BUILDING AN RMC TYPE ‘B’ ENGINE
Part four by Jason Ballamy
BUILDING AN RMC TYPE ‘B’ ENGINE
Part four by Jason Ballamy
The drawings include details for a home made spark plug to suit the engine so I had a go at making one. Well, two actually as the extra can be used in the Type D when I get round to making that.
The body started out being turned on the end of some EN1A bar and then screwcut 1/4 x 32 UNEF as I only have a tap that size. The large picture makes it look rougher than it is.
A suitable female thread was tapped into the end of a bit of scrap so the body could be held to finish the top end.
The insulator is a length of 3mm glass tube which cut very easily with a diamond coated disc in the Dremel, I used the slowest speed to avoid heating the glass and then just twisted the glass in my fingers against the disc to chamfer off the sharp edges
The central electrode is a piece of 0.5mm tig welding electrode and the final part is a small brass cap with a groove to accept the wire clip. The electrode is trimmed to length after assembly.
Unlike a conventional plug the spark does not travel from the central electrode to the plug body but to a long screw that enters from the opposite side of the cylinder. The plug gap is adjusted by turning this screw and securing with a locknut.
The ‘hemi’ cylinder head was turned from some cast iron and, as I didn't have the large diameter ball nose cutter suggested, I first drilled to depth and then hand cut the shape.
It was then held the other face out in the soft jaws and the outer curve also shaped by hand turning with a flat ended tool.
Finally over to the mill to drill for the fixings
The fairly long piston can be turned from the chucking spigot that was cut off of the base casting but I chose to use some 25mm CI bar. After turning and cutting the groove for the quad ring it was held in a collet block to have assorted holes and notches cut which provide the porting for the Loyal cycle.
Modelengineeringwebsite.com
the only free and the only weekly magazine for model engineers.
Editor: David Carpenter