply drilled higher on the rod, therfore effecting the longer distance between big end eye & little end eye.

I can`t see a problem machining a 1275 block down enough to allow the short stroke 1071SA crank, that`s what i`ve done anyways. But i`m just using the Bimmer head bolts & there`s still plenty of meat left, just that i`m not using the A+ type block tho. I`n not a big fan of A+ blocks at all.

When`s the Bimmer Twinky forum happening sprocket-myster??? Way Kewl!!! Can i be like one of the founding fathers? so to speak,,,can i be on the front page? can i? can I? huh??? Huh???

Edited by MadMatt on 30th Aug, 2006.

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