Half-Scale Gardner Model 0 Build – Part 1 of 2

By Staff
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Peter Rooke’s half-scale Gardner Model 0.
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The details of a hot tube, which uses a heated tube to ignite fuel to initiate combustion.
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Individual casting pieces for the Gardner scale engine.
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Machining the base for the crankshaft bearings.
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Checking bearing alignment.
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Boring the cylinder block for the liner.
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Cylinder block with liner fitted and faced off.
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Ready to press the broach through to cut the flywheel keyway.
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The piston with wrist pin.
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The almost finished crankshaft.
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Finishing the connecting rod on the lathe.
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The finished connecting rod with bearings.
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The air inlet for the valve chest.
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The valve chest before after machining.
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Hot tube fitted to the valve chest.
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The hot tube chimney and cap.
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The Gas burner for the hot tube.
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The assembled valve chest, burner and hot tube
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The piston rings were made from a piece of the cylinder liner.
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Splitting the rings
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The finished piston rings.
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Setting the rings.
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The finished piston with rings on the connecting rod.

Scale Gardner Model 0

Manufacturer: Alyn Foundry, North Wales, U.K.
Year: N/A
Serial No.: 2292
Horsepower: 3/4 hp @ 450rpm (full-size engine)
Bore & stroke: 1-3/8in x 2in
Flywheel: 9-1/2in
Ignition: Hot tube
Governing: Volume
Cooling: Tank-cooled
Weight: 39lb

Gardner background

In 1868, Lawrence Gardner founded a business working out of the common basement of four row houses in the Stretford area of Manchester, England. The business started trading as Machinists and General Engineers, but before long started to develop a range of products including sewing machines, coffee roasters and dentists’ chairs. On Lawrence’s death in 1890, his sons took over the business and formed L. Gardner & Sons.

The firm moved to larger premises, and started building A.E. & H. Robinson hot air engines under license until around 1914. The experience gained with these engines prompted the design and building of an internal combustion engine. The first engine, called No. 1, was built in May 1894. When coupled with a small generator it was used to light a room at the works. The first Type 0 engine was built in May 1895. It was rated at 0.55 hp at 450rpm, and the bore size was later increased to give 3/4 hp.

Oil vaporizer engines came later, and the company continued to expand its range of engines, which were also used to power automobiles and trucks, as well as for marine use. Production of new engines ceased in 1990.

The castings for this model engine were purchased many years ago from Alyn Foundry (now out of business) and had been left sitting on a shelf in the workshop without being finished. Although Alyn no longer produces these castings, a few years back it was rumored that the Anson Engine Museum, Cheshire, U.K., might produce a few castings from the original patterns.

A note on hot tubes

A hot tube is exactly what it sounds like: a thin-wall tube with a closed end. The tube is heated by a blowlamp or an integral burner, and surrounded by a chimney that’s generally insulated to some extent to prevent heat loss. Hot tubes are mounted upright on a cylinder or cylinder head adjacent to the combustion chamber.

The hot tube is heated to anything from dull dark red to bright orange, depending on the needs of a particular engine. On some engines, the tube had to be really hot to get the engine started. Then, by adjusting the burner flame, it was allowed to cool down a little to both extend the life of the hot tube and save fuel for the heat source.

Modern hot tubes tend to be made from stainless steel as it is far more durable and longer lasting when exposed to extreme heat than the black steel that was used when hot tube engines were first made.

To start a full-sized hot tube engine, you turn on the burner and heat the tube bright red/orange. Then open the fuel taps, and after priming with fuel turn the flywheel in reverse so on the compression stroke the fuel air mix is forced into the hot tube. When the mixture reaches the bright red section of the tube it ignites, generating a flame that travels back to the combustion chamber, igniting the fuel mix and moving the piston to start the engine cycle.

The Gardner kit

The kit consisted of a set of 20 castings, a poor-quality picture of the completed engine, and several pages of typewritten notes. These notes included points to watch out for when machining the castings as well as set up instructions to run the engine on gas. There were four sheets of drawings. These were hand drawn and care had to be taken to double check the dimensions, which were given in fractions of an inch in small, handwritten figures that could easily be misread. A couple of small errors were found.

The castings themselves were of good quality cast iron that machined easily once through the hard cast skin, with no imperfections. The first task was to clean off the casting residue using the bench grinder. It was my intention to run the engine on a butane/propane mix provided by small disposable gas tanks, which has proven suitable to power similar small engines.

Base and flywheel

The first task was to start on the main body casting and true up the bottom of the base to provide a stable platform. A grinder was used to remove the obvious high spots before engineer’s blue was applied to the marking out table. The casting was placed on it, and then the marked high points on the casting were removed, first using a grinder and then after repeated fits with a file to clean it true.

Once the base was even, attention turned to facing the supports for the crankshaft and its caps. This necessitated a mishmash of clamps to get the correct angle, with there being little room and clearance on the milling machine table.

The crankshaft bearing caps were faced on their underside, with oil reservoirs cut and oil passages drilled along with clearance holes for the securing bolts. The main engine block was next fitted flat on the milling table and the area for the cylinder mounting faced with a large cutter. This provided a true face for the base to be mounted on the 90-degree angle plate. After fitting the crankshaft bearing caps to the base, the bores for the bearings were drilled. At the same setting the area that the governor mechanism mounts on was also faced. The crankshaft bearings were turned from leaded bronze and then split in half.

The flywheel casting was turned on the lathe to clean it up and face the rim, with the hole for the crankshaft then bored true. The tapered keyway was then cut using a broach and press.

Cylinder and piston

The cylinder consists of two components; the external block and a cast iron tube for the liner. The tube was overlong so that part of it could be used to make the piston rings.

The internal dimensions of the cylinder liner were first turned on the lathe to a size 0.001 inch smaller than the plans to allow for honing. The rear or crankshaft end of the liner was machined with a slight chamfer to ease the fitting of the piston and rings. After mounting the cylinder on a 90-degree angle plate the inside was bored out so the liner was a tight slide fit.

The base of the cylinder block was machined square using the mill to provide a reference point. This followed careful measurement to ensure the center line of the cylinder aligned with the middle of the crankshaft. The block was then mounted on the milling table using an angle plate to bore out the inside for the liner.

The liner was cut 0.010 inch over length so that when it was fitted and held in place by Loctite, the outside end could be dressed off with a file. Once fitted and after drilling the hole for the oil drip feed the liner was given a light hone.

The other faces for the valve box, end cap, water way and exhaust were cleaned up with a milling cutter. The remaining holes detailed in the plans, some threaded, were drilled in the block, the majority being completed using the various caps and blocks that had earlier been finished as guides.

The casting for the piston was furnished with a generous chucking piece enabling it to be easily turned to size. It was turned 0.001 inch smaller than the bore diameter before removing the chucking piece. The piston ring grooves were cut with a freshly sharpened parting-off blade 0.0625 inch wide that was moved to create the 0.078-inch slot. All that remained was to cross bore for the wrist pin, which was made from stock drill rod. Two holes were drilled in the piston then threaded 4BA to fit two bolts to hold the wrist pin in place.

The test for a good piston fit in a model engine is to put it in the cylinder without piston rings. If it remains in the bore when the cylinder is up ended with the inlet and exhaust ports sealed, yet moves when one port is open, it is a perfect fit.

Crankshaft and connecting rod

The crankshaft was fabricated from two lengths of drill rod 0.50 inch in diameter, and some 0.437-inch by 0.750-inch steel bar for the throws. The steel for the big-end journal was slightly longer than needed so that it could be trimmed to size after assembly. The steel blocks were clamped together and the holes drilled through them, then reamed for the main shaft of the crankshaft and the big-end journal. After applying flux these pieces were silver-soldered to form the crankshaft, with the main shaft kept as one length during this process to keep everything true. A length of tube cut in half was used to ensure the correct spacing between the throws. When the soldering had cooled, the middle part of the main shaft was cut out from inside the throws. The connecting rod was turned on the lathe to trim the outer sides of the throws as well as round off the outer ends. To complete the crankshaft, the keyways were cut and a hole drilled in the big end in accordance with the plans for the oil splash system to lubricate it.

The connecting rod was made from length of 1.25-inch by 0.50-inch steel, 5.5 inches long. Holes were drilled for the big end cap mounting bolts at one end before the mill was then used to rough out the top and bottom of the rod. A short length of this steel was used for the big end cap, and it was drilled with similar holes to the main part, enabling temporary bolts to be fitted to hold it in position for machining. The two holes for the big- and little-end bearings were then drilled through the sides.

After drilling holes at each end of the rod and bearing cap with a center drill the connecting rod was transferred to the lathe, held between centers and turned to dimensions. At the head stock the center was fitted inside the four-jaw chuck so that its jaws could be used to hold the connecting rod to turn it. The section between the big and little ends was profiled to a taper by setting over the top-slide.

When the lathe work was done the oil groove and hole were milled in the top of the little end, and the surplus metal at each end for the center holes cleaned off. All that was left to complete the connecting rod was to turn the bronze bearings, slitting the big end in half.

Once completed the piston, connecting rod and crankshaft were assembled and fitted to the base. The cylinder block was then put in position and adjusted so that when the crankshaft was turned the piston moved smoothly in the cylinder. Clamping the cylinder in this position, four holes to secure it were drilled through into the engine body, the holes threaded and tapped for studs. Temporary bolts were used while the cylinder and other parts were being trial fitted.

Valves and valve chest

The valve chest involved several drilling and milling operations, with minimal clearance between holes in some places. The guidance notes for the kit said that care had to be taken, and on several occasions the part was put down and a different part completed before returning to the previous step to reassess it with a clear mind.

The two inlet valves for both gas and air were turned from drill rod before work started on machining the block. The collets to retain the valve springs were made from ordinary steel. It was necessary to make a small valve-seat cutter from hardened drill rod to cut the seats. The seats were finished off by grinding in the valves.

The air intake was made from a piece of steel tube capped with brass, the top being threaded to mount it on the underside of the valve chest.

Burner/hot tube

The ignition source is a hot tube. This was made from stainless steel, machined to give an internal diameter of 0.187 inch, and closed at the top end. This was threaded to fit the top of the valve chest chamber. When assembled the threads were sealed with a high temperature sealant.

The base of the burner itself is a small casting that has to be machined to provide mounting lugs, as well as a passageway and a burner plate made. After centering and then machining the supplied casting, pressure at the wrong point resulted in one of the mounting lugs breaking. This was at a point where the wall thickness was less than 0.0625 inch. With no spare casting available, this meant a replacement had to be machined from a lump of solid cast iron, so the opportunity was taken to make the walls a little thicker than the original. After machining and drilling the various holes in the cast iron, a burner plate was made from brass sheet and drilled with 12 holes. This was then silver soldered in place.

The hot tube chimney was supplied as a casting and the inside was bored out to 0.875 inch and the mounting points drilled and threaded. A cap to rest on the top of the tube was turned to size and then drilled with a series of equally spaced holes.

On some full-size hot tube engines the inside of the chimney was originally lagged with asbestos to retain heat, as well as protect the hot tube from excessive heat. The guidance notes suggested that the outside of the chimney could be covered with fireclay as an insulator.

Piston rings

There are various methods described to make piston rings, but the following method has regularly worked for me in the past.

The rings were to be 1.375 inch in diameter by 0.078 inch wide and 0.070 inch deep. The remaining small piece of the cast iron for the cylinder liner was turned to an internal diameter of 1.235 inches before being remounted on a specially turned mandrel. Some super glue was used to hold the cast iron on the tightly fitting mandrel. This mandrel was set in the four-jaw chuck to run true and the cast iron then turned to an outside diameter of 1.375 inches.

While still on the mandrel the cast iron was cut at intervals with a thin-blade parting tool to give rings 0.080 inch wide. As many rings as possible were cut to give spare rings. This cut was taken into the alloy mandrel to give a clean ring and when all the rings had been cut the alloy was lightly heated with the gas torch to destroy the adhesive, enabling the rings to be removed.

Each of the rings was then rubbed in a figure-eight pattern on fine abrasive paper, held on a true flat surface, to clean them to a thickness of 0.078 inch.

The rings were split by resting them on a length of steel rod, putting the cutting edge of a knife blade on the ring then tapping with a hammer. The gap was then trued square with a fine needle file.

A small piece of steel, 0.150 inch thick, was then used to force the rings open and create a gap. The rings that were then clamped together between some 0.125-inch-thick steel plate with a bolt. This helped to prevent distortion of the rings when heating to set them. This plate and the rings were placed in a dark corner of the brazing hearth and heated with a torch until they just turned dull red. They were held at this temperature for 10 minutes before being allowed to cool naturally. Each ring was then rubbed in a circular motion on an oil-stone until it fitted the piston ring groove precisely.

To set the ring gap, a length of tube was placed in the cylinder and the ring fitted in the bore and the ring gap adjusted with a file to give a gap of 0.003 inch. Extreme care had to be exercised when expanding the rings to fit them on the piston and it proved fortunate that several spares had been made. The piston was then moved in the bore to start bedding in the rings, before removing the piston, cleaning both it and the bore and then refitting it.

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