I'm new to this post. I have a marinized OM621 in my sailboat. I am not certain of the year though as the engine has been through a rebuild and has been sprayed and the original vin plates are nowhere to be seen.

The engine is raw water cooled and the exhaust manifold has quite a bit of corrosion due to salt and vibration. I'm trying to locate gaskets and a replacememt manifold , however this is where i get confused. The first 3 numbers should depict the model # right?? i have a service manual and everything in the manual leads me to believe it is an om621. However the numbers on the manifold are 615 142 0701 ? the intake numbers are 621 141 0501. I will be looking for other spares for this engine as it runs well. If anyone could point me in the right direction i would be most thankfull

The OM621 was part of a new family of engines that came out in the 1950's. The OM621 was followed by the OM615 and the OM616, which was used through the 1980's (and later in some parts of the world). These engines are all very similar. I'm in the process of putting an OM616 in my 1960 190d that originally had an OM621 (but was switched at some point to the gas version, the M121). For the most part it's a direct bolt-in replacement (have to relocate the oil filter and some other minor sorting).

I'm pretty sure the manifolds from any of these engines could be bolted to any of the others (and their gasoline counterparts). The differences are in the exhaust pipe connection location. If your manifold part number starts with 615, then you've got a manifold off either an OM615 or an OM616. If you use an OM621 manifold, it will bolt up to the engine but may not line up right with your exhaust pipe. Your exhaust manifold looks like mine, which is from a W115 chassis car. Your intake manifold definitely looks like an early OM621 manifold.

In terms of determining what exhaust manifold to use, it doesn't really matter if you've got an OM621 engine with an OM615 exhaust manifold bolted onto it, or an OM615/OM616 engine with an OM621 intake manifold. I think what's going to work for you is an exhaust manifold from a W115 chassis 220d (OM615) or 240d (OM616). That means pre-1977, which is the year the W115 240d was replaced with the W123 240d, and the manifold from the W123 is very different. It's possible that a manifold from an OM621 from a fintail would work (probably not easy to find though), but I dont think the ponton version will work.

I did a quick ebay search and there's a guy that's got several manifolds that are listed as 1974 240d manifolds. If they are what he says they are (there are no pictures, no indication of condition, and his ad doesnt give me confidence that he really know what they are) then that may be a good solution. Somebody on this forum probably has the right part.