South African 1098 engine

[DomMINIque]

Considering that all mini literature talks about the 1098 in terms of the UK version, I thought we could create a 1098 thread purely based on the technical info and possible mods that can be effectively done to the South African version of the A series 1098.

I barely have enough knowledge to make myself dangerous so if some of the resident experts please contribute it would be much appreciated. 

What I know:

Engine number prefix 10H - 1098cc


Block is the same as the 1275, with the same bore.

The SA 1100 has a shorter stroke to the 1275 (not sure what it is exactly)

Some other things that could be added:

• What standard SU carb the 1098 came out with
  
• Is their any potential with the SA 1098
  
• Performance upgrades to the 1098 in terms of ease and cost
  
• At what point is it time to move to a 1275
  
• Other tell tale signs that you have 1098 parts (Piston differences, conrods, anything else)
  
• The 1098 vs 1275 and which is better for your objective (Full race car vs daily driver)
  

[theMINIguy]

Stroke: 69,85 mm
Bore: 70,64 mm
Compression ratio: 8:1

[GTSPhil]

Stroke: 69,85 mm
Bore: 70,64 mm
Compression ratio: 8:1

The SA 1098 came with SU HS4 carb as standard.

Crank part number is 12G2827.
Pistons is a major problem I have been informed that the company that made them for Leyland stopped making them in 1983.  The UK 1098 piston is different from the SA one.  Either get a New Old Stock set if you can or second hand set will have to do.
Just to show difference 1275 piston on the left, 1098 on the right.  1098 Pistons come in 10, 20, 30, 40 and 60 thou oversize vs 1275 at 20, 40 and 60 as the standard sizes before you go to 73.5mm etc.  I have recently had a client with a 1098 crank with 1275 pistons, needless to say the pistons was about 6.5mm from the top of the bore when measured.  

   

Due to the off set of the journals a 1098 crank can be cut to 60/60 and still be very strong and usable.  I know 60 thou bearings will be hard to find.
I have a 1098 with Mazda pistons and it runs very very well, seeing as the engine is almost square (bore and stroke almost equal to each other).  Please note to do this conversion the block needs to be modified heavily.

The bearings and piston rings are the same as 1275 items (please note some pistons have 1.5mm compression rings vs 1.6mm compression ring, on the oil rings 3mm vs 4mm).

Further using the engine number to ID is good, but not fool proof as engine ID tags could have been lost and or moved from one engine to another after 40 plus years of different owners.  The best way to ensure what you have is check crank part number, as above 1098 is 12G2827 and a 1275 crank is 12G1683 or 12G1505 the latter sometimes reworked with a AEG number.

Heads will be interchangeable but the 12G940 is still a favourite to use.

With enough time and money a 1098 can be made to scream and last long, but a over-bored 1275 will still make more power.  Due to availability of 1275 pistons go for it, IF you can find a crank.  1098 cranks are much easier to get hold of, but the pistons will then be the issue.  Use what you have and or can get to build your engine.  What ever you plan to do on a 1275 can be done to 1098 also obviously.  Run a nice cam, lighter flywheel and back plate (balanced naturally), ported head and a branch or LCB.  Carburation will depend on what you have vs what you can get vs money you want to spend.  Some people swear by a Weber DCOE 40 or 45 (very scarce the latter) or a single SU vs Twin SU.

Lastly do not forget to upgrade your cooling system with any engine and or power upgrades.

[Miniac]

Dom, this is a very nice concept as what you say is very true in regard to everything being based around the UK spec 1100.

Nice amount of information Phil and Malcolm.

[DomMINIque]

Awesome this is going well so far!

Yea Miniac I thought we can get a cross between the "tuning the a series" and Haynes manual for SA 1098 users since thre is no info for us newbies to the mini world.

So far it's looking, thanks to Malcolm and Phil for the info & pics.

[Jared Mk3]

So, if one were to use 1275 pistons in a 1098 block on GTS rods or similar, would the block need decking?

[Enzio]

Yes, you need to deck the block and use 998 push rods

[Jared Mk3]

Yes, you need to deck the block and use 998 push rods

How much would you suggest decking it by? Or does that depend on the compression ratio that you're after and/or the use of flat top pistons?

[Boyscout]

I considered going this route when I built my Mini. 1098 crank with 1275 pistons. It would need close to a 1/4" to be removed from the deck. That meant it would need to be decked 3 times to get that much off. Would cost a bit much. Luckily I managed to get a 1275 crank so it was a no brainer.

I still think if you go this route you can make a real screamer. Very close to the dimensions of the 1071.

[Enzio]

Hi Jared, yes - how much you remove would depend on your pistons, combustion chamber CC and your required compression ratio.

And yes, a screamer it can be....which is why I want to build one