Originally in a 2CV from 1960 a 425 CC 12HP engine was mounted. I do have the original unit but when I bought it a 425CC 18HP unit was mounted. Looking at the state of both engines and the future use of the 2CV, using it regularly in town, I decided to remount the 18HP engine. This 18HP engine was mounted from 1963 until 1970 and is very similar in construction as the 12HP engine. The easiest to recognize a 18HP engine compared to an earlier (9, 12, 13.5, 15HP) engine is the way the exhaust manifold is constructed (with the spark plug between the air inlet and outlet).
Before starting the work I collected some parts I needed for the engine like new exhaust manifold, brake cylinders, brake pads and a complete gasket kit
I started to disassemble the engine. I dismounted the cylinder heads and took them apart. The heads looked in a good condition as did the cylinders and pistons. I cleaned the valves the inlet ports and checked for wear. I grinded the valves and the valve seats. I reassembled every thing and replaced old seals at the same time.
After this step I thoroughly cleaned the oil cooler and oil pipes and remounted them.
During my search for parts I found some second hand carburetors for a very small price. I selected the carburetor with the least wear on the primary shaft and cleaned it. Overtime I will correct the wear on the primary shaft as it is not perfect.
Then I started to work on the plating around the cylinders to guide the forced air around the cylinders. The plates, which were mounted when I bought the car, were not suitable for my 2CV. I needed a set of plates with a box section behind the cylinder, which could either let the air out or guide it into the interior for heating. Luckily some plates were supplied with the car but they had to be put in shape and some part needed to be renewed. Some hours of panel beating, welding and painting later they looked like new. The part around the fan needed the same treatment as this part looked like it had been torn off without loosening the screws first. I tried to get hold of a replacement part but did not succeed so I mounted the old unit. All in all it looks acceptable now.
I mounted the new exhaust manifold with new gaskets and mounted the carburetor. It started to look like a real engine again. The ignition was checked and I renewed the shaft which opens and closes the contact points as there was excessive wear. I renewed the contact points and adjusted them to open .4mm I also adjusted them to just make contact with the 6mm pin inserted in the flywheel.
I mounted the fan. Then I checked the gearbox and clutch. The clutch is the automatic type which connects the gearbox to the engine above 1000 r.p.m. The visual check did not show any excessive wear so I left that to what it was. Then I moved to the front brake drums. It already occurred to me from the outside that they were a bit greasy. I took the drums off and both brake cylinders leaked heavily. I replaced the cylinders, and had the brake drums refurbished (degreased and the brake area renewed on a lathe). I reassembled the brakes using new brake pads and the drums and bolted the gearbox to the engine. Additionally I checking the start engine and mounted that to the engine.
The engine was now ready to install in the car. I waited with the mounting of the other exhaust parts until the engine was lowered into the car to be better able to check how it would fit in the limited room between the chassis and the engine.