In the UK, Commer had a screamer of an opposed piston two stroke diesel in their medium duty trucks around the late 50's/early 60's. You could hear them coming for miles. In the US, submarines used an opposed piston Fairbanks Morse diesel. I guess because of its shock (hence seismic) qualification, it was also used as a backup generator prime mover in nuclear power plants where it got a reputation for exhaust fires. I haven't got personal experience of running them in that configuration, but suspect that it might have had something to do with keeping constant luboil flow because of their standby status. Since one crank was above the combustion chamber, oil may have been flowing into the cylinder and getting thrown up the stack on start up. On the other hand, maybe it just had a propensity to throw oil like the Deltic......