970 engine using 1275 rods

General Chat with an emphasis on BMC Minis & Other iconic cars of the 1960's. Includes information on MK1 Action days.
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970 engine using 1275 rods

Post by minimad »

Does anyone have any experience of building a 970 S engine but using the shorter 1275 S rods ?
251 ENG
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Re: 970 engine using 1275 rods

Post by 251 ENG »

We had one to put right that belonged to someone on this forum.

It had be rebuilt by a very well know A series specialist previously.

Think is was about 7 / 1 compression ratio from memory.

You can machine the block down but then its next to useless for anything else .

Best just to get some 970 rods
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Re: 970 engine using 1275 rods

Post by mk1 »

Or if you can't get any 970 S rods, order some custom ones of the correct length.

This is surprisingly inexpensive nowadays.
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Re: 970 engine using 1275 rods

Post by Gray »

That was my engine that Simon and Rod corrected for me and it was so bad with no power at all so don't bother, once SMMC put the correct rods in it and worked their magic it was brilliant (for a 970!) Graeme
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Re: 970 engine using 1275 rods

Post by kit of bits »

I bought a 970 engine with 1275 rods I didn’t know you could dec a block that far it was a complete boat anchor, well a part from the speedwell 163 head.. 😁
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Re: 970 engine using 1275 rods

Post by Meister-Mini »

Original 970 rods are same cast and number (AEG177) than early 1275 or 1070 but machined differently.
Only on spare parts the number was sanded out and stamped new with AEG309
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Re: 970 engine using 1275 rods

Post by Terrapin-52 »

HI minimad

I have just picked up a "S" block and it has been bored, I hope it has not had anything plained of the top, I have droped in the 970 crank and the 970 rod/piston in 1 bore, with 1 of the original rod's/piston in the next cylinder, then took some sizes for you

the block is 225.5mm from top to bottom, don't know if that is Std?

970 crank in the block, 61.01mm stroke

970 rod and ? piston fitted (now I do not know at this stage if the piston has been decked to the original 1300 block it came out off, as that block had 12.5mm of the top compared to a Std 1300 block I have hear) and is 4.65mm down from the top of the block

original rod/piston (poss' 1275) in the bore next and it is 10.50mm down the block

with the 1275 having a stroke of 81.3mm and the 970 at 61.01mm, with that it look like the block is around Std hight

hope this might help and maybe some one can correct my findings

regards mike
1982 mini City
Terrapin chassis No'52, with A series engine/box
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