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Block dimensions
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Author:  Kennomini [ Thu Jan 17, 2013 4:54 pm ]
Post subject:  Block dimensions
Are their any differences in the external dimensions of the different mini blocks? From memory I thought the 998/1098 blocks are slightly shorter in height than a 1275, correct?
Also A+ blocks are slightly wider due to the extra external webbing correct or is it so minimal it's not an issue?
Author:  drmini in aust [ Thu Jan 17, 2013 6:13 pm ]
Post subject:  Re: Block dimensions
Kennomini wrote:
Are their any differences in the external dimensions of the different mini blocks? From memory I thought the 998/1098 blocks are slightly shorter in height than a 1275, correct?
Also A+ blocks are slightly wider due to the extra external webbing correct or is it so minimal it's not an issue?


1275 block is about 10mm taller than all the others. Applies to A and A+.

A+ webbing made hardly any difference to width at the bottom flange. A series and A+ blocks are pretty well interchangeable. Use wot ya got.

BTW, Vizard confused some people when he implied in one of his books that 1275 blocks are longer than smallbores. They are not.
However, the oil pump recess is shallower on a 1275, so the length "from front block face to the oil pump" is longer. He just didn't explain this very clearly. :wink:
Author:  miniron [ Fri Jan 18, 2013 10:55 am ]
Post subject: 
There is a small difference in the front flange to gearbox face on 1275 blocks. The centre to centre distance of the bolt holes between front and rear faces is the same but the 1275 front flange is approx 1/8" further forward than on a small bore block. This is to provide clearance for the longer stroke on 1275 blocks. The 1275 front flange gasket is different to match the flange. Don't use a non 1275 front flange gasket on a 1275. If you do the big end will hit the gasket and you will end up with gasket material going through your oil system. I dont know if this change also applies to the shorter stroke 970 and 1071 S blocks.

Edit: A bit more info. IIRC 970 and 1071 S blocks are 1275 block castings with 1/4" machined from the top face. You can tell by the amount of material above the 4 cast lugs on each corner of an S block.
This is POSSIBLY the reason the extra front bolt torque is 25 lbft as there isnt a lot of material left to put a thread in. The standard helicoil insert helps to spread the stress on the threads. The front bolt hole also goes through to the water jacket.
Non S 1275 blocks are cast differently in this area. There is a lug cast into the water jacket at the front bolt position and if you put in the extra bolt/stud it doesn't go into the water jacket.

RonR
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