Marine Compound Engine

February 2010.

John R. Bentley 2010.

Machining the
Lower Cylinder Covers
-  for the Stuart Compound Launch Engine  -

Unlike the top covers, the lower cylinder covers on this engine are key components in the drive train from the pistons to the crankshaft. They support the upper ends of the crosshead guides and consequently define the location of the supporting bracket for the guides on the engine's columns - a component which also locates the reversing shaft.

These covers determine the degree of parallelism between the crosshead travel and the piston rod travel. Of course in addition they contain the packing glands for the piston rods. The lower covers are not at all difficult to machine, but the builder should adhere closely to the stated dimensions on the plans. (I do take exception to the suggested depth of the crosshead slider mounting screws however and I have made more comment about that later on this page)

Here is a bottom view of the castings showing the stuffing boxes

Above and Below: spotfacing for the mounting nuts

Taking a reference position from the bottom edge of the cover with the point of a 1/8" centre drill

Drilling the holes for the crosshead guide attachment screws

This job went very well - you can see that two photos down. However at a later point in construction I managed to get into a considerable amount of unnecessary trouble as a result of following the plans too closely regarding the depth of these threads. If you want to read more Click Here

Spotfacing for the stud nuts on the H.P. cover

Spotfacing this hole and its counterpart left a rather unusual shape...

So I shaved off a bit of metal with the endmill so it would look better.

Now to the big cover -

Perhaps the most important stud hole - drilled on the centerline halfway between the two cylinder walls

Marking the H.P. cylinder stud holes in the block using the cover as a guide

Note that a clearance drill was used - but only to mark the holes

The marks ready to be drilled and tapped for the studs

No - those studs are not leaning outward
(it's the camera lens causing "diverging verticals")

Begining the milling of the "flat spot" which will bisect one mounting hole
(where both covers share a single stud)

Same drill as before
No pun intended :-)

(marking the L.P. lower stud holes)

Ready for drilling and tapping

Compound Launch main page


Castings, Materials and Fastenings


Cylinder Block

Top Cylinder Covers

                 Lower Cylinder Covers (this page)

Steam Chests

Crosshead Guides and Bracket




Connecting Rods and Crossheads

Main Bearings


Fittings: Oil Cups

Fittings: Drain Cocks

Fittings: Exchange Pipe, Flanges and Glands

Stephenson Link Reversing Gear (5 pages)

Completing and Erecting the Compound Launch Engine


Return to main website home page

(c) John R. Bentley 2010.