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I wonder if this has ever been discussed here. If so, please let me know.

Has someone here got a deeper insight into the different 6C 2300/2500 engine block designs and ist it possible to narrow down the exact period when they were used?

Basically, I have seen three different types of blocks:
1. The 2300 blocks with the large water-cover on each side (stadium-shaped and bolted on)
2. Smooth blocks with the round water plugs on each side, but no reinforcement ribs
3. The later blocks with round plugs and horizontal and vertical ribs.

So far, I thought the blocks were redesigned when the model changed from 2300 to 2500 and one design followed the other to improve the stability.

But.. I have an engine here, No 923892 with the large lids like on a 2300, but with a 72mm bore and thicker cylinder walls, so basically a 2500 engine with a 2300 look. The number appears to be original. The car it refers to was delivered in 1940. So, is it correct that the very early 2500 had the same block as a 2300, apart from thicker cylinder walls? Are there other early cars with these kind of blocks? The Anselmi book, page 25, shows a technical drawing from 1939, marked 2500, which also shows the 2300 side lids in a cross section. Did this go into production?

To the second type: I thought that the smooth sided blocks would have been a redesign of the 2300 to add rigidity and would therefore fall in a time between the open blocks and the ribbed ones. But it might also be that these blocks were for applications which put less strain on the material, like marine engines or Coloniale. Does someone here have further information?

The ribbed blocks are pretty clear. Independent from the engine numbers, which were obviously a bit mixed up, they seem to have found their way into production right after the war. This is at least what the pictures in the Anselmi book suggest which show an engine of this design dated 1946. Are there earlier examples?

There also seems to be a greater number of oil pan designs etc. Would be interesting to share details about these changes during the production timeline.
 
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