Technical 1242 piston conversion

[M@nticore]

I want to know if it would be possible to fit 1242 pistons to my 1108 with 1108 conrods and crank, i know that the piston is .6 or something mm bigger, but that can be bored out on the 1108 block. i know the stroke on the 1242 is different, but the block is 10 mm higher. any help would be appreciated.

 

[Chas Uno]

It seems perfectly possible to bore out the 1108cc engine to take 1242cc pistons. As you mentioned, the 1242 has a longer stroke and a taller block, so the new capacity of your bored out 1108 will be smaller than 1242 but bigger than 1108. There is a formula for working out cylinder displacement based on piston size and crankshaft stroke, but I can't remember it!

Thing is, 1242 pistons won't be cheap, and I've heard (not sure on this) that the FIRE engines don't like being over bored. Also, it would be quite expensive to do this. Probably a lot more than buying a whole 1242 engine! I saw a Punto 75 FIRE engine (1242 MPI with the hot cam ) go on Ebay for about £100!

Can you not find a 1242 engine to swap over for the 1108? That would be the easiest and cheapest way to increase the capacity.

 

[M@nticore]

I want to buy a 1242 but they are very scarce here in South Africa, thats why i thougth of putting the 1242 pistons in, so the engine would be roundabout 1150cc and the compression ratio would be a bit higher. +- 10:1 without skimming the head.