Good photo showing the Stephenson linkages in the reciprocating engines

  • Thread starter Gene McCullough
  • Start date

Gene McCullough

I am looking for a photograph - or alternatively a drawing - showing the Stephenson linkage for at least one cylinder of one of the reciprocating engines. I have seen sketches of the linkage itself and an animation of the mechanism in operation but nothing that shows the size and position of the eccentric rings relative to the whole structure.

Can anyone provide either a source or an image?


Bill West

A while back the HospitalShipBritanic site had some good engine drawings but they are no longer there. They came from a French Journal about the Britanic.

The design of all Stephenson eccentrics and straps (rings) ever built seems to be surprisingly uniform. Virtually any picture or drawing will give you a correct impression for the Titanic. The location of the valves shows well on any Titanic engine photo or drawing, the eccentric disks are always located directly below them so that shows you where they are along the crankshaft. They are between the A frame of one cylinder and the A frame of the next. The pair of them appear to be about 4 feet in diameter and the high point of each is approximately 45 degrees before or after the crankpin they are associated with. The high point is about twice the radius of the low point. The strap is split with a bolted cap for the bottom half and has a rectangular groove in it. The disk has a matching alignment ridge and has lightening holes in the body of the casting. It about a foot thick and is also 2 halves bolted together. Typical of marine work, the link rod is round and bolted onto the strap.

Oh, I just found a mislabeled photo from an artifacts tour. This is one of the recovered eccentric straps.


Kelly Anderson

This photo shows twin compound engines for a small ship. Note that these engines are equipped with slide valves which always admit steam past their outside edges. An engine with piston valves may be designed for outside or inside admission. This difference would change the rotational location of the eccentrics in relation to the crank.

Also, note the these engines are set up for “crossed” rods, it that when the valve gear is shifted into forward motion, it is moved in the opposite direction compared to the direction the engine will rotate when the throttle is opened. This can be seen by observing where the drag links are connected to the expansion links. If the engines were set up for “open” rods, the valve gear would be shifted in the same direction as engine rotation. This would require a redesign, moving the reverse shafts to the outboard sides of the engines.

Note that the valve gears are set in forward motion in the photograph.


Lajos Berínyi

Hi, guys!

I've seen one photo on the RMSTI's page / /of the Stephenson linkage, maybe. They call: "Eccentric Strap". My questions: For what piece of the engines was made the photo? And are those the Stephenson linkages? And is this one Olympic class ship's engine?