A Bull Dog gets its bite back
Editor’s note: The following is Part 4 of a four-part series on Peter Rooke’s restoration of a 1-1/2 HP Bates & Edmonds Bull Dog.
All that remained of the original fuel mixer was a broken rusty stub in the cylinder head. I had been able to take some external measurements to go with some photographs that had been taken of a friend’s mixer.
The first item that I needed was a cast pipe fitting that could be adapted for the bend and mounting to the cylinder head, part of which was cut off to get the right profile. To make it easier to machine the mixer, the main body would be fabricated from six pieces of steel!
A 2.5-inch length of 1-inch internal diameter iron tube was turned to match the smaller diameter of the pipe bend and then bored out smooth. The venturi was then machined from a 2.625-inch length of solid steel, a 0.500-inch hole first drilled through the length of the steel before cutting a taper in both ends, leaving approximately 0.750 inch in the center as 0.500 inch outside diameter for the constriction.
The diameter of the venturi piece was reduced to fit inside the tube leaving 0.125 inch protruding to fit into the end of the pipe bend in order to provide a locating lug when brazing together.
A piece of 2-inch diameter steel was machined next to form the outside of the bell mouth at the bottom of the mixer, cutting a parallel taper inside.
The bell mouth, center tubes and venturi were the first components to be brazed together and were then cleaned up. This part of the assembly was then put on the lathe and the internal tapers tidied up, to ensure a smooth surface with no ridges to interrupt air flow. At the same time the shoulder was cut to take the fixed part of the choke plate.
A 0.625-inch hole was then drilled through the center section of the mixer level with, and at right angles to, the center of the venturi. A 2.250-inch length of 0.625-inch steel was drilled through 0.438 inch and tapped 0.250 inch NPT to be used for the needle valve fitting and its seat. This stem was brazed into the drilled hole, being fitted as one piece to preserve complete alignment. The center section was next drilled out and reamed 0.500 inch to match the bore of the venturi.
Finally, the top section of curved pipe was brazed to the main body of the mixer, ensuring that the needle valve would be correctly aligned, parallel to the cylinder.
Once the body of the mixer was complete, some 3.000-inch diameter steel was used to machine the choke and tray for the mixer. The rotary table was used to mill out the complementary pieces of the air baffle, one plate to fit in the bell mouth of the mixer, and the other to be brazed to the bottom tray.
The needle valve and seat were machined from stock brass, dimensions being assessed from the photographs and relationship to the other parts. An assumption was made that all sizes would be a fractional size of an inch. If any reader wants detailed dimensions I will be pleased to e-mail a copy of the rough plan I drew. Just contact at me at the e-mail listed at the end of this article.
The most difficult part was the needle and seat, the needle being fabricated from 0.188-inch brass, brazed to a head of 1.000- inch diameter brass. A 0.250 by 20 thread was cut on the needle, and the taper was copied from a reamer of hardened drill rod I had made for a previous job. The internals of the valve seat consisted of cutting the seat using the reamer and drilling a 0.040-inch hole through the fitting for the fuel. This was later increased to 0.050 inch after test running.
A 2.250-inch length of 0.5625-inch hexagonal brass was used to make a check valve. One end was cut with a 0.250- inch NPT thread to match the hole in the casting with a 0.188-inch hole drilled right through. At the other end a 0.438-inch hole was drilled and a seat cut for a 0.375-inch check ball, a 0.375-inch NPT thread being cut on the end for the connection to the fuel line. The pipe fittings were all straight forward machining operations.
The name tag for my engine had long since disappeared and I started to investigate sourcing a replacement. While there are people who offer a service to make substitutes I decide to experiment.
Fortunately, I had been able to obtain some good photographs of original name tags of different styles and I was able to match a plate to another engine that had grease cups on the main bearings rather than oil cups.
To make life easier, the photo needs to be taken square on so that it is completely symmetrical. Ideally it should be in black and white rather than color as this will save a lot of work later.
To make the name tag I prepared a mask for the brass plate in order to etch it using electrolysis. My best photograph was in color so I used the tools of Adobe Photoshop to change the pixels to black or white – time consuming but very effective. If you use this sort of program to convert a color image to black and white, it will tend to use shades of gray and not produce a sharp enough image. This image was then converted to a photo negative, again using a computer photo program, and then resized to produce a printed image the size of the name tag.
The mask was next printed on photographic paper using laser toner. (If you do not possess a laser printer then prepare the image using your ink-jet and use a photocopier to get the toner copy). The choice of photographic paper was important and I experimented a bit before finding that ordinary quality Epson glossy paper worked better than premium.
The brass plate was prepared next by making it larger than needed so it could be filed to size when etched, and the fixing holes later drilled to ensure that the image was accurately centered. The brass plate was polished with fine steel wool and carefully cleaned with alcohol cleaner so that the toner would stick to it when heated.
The brass plate was taped to the mask, taking care not to touch the polished surface before using an iron on maximum heat (not steam mode) to press the mask onto the brass plate. The heat was applied for a couple of minutes before a roller was used to press the mask onto the brass. To ensure the effectiveness of this process the heat was applied again and I then kept rolling until the brass started to cool.
Once the brass was cold the plate was immersed in warm water and left for a while for the paper to soften and lift off the toner. It was necessary to carefully peel one layer of paper off then repeat the soaking until all paper was removed. A grey residue was left on the toner and this was gently cleaned off the brass to be etched, using a small brush. A waterproof marker pen was used to touch up areas of the mask when the toner had not adhered, and the plate was then ready for etching.
The edges of the brass plate and back were protected against the action of the etching process by covering them with tape. After experimenting with chemical etching using ferric chloride obtained from a local electronics store, I decided to use electrolysis, which seemed easier to control and more effective.
Some copper sulphate solution was mixed up and poured in a plastic tub. The brass plate was connected to the positive lead of a battery charger and the negative to a piece of scrap brass used as an anode.
The length of time to etch the plate depends on the strength of the solution it is immersed in and the depth of etch required. I monitored progress by switching it off, removing the plate and brushing off any residue, checking if the mask was still intact. When satisfied with the depth of the etch, the plate was cleaned with fine steel wool to remove the remains of the mask, filed to size and the mounting holes drilled.
Before starting to paint this engine I decided to run it in first. As numerous parts had been made to rough measurements some adjustment might be needed to get the working relationship right, and constant removal and fitting of parts increases the risk of damaging that paint job. How right I was!
The engine was bolted to two spars of old wood as a test rig. Before trying to start the Bull Dog, all moving parts were given a generous coating of oil and the grease cups filled and the bearings lubricated. My first attempts to start the engine resulted in failure, but it was winter and the workshop was not heated over night so the engine block was cold. While I could have filled the hopper with warm water (never put boiling water in a cold hopper because you might crack it) I envisaged having to frequently fill and drain the hopper. I therefore left the engine for a few weeks until the weather warmed up. This was a wise decision as it later started fairly easily but did not run for long, and would only start on a rich mixture then flood.
There, then, followed several days experimenting with different settings. First the governor was removed to reduce the number of variables. The fuel lines and check ball were examined and found to work correctly.
Eventually, I made a new needle valve and seat, increasing the hole in the valve seat to 0.050 from 0.040 inch, giving the needle a slightly longer taper.
The firing improved and gradually the engine settled down, timing being adjusted and the governor fitted, with the correct spring tension being found for its spring so the speed was a steady 400 RPM.
The engine was allowed to run for a couple of hours to bed everything in, and there was a real sense of achievement in getting an engine running that others might have consigned to the scrap heap.
This is a very heavy engine for its size (the published ex-factory weight being 350 pounds) so clearly a sled with wheels was required. I had a thick length of oak left over from renovating the kitchen some five or more years ago that I was saving for the right project – this was just that case. I cut two 32-inch lengths of 2-inch-by-3-inch from the plank and rounded the ends, still leaving enough for another cart in the future. These dimensions were obtained by scaling a couple of old factory prints on brochures.
I decided to lift the engine on cross pieces rather than bolt it to the long spars, in order to raise the height of the muffler. On my test rig, it was too close to the two main spars and was spewing muck on them. This also enabled me to widen the cart slightly to increase stability. After cutting the cross pieces from some off-cuts, they were bolted to the main spars and everything was given several coats of varnish.
The next problem was to find some suitable iron wheels. Unfortunately, all that was left in my shed were over 12 inches in diameter which I had to use. The hunt is still on to find some smaller ones.
Given the overall size of the engine I decided that I could manage without a turntable, which would simplify construction.
Without a turntable it was a simple matter to make two axles and use some bent 0.375-inch rod, threaded at each end, to secure them to the main spars. I did not bother with a handle, opting to move the engine around by holding on to the flywheels.
The engine casting was riddled with holes from deep rust with no trace of any original paint and numerous components were “as new.” Therefore there was no point in leaving the engine “original and as found” – a paint job was necessary.
I prefer to paint engines in a stripped down condition, then hand paint the nuts and bolts after assembly and testing. This means that if I need to strip the engine for any reason, I will not run the risk of damaging the finish if parts are stuck together or pull areas of paint off the engine when they are removed.
The casting had already been given a good cleaning with wire brushes so the first step was to fill the rust pits in the casting using car body epoxy filler. This was then sanded down and it took a few coats to get it relatively smooth. The next step was to use a high-build auto primer to provide the base coat before applying the top coats of enamel paint. If you cannot get this thick primer, a substitute can be made by mixing decorators filler powder in the primer until it has a creamy consistency. The trick is not to make it too thick else you will give yourself more of a job to sand it down. Several thin coats are best.
After a couple of coats of this filler/primer the casting was sanded again using 180-grit wet-and-dry to get a smooth surface on all visible areas. As usual I managed to cut through this primer in one or two spots, so when satisfied with the smoothness of the finish the engine was wiped with a new tack cloth and then given a coat of spray primer. This process lays the foundation for a high quality finish, which will undoubtedly be better than the factory original but after all the work in restoring the engine I wanted something that would stand out.
The color of Bull Dog engines has been the subject of some debate. C.H. Wendel states the correct color is a deep maroon and an old Dulux paint code is quoted on some websites, although this is not much good to me in the U.K.! It also appears that some people advise that engines were finished in brown paint, which is seen here in the U.K. although I wonder if this has arisen from weathering and aging of the original maroon paint. I eventually decided to paint the engine in a reddish brown.
One thing that did appear common is that the cylinder head, crank shaft and connecting rod were all painted silver.
The engine had several coats of paint and this was left to harden for a couple of days before cleaning any marks off the finish with 1000-grit wet-and-dry and auto paint scratch remover. The engine then had several coats of wax polish to protect the paint.
The secret with paint jobs is not to rush, allowing the paint to dry thoroughly and harden before attempting to assemble, and take your time to avoid accidental damage.
As can be seen from the finished engine photos, the final finish has a deep color and a good shine.
I understood that some engines were pinstriped and an exchange of e-mail messages with Randy Hart resulted in information about his larger Bull Dogs that still retained some original finish. Based on these photographs and supporting information, I line-striped my engine in yellow to complete the paintwork and highlighted the words Bull Dog in gold paint.
Since completing the engine I have acquired a Webster CMM magneto. This will need conversion to anti-clockwise operation and a new igniter/bracket made to finally restore the engine to its original state. Read the first part of this project in the June issue of Gas Engine Magazine.