Fixing a 2-1/2 HP Ottawa Gas Engine

Peter Rooke fixes the round fuel tank, Webster magneto and more on his 2-1/2 HP Ottawa gas engine.

| December/January 2014

  • Peter Rooke’s unrestored 2-1/2 HP Ottawa
    Photo By Peter Rooke
  • Sheet metal marked out for the top, bottom and side piece of the fuel tank.
    Photo By Peter Rooke
  • Folding the lip on the side piece.
    Photo By Peter Rooke
  • Using the wheel former to start shaping the lip to the base.
    Photo By Peter Rooke
  • The fuel tank being tested for leaks, while at the same time cleaning the flux from the inside with hot, soapy water.
    Photo By Peter Rooke
  • Working out the position of the filler cap and draw-off pipe.
    Photo By Peter Rooke
  • Complete tank, two of the four securing tags are clearly visible.
    Photo By Peter Rooke
  • The igniter bracket.
    Photo By Peter Rooke
  • Magneto as purchased.
    Photo By Peter Rooke
  • The rotten insulation block.
    Photo By Peter Rooke
  • New insulation block with old coils still in place.
    Photo By Peter Rooke
  • The rusty armature.
    Photo By Peter Rooke
  • Poor state of the coil, with rust on the pole pieces.
    Photo By Peter Rooke
  • New coils fitted.
    Photo By Peter Rooke
  • The cleaned up bracket.
    Photo By Peter Rooke
  • The magneto and igniter assembled.
    Photo By Peter Rooke
  • Temporary frame being used to get the shape of the crank guard.
    Photo By Peter Rooke
  • Starting to hollow out the main part of the guard. The “anvil” is in the background.
    Photo By Peter Rooke
  • The completed guard after grinding down the weld.
    Photo By Peter Rooke
  • Boring a hole for the threaded section for the connecting pipe.
    Photo By Peter Rooke
  • Heating the metal plate prior to doming. The second piece is resting on the top of the bricks, with a slight hollow in it.
    Photo By Peter Rooke
  • The domed metal after planishing, one piece being rough sawn, ready for rounding.
    Photo By Peter Rooke
  • The completed muffler.
    Photo By Peter Rooke
  • Ready to braze the boss to the body, the rivets and spacers shown alongside.
    Photo By Peter Rooke
  • The old and new pushrod.
    Photo By Peter Rooke
  • The pushrod support with new plate and retaining nuts. The shim is just visible.
    Photo By Peter Rooke
  • The hole in the pushrod spacer for rebound spring hook.
    Photo By Peter Rooke
  • The broken fitting for the drip oiler.
    Photo By Peter Rooke

Fuel tank

The original round fuel tank on the 2-1/2 HP Ottawa was 9.50 inches in diameter with 0.250-inch seams, 3.25 inches high, constructed from 26-gauge (0.18-inch) galvanized steel. This struck me as being a little thin for durability, so I used 18-gauge (0.48-inch) ungalvanized steel left over from an earlier project.

I first decided how to cut out the three pieces needed for this tank while wasting the smallest amount of sheet metal. I drew two circles 10.125 inches in diameter, including 0.625-inch extra for folding the seams, and a piece 28.8 inches long by 3.75 inches wide for the side. I also drew lines marking the folding points for the seams before the three pieces were cut out with heavy metal shears.

To start, I clamped the long-side piece between two strips of flat bar at the marked line for one of the seams. I held a hardwood block against this seam that I then folded it over by hitting with a hammer. Once the two seams were folded, I turned my attention to the two round pieces for the top and bottom, with a former being needed to create the lip on them.

I found a cast iron wheel with a good, clean, square edge, but it was not quite big enough. I bent a length of scrap metal sheet then tack welded it to the wheel, thus providing a former the exact size needed, 9.50 inches. I used this to create a 90-degree bend to form the lips of the top and bottom pieces.



I rolled the side piece to the rough diameter of the base by gently easing it around the wheel former with hand pressure. After I removed short sections where the top and bottom lips of the side piece overlapped, I adjusted this side piece to fit inside the base. Once satisfied with the fit, I cleaned the mating surfaces where the ends met and fluxed then tinned with high temperature solder. I again fitted the side piece inside the base piece so that I could solder its ends together.

Four tabs fitted to a ring of 0.091-inch thick wire resting on the bottom lip of the tank would hold the tank in place on the cart timber. I cut a length of this wire and made a half lap joint in each end before I brazed them together to form a ring that would just slide over the side of the tank.