Converting Madeira 40 to Madeira 50 (Part 3)

I still want convert my Madeira 40 to 50 and I know that the engine head is different, Selva 40 XS has the same head as Madeira 50.

I tried to order Madeira 50 head via Engine Marine Part, the part number is 2020306 (Testa Madeira 50 / Head Madeira 50). The price was 174 EUR, unfortunately Selva was not able to provide the spare part although I waited for five months 😒

So how Selva 40 head is different from Selva 50 head ? I don't have the service manual so I can't say for sure but I bet the compression is different. I have measured my Selva 40 compression and it is around 130-132 PSI.

I decided to increase the compression by cutting (i.e. shaving) the Selva 40 engine head.
The guys at Screamandfly.com suggested that I should cut 0.5 millimeters (~ 20 thousand of an inch, aka thou) from the engine head and that is what I did. I took the head to GT Motor and they milled the head and the cost was 70 EUR.

I bought new head gaskets and assembled the head and did a new compression test.
The compression test now showed 150 PSI in both cylinders which is a quite good reading and still not too high for regular gasoline, I'm using always 98 octane gasoline.

The actual effect of the increased compression will be evaluated in a later post.

The compression with stock cylinder head is a little above 130 PSI.

Selva 40 engine head removed.

Selva 40 engine head opened.

Selva 40 stock head thickness is 39.72mm.

Head thickness after shaving is 39.27 mm.

Compression after engine head shaving is about 150 PSI.