The testplate in the article was one of a batch I produced for Michael Breeding, but basically you could cut one out of wood if you like. Regulated pressure from a compressor is more important.
Beware, however, that testing the individual nipples into each cylinder can only be accomplished with a large stopper or cork, as the seam between nipple and casting will be obscured by the nut.
Carbon in the rear cylinder exhaust suggests the leak is to the front.
PEEK seals are a blessing of the spaceage, (such as Moldthread's http://enfieldracing.com/8.html
) but beware that the manifold must be pristine, and of perfect OEM dimension,.. or reconditioned for custom-cut seals.
They must be a very tight fit upon the spigots, and any blemishes upon the spigots will severely reduce their re-usability. With pristine, un-blemished, round and true spigots, they will last indefinitely.
Considering the expense of the material, that is a significant concern.
Still, it is worth the update to avoid over-torquing the nipples, and achieve a seal that is manageable with routine re-torques. Brass work-hardens, and is un-forgiving. It's just all the Founders had.
And thanks Dave,
but bubble-testing should be credited to Heron of Alexandria, who probably recorded it around 150 AD!