The big bore kit is a conversion for the standard 2CV6 engine (602CC) and brings the cylinder volume to 652CC with a compression ratio of 8,5/1. This results in more power and torque. The kit comes with the pistons and rings all ready fitted and jets for the carburettor. The jets are specially for the latest model Solex carburettor (1978->). The venture sizes are 26mm and 18mm (marked on the side of the carburettor).

Three options to get a 652 2cv.

1. Bore out the 2cv barrels. This leaves them very thin and prone to piston slap. To keep it all cool, the engine I used to have had been jetted very, very rich - so thirsty.

2. Fit Visa barrels. Much machining required, because the Visa barrels have the pushrod tubes built in, whilst the 2cv ones don't.

3. Fit a Visa engine. If you stick with the Visa ignition, you need to cut some holes in the bellhousing for the sensors (which hang off a mounting bar from the engine bolts). You also need to fanny slightly with the starter/ring-gear.

3 is the simplest and most reliable. If you can find a half-way decent Visa engine.

piston slap would be the result of making the clearance between piston and barrel greater than the ideal ( 3 thou?), not because the barrel wall thickness had been reduced.
The real problem with taking so much out of the barrel walls is their increased tendency to distort, with partial or complete seizure then a probability.

Wouldn't that presuppose they distort inwards, whereas they could distort outwards...?