Return of the Opposed Piston Engine


I understand a horizontal will produce torque more than any other arrangement. I was startled to see a new BMW Motorcycle vertical the other day!!, VW had them, not sure what a corvair had. EMD went 4 stroke recently, I’m not sure how that worked out but to see they are going 2 stroke with nat gas seems right, they had locomotives and ships pretty well nailed for 2 stroke. Don’t forget: right now the new diesels have a additive you have to put in a separate tank. And yea, the electronics now… about all we can do is replace modules but they are so expensive just how many are you going to keep aboard?


The horsepiss? Urea is for the exhaust treatment system.


My first car was a Corvair. They were air cooled and the pistons were opposed.


Whoa man, bet you got all the girls. The shift lever on the dash?


The cylinders were horizontally opposed, the pistons were not opposed. It was not an opposed piston engine as discussed.


like a Subaru.


And Porsche


Four on the floor. As for the girls, only in my dreams.


My dad’s mother got a red and white Monza with automagic transmission and loud pipes. Dad hated it (one mustn’t ever have fun driving), and hated it even more after he put his clutch foot through the wide brake pedal and threw me and my brother into the windshield. Lots of grumbling about how automatic transmissions were meant for tanks so they could knock over trees without stalling… :slight_smile:


\m/ The girls with the bodies love boys with Ferraris. \m/


I’m surprised at these disparaging remarks about the Covair! The front seats reclined and the back seat folded down. The trunk-in-the-front held 3 cases of beer iced down with a drain plug. Mine morphed into a dune buggy and a year later, the engine powered my air boat. Got my money’s worth!

Now back to the OP. The last vessel I sailed with OPs was a research vessel carrying the R.U.W.S. We were anchored in Kawaihae in December '79 when hit by a tropical storm. I had to run one engine at a time to compensate for the surge. The offline engine exhaust piping had to be drained of lube oil before going on line. After 4 days of this, we finally got underway. The CG thought we were on fire from all of the exhaust smoke. It finally cleared up by the time we got to Kaneohe Bay.

Great engines, as long as you keep a load on them.


I was being sincere. At my school cool kids had VW’s. Then was Corvairs. Then kids who had their folks car. Then the kids who had no cars. And below that, way down there, was me with a Chevy Vega. I wish I had a Corvair.

Funny you mention Hawaii. Honolulu was where I got off that tug might have been 1977. Heard it was sold to a dredging outfit and was headed to Persian Gulf. Don’t remember the oil but wasn’t on there long.


I sailed on a tanker equipped with a Doxford 56LB4 (Opposed-Piston Engine) which generated a power of 2800 PS, had a RPM of 110 and a speed of 10,5 knots. Doxfords had a direct driven screw: The engine can be started ahead or astern with the help of compressed air. The bang of the compressed air at start up was deafening. On the bridge wing we did not only hear but also could feel it in our stomach. I liked that but not everybody did.

Often the start had to be repeated, sometimes two times, because it misfired. We could tell by the misfiring which engineer was handling the start of the engine, The third engineer had the contraption always running on the first try.


Engineer at the Doxford manoeuvring stand.

In general you either loved the machine or hated it. It was a very complex machine which required a lot of maintenance. British design is often complex, why make it simple if you can make it complicated. There were a lot of gears and chains which continously gave trouble as well as cracked piston heads and even a crankshaft. Too often, too quick the piston rings were either broken or worn down. That happened at the most unexpected moments, in bad weather or near the coast. I admired the engineers who had to pull pistons on a rolling ship, like acrobats, with danger for life and limbs.

I remember one occasion were the engine broke down again and where we could anchor near one of the islands of the Azores. After six hours the wind increased and became almost gale force. The anchor started dragging towards the nearby rocky coast. The second anchor was lowered but both anchors did not hold, also giving more slack on the anchor chain did not help and the coast came nearer and nearer. Finally after which seemed an eternity the repair was done, The captain ordered the Chief Engineer that the Third Engineer had to start the engine, nobody else. And indeed it started in one go. As quickly as possible the anchors were winched in and just in time we escaped disaster.

The number of repairs at sea were also due to the fact that we were in port for only a short while. The Doxford was in fact unsuited for the tanker trade because of this fact. It needed long lay overs to do all the maintenance. Wrong engine…

An disadvantage also was the large height of the engine, due to the two opposed pistons, so that tranverse beams and other strenghtening structures could not be realized. Shipbuilders were not happy with that.

A big advantage was the extreme low fuel consumption, only 6 tons per day and the fact that it was almost vibration free, it spun like a kitten. There still is the ‘Doxford Engine Friends Association’. Remember that they built many hundreds of engines, almost the entire British fleet was fitted with Doxfords.

The company went out of business because much more powerfull engines were required by the new bigger and faster ships. They tried but failed miserably because the concept was not suited for that new type of engine.


In the Rotterdam Maritime Museum is a working replica of exactly of this type of engine, height 1.87 meter. It was built by the Yards apprentice school.

History of Diesel Displacing Steam in U.S. Merchant Marine

I worked on the tug Geronimo, every time we cranked up, pier 17 was under a smoke screen, we had to wear garbage bags to keep the oil that was spewing out of the stacks from coating us. Other than that, I enjoyed my years with OP’s


great story Dutchie, thanks. I’ve only heard of Doxford’s … fortunately i suppose.


Before departure a so called Air Blow was carried out. The engine was cranked one full revolution with opened indicator cocks.


ok, so far so good or am i missing something?


The ultimate in terms of Weight/HP engines must be the Opposed Piston Napier Deltic.
That was the engines that powered the Tjeld-class MTBs, (AKA Nasty, or PTF):

With 3 cylinder/6 opposing pistons per block, 18 blocks and turbo chargers they could obtain 3140 Hp per engine, or total 7280 Hp at 2100 RPM. But that was only used on rear occasions and tests, as the maintenance interval would be very short if used regularly.

Normal transit was done at 1750 RPM, which gave a speed of 36 kts. (With full Fuel and Amo load and peace time propellers installed) Still the work shop maintenance intervals were only 1500 hrs.

Watch the functions of a Napier Deltic engine in animation:


No-ah. I reckon the CHB Evo has better weight/hp.


The Napier Nomad was the most efficient diesel built: