There are a number of known problems with the engine
I have run into a number of other
problems associated with my level of skill!
This page attempts to list them so
that other builders can avoid them.
Some of these problems are minor design glitches
whereby a part made to its drawing doesn't match up with a corresponding
Some problems are potentially catastrophic in terms
of collisions of major components.
Some are annoying drawing mismatches.
The numbers in the table are simply to help
identify the issue and do not, at this stage, give any priority.
arms (part of the box guides) will collide with the wayshaft at the top
of the stroke of each cylinder by between 0.250" and 0.375"
REVISION 24 December 2002
This collision problem ceases to exist
if you choose to redesign the wayshaft pivot to port as described below
This depends on when you find out about
You won't know how bad the problem is
until you assemble everything. My interference was a bit less than 3/8",
made worse because my main bearing centreline is level with the top of
the bedplate rather than 1/8" below as the drawings suggest.
If you haven't machined the columns make
them 0.750" longer below the cross bar holes. This allows plenty of room
for a nut on top of the pump arm for the pump rod.
If you have machined the columns then:
Shorten the connecting rods, the feet
will end up at around 7/16" thick
Machine pads for the bottoms of the
columns around 3/8" thick if you have enough thread or 1/4" for the top
if you don't.
Either pad the feet of the slide bars by
1/4" or slot the bottom mounting holes.
You may have to thin the pump arms a bit.
holes for the LP valve chest are drawn at 3/8" diameter while the holes
in the cylinder block are for 5/16" UNC studs
||I found out
after I had drilled the valve chest holes...
5/16" fasteners would probably have
If machined to the drawings the
connecting rod top bearings foul the slidebar aspect of the crossheads
as the crank approaches 90 degrees and 270 degrees. ie the wristpin is
too close to the slidebar face of the crosshead
These photos show how another builder
overcame the problem
fortunate in finding out about this one before I bored the holes in the
crosshead for the wristpin!
solution is to move the wristpin bore and the threaded hole for the
piston rod 1/8" away from the slide bar and to move the slidebars 1/8"
This led to some mischief when
mounting the slidebars to the bottom cylinder covers but that is a devil
of a job anyway.
Plenty of room!
Slidebar feet (IP)
||The design of
the valve gear regulating arms is incorrect
The drag links should be horizontal in
the ahead position so that sideways movement of the links is minimised.
The engine has the draglinks
horizontal in the midgear position and inclined at an angle of about 20
degrees in the ahead position
This means that about 5/16" of lateral
thrust is given to the end of the regulating arms with every stroke of
the valve resulting in a lot of clatter and/or severely strained valve
Showing the inclined drag links in the
engine built in Maine
Measuring regulator arm
"kick" as designed
Showing the mockup I
used to optimise the wayshaft position, shown here in astern
The extension piece
|This is the
hardest one to solve and probably the most serious in terms of engine
silence and longevity.
separated from this by about four months or the time it takes to machine
all of the valve gear components
Ideas floating around at the moment
lean to recasting the regulating arms about 1 1/2" longer and altering
the valve gear regulating slots so that they are horizontal (maximum
effect) when the regulating arms are down close to the engine.
The ideal solution would be to
lengthen the arms and move the wayshaft sideways by about 2 ".
Update 24 December 2002
After much head-scratching, experimenting
and lost sleep I decided to move the wayshaft pivot point 2.500" to port
and down by 0.375"
achieved by extending the part of the lower valve chest covers that
support the wayshaft using an extension piece machined from mild steel.
By utilising the existing regulator arms
I am able to obtain horizontal drag links in both ahead and astern and
reduce link slip (or regulator arm "kick") to around 0.105" rathe than
the 0.190" measured in my experiments with the "as designed " pivot
With everything assembled
and running there is negligible regulator arm "kick"
||I have had
continual problems with collisions and misalignments along the long axis
of the engine.
From lining the
big ends up with the crankshaft to the HP & IP valve gear colliding with
the crossheads or the columns.
The most serious of these is the need
to offset the HP valve trunnion forward by over 1/8" so that the
eccentric rod top bearings clear the forward columns
The HP valve gear
showing an offset of 0.190"
The drawings require
the valve trunnion to be offset by 0.125"
I can't move the
quadrant etc. back due to fouling of the forward column and the
eccentric strap fouls the bedplate
The finished HP trunnion showing the
marked offset necessary
are, to a large part, my own fault.
When "targeting" the cylinder block I
started measuring from where I thought the LP port face would be.
I should have started measuring from
the centre of the IP bore so that my errors started in the middle and
did not accumulate the full length of the block.
Similarly I targeted the bedplate from
the centre of the landing pads for the columns rather than the centre of
the IP crank web "pit"
A beginner's error!
||A blowhole in
the IP bottom cylinder cover above the gland
When I machined the cover I noted the
hole but didn't consider that it may have passed right through the
This explained the loud hiss with the
engine running on air despite various attempts to tighten the packing
gland and I could feel a draught from somewhere!
From inside the cover
|I bored out
the gland deeper and inserted a "bush" with a press fit