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Diesel Engine Tips and Information


        Diesels have no spark plugs. They obtain the heat necessary for combustion by gathering the heat content of the outside air
and putting it into one small area. The result is an increase of temperature. If 50F degree air is compressed at a ratio of 20 to 1, it
will yield air at 1,000F degrees (20x50=1000). Diesel fuel will instantly combust when sprayed into such a hot and oxygen rich
environment. The rate at which the compression takes place has little influence on temperature. In other words, it doesn’t matter
how fast you crank a diesel. What matters is the outside air temperature and the volatility of the fuel. The most common problems
with a diesel center around fuel quality and fuel delivery problems. One needs to pay particular attention to the bleeding of  high
 pressure and low pressure fuel lines and also the stoppage of filters. If you get your fuel right, a diesel will almost always run.

A. Bleeding Fuel Lines
        Because a diesel engine is highly efficient, it injects only a very small amount of fuel into the cylinder with each stroke. It
can take a huge amount of engine cranking to work out an air bubble. That is why bleeding air out of fuel lines is so very important. 

        First, check the low pressure fuel line to see if fuel is getting to the injection pump. The best way to do that is to remove the
fuel hose on the end closest to the pump. Keep a rag handy and reattach the fuel hose while the fuel is still running out. It does cause
 a mess, but is the most effective way to eliminate air bubbles.

        Next, bleed the high pressure fuel line. That is done by loosening the steel pipe ferrule on the high pressure fuel line closest to the injector. Set the throttle to maximum, hold down the compression release lever and crank the engine over until a small drip of fuel comes past the connection. Retighten the fuel line, reset the throttle to one half and you are ready to start the engine.

B. Breaking an engine in
        Modern synthetic oils are amazing products. However, you don’t want to use them in a new engine. Synthetics lubricate so very well that a new engine will never seat the rings properly. It is best to start a new engine with frequent oil changes of a non-synthetic oil for the first 100 hours. After the engine has been broken in, then switch to a good synthetic. You will find that these small diesel engines will deliver an amazing amount of service if properly maintained.

C. Cold Weather Starting
        A diesel engine considers anything below 40F degrees to be cold weather and can be hard to start. That's because there isn't enough heat content in the outside air to get the temperature of compression high enough to detonate the diesel fuel. Another problem is that oil companies change the fuel formula from summer to wintertime blends.
        If you get stuck with summer fuel in a winter situation, then a diesel can be just about impossible to start. Take a tip from the "old time" truckers. They would mix about 5% gasoline to their fuel to assist in cold weather starting.
        Glow plugs on these small diesels are available, but end up being a wasted effort. The glow plugs are mounted in the manifold, not in the cylinder. These diesel engines are not typically used in wintertime applications, so the manufacturers just don’t provide for proper glow plugs inside the combustion chamber.
        If you really need to run one of these engines in the winter, then I would go the 5% gasoline fuel mix and find some way to heat the engine crankcase and especially the incoming air. I have successfully used a hair dryer to blast warm air down the intake manifold to raise the temperature of compression.

D. Recoil Starting
        The high compression of diesels can make them hard to recoil start. Almost everybody knows to jog an engine up to the compression stroke, set the compression relief and pull start the engine. This old method yields about 2 turns of pull before the next compression stroke. There is a trick that will get you a full 1/2 turn more of momentum on the flywheel.
        To do that, set the compression relief lever. Slowly jog the engine over until it releases. You are now on the exhaust stroke. Keep slowly jogging the engine and pressing the relief lever until it will hold down again. You are now at the end of the exhaust stroke. Give the rope a long, hard pull. The secret is in the long pull. The intention is to get as much momentum as possible into the flywheel to start the engine. Another compression stroke actually does come around, but it is skipped because an exhaust stroke did not precede it. You jogged your way past it. The compression stroke after the skipped one is the stroke the engine will fire on.
    Don't believe me? Try it .... or check out the table listed below: Keep in mind that the compression relief lever keeps the exhaust valve slightly open until the cam actuates the exhaust valve and loosens the compression release lever.
    In reality, the situation is a little more extreme than that. In the old method (blue line on the chart) compression stops the crank part way into the compression cycle. That "part way" will give you a little less than 2 turns of remaining pull .... probably 1/8 of a turn (a guess).
    With the new method (red line on the chart), the compression lever will start to hold a little before the exhaust stroke is complete. Let's guess that also at 1/8 of a turn. But that 1/8 turn is added to your potential pull. That gives you a total of 2-3/4 turns of pull. That additional 3/4 of a turn can make a lot of difference between a start and a no-start situation. Examine the chart below.


E. Diesel Smoke.
         Diesel smoke is unburned fuel. The only way to reduce how much a diesel smokes is to reduce the unburned fuel. Either decrease the fuel input or increase the amount of oxygen to the engine. Turbo chargers do a good job of oxygen increase. In non-turbocharged engines, the only choice is to decrease fuel input for the present load. That may mean downshifting to reduce load. Or a person can get an engine that is oversized and simply not work it as hard. Increasing throttle position beyond the torque an engine can produce does not increase power or speed. It just increases smoke.

F. Compression Relief
    Compression relief is a very useful thing. Useful in reducing wear and tear on the starter and also when bleeding fuel lines. It's an absolutely necessity when rope starting. A compression relief can also stop a diesel "run away" condition.
    Unfortunately, due to the popularity of electric starters and the lack of general diesel knowledge by the public, manufacturers are beginning to discontinue the compression relief lever. Lower cost is probably also a reason. I wish they wouldn't do that, but it is probably a reality we must live with in the future.

G. What is Diesel Run Away?
        Diesel run away only happens with extremely worn out engines and usually only if they have become very hot. What happens is that on the intake stroke the piston draws some air from the crankcase that is rich with oil mist, past the rings into the combustion chamber which acts as a fuel. Because there is no control over the air intake, the engine will continue to run on its' own even when the fuel has been shut off. It will keep running until it has exhausted the crankcase oil and possibly seize the engine.
        It's a bad situation and doesn't happen very often. The only way to stop the engine is either hold down the compression relief lever, stall the engine or find some way to totally cut off the intake air.

H. Electrical Considerations
        These engines are designed for off-road stationary power use and to just recharge the battery from starting. People have used them for all kinds of things .... lawn mowers, rototillers,  stump grinders, electric power, sawmills, garden tractors and even crazy stuff like sailboats, motorcycles and airplanes. It is possible to increase the windings in the stator and about double the electrical output. If you need more than 8 or 10 amps, then check out the forum on A member there called "ThunderCougarFalconBird" has posted a good series on how he rewound a stator with good success.

I. Battery Size
        Question: How big a battery should I use?
        Answer: As big as you physically have room for.
    A battery will wear out in direct proportion as to how hard it has to work. The typical garden tractor size battery seems to work very well with these engines. People have used motorcycle batteries, but I would suggest you get the biggest one you can fit into your battery box.

J. Low Battery Dangers
        Danger One: An inertia type starter won't have the proper "quick spin" to fully engage the pinion gear and grinding of teeth will result.
        Danger Two: Probably the most serious situation is that a solonoid type starter can keep running and explode the armature!
        What happens is the battery voltage has dropped off, so the starter pulls more amps to compensate. The electrical contacts can "weld" together and keep the starter running. The only way to stop the starter is to remove a battery cable. Not an easy thing to do in a panic situation. Eventually the bushing on the starter drive will lock and spin up the armature with enough centrifugal force to make the windings fly apart. A big battery that is discharged seems to cause this more often than a small battery that is discharged.
K. Starter Fluid
        Oh what a very big No No!
        About the only problem we have had with these engines is with starter fluid. Typically someone runs out of fuel and has trouble restarting the engine. That's because these is now air in the fuel lines. So, they attempt to "pop it over" as you would do a gasoline engine and run it long enough to get fuel worked through the engine. That is not going to work for two reasons.
        Reason One: Diesels are very efficient and only inject a very small amount of fuel on each stroke. It can take a very long time to crank out an air bubble. Opening the throttle all the way and holding down the compression relief will help, but still it's a whole lot of cranking and you will probably run down the battery several times before the bubble is worked out.
        Reason Two: Because of the high temperature of compression the starter spray will ignite before top dead center and cause engine to kick backwards. If the engine kicks back fast, it will usually break the starter drive gear or the starter nose cone. If it kicks back slow enough, it can get the armature spinning in reverse and cause enough centrifugal force to cause the armature to explode.
        If you run out of fuel you need to bleed the fuel lines.  A word to the wise is never run a diesel dry and never, never introduce any type of fuel into the intake manifold.

L. Starter Types
        The most common complaint we have is about starters. Normally it is a result of fuel issues, bad batteries or starter spray that has caused over work or damage to the starter. If a person is aware of the various types of starters and their various strengths and weaknesses, then possibly damage to the starters can be reduced.   

        1. Inertia Drive Starters
        Inertia drive starters are the most common type found on small engines. They are small and inexpensive to manufacture.
They work just fine, however they do suffer from a few problems. If they lose lubrication on the worm drive they will have problems with kicking in. Also, they need a fully charged battery to insure a quick snap of the armature to kick in the drive gear without grinding teeth.
        2. Solenoid Starters
        The public is more familiar with solenoid starters as they are the same type found on automobiles. They will kick in fine with a low battery but will just crank slowly. That's a good thing because the average person will understand that their battery is weak.
        3. Gear Reduction Starters
        Gear reduction starters are the best. They are more expensive to manufacture, but are smaller and generate a large amount of starting torque. They are more efficient, so they are more tolerant of an undersized or weak battery. Normally they are considered to be optional equipment. The one cylinder engines do fine on a direct drive starter. Most of the v-twin engines do have direct drive starters, but we are encouraging the manufacturers to make gear reduction starters standard for all the v-twin engines.

 M. Vibration Issues
        1. The one cylinder diesels seem to run pretty smooth. They have an internal counter balance shaft that runs at the same speed as the crank shaft but in the opposite direction. It will cancel most of the vibration from piston movement. Experts have argued that you cannot cancel a linear vibration with a rotational vibration. In the strictest theoretical sense that is true. However you can reduce the overall net vibrational effect with the proper use of a counterbalance shaft. The Winsun 13hp engine runs particularly smooth for being a light weight diesel engine.
        2. The v-twins are another matter. There is no practical way to mount a counter balance shaft that will cancel the complex vibrations of a 90 degree v-twin engine. All v-twin engines vibrate to some degree. Usually they will have one or two "sweet spots". The problem is not all that bad .... Harley Davidson motorcycles have always suffered from vibrational problems and there are thousands of them running down the highways every day. Ken Mosi built a Punsun v-twin scooter that has a directly bolted down engine. He rides the scooter every day to work and has no problem.
        3. The only vibration issue we have experienced is sometimes on a v-twin, the thin steel high pressure fuel line will crack from vibration. I understand from diesel truck mechanics that this is a common problem. It is due to the individual harmonic vibration frequency of a particular fuel line. Repair is by replacement of the fuel line and possibly adding some support or a loop to change the natural resonant frequency of that line. Fortunately, it is a fairly simple and inexpensive repair. The lines are standard metric sizes that almost any hydraulic supply house can fabricate one if you give them the old line as a sample.
N. Flywheel Stub Shafts and Custom Power Shafts
        From time to time we get requests for engines with stub shafts on the flywheel or custom size power shafts. People are trying to replace the engine in their unusual make or model garden tractor or lawn mower. In the past, we have made attempts to have the factories in China manufacture these items. The willingness and friendliness of the Chinese manufacturers has been good. Unfortunately, the results of these custom jobs has not turned out to be as good as one would hope. Both the V-twins and 1 cylinder engines come with 1 inch diameter power shafts only.
    Although we have sold many successful lawn mower and garden tractor replacements, we want to leave the custom work in the hands of the consumer. We are a low cost diesel engine supplier and have no facilities to do custom machine work. Please do not ask us to arrange or do custom machine work. All the custom stuff is up to you.

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