South African 1098 engine

[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.