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



HP Ottawa

Peter Rooke’s unrestored 2-1/2 HP Ottawa

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.