Having now completed the machining stage the engine should be given an initial assembly
of the major parts to ensure that everything goes together as it should, or perhaps
nearly everything. If though you find a screw here or there will not enter fully
due to some minor misalignment do not be overly concerned you will be keeping me
company. I do tend to start off with minimal clearance in my clearance holes for
screws so its not that surprising. If you find yourself also in this situation open
up the offending hole by a drill size and try again.
The main purpose of this stage is to determine that the mechanisms work and this
is best done a stage at a time. Typically, first assemble the crank shaft into the
bearings and these onto the soleplate and check to see that the crankshaft can be
turned reasonably freely, making any adjustments found necessary. Do not be over
concerned about a little stiffness, probably a good thing as it proves you have not
made the parts with a too generous clearance. Add the remaining parts a group at
a time, testing the completed assembly as each addition is made.
Even if you do not intend to run the engine, just having it as a display model, you
will still want to display to your friends just how smoothly it rotates and may therefore
need to run it in by some means to achieve this. If just a very little stiff adding
say a large tap wrench to the crankshaft and spending a minute or two turning it
by hand may be all that is needed. If though this is proving to be a slow process
than driving it from some external source is really the only option.
One way of doing this is to add a piece of wood to the cross slide, typically using
the top slide fixings, and securing the engine on this using wood screws through
the holes in the boxbed. Place a short length of steel in the three jaw with a piece
of rubber tube forced onto it and with that done the cross slide can be used to bring
engines fly wheel into contact with the rubber and the lathe started on a low speed,
do though turn it a few times by hand to be sure all is OK. After running for a short
while it should be found that the engine runs smoothly, Photograph 70 shows the setup.
An advantage of the method is that the drive can easily be disconnected by moving
the cross slide back for testing the result and then forward again if needing to
be run further. A little oil can be placed in the appropriate places to assist in
achieving a smooth running engine but do not overdo this as if oil gets onto the
castings it may cause a problem at the painting stage.
A good method of applying small amounts of oil is to place a very small amount in
a bottle cap and use your scriber tip to pick up a droplet then placing it in the
required position, a method used by clock makers I believe.
The engine should now be dismantled for the finishing stage which is largely divided
into two tasks,1. surface finishing for either visual impact or in preparation for
painting and 2. painting, just one area going beyond this. The working surface of
the slide valve and its mating surface on the cylinder should be lapped on a flat
surface using a piece of say 400 grit emery paper, then being finished by progressively
using finer grades up to around 1200 grit. The purpose of this is to improve the
seal between the two parts when working.
Cast iron parts where painted should be tided up removing all irregularities as no
mater how much paint you apply they are still likely to show, in fact, with gloss
paint, they may even show more. Do not therefore rush over this stage.
Areas that are machined but not painted should be surfaced with 400 grit paper, at
least sufficient to remove machining marks, the outer rim of the flywheel will though
benefit by having an almost a mirror finish using up to 1200 grit and being done
whilst it is once more held on the taper stub mandrel and the lathe running. Do take
care though you do not want to get your fingers caught in the rotating spokes.
One area that needs a little more attention is the valve chest and valve chest cover,
having machined them independently it is unlikely that their widths and height will
match perfectly. Therefore, assemble them as a pair using the provided studs and
lap the sides on a piece of emery paper. The ends will have to be done with needle
files and finished with a strip of emery paper.