John Smyth 4-1/2 hp Restoration – Part 4 of 5

By Staff
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Peter Rooke's 1914 John Smyth
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Fitted sleeve butted up to the shoulder left in the cylinder bore.
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The rigid hone used to remove a final 0.002 inch from the bore.
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Finished bore with spacer fitted and igniter port cut.
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Setting up the piston on the lathe to run true.
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Machining the piston ring grooves on the lathe.
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The old and new wrist pins.
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The worn connecting rod little end bearing.
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The plugged oil hole in the connecting rod little end.
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Machining a new bronze bearing for the little end on the lathe.
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New bearing and wrist pin fitted.
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Used pressure tank for gas tank.
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Cutting open the seam.
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The inside of the pressure tank, showing the bag.
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Welding holes closed.
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Ready to fit the filler cap.
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The finished gas tank.
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The finished gas tank.
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Drilling holes in a support for cut-outs.
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Bending steel for the top of the support stands using rollers.
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Parts for a support stand cut, marked and ready for welding.
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Welding all the parts for a support stand together.
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Milling the elongated mounting holes on the milling machine.
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Bending a mounting strap around a pulley to get proper radius.
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The finished gas tank secured to the side support stands.
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The stripped Lunkenheimer mixer showing the brazed needle.
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The side of the mixer had been flattened, closing the fuel passage.
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Damaged area removed with brass tube in place ready to be soldered.
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Cleaned needle aperture showing remains of thread, and new fitting.
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Cleaned needle aperture showing remains of thread, and new fitting.

This is the fourth in a five-part series on Peter Rooke’s restoration of a 1914 John Smyth engine. Read Part 1, Part 2 and Part 3 for earlier stages of the restoration.

Fitting the Sleeve

Taking light cuts at the end of the boring process left a fairly smooth bore so it was not honed to ease the fitting of the sleeve, as some people suggest. The sleeve itself was measured at six different points around the diameter and it was a constant 4.753 inches. The cylinder had been bored to 4.751 inches so that there would be 0.002-inch interference fit, less interference than the 0.003 inch recommended, but ample for this engine. This fit would be plenty strong enough and it would not be necessary to use Loctite, as well.

Prior to fitting the sleeve, a steel disk used to check the bore diameter was skimmed so that it was an easy fit in the bore, with a step cut in it to fit inside the sleeve so it could be used as a press plate. A hole of 0.500 inch in diameter had been drilled through it so that it would take a threaded rod if it proved necessary to press the sleeve into place. One end of the sleeve was already chamfered by the manufacturer to make it easier to slide into position.

The sleeve was put in the freezer overnight with the expectation it would shrink by some 0.001 inch. With the steel disk in place it was found that it only took light tapping with a rawhide mallet to fit the sleeve, butting it tight against the shoulder that had been left at the crankshaft end.

Once the liner was fully in place the distance from the cylinder head end of the liner to the end of the cylinder was measured and a spacer ring trimmed on the lathe to 0.010 inch longer. The internal diameter of the tube used to make the spacer was slightly larger than the new bore diameter, but this was not of consequence as it was well away from the end of the piston travel. As this was a ring with a narrow cross-section that could be easily damaged, it was made to the cut diameter of 4.751 inches, with Loctite used to hold it place and keep it from rotating.


To accurately hone a bore an adjustable rigid hone is necessary rather than a spring-loaded glaze breaker. After fitting the sleeve the cylinder was bored out to 4.488 inches, with the final 0.002 inch to be removed with the hone. This smaller diameter allowed some tidying up of the piston.

There are differing opinions on using hones wet or dry, but in this case it was thought that using honing oil to lubricate and cool the cutting process would give a good, even finish, with the bonus that the stones would be protected from excessive wear. The instructions with the hone were followed, recommending an 8:1 mixture of kerosene and oil as the lubricant.

The stones on the hone were fitted, then trued to be parallel to each other by measuring with calipers and using the supplied truing paddle. The hone was first set up to the bore, following the manufacturer’s instructions. The drill worked around 400rpm and was vigorously moved up and down numerous times, the movement being adjusted to the drill speed to produce a 45-degree cross hatch pattern. The majority of the hone was kept in the new part of the cylinder with no more than 30 percent protruding from each end to prevent belling the bore.

Using a small spray bottle, lubricant was frequently applied to keep the bore wet. Frequent measurements were taken throughout the process, which started with coarse grit stones before finishing with medium grit stones.

After honing, scrupulous cleaning is necessary to remove all foreign matter from the bore of the cylinder, particularly any grit that might remain in the pores of the cast iron. This was left until all other cutting operations were completed. The engine casting was tilted up to allow a tray to be fitted at one end and then warm, soapy water was scrubbed into the bore. This was then wiped with a clean cloth and the operation repeated until the cleaning cloth no longer showed black marks.

Finishing the Sleeve

Once the sleeve was finished to size, it was necessary to remove the small step at the crankshaft end where it met the old bore, so that the rings would not be damaged when fitting the piston. This step was only a matter of a few thousands of an inch and was not consistent given the oval nature of the bore. The shaping was achieved using a small hand grinder, then a scraper, followed by emery cloth.

The hole for the drip oiler was opened up by drilling from the outside and down through the sleeve. Care was taken not to splinter the liner by being aggressive.

The port for the igniter had to be cut. This point was the area where the sleeve and spacer met, so extra care was needed to prevent a chunk of either breaking off. A series of small diameter holes were drilled following the outline of the port, but 0.125 inch inside the edge. Once the main part was removed the edge was then cut back using a fine rotary file at high speed before finishing with a medium hand file. Finally, scrapers were used to level the small amount of spacer ring that protruded from the end of the cylinder.


Once the cylinder had been honed the piston could be renovated. The bore had been finished 0.010-inch undersize at 4.49 inches so the piston could be trued. Measurements had been taken before starting to re-bore the cylinder, with up to 0.007-inch differences being recorded around the same points of the piston. Once more it was clear that this engine had suffered some abuse through hard work.

Surprisingly, the piston was fitted with 0.25-inch rings in 0.3125-inch grooves, so probably no attempt had been made to run it. The edges of these grooves were rounded so they needed squaring, and once again Dave Reed supplied new rings and ring spacers.

First the piston was set up on the lathe using the 4-jaw chuck normally said to run true, but in this case it was a bit of a judgment call given the irregularities on the outside of the piston.
For a 4.49-inch diameter bore the piston measurements should be:
Top Land: 4.473 inches
First Land: 4.478 inches
Second Land: 4.481 inches
Skirt: 4.486 inches

The piston was turned to these dimensions before attending to the ring grooves. For accuracy, high speed steel left and right hand tools were used to clean up the grooves, rather than a parting blade. The ring grooves had to be finished to a width of 0.3425 inches to accommodate the new 0.3125-inch wide rings and the 0.030-inch spacers. Any clearances needed were built into the rings and spacers. First the bottom side of the top ring and top side of the bottom ring were made square. Next the opposite sides were trimmed to get the width needed, progress being measured using a square of high speed steel and feeler gauges. This approach was taken to remove most of the metal away from the central ring so as not to overly reduce the two middle lands. The center ring groove was then machined.

The piston was thoroughly cleaned after machining and lightly oiled before the new rings and spacers were fitted. The spacers were fitted at the top of the rings.

The old wrist pin had to be replaced as it was heavily rusted, so a new one was made from a 4.360-inch length of 1-inch diameter drill rod. The ends were chamfered and recesses cut in the side for the securing bolts.

The little end bearing of the connecting rod was worn thin at one side, and at some stage a metal shim had been fitted around it to compensate. Furthermore, the oil hole was filled with a copper plug hammered into place. This bearing was discarded and a new bearing machined from leaded bronze. An oil hole was drilled through the bearing. New shims were made so that the gudgeon pin still turned freely when the clamping bolt was tightened. After finishing, the piston was fitted to the connecting rod before the ring compressor was fitted, ready to insert the piston into the new bore.

Gas Tank

The gas tank posed a problem as some original models were domed at both ends. To duplicate this style would require quite a bit of metal bashing to get it right. Before purchasing any sheet metal to make a tank, a little time was spent searching for any commercially made product that could be adapted. After making some enquiries it looked that it might be possible to join the domed ends from old fire extinguishers to make the tank. The basic dimensions that had been given from an original tank were 8 inches in diameter and 14.5 inches long.

A phone call from one of my friends brought the solution; the pressure tank from a central heating system that was being replaced. The measurements of this were nearly spot-on to the requirements, and furthermore one of the outlets was nearly in the right place for the fuel pipe.

The pressure tank was used to maintain water pressure in a piped heating system. It had a butyl bag inside that was used to maintain pressure and some redundant outlets. The first job was to cut the tank in half around the prominent seam using a hacksaw and small cutting disk, thus enabling the bag to be removed. The thick layer of red paint was removed next, then the rim was hammered flat and trimmed smooth to look more like a conventional fuel tank. The rim on one half was hammered on the edge of a piece of plate steel so that it was left with a step so that the other half of the tank would slide into it.

The next step was to hammer out the recesses of the redundant holes in the side before MIG welding them closed, discs of steel being used inside to ensure a good seal in the tank. A hole was cut for the filler cap fitting and the ring for this was then soldered in place. The final step was to tin the mating edges of the tank with solder before applying more flux, sliding them together and sealing them with gentle heat and more solder. After soldering, the outlet was capped and the tank filled with hot water and tested for leaks. After repairing one leak the tank was ready to be used.

Different types of stands to hold the fuel tank in place appear in photographs, ranging from a cast design to simple straps. The cast design with rods used as clamps was sketched out, and templates produced so some 0.25-inch-thick steel plate could be cut to size for the support stands. The templates were glued to the steel to aid cutting out.

Other parts for the tank’s stand were then cut and bent to shape, ready for welding. Once welded the slots were cut for the mounting bolts and holes for the straps. The straps themselves were made by threading the ends of two 24-inch-long lengths of 0.25-inch-diameter steel before they were bent around a pulley and fitted. They were cut more accurately to size once fitted.


The mixer, a Lunkenheimer type, had seen a lot of abuse, and even a cursory examination revealed a number of problems, particularly with the adjustment needle. The mounting for the needle had been repaired with a lump of braze and a small needle, adjusted with a screwdriver, fitted. The spindle for the compensating valve was badly rusted and would be replaced.

The repairs to the needle appeared to be a mixture of braze and lead solder, so a start was made by cleaning up the repairs and the surrounding area with a sanding wheel so that the edges of the different metals could be seen. First the lead solder was removed with a small burr wheel and then some of the old braze, with the result the needle and replacement seat fell out. Sections of the original hole for the needle were partly missing, but a small length of thread remained. These threads were filled with something that looked similar to JB Weld so they were cleaned out, finishing with a 0.25-inch NPT tap.

Before starting to repair the needle the insides of the needle seat and fuel inlet were cleaned. At this point an attempt was made to clear the passageway for the fuel from the inlet to the needle area. This was blocked with something more than dirt, and on closer examination it appeared the side of the mixer had been hit and damaged, to the point that the fuel passageway had been forced closed. It was clear that if it were drilled out, the drill would pierce through the outside of the mixer, so the hole was purposefully drilled oversize so that a piece of 0.156-inch brass pipe could be silver soldered in place. This hole was opened up with a rotary burr so that the tube could be accurately fitted, then fully covered in solder to ensure a leak-proof joint.

To repair the needle a fitting was made that looked similar to photographs of an original. However, given the damage to the thread the fitting would be brazed in place rather than screwed into the mixer body.

A piece of brass rod was threaded internally 0.25-inch UNC for a new needle and on the outside a 0.25-inch NPT thread was cut at one end and 0.437-inch UNC thread at the other for a sealing nut around the new needle fitting. The shaft for a new needle was made, the point tapered with an included angle of 30 degrees. At the same time that the compound slide was offset to cut this, a short length of steel was tapered to the same setting to make a reamer. The taper would be filed to half the diameter and the shank turned to a diameter of 0.205 inches so that it would easily slide through the 0.250-inch UNC threads. This temporary reamer was then heated until red-hot before being quenched to produce a hardened cutter, a diamond wheel being used for final sharpening.

The new fitting was tested for fit and adjusted so that when looking at a light source through the hole for the needle, the tapered hole in the mixer hole appeared in the center of the new fitting. The needle fitting was then brazed in place, and when cool the reamer was used to re-cut the needle seat. The effectiveness of the fit was tested by blowing through the fuel supply connection at the same time as the needle was turned.

Once happy with the fit of the needle it was cut to length (2 inches) and a new knurled knob made and then soldered on. All that remained was to make the sealing nut and a narrow nut to hold the spring to fit the knurls on the knob. An O-ring was used between the new needle and the sealing nut.

The rod for the compensating valve was badly pitted and the hole for it through the bottom of the mixer had been damaged and was oval. To restore the hole, a section of steel rod was cut to various diameters from 0.25 inch up to 0.4375 inch. The steps between these diameters were tapered. This rod was carefully hammered into the hole, gradually opening up the hole to the original diameter.

The original rod for the valve had been peened over to hold the brass disc in place. This was ground off to separate them. A new length of rod was turned to a diameter of 0.28 inch and then taper cut at the top to match the original so that the disc was a good fit. The tip of the rod was then heated and peened over like the original. All that was then needed was to find a suitable spring and drill a cross hole through the bottom of the rod for a split pin to hold it in place.

Contact Peter Rooke at Hardigate House, Hardigate Rd., Cropwell Butler, Nottingham, NG12 3AH, England •

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