Restoring a 1-3/4 HP Monarch, Part 3

Reclaiming its crown

| August/September 2010

  • monarch 1
    The cylinder head as removed from the engine, showing the broken pushrod bracket and exhaust arm.
    Photo by Peter Rooke
  • monarch 3
    The cylinder head after testing on the surface plate, showing the lack of contact
    Photo by Peter Rooke
  • monarch 2
    Grinding the second valve, the clean ring from fitting the first valve can be seen.
    Photo by Peter Rooke
  • monarch 5
    Fluxed bracket on the hearth ready for brazing.
    Photo by Peter Rooke
  • monarch 7
    Repaired pushrod bracket and new take-up and screws.
    Photo by Peter Rooke
  • monarch 4
    The cylinder head showing good contact after scraping.
    Photo by Peter Rooke
  • monarch 9
    Fitting the cylinder head gasket before cutting out around the bore.
    Photo by Peter Rooke
  • monarch 8
    The refurbished mixer.
    Photo by Peter Rooke
  • monarch 10
    Wooden dowel used to align the section to be joined to the main part of the tap.
    Photo by Peter Rooke
  • monarch 11
    Components of the finished tap.
    Photo by Peter Rooke
  • monarch 12
    Cut sheet metal with the lines marked for bending and hole drilling.
    Photo by Peter Rooke
  • monarch 13
    Making the final bend in the sheet in the main body using folding bars.
    Photo by Peter Rooke
  • monarch 16
    Fitting for drain plug ready for soldering in place.
    Photo by Peter Rooke
  • monarch 17
    Top plate ready for soldering after fitting necks.
    Photo by Peter Rooke
  • monarch 14
    Trial fitting the end plates.
    Photo by Peter Rooke
  • monarch 18
    The completed fuel tank.
    Photo by Peter Rooke
  • monarch 20
    Measuring bore diameter.
    Photo by Peter Rooke
  • monarch 19
    The fuel pipe and check valve.
    Photo by Peter Rooke
  • monarch 22
    Pitting in the cylinder bore, even after honing!
    Photo by Peter Rooke
  • monarch 21
    Using a bore hone.
    Photo by Peter Rooke

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The following is Part 3 of a four-part series documenting Peter Rooke’s restoration of a 1-3/4 HP Monarch antique gas engine badged by Nelson Bros.  Read Part 2 .

Cylinder head
Apart from the broken rocker arm at the point of an early welded repair and a split pushrod guide, the cylinder head appeared in good condition and the valves appeared new. However, the valve seats showed signs of rust.

After stripping the cylinder head by removing the valves, mixer, rocker arm and pushrod guide, the old paint was removed revealing bare metal. It was also necessary to scrape a thick layer of gasket sealant from the inside bearing surface.

The valve seats had to be polished to remove a thin film of rust. The contact surface of the valve was coated with fine grinding paste before using a grinding stick, which was rolled backward and forward between the hands to grind the seat. The valve was frequently lifted up and the paste re-distributed to ensure continued cutting. This was done until there was a clearly defined ring of polished metal around the seat. At this point, the valve was removed, cleaned of all traces of grinding paste and put in a plastic bag, marked with the type of valve – inlet or exhaust – so that it could be fitted to the correct seat later.



After both valves had been fitted, the head was carefully cleaned to remove all traces of the abrasive paste. A straight edge was held across the cylinder head and it appeared true. I later found that there was a compression leak from the bottom of the head so it was checked again by spreading some engineer’s blue on the surface plate. As can be seen from the photo on the opposite page in the middle, there was an area where no contact was made with the surface plate between 3 and 6 o’clock.

The quickest way to make level the cylinder head is to set it on the lathe and take some skim cuts. However, there was not a lot of metal on this head, and when skimming you could loose a few thousandths of an inch in setting it up. As the straight edge had shown no major defects I decided to scrape it. The area of contact on the head, shown by the blue, was scraped off and the cylinder head marked again.