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1275 crank in 1100??
https://www.ausmini.com/forums/viewtopic.php?f=2&t=50000		 Page 1 of 2
Author:  yeehaa [ Thu Feb 05, 2009 9:14 pm ]
Post subject:  1275 crank in 1100??
Hi is it possible to put a 1275 crank into an 1100cc block??

AS a car i am looking at and am interested in the fella says he put 1275 pistons and crank into an 1100 cc motor, i know you cant stick 1275 pistons in an 1100 but wasnt sure about the crank...

Just trying to sort out the possibilities from the imposiibilities

Thankyou
Damian
Author:  drmini in aust [ Thu Feb 05, 2009 9:20 pm ]
Post subject: 
No way you can put one into an 1100 (1098) block. An 1100S block yes, because it's a 1275 already.
Main bearings in a 1098 are 1.75", a 1275 crank is 2".

Nor can you put 1275 pistons in an 1100.. there's no room.

There is only one way I know to fit a 1275 crank in a 1098 block....
Find a late 1098 Mk2A Sprite block, engine prefix 10CC, they use 2" main bearings same as a 1275. Block will bolt onto a Mini gearbox after minor mods to the rear main bearing cap.
Author:  david rosenthal [ Thu Feb 05, 2009 9:56 pm ]
Post subject: 
The only other way is to make new main caps and line bore the block/caps to 2". As for boring from 64.59mm to70.60mm forget it!!!
You have to do some tricky reboring and use shrink fit liners, even then the walls are as thin as paper and would not last. I tried and just wasted a lot of time and money.
If you want a 1275 eng just buy one!
Author:  Graeme H [ Fri Feb 06, 2009 12:55 am ]
Post subject: 
Is it a South African 1098?
They're basically a short stroke 1275, and the swap would work.
Author:  mini-dunger [ Fri Feb 06, 2009 7:59 am ]
Post subject: 
drmini in aust wrote:
No way you can put one into an 1100 (1098) block. An 1100S block yes, because it's a 1275 already.
Main bearings in a 1098 are 1.75", a 1275 crank is 2".

Nor can you put 1275 pistons in an 1100.. there's no room.

There is only one way I know to fit a 1275 crank in a 1098 block....
Find a late 1098 Mk2A Sprite block, engine prefix 10CC, they use 2" main bearings same as a 1275. Block will bolt onto a Mini gearbox after minor mods to the rear main bearing cap.



why would you tho? you would just end up with a short stroke 1100. Why not just fit a 998 crank.
Author:  drmini in aust [ Fri Feb 06, 2009 8:55 am ]
Post subject: 
mini-dunger wrote:
drmini in aust wrote:
No way you can put one into an 1100 (1098) block. An 1100S block yes, because it's a 1275 already.
Main bearings in a 1098 are 1.75", a 1275 crank is 2".

Nor can you put 1275 pistons in an 1100.. there's no room.

There is only one way I know to fit a 1275 crank in a 1098 block....
Find a late 1098 Mk2A Sprite block, engine prefix 10CC, they use 2" main bearings same as a 1275. Block will bolt onto a Mini gearbox after minor mods to the rear main bearing cap.



why would you tho? you would just end up with a short stroke 1100. Why not just fit a 998 crank.

This is true, there really is no point I agree, but yes it is possible.
:lol:
Author:  mini-dunger [ Fri Feb 06, 2009 10:43 am ]
Post subject: 
I would still like to look into offset boring and really big over bores though.
Author:  drmini in aust [ Fri Feb 06, 2009 10:51 am ]
Post subject: 
mini-dunger wrote:
I would still like to look into offset boring and really big over bores though.

I have offset bored 3 998/1098 blocks to 68.0mm, with a 1098 crank and Hillman Imp pistons it gives you about 1220cc.
That is .134" overbore. And you have to mill about .150" off the block with these short pistons.
At 68mm with offset bores you have to be careful not to hit the oilway from pump, in #4 bore.

These days it's easier to just go .100" or .120" oversize, you can get pistons from Russell Engineering or Minis Plus.
Author:  Bubbacluby [ Sat Feb 07, 2009 7:53 am ]
Post subject: 
The motor was an s/african 1100 motor that my brother was looking at, we thought they were the same as aussie ones but now we know different.

Thanks
Author:  david rosenthal [ Sat Feb 07, 2009 1:37 pm ]
Post subject: 
Bubbacluby wrote:
The motor was an s/african 1100 motor that my brother was looking at, we thought they were the same as aussie ones but now we know different.

Thanks


That's interesting. I have not been able to look at one of those engines,but many years ago I saw a small bore block [tappet covers and no extra studs] that was bored to 70mm. The bloke who owned said that it was a s/african block bored out. I assumed that it was a 970 cooper block,with a longer stroke crank fitted.
It might be worth while trying to measure the thickness of the cylinder walls. There may be a big difference to the aust 1100 blocks.
What dia were the mains on a 970 cooper eng ?
Author:  drmini in aust [ Sat Feb 07, 2009 1:44 pm ]
Post subject: 
Sth African 1098 was 1275 bore and short (70mm?) stroke.

970S has 2" mains, as do all Ss, 1275 and the Sth African 1098.
Author:  paul_ewins [ Sat Feb 07, 2009 2:01 pm ]
Post subject: 
So does it have longer rods to compensate for the short stroke? The 970 had longer rods while the 1071 was a shorter deck height, but if you can put in a 1275 crank and get it to work I can't imagine that it has a short deck.
Author:  drmini in aust [ Sat Feb 07, 2009 2:08 pm ]
Post subject: 
970S rods are 5.875 centres, all others here and UK are 5.750". Not sure about the SA motor I suspect pin height in piston may be different.
However, 1275S has a taller block than the 970S and 1071S.
Author:  mini-dunger [ Sat Feb 07, 2009 3:55 pm ]
Post subject: 
would partial resin filling of the block compensate for thin walls?
Author:  drmini in aust [ Sat Feb 07, 2009 4:08 pm ]
Post subject: 
No. :wink:
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