9 replies to this topic

[Minidarren83]

Hi there could somebody please clear up some confusion I have. I have a spi 1300 engine for my project that I am rebuilding and just assumed it was all the same 1275 and 1300 but minispares list parts for both separately so what is the difference? Is it just larger mains and big ends or is the stroke longer and are the pistons just standard 1275 items or do I need to buy special ones I was planning on a set of AE high comp +40 as my pistons have standard 1275 part number on top and I am just getting lost in it all

Please help me before I lose more hair
Darren

[racingenglishcars]

The Marina 1300 had a cast crank with larger big-end journals and larger rods, but same pistons. It also had the oil filter mounting cast directly into the block. How that transfers to the Mini 1300 I can't say.

[Artful Dodger]

A 1275 engine IS a 1300 engine! . when they were made people just rounded up the numbers to make it easier to say an make it sound faster than it is!! There is no difference in stroke, bore unless the engine has been bored out and had bigger pistons fitted.

The only difference in those engines is a series and a+ engines. The later A+ engines were fitted to metros etc and the A series to minis. There are many guides to distinguish between the two here and you will need to know the difference. Some parts do not work on both!

[Minidarren83]

Hi thanks for the response and clearing up the piston and stroke issue I understand the difference between a and a+ and that some parts are not compatable with each other but the thing that has got me confused is there seems to be a variation in the size of the mains and big end journals I understand that they can be +10 or +20 ect for reground cranks but there is two sizes listed one for 1275 a+ and one for 1300 a+ so do they refere to 1300 as late 1990+ a+ engines and 1275 for earlier a+ engines, if that's the case then I need the ones listed as 1300 for larger journal size arghh why don't they just put 1275 a+ 1990 on or before it would make it much easier lol

[Artful Dodger]

I don't think they changed the journal sizes in the STD 1275 throughout its life, from the a series to A+. All ou can get are thicker ones for when you grind te journals during a rebuild.

[MrBounce]

I fyou are ever uncertain which ones you need you could give the supplier a call - they're usually pretty helpful with this sort of thing?

[Cooperman]

The confusion may be because the original Cooper 'S' 1275 had certain differences. The 'S' crankshaft is of different material, being EN40b forged steel with 1.625" diameter big ends whilst all other 1275/1300 engines have 1.75" big-end journals

[ACDodd]

The differences lay the in fact that after '84 all A+ blocks used the turbo type bearing with the centre locating tang on the bottom half of the main bearings. Also, the nominal sizes on the pre A+ cranks are smaller at 2.0011 to 2.0005". The later being 2.0011 to 2.0017". Its small diferences like this that can make or break an engine build. There are also standard duty bearings which are made of aluminium, which are cheaper and good for a long lived engine, however they won't take the punushement of a fast road engine. These aluminium bearing also came sized to fit the original A-series sizes but in A+ fitment! somthing that just about no-one I speak to actually realises!!

The big end journal sizes as produced byt he factory ar actually too small for after market bearings. So rebuilding an engine even if the big end journals are to original factory size are actually too small for the bearings you can buy!!! You need to ensure that the crank is sized correctly for the bearings you have.

AC

Edited by ACDodd, 13 November 2012 - 11:51 PM.

[Minidarren83]

Thanks everyone cleared up all the mystery for me
Darren

[bmcecosse]

And just to add - the Marina engines certainly DO NOT have larger bearings than the other 1300 engines.......