This from a YW listing.Not familiar with the BTDM part. Lots of 4BT3.9-M engines at 150hp out there.
Basically the same as the 6BT 210 but 4cyl vs 6. Solid engine, but low and high speed vibration make it a good bit less "social" than the six.
Might have started life as some sort of auxiliary engine (gen, pump, hydraulic, heavy equipemt??). That might be where the extra letters come in.
Got some pics??
This is all that’s shown .Looks like a typical full marine 4BT.
That exhaust hose sure looks like it goes uphill!!! Is that what I am seeing?? If so, deal killer!!
Got any more pics of the turbo exhaust outlet area, rear of engine?