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.
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.
This was repeated until there was more than 75 percent coverage of blue around the head. Engineer’s blue was then applied to the cylinder head, which was then bolted in position to check the fit against the end of the engine block. This fit was found to be acceptable.
After painting with heat resistant paint, the valves were assembled using the old springs that still appeared serviceable. A pin was made to replace the rusted pivot for a new rocker arm, which had already been obtained from Starbolt.
The pushrod bracket was broken in two, so both sides of the break were first cleaned with a wire brush before a final cleaning with a brass brush. I found that the brass brush made it easier for brazing. The two parts were covered in flux, heated until the flux was black and then cleaned with the brass brush again. This was repeated until most of the dirt was removed. Finally, the two parts were fluxed again and put on the brazing hearth for brazing.
To complete the bracket, a new take-up used to apply light pressure to the side of the pushrod was made by milling out some 1.250-inch-wide steel with a slot 0.125 inch deep to fit the width of the bracket.
The needle valve was removed and found to have a clean taper with no ridges. The seating in the mixer is not visible to allow its condition to be assessed, so rather than lap it at this stage it was left to see how it worked.
The air regulator (choke plate) was missing so a replacement was cut from 0.156-inch steel, and a suitable replacement retaining bolt and spring were found from the spare parts bins.
The old cylinder head gasket was securely bonded in place with sealant, as was the igniter gasket. These were both destroyed when stripping the engine and it took some work with the scrapers to clean the bearing surfaces.
New gaskets were cut using the cylinder head and igniter as templates, cutting the outer edges with a sharp craft knife before using a punch to cut the stud holes. After some minor adjustments with a round file, the gasket fit and the top was marked with a pencil.
To cut out the middle, a sharp knife was used to make several cuts from the center to the edges and then I carefully trimmed around the inside edge of the cylinder.
The original drain cock was long gone and examination of numerous photographs had shown no light on the exact style used. The outlet for the tap was on the side of the casting, so it made sense for the spout of the tap to be some distance away from the engine so that any draining hot water would not fall on the skid. In one photograph that I saw, the drain tap was simply a length of tube with a cap on the end. I decided to make a long tap similar to the drain cock on my Stover.
To make the tap, a piece of 0.625-inch brass rod was turned down to leave a ridge on the end before drilling it through with a 0.312-inch drill.
The main body of the tap was made from 1-inch diameter brass, which was first drilled right through the center with a 0.250-inch hole. It was next cross drilled halfway along with a 0.312-inch hole, opened up on one side.
A 5-degree taper was then cut into the body of the tap to a maximum diameter of 0.725 inch. Using the same setting, some 0.750-inch brass was turned to match it. This plug was next drilled with a 0.250-inch hole in the bottom end into which some 0.250-inch threaded brass rod was soldered. The plug was next inserted into the body of the tap and tightened so the cross hole could be accurately drilled.
The last major part was the threaded hexagonal piece, 0.750 inch wide with a 0.375-inch National Pipe Thread (NPT) being cut on one end. Again, this was drilled through with a 0.312-inch hole to match the others of the tap. A 0.750-inch-wide slot was finally milled across the side of the center section so that the hexagonal piece could butt against it.
To ensure everything remained in complete alignment when soldering, a wooden dowel was inserted through the three main parts of the tap.
Finally, a tap handle was shaped and soldered in place on the taper plug and the lock nut with washer completed the tap.
Before fitted to the engine, the finished tap was cleaned with a fine needle file to remove all burrs and some fine grinding paste was used to bed in the tapers.
With no fuel tank as a pattern, the dimensions and style for the tank had to be found. This was not easy as inquiries of various people identified a number of styles; all of which were supposed to be original, yet they all looked different! There were some basic parameters to follow: The tank needed to fit between the side pieces of the skid, be no deeper than the depth of the wood at the front of the skid and have a filler cap plus a screw cap for the feed tube with check valve. Additionally, it would make sense to add a drain plug so that fuel could be easily drained to stop it from evaporating and gunking up the tank.
The second decision was how to fit the tank to the sled: use hanging brackets or leave lips on the top to rest on the side of the skid? In the end, lips on either side of the tank worked best and were achieved by making the body from two pieces of sheet metal, with an additional two pieces for the end plates. Of course, it is possible to make a tank from a single sheet by carefully laying out the dimensions and seams, known as “drawing the development.” If this process is followed, the sheet needs to be cut precisely and all bends need to be accurate and square. As I possess limited bending tools, it was better for me to fabricate the tank in four pieces so that each piece could be adapted to fit.
To fit between the sides of the skid, the fuel tank needed to be no more than 6 inches wide and 2.75 inches deep. The tank needed to be long enough so that the filler cap stood clear enough of the cylinder head for ease of filling.
Some 0.025-inch-thick sheet metal was used for the main body with 0.050-inch steel sheet for the top piece. A paper plan was drawn with the dimensions of the pieces to be cut. Each end cap included an allowance of 0.375 inch on each side for the soldering tabs, minus a reduction in the width of 0.050 inch and 0.025 inch top to bottom to allow for the thickness of the metal sheet sides. For the top and main body, an extra 0.750 inch was added to each side to form the lip to fix it to the wooden skid. As the metal sheet was not thick no bending allowance was made for the thickness of the metal in the measurements.
Engineer’s blue was painted on the parts of the sheet metal where lines would be scribed, and the details of the plan were then copied to the sheet metal. The pieces were then cut out using a metal nibbler for the bigger bits. A sheer press was used for the smaller ones that would fit in, and files and snips were used for the small cuts and to finish it off.
Two screw caps and necks were needed, so a few old screw cap cans were found, on which the fittings were a little stronger than some of the modern fittings that are available. These allowed the necks to be cut off leaving a small rim of 0.250 inch or more that would help when fixing the neck in position.
The position of the drain cock bushing, filler cap and fuel line cap were marked next on the sheet metal and holes drilled using either metal hole saws, or, in one case, a sheet metal punch. The drain cock bushing was made from 0.750-inch outside diameter brass, part of it being turned down to 0.625 inch to fit the hole in the tank side and leaving a 0.750-inch shoulder on the outside. It was drilled then tapped 0.250-inch NPT for the drain plug.
While the small sheer press could have been used to complete some of the smaller bends, two pieces of rectangular steel were used as folding bars for all parts of this tank. Starting with the main body, the two bars were clamped to the sheet at the precise point of the bend, and the tops of the bars were level with each other. The two bars were then held securely in the vise and hand pressure was used to start bending the metal taking care to ensure that it was being bent in the right direction. To complete the bend, a rubber mallet was used taking care not to hit too hard and deform the metal. One way to ensure that the metal sheet is not dented is to place another piece of steel bar on top of the sheet metal and hit that.
Once the main body was finished, measurements were checked as well as the angle of the bends using a set square.
The two end caps were made next, which involved bending the soldering seams on all four sides. Two sides could be bent using the press or folding bars, but for the remaining sides the fingers were in the way. To complete this step, trim a block of hardwood to the internal dimensions or find a piece of steel the right size to fit between the lips. Then use a wooden mallet or vise press to form the fingers around this block.
Once the first lip was bent, measurements were checked to the already formed main body so that necessary adjustments could be made to the position of the bend.
Once the pieces were finished they were trial assembled to check the fit before cleaning. The next step was to fit the necks for the filler caps and the drain bushing using a higher temperature solder so they would not move when soldering the remainder of the tank. When using the higher temperature solder and a gas torch take care not to overheat the sheet metal as it might distort.
Once the filler caps and drain plug were fitted, the metal was cleaned well and flux applied before heating. It is best to use a copper tipped soldering iron or a torch with a small flame so that the area of metal that is being heated can be controlled. Do not overheat the metal or else the flux will be destroyed and you will find the solder will not flow across the metal.
First, all parts to be joined were tinned by fluxing, heating and applying a thin layer of solder. After tinning, the first end cap was re-fluxed then clamped in position before heating with the soldering iron and applying solder. Then the clamps were moved and the soldering completed.
The next step was to fit the second end cap, again clamping it in position. Finally, the top sheet was fluxed, clamped in place and solder applied.
The fixing holes for screws into the skid were then marked and drilled before testing the tank. Fitting the drain plug, the tank was then filled with hot water so that it would melt any flux that might prevent cold water from leaking. Any leaks were marked with a wax crayon before thoroughly drying the tank, fluxing the marked areas and then heating to clean it. After brushing again with a brass brush, it was fluxed and the soldering iron was used to seal it.
To complete the fuel tank, a pipe was needed for connection to the mixer. Some 0.250-inch brass tube was used and the end fitted with an inline check valve fitted in the tank. To get the profile of the bend right, a piece of wire coat hanger was first bent and then used as a template so the bend in the brass would be right the first time and expensive tube not wasted.
A new check valve was used, but before fitting, a small slot was cut with a needle file above the check ball to allow fuel to flow up the pipe even if the check-ball lifts up. Another piece of brass was soldered to the bottom of the check valve so that it reached the bottom of the tank. If there are any concerns about dirt in the fuel then a cone of thin brass gauze could be fitted in this lower pipe to act as a filter.
Bore and piston
The piston and rings had already been removed when stripping the engine.
The cylinder bore was cleaned out using kerosene and a clean rag. It was soon evident that there was a lot of rust pitting near the top of the cylinder.
An internal gauge was used with a micrometer to measure the bore and assess the damage as well as check the fit of the piston.
The 3.5-inch piston had not been damaged, and it measured within normal tolerances. The bore, however, was a different story. Where it was untouched by pitting, the bore was 3.507 inches, which is well within accepted tolerance of 0.020 inch. However, where there had been rust, the bore increased to 0.017 inch oversize and required re-boring. The problem with a re-bore is that an oversized piston is needed, or a sleeve must be fitted and the old piston retained.
As the damage was not widespread, no major action was taken until after the engine was assembled and compression checked. If there was sufficient compression for the engine to work reasonably well, the bore would be left as it was. Otherwise, remedial action would be taken.
To clean up the bore, a hone was used to skim the surface lightly. Lubrication was provided by water rather than oil, which tends to clog up more.