Tag Archives: making gaskets

Gaskets and Unions

Well, the last week or so has been dedicated to finishing the air pump and feed pump assembly. The original owner of the castings had partially machined and assembled the main air pump castings, but they needed “fettling” to fit. This ranged from minor adjustment of PCD bolt holes, replacement of pump rod, and other minor work thru to remachining / truing of all of the mounting faces, fitting o-ring to undersized piston, reboring the feed-pump rams (to provide increased capacity needed for geared-down operation), the making of all the feed-pump valves and manufacture of all (bar one) of the pipe unions.

This involved a variety of odd-ball threads… I think this assembly now includes all the following:

  • 1/4 x 25 TPI British Standard Fine
  • 3/8 & 1/2 British Standard Pipe (parallel)
  • 9/16 x 26 TPI (actually a British Standard Cycle Thread)!
  • 2BA (British Association)

The larger ones of these were either entirely screw cut on the lathe or screw cut and then “chased” with a standard split die. With the new insert/index threading tools this all went really well.

Interestingly (and as a demonstration of the value of “keeping everything”) a great many of the bolts on the engine are 1/4 BSF, and luckily at a club Auction at Guildford Model Engineering Society (I used to be a member), I managed to purchase a bucket of 1/4 BSF Allen Bolts for about a fiver …. I just had to look after them from 1985 ’till now to find a use for them!

The assembly also needed a number of gaskets (about 7) and these were all cut using a ball-peen hammer and centre punches to tap them out from the components they were sealing. This is such a simple and effective process (but one that many people seem not to know) that I included some pictures of the process in the slideshow below….

(also see link about drawing errors on this part here)