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David Kerzel, Pompano Beach, Florida david@FloridaAME.org 12/26/2018
Chinese Hit & Miss gas Model Engine
I was looking at the Banggood.com web site and came across this hit and miss model engine. I ordered one for myself as a Christmas present. It looks a lot like my HHM1 engine from 2002 that is on the FloridaAME.org web site with complete plans at www.floridaame.org/GalleryPages/g1h0106.htm .
In 2002 someone making these and selling them would have bothered me. Today, seeing the opportunities that open source builds I am glad to see someone take interest in the model engines. I am troubled some by it being completely built and ready to run. My first one took about 6 months to build and another 3 to make it run good.
One thing that is missing is any history or explanation of the engine. So I am putting this page together to review the model and add my thoughts and some explanations.
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Chinese Hit & Miss Gas Model Engine
STEM Full Metal Combustion Engine Hit & Miss Gas Model Engine STEM Science Developmental Gift Collection Toy
It is a good looking model. The bulk of it is made of powder metal that has been anodized blue. The anodizing highlights the grains of metal.
These engines are often called farm engines. They were used on small farms to power various stationary machines before electricity was available. Typically they were 1.5 to 10 horsepower and made to run on most any fuel.
The workmanship is good. The fly wheels are powder metal centers and steel rims to get the needed inertia.
The 2 weights on the left fly wheel are pulled away from the hub as the engine speeds up. They move to bobbin towards the flywheel which moves the lever so it can prevent the exhaust valve from closing after the next cycle. With the exhaust valve open the engine free wheels and does not pull in any fuel. It does not fire again until the speed drops, the weights move in to reset the bobbin and release the exhaust valve. Then fuel can get pulled in and the engine will fire on the next cycle. This regulated the engines speed and reduced fuel consumption when the engines load was low.
The blue disk on the left side has a magnet for a Hall Effect sensor for the ignition.
A real hit and miss would have the ignition timing on the exhaust valve so that when the engine was not firing not only would it not waste fuel but it would not waste the battery. Many time these were run using 4 large dry batteries that were expensive if the farm did not have a generator to recharge a storage battery.
You can see the lever that keeps the exhaust valve open on the right side. The silver part left of the large gear follows the cam that operates the exhaust valve.
The head is basic, the rocker arm pushes the exhaust valve open when needed or to cause miss cycles. The intake valve works on the suction caused by the piston being pulled to the bottom and is simply spring operated. They use a nice manufactured plug that they also offer as a spare part.
The carburetor is a simple jet in a venture with a fuel flow screw. Not much is needed since the engine is intended to run at a relatively constant speed.
This is the pack of parts that comes with the engine.
I am not sure why the fuel tank is green with a blue engine but I think I can get the anodize off and have a silver one
They include an extra hall sensor. Lots of people have problems with them. There are 2 things that must be done for hall sensors. Ground the engine to battery negative. The small red wire in the fluid tube is the ground wire. Scrape off some anodize where you connect it. The other thing is to add a small capacitor .1uF, 25V ceramic across the red and black leads of the hall sensor. The hall sensors are very sensitive to over voltage spikes.
The Banggood video shows it running on 3 AA batteries https://youtu.be/rMBthroYU9U. I think I will use a 7.2V Lithium ion pack for a RC car.
The green O-ring is a clue they use an O-ring for a piston ring. Sone people have had good luck with them. I checked and the cylinder has a steel liner so the O-ring should work well.
A little dusty but still one of my favorites.
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