The Internet Craftsmanship Museum Presents:

Find Hansen

Added to Museum: 1/7/10

Building running model "hot bulb" engines takes him to rarely traveled territory in the world of model engineering

Find Hansen displays a few of his hot-bulb engines.

Introduction—What is a “Hot Bulb” engine

Early 4-cycle engines often were not ignited by a spark plug, but rather were ignited by an element heated by a blowtorch—a hollow ignition tube or hot-bulb that was connected via a throat or channel to the combustion chamber. In very early hot-tube ignited engines the fuel and air were sucked into the combustion chamber via one or two intake valves. Some engines had an intake valve for fuel (often gas) and one for air. Then the mixture was ignited by the compression into the hot tube. The ignition timing could be controlled by moving the blowtorch in or out along the hot tube.

A typical hot-bulb type ignition was often bigger with a larger inside volume and different shape from the ignition tube, and the fuel was often injected by a low pressure injector directly into the hot bulb at the inlet stroke. The injector was, in most cases, water cooled to prevent the fuel from boiling. The ignition timing depended of several things: 1) the amount of heat in the hot bulb, 2) the inside volume of the bulb, 3) the compression ratio, 4) the type of fuel and 5) the injection timing of the fuel. On some engines the compression ratio could be changed by a cast iron block to suit the available kind of fuel. The cast iron block had two different shaped sides and was bolted to the compression camber. By turning the block upside down the compression chamber got smaller or bigger, thereby changing the compression ratio. Water injection was sometimes added to cool down the hot-bulb on a hard working engine, thereby preventing pre-ignition.

One of the reasons for the popularity of hot bulb engines was better fuel economy compared to other engine types and the ability to use cheaper fuel, as most engines ran on some kind of inexpensive oil.

One of the pioneers in making hot-bulb engines with injected fuel was English engine builder Richard Hornsby, starting about 1892. In Denmark an engine builder named Hein got started in about 1902 and made hot-bulb engines, most of which were used in fishing boats. Later the four-stroke hot bulb engines were replaced with 2-stroke hot bulb engines, then semi-diesel engines and finally diesel engines.

About Find Hansen

Find Hansen was born in 1948 and lives on a small island called Bornholm, which is a part of Denmark, in a city called Gudhjem close to the Easter Sea. He came from Copenhagen to Bornholm 1970 and bought an auto repair shop in 1972 in a town called Østerlars. He still runs the shop, repairing vintage cars and old sports cars like MGs, Jaguars and Porsches.

Find bought a house in Gudhjem in 1999 where he and his wife live now. One nice thing about the new house is a splendid view of the sea and plenty of room for an indoor work shop for Find. Another plus is a big room for his wife for her weaving. He has two small lathes and an assortment of hand tools in his home work shop, and when it comes to bigger things like turning flywheels, welding steel bars, using a metal bandsaw or an angle grinder, he goes to his auto work shop, where he has an old but accurate English 1-meter lathe.

He has no formal education in car repairing or engineering and is completely self-taught. He does like the excitement and challenge when new engine parts are to be made, with many thoughts going through his head. Things to be considered include what material to use, choosing the right scale, what machinery to use, where to begin and where to end and, of course, making the necessary drawings. But one of the most exciting times for Find is the first test run or “first pop” of a new, finished engine. Does the engine start easily? Does the injector and injection-pump work properly? Is the compression good with no leaking valves piston rings or gaskets? Naturally, there are always some adjustments to be done.

There are certain demands to a small lamp-start, hot-bulb engine that works with injected fuel if you want it to run properly and slow at about 350-400 RPM and you want it to run without a continuous blow-lamp. The fuel must be right. He has tried fuels from diesel to turpentine, and the engine works on either. Diesel is smoky and sooty but easily keeps the hot-bulb system hot, while turpentine burns much cleaner but vaporizes faster than diesel, thereby “stealing” more heat, which means a colder hot-bulb system.

The compression must be good because the heat from it is important for the ignition. Most of the combustion must take place in the hot-bulb so a compression ratio of at least 7:1 is needed.

The hot-bulb system must be slightly different compared to the hot-bulb system of “the big engine.” It cannot just be scaled down.

A reliable injector and injector-pump and a working governor system must be made. There must be good cylinder lubrication, because when you are dealing with vaporized fuel like kerosene or turpentine it will have a tendency when the engine is cold to wash the oil off the cylinder wall, but this and other problems will be addressed below.           

Find Hansen has made model engines for many years, starting, as he recalls, around 1980 with steam engines, then four-stroke gas engines with high tension or hot tube ignition. His latest models are four-stroke, lamp start, hot bulb engines with a bore of 20 mm and a stroke of 30-36 mm. None of his engines are scale models, but are so called “freelance” engines of his own design. Their look is inspired by engines built in England around the turn of the previous century such as Crossley, Hornsby and Blackstone. Mr. Hansen submitted the following essay on why he likes to work with the design of old engines.

Why I like old stationary engines

By Find Hansen

Some years ago I started visiting a friend of mine called Poul. He vas a collector and had collected, among many other things, stationary engines. He often started an engine when I came, and one day he started a horizontal 5 hp gas engine—an English engine called Crossley build 1896 with a big curved-spoke flywheel. The engine was “born” with hot-tube ignition (the tube was made of porcelain) but was later converted to high-tension ignition and a Ford Model T carburettor, using petrol instead of gas. I was very interested in the engine and it was fascinating to see it run. It was a real slow runner, turning only about 120 RPM. Most engines were quite open at that time. They were often called “open crank” engines, and that is an engine type that I do like. You can see all the mowing parts, the piston travel in and out and even if you are not an “engine man” you will get an idea of what is happening and how things work.

I think that many model steam builders feel the same about steam engines. There are certain sounds when an old engine is running; the clicking cam followers, a hollow sound when the piston returns, a deep weak rumble from the main bearings, the intake and, of course, the exhaust, and if you are listening very careful you can sometimes hear the ignition.

When engine builders in those days build engines, they were made to be good and reliable and have a long lifetime, but another very important thing was the appearance of the engine. I think that you can call it some kind of “engine art,” because some of the engines were really beautiful to look at and many things were done to achieve that look; for example, the shape of the base and its profiles, the brass handles the copper pipe work, the fly-ball governor, the oilers and sight feed lubricators, and last but not at least, the finish the painting. A lot of grinding work had to be done to the rough cast iron before painting.

Well, back to Poul and his Crossley… We talked about making a model of the engine, and I thought it was a very good idea. I did some measuring of the flywheel crankshaft base, piston etc. and drove home to start making the drawings.  It should be a scaled down 10-to-1, as at this size you can display it on a shelf in the living room. I finished the engine, but it never became exactly the same engine as Poul’s, nor was it ever meant to be that either. I would just try to make an internal combustion engine and get it to run, and so it did.

Then came my “hot-bulb model-engine life”

On another visit to Poul’s he started a lamp-start, hot-bulb engine called Bornholms Maskinfabrik that was build on my island 1906. The engine had spent its working life at a farm before electricity. With this engine the start procedure was a bit more exciting. The hot-bulb had to be heated before starting the engine using a blowtorch. The original blowtorch was missing, so Poul used a gas blowtorch. While the hot-bulb is heating you have time to check the engine: top up the oilers, lubricate mowing parts, check for water, check fuel level and bleed fuel injection system if necessary.

A typical hot bulb engine. The unpainted component at the end of the cylinder housing is the hot bulb cover. Inside is the hot bulb and the vaporizer tube. The polished brass item below it is the blow lamp that functions like a small torch to heat the hot bulb until it glows. This ignites the mixture inside the cylinder without using a spark. (Click on photo to view a larger image.)

Starting a Hot-bulb engine

Heat the hot-bulb until it becomes brown red with the blowtorch. This takes about 5-10 minutes. Then two quick pulls at the injection- pump handle, or if no start-handle is available, turn the flywheel by hand slowly forwards until the compression just begins, then turn the flywheel backwards as fast as possible and let go of it just before compression. If everything is OK, the engine will ignite and turn forwards. (This requires a bit of practice.)  A funny thing about hot-bulb engines whether 2- or 4-stroke is that most are available to run both forwards and backwards, and when it happens that the engine runs backwards most engineers know how to return to forwards without stopping the engine, just using the injection pump handle at the right moment.

Poul and I talked about building a lamp-start hot-bulb engine and Poul said, “This time you will have to deal with many difficult things. First, you will have to make a useful workable mini-injection pump and governor system, (injection engines must have some kind of governor system or they will be completely out of control) an injector that must be water-cooled to prevent the fuel from boiling and a hot-bulb of the right size. I wont say that it is impossible, but it will be a very difficult job.” Then I said to him, “I will give it a try. The more the difficulties, the greater the challenges.”  I went home and started to build my first hot-bulb model engine. I finished the engine and after a long time, and with many experiments I got it to run. After that I have improved many things on my engines, and today I think they run properly.

Building the parts

Find enjoys making the drawings, and he makes all of the parts for the engines by himself. None of the parts are made in a foundry, but rather they are constructed or fabricated from billet stock. The bases are made of flat steel bars cut with a bandsaw to get the right shape, bent and then welded together. The parts for the flywheel are three large steel rings with different diameters, six spokes (straight or curved) and a hub. Six holes for the spokes are drilled in the smallest steel ring and in the hub, and then the ring, spokes and the hub are silver soldered together. After that, the two larger steel rings are soldered together with the smallest steel ring. Then the flywheel goes to the lathe for turning the sides and the outer rim. After painting the flywheel, it is put back in the lathe for boring the hole in the hub to fit the crankshaft.

The crankshafts he makes are not built up in several parts, but rather are made from a solid round steel bar or a flat square steel bar using the lathe and a four-jaw chuck with independent adjustable jaws. When a flat square steel bar is used he first uses his metal bandsaw to cut off unnecessary material. The cylinder is made up of two pieces; a liner with space for the water and around this a sleeve to make the water jacket. The piston is made from a solid round bar which is 20 mm longer than the piston’s final size.

First, he bores out the inside of the piston, and then he turns the outside of the piston to be a bit larger than the finished size. Then the piston goes to a four-jaw chuck on his Myford ML7 lathe to be cross-bored to fit two large piston pin bronze bushings. The bushings are then silver soldered to the piston. Then the piston goes back to the lathe to finish the outside surface, cut grooves for the piston rings and to cut a bit off the end of the piston to give it the right length. The cylinder head is made from a solid piece of steel bar stock which is drilled, bored and turned to make the valve chambers, valve guides and seats, the combustion chamber, holes for the cylinder bolts and threads for the hot bulb, the hot bulb cover bracket, the rocker arm bracket bolt and a short sealing bolt.                                  

Find does not have a milling machine to make the worm gear wheels so he uses a lathe. The teeth are cut out bit by bit, tooth by tooth. He uses a tool bit, ground to fit between the teeth of the worm gear. The headstock is connected to the leadscrew with gear wheels in the right ratio, and then the leadscrew is turned by hand.

Solving problems inherent in scaled-down engines

There are certain difficulties encountered when making a small four-stroke, lamp start, hot bulb engine with injected fuel. First, the hot bulb system: It is difficult to scale a hot bulb system from full-size to a small engine if you want the engine to run without a continuous flame from a blowtorch. The heat from the hot bulb will soon escape to the cylinder head and the water-cooled injector because of the short distance between these two elements. Therefore, he had to make his own hot bulb system. After making several different hot bulbs and spending many hours with experiments he ended up with a useful one. To prevent the heat from the hot bulb from escaping to the cylinder head, the hot bulb has a long, thin-walled neck with a wall thickness of 0.20 mm. To prevent the heat from escaping from the bulb to the injector, he has moved the injector from the bulb to the cylinder head, thereby having an indirect injection—not into the hot bulb, but on a vaporizer tube connected to the inside end of the hot bulb. Now, when the hot bulb is heated, the vaporizer tube is heated too. On its hot bulb end the vaporizer tube is cross-drilled with several holes, and the vaporizer tube on the injector end is cross-drilled with only one hole into where the fuel is injected.

Parts of the hot bulb system include the hot bulb cover (top left), the hot bulb (lower left) and the vaporizer tube (lower right). (Click on photo to view larger image.)

Next, he had to make a governor system, an injection pump and a useful injector. The governor system could be a hit-and-miss system, but he rather likes a fly-ball controlled injection plunger pump. Therefore, he made a system where a fly-ball governor is connected with a conical bar. This bar is situated between an injection pump cam and an injection pump plunger so when the conical bar is moved in and out by the fly ball governor, the stroke of the plunger will be changed as well, thereby giving more or less fuel to the injector. He soon learned that there must be no leak at all between the ejector valve and the valve seat. It would stop the engine if just a tiny bit of air from the compression or gas from the combustion got into the injector. The valve has a valve head which is turned in the lathe to have an angle of 14° and then polished with very fine sandpaper. The valve has a threaded stem so that the valve spring can be adjusted to the right fuel pressure with one nut and locked with another nut, and the valve stem is 0.90 mm thick. The injection pump is an ordinary type with one inlet and one outlet ball valve and a plunger. The balls are 1 mm and the plunger is 18 mm long and 2 mm thick. He found that when the engine runs at an idle speed of about 360 RPM with no load, the plunger only moves 0.03 mm.             

The blowlamp or blowtorch works with lighter fuel, and the gas is filled from the bottom. The gas flame is controlled by a small needle valve. The problem with a blowlamp so small that must deliver enough heat to warm the hot bulb is the short, thin flame tube. If you turn the gas needle valve up too much the flame will blow out. His solution was to cross-bore the flame tube so that a small bar could be placed there. This split the gas flow to slow it down, and that worked.

Find Hansen and his wife enjoy restoring and driving their vintage Ford Model T. (Click on either photo to view a larger image.)

You can learn more about the problems find encountered and how he solved them at his web site at

Videos—Find's Hot Bulb Engines in Action

Click on any of the links below. You can also open any of the links below and then access the other videos from the "More from Boksermotor" on the right-hand side of the YouTube page.

• Part 1:

• Part 2:

• Part 3:

• Part 4:

• Part 5:

• A twin cylinder hot bulb engine:

• A twin opposed hot bulb engine in action:

• A vertical hot bulb engine with inverted blowlamp in action:

Some new videos were added in September, 2010:

• Running a four-post engine:

• Running a six post engine of Find Hansen's own design:

• Running a semi diesel engine:

• A demonstration of Find's very first built hot bulb model engine:

Find's 12cc Diesel:

• A video demonstration of how the Dieel engine is started and controlled:

Building a 12cc Diesel Model Engine

Find Hansen first started working on a Diesel engine in 1995. In 2011, 16 years later, he finally has one that runs to his satisfaction. More photos of the engine can be seen in the photo section below and a video link is provided above. (Click on any of the three images to view a larger image.)

In 1995 Find Hansen tried to build a true diesel model engine with injected fuel, but with no success. It ended up being a hot bulb engine. Since then he had dreamed of building a diesel engine again, and now he has one running. The engine has a bore of 20 mm, a stroke 40 mm, and a compression ratio of 21:1. The engine does not use a pre-chamber, but has direct injection, and the fuel is for now kerosene.

The engine is vertical and has an A-frame construction like the old Danish-built B&W blast injection diesel engines. He built the engine and the crankshaft stronger this time with thicker journals to withstand the high compression. Then he drilled an oil passage in the crankshaft to have a continuously lubricated big end.

Starting the engine

Find notes, "At the first start attempt I tried to start the engine using Ether Diesel start. It started and ran, but only on the Diesel start, not on the engine fuel. At the third attempt the flywheel broke loose. I fixed the flywheel, tried again still using Diesel start. This time it started and ran on the fuel. I tell you I was happy." On the next start attempt still using Diesel start, the engine started, but with an awful noise. The connecting rod was bent, but luckily nothing else had happened to the engine. He made a new connecting rod, now 6 mm thick. (The old one was 5 mm thick.)

At the next start attempt he thought, "No more Diesel start, why not try to use my wife’s hair dryer?" He did try the hair dryer, and when it was about hand warm, he tried to start the engine. He found he could not hand crank it because of the high compression, so he used an electric drill, and to his surprise it started and ran. Since then he has experimented with the injection pressure, the injection timing and different kinds of fuel. He found that it is very important that the injection timing is just right. A few degrees before or after and the engine will not run properly.

Find's thoughts about building a small scale working diesel engine

1. The compression must be about 100% with no leaky piston rings, gaskets or valves, because the compression heat is the only igniter.

2. The compression ratio must at least be 20:1 for an easy start and 22:1 would be better. You should not be afraid of the high compression. The engine starts, runs and works much better.

3. The injector must atomize the fuel very well, because the compression heat is the only thing to vaporize the fuel before it is ignited.

4. Using a light fuel such as kerosene instead of diesel is better, because it vaporizes and ignites more easy and is not as smoky as diesel.

5. The crankshaft, crankshaft bearings, big end bearing, piston pin and connecting rod must be made bigger and stronger to withstand the high compression, because the load on about a 20 mm piston with a compression ratio of say 21:1 is about 160 kg, and when the fuel is ignited the load is about 180 kg. When pre-ignition occurs (Diesel knocking) the load rises to about 220 kg. It is a wonder that the engine will stand this heavy load. Also, the whole engine construction must be made stronger.

6. The main bearings and especially the big end bearing must have good, continuous lubrication while the engine is running.

Here are photos of several examples of Find Hansen's work:

(Click on photos to view larger images.)

Hot Bulb Engines


Find's very first engine was built in 1984. It was inspired by a Crossley gas engine, several of which can be found on the island where he lives. The engine has a high tension ignition, is fueled by lighter fuel and has a bore of 20 mm and stroke of 42 mm.


His second engine was built in 1988 and was inspired by an engine built on his island in 1906 called a Bornholms Maskinfabrik. It is a four-poster hot bulb engine with fly-ball governor that controls the injection pump (see second photo) and a water cooled injector (see third photo above the flywheel rim). The engine needs a continuous flame from the blow-lamp to run. The bore and stroke are both 20 mm and the fuel is kerosene. (Kerosene is referred to as "petroleum" in Denmark.)


Built a year later in 1989 is this inverted hot tube gas engine. It features a fly-ball governor controlled "hit and miss" system keeping the exhaust valve open at a certain speed (see third photo) by means of a lever connected to the exhaust valve rocker arm that hits a part of the fly-ball governor when it is open. Photo 2 shows the hot tube and burner. The bore is 20 mm and stroke is 24 mm and it runs on lighter fuel.


The next engine from 1990 is a horizontal hot bulb engine. It still uses a continuous blowlamp (blowtorch) to heat the hot bulb and has a water cooled injector. The bore is 20 mm and stroke 24 mm and it runs on kerosene.

The third photo in this section shows a close-up of the fly-ball governor, side shaft with injection pump cam and valve cams and a cylinder head with a inlet valve on top and exhaust valve on the bottom. He made the worm gears that connect the crankshaft to the side shaft and the side shaft to the fly-ball governor on a lathe because he didn't have a milling machine. The teeth were cut one at a time, a little bit at a time. He ground a tool bit to fit between the teeth of the worm gear, connected the headstock spindle to the leadscrew with gears in the right ratio and turned the leadscrew by hand, much like cutting a thread.

This engine, built in 2002 was one of Find's first lamp-start hot bulb engines where the blowlamp can be extinguished when the hot bulb is warm and the engine is running. On his earlier engines the hot bulb would tend to lose heat to the water-cooled injector and the cylinder head, thereby causing the engine to quit. He moved the water-cooled injector from the hot bulb to the cylinder head and made a new hot bulb with a long, thin-walled neck (0.20 mm wall thickness). Then he made a long vaporizer tube and connected it to the inside of the hot bulb end, thereby creating an indirect injection, not into the hot bulb but rather onto the pre-heated vaporizer tube which solved the problem. The bore is 20 mm and stroke is 30 mm. The 4-stroke engine runs on kerosene.

This is a similar engine to the one above and was built in 2003. It has the same hot bulb system and same fly-ball governor injection system but a bore of 20 mm and slightly longer stroke of 32 mm. It also runs on kerosene.


Also built in 2003, this is another lamp-start, hot bulb engine. It also has a bore of 20 mm and stroke of 32 mm and runs on kerosene.


This photo shows the hot bulb components. At the top left of the photo the large item is the hot bulb cover. The bottom row pieces are the hot bulb (left) and vaporizer tube (right).


Three injectors are compared in size to a wooden match. The two on the left are partially assembled.


Find designed and built this rig to test injectors.


This engine from 2003 has a bore of 20 mm and stroke of 32 mm and runs on kerosene.

This engine of similar size and function but slightly different layout was built in 2004. One common feature of all Find's engines can be seen here as well—a really nice paint job.

These inverted, lamp start, 4-stroke hot bulb engines are freelance designs by Find Hansen built in 2003 and 2004. They use an injection pump and injector controlled by a fly-ball governor like the other engines. This engine has a larger combustion chamber because of the separately connected inlet/exhaust valve chamber on the outside of the cylinder bottom. This meant Find had to increase the compression ratio to keep the hot bulb warm. Again, the bore on these engines is 20 mm and stroke 32 mm and they run on kerosene.

Here you can see a close-up of part of the first engine shown above detailing the water pump and its worm gear connection to the side shaft. Three sets of worm gears are used on the engine: 1) connecting crankshaft to side shaft, 2) connecting side shaft to camshaft and 3) connecting camshaft to fly-ball governor.
Another view shows the fly-ball governor and the governor handle in the top right of the picture. The camshaft and worm gear are seen in the middle of the photo. The injector (lower center of photo) and hot bulb cover (near bottom) can also be seen.
A special blow lamp had to be made to accommodate the low height of the hot bulb on the above engines. The second photo shows some additional configurations of blow lamps, each sitting atop a wine cork for size reference.
A "four-poster" engine with a bore of 20 mm and stroke of 34 mm uses Find's now-proven hot bulb with fly-ball governor-controlled injection pump system as on the horizontal engines. The third photo is a detail of the fly-ball governor.
This vertical four-poster was built in 2006.
Another engine built in 2007.
Built in 2007 as well, this is another  four-poster hot bulb engine. The second photo shows a detail of the water pump connection. The camshaft governor system is shown in photo three, photo four shows a detail of the cylinder oiler, and the last photo shows a detail of the cylinder head and rocker arms. The hot bulb cover is the black mechanism to the left with the blow lamp below it.
This is a 2-cylinder, 4-stroke "Six-poster" hot bulb engine with lamp start. Find used the same governor system as was used on the single-cylinder engines, but it took some time to synchronize the injection pumps for a steady idle speed. Engine number 2-06 was built in 2006 and has a bore of 20 mm and stroke of 34 mm.

The third photo shows a detail of rocker arm injectors, while the last photo shows a detail of the blow lamps and hot bulb covers.

More details from the above 2-cylinder engine show the camshaft, cam rocker arms with the rollers and the worm gears.
These close-up photos of the above engine show the cylinder oilers in the first photo and a detail of the crankshaft in the second photo.
This double opposed 2-cylinder hot bulb engine was inspired by an engine built by Blackstone in 1904. Find's engine number 1-08 was built in 2008 and has a bore of 20 mm and stroke of 34 mm. It runs on turpentine and uses the same governor system as his previous engines.
Some details of the above engine show the universal joint in the side camshaft and the rocker arms and pushrods at the end of the shaft.
Here we can see the fly-ball governor that controls the injection pump in the first photo, while the second photo shows the crankshaft main bearing with the oilers on both the main shaft that drives the flywheel and the ends of the connecting rods.
A twin-cylinder horizontal engine is the most recent of Find's creations. (Photos added 9September, 2010)
More views of the "twin motor" hot bulb engine
Details of the fly-ball regulator and the crankshaft
In the first photo, a side view, the twin brass glow lamps can be seen at the lower left of the image. The second photo shows intake-exhaust valve, valve chambers, valve springs etc. At the bottom are the rocker arms with push roads.

Diesel Engine Project

After first attempting to build a running Diesel engine in 1995, Find Hansen was finally successful with this Diesel, completed in 2011.

In the first photo the handle being operated is the governor spring handle for controlling speed.

The second photo shows the operation of the injection pump handle, used to bleed the fuel system. Find used the same well proven, governor controlled injection pump system he used on his previous hot bulb engines. It seem to work very well on the Diesel too. He was afraid that the injection pump would not stand the high injection pressure, but it did.

A video on YouTube explains the operation of each valve. See to watch the video.

In the first photo Find is operating the handle for the inlet rocker arm. This changes the stroke of the inlet valve, thereby changing the compression pressure. The engine needs a high pressure to start, but when it is hot the pressure can be adjusted down.

In the second photo, the handle coupled to the governor system is being operated. It controls speed and is used for stopping the engine.

The second photo shows the builder's plate--the finishing touch on a fine, working model.

The large flywheel, though good looking, turned out not to be as necessary for the Diesel as it is on the hot bulb engines.

When building a new engine, things don't always work the first time.

In the first photo we see the flywheel and crankshaft being cross-drilled for a pin, as it came loose on the third attempt to run the engine.

The second photo shows the bent 5mm connecting rod on the bottom and the stronger 6mm rod that replaced it above, next to the piston. The 5th attempted start of the engine proved too much for the 5mm rod.

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