Often valve springs are only inspected optically and if they look good they are reinstalled, this is not the correct method. You should always measure them to see if the load on the springs is still correct, you can't see it from the outside.
25 and 30 hp engines
New valve springs should give 33.4 kg pressure at 28 mm compression with a maximum tolerance of 5%, a maximum load loss of 10% is allowed on used springs.
1200 cc (34 hp) and Type 3engines(until July 1964 )
They should give 45.6 to 52.4 kg pressure at 32.0 mm compression. For these engines you can fit valve springs intended for 1300, 1500 and 1600 cc engines without any problem, the slightly higher pressure is not original for the 1200 cc Type 1 and Type 3 engines until July 1964 but can't hurt.
1300, 1500 and 1600 cc engines
The pressure gauge should read between 53.2 and 61.2 kg at 31.0 mm compression.
As you can see, the measurement has to be done quite accurately. So you will not be surprised to learn that most old cylinder heads need new valve springs.
Mounting: The side where the windings are pressed the most is the cylinder head side.
Useful information from Paruzzi magazine and from our YouTube channel :
Look for more technical articles on the page Paruzzi Magazine