Long Live the Engine

Regular preventive maintenance, periodic tune-ups and careful troubleshooting help keep 4-cycle gas engines running. Start the spring season with a new maintenance program.

Besides daily inspections of your gas engines, you need to set up a regular schedule for more thorough inspection and maintenance. If you don't already have your engines on a scheduled maintenance program, start one. A preventive maintenance schedule is organized by operating hours. Just as you change the oil in an automobile engine after so many miles, you should change the oil in your equipment engines after so many hours of operation. Look for maintenance checklists based on operating hours in the service manual, which is available from the engine manufacturer. Your maintenance schedule can be anything from a chart on your shop wall to a calendar marked with the maintenance tasks to be performed. Set aside a certain day of the week for specific tasks. For example, if you operate an engine 25 hours a week and the recommended oil change interval is 25 hours, change the oil every Friday afternoon.

Check off each service as you perform it so there will be a permanent record of operating hours and maintenance.

Checking the engine

You don't have to be a certified mechanic to successfully manage a maintenance program and inspect engines periodically. Clean or replace dirty parts and repair any problems you find when making the following inspections:

  • Check the air-cleaner assembly. Is it tight, intact and not bent or damaged? If dirt enters the engine through the air cleaner, it can cut engine life in half, possibly ruining an engine in a matter of hours.
  • Examine the air-cleaner element. Is it dirty, plugged or damaged? Test for punctures by holding a light bulb inside the element. Inspect the air-cleaner back plate and cover. While the air cleaner assembly is apart, look at the back plate and cover for damage or traces of dirt that would indicate leaks.
  • Check the carburetor throat. Before reassembling the air cleaner, check the carburetor throat for dirt. This is another indicator that dirty, unfiltered air is entering the engine.
  • Examine the air intake screen. Is the air (flywheel) screen on the engine plugged or restricted? Can air get through to the cooling fins? Are the fins clean? Engines can overheat when cooling fins are clogged with dirt and chaff.
  • Check the oil. Is the oil on the dipstick within the proper operating range—between "full" and "add?" Does the oil appear dirty or thick?

A good mechanic will inspect a faulty engine thoroughly before taking it apart because he knows that the conditions of the oil, the air cleaner, the air intake screen and the cooling fins are good indications of what he will find in the engine.

Use the right fuel

Use the recommended fuel, and keep it clean. Instruction manuals vary widely in their fuel recommendations. Carefully follow the instructions provided for each engine. Even though most engine manufacturers have begun using materials more resistant to alcohol-containing fuels, reformulated gasoline has caused problems in many small engines. Be sure to confirm that the engine will not be damaged with such fuel.

Mixing oil and gasoline for 2-cycle engines can be confusing. Recommended ratios range from 16 parts gasoline to 1 part oil, to as high as 50 parts gasoline to 1 part oil. Unless you use the proper ratio, you could damage the engine and void the warranty.

Quality oil is good insurance

With 4-stroke engines, you should check the oil every time fuel is added. Equipment owners who have the lowest repair cost per hour of equipment operation often report that they buy the highest-quality engine oil available. They contend that the few cents per quart difference in cost between premium and cheap oil simply helps ensure more trouble-free operating hours.

Which viscosity is best?

  • For some 4-cycle engines, single-viscosity is recommended. Other 4-cycle-engine manuals recommend single- or multi-viscosity oil depending on the ambient temperature.
  • During cold weather, always use lower-viscosity oil. High-viscosity oil flows too slowly to provide adequate lubrication when a cold engine is started, although it performs satisfactorily after the engine warms up.
  • Use multi-viscosity oil only when recommended.
  • Use oil with the American Petroleum Institute (API) Service Designation (or SD) to ensure that you're getting oil with the necessary additives and lubricating qualities needed for a particular engine.
  • Keep dirt and moisture out of oil containers, and use only clean funnels if oil cannot be poured directly in the engine.
  • Use the right amount of oil. If specifications call for 7/8 quart of oil, do not add a full quart. Overfilling the crankcase results in hard starting and possible engine damage.

Tuning up the engine

Small engines are similar to your automobile in that they need periodic tune-ups to ensure top performance. At tune-up time, inspect the engine to gauge its condition, and replace worn parts that could give trouble in the future.

  • Clean the exterior of the engine thoroughly, especially the cooling fins and air intake area.
  • Test vacuum and/or compression by following instructions in your service manual.
  • Service or replace the air cleaner element.
  • Replace the spark plug(s).
  • Replace the breaker points and condenser or solid-state module, if needed.
  • Check the valve clearance and adjust it if necessary.
  • Clean the breather and install new gaskets.
  • Check the ignition and adjust the timing.
  • Change the oil.
  • Start the engine and adjust the carburetor under load, if possible.

Even with regular maintenance and periodic tune-ups, engines don't last forever. You can overhaul most engines up to three times to get a new lease on life each time. But when should an engine be overhauled again and when is it wiser to replace it? Your mechanic or the dealer who services your equipment can help you answer that question. You will want to consider the equipment age, overhaul cost and parts availability.

Improve your program

You can save yourself a lot of time and money by permitting only trained, qualified personnel to perform more complex equipment maintenance (carburetor adjustments, installation of breaker points, etc.). If certain personnel lack the skill, instruct them not to attempt any engine adjustments or repairs on their own initiative. Focus their training on proper operating techniques and recognition of developing problems that could damage equipment or possibly cause an accident. Trained backup personnel then can provide necessary additional care and repair. If you lack equipment, facilities and personnel to make repairs, rely on equipment dealers who are prepared to offer those services.

If you have a competent mechanic on your staff, rely on him or her. Have your mechanic attend engine service schools that manufacturers or distributors offer in your area. If you service enough power equipment to justify the cost, consider purchasing a master service manual from your engine manufacturer.

Ignition system tune-ups save time and fuel

Estimates vary, but poorly tuned ignition systems in spark ignition engines can easily waste 15 to 20 percent of the fuel burned. That means an engine could be losing 1 of every 5 or 6 gallons of gasoline consumed. With today's fuel prices, it is easy to see the value of keeping ignition systems in top condition.

Most manufacturers recommend ignition system tune-ups at intervals from 25 to 1,000 hours of operation, or at least once a year. Check the operator's manual.

Spark plugs. Checking and cleaning or replacing spark plugs is usually the most simple step in ignition system servicing. Remove spark plug wires by pulling on the terminal over the end of the plug. Do not pull on the wire because this can break the electrical wire or conductor inside. Be sure the area around the plug is clean and free of dirt, chaff and debris before removing the spark plug to keep dirt from entering the combustion chamber. Remove plug(s) with a deep socket wrench or special spark plug wrench with rubber inset which reduces danger of dropping the plug.

When servicing multi-cylinder engines, arrange spark plugs in the order in which they were removed to permit identification of specific cylinders in case of abnormal deposits on plugs, plug damage, etc.

If removed plugs are covered with wet, sludgy deposits, excessive oil is entering the combustion chamber through worn rings and pistons, around valve guides and stems, or past loose bearings. Dry, fluffy black material on plug electrodes dictates incomplete combustion fuel—a too-rich air:fuel mixture, or that the coil, ignition points or wiring are defective. (Check air:fuel mixture first; it is simplest.)

Plug electrodes coated with hard baked-on carbon indicate weak ignition, improper plug, dirty air cleaner, or a too-rich air:fuel mixture. Electrodes and center insulators that appear burned or blistered indicate engine overheating (from improper ignition timing, incorrect fuel, loose spark plug (poor heat transfer to engine block), improper plug or other factors. White powdery deposits indicate the use of highly leaded or premium grade gasoline in engines not designed for such fuel.

If plug deposits appear hard and scratchy, they cannot be cleaned. Such deposits are formed when fine sand particles combine with anti-knock compounds in the fuel. (Check the air cleaner for possible leaks; the condition is usually worse in dusty areas.)

lf the engine and ignition system are functioning properly, plug electrodes will have a light powder deposit that appears rusty brown to gray-tan. Electrodes show minor erosion.

When checking the gap between spark plug electrodes, always use a wire-type feeler gauge rather than a flat gauge, which cannot present an accurate indication of the gap. The recommended electrode gap varies with different engines, so refer to the operator's manual for the proper setting. When adjusting the gap, carefully bend the outer electrode forward or away from the center electrode. Do not bend the center electrode.

When replacing spark plugs, always use the plugs recommended by the engine or machine manufacturer. Be sure plugs have the proper reach and heat range. “Reach” refers to the distance from the spark plug seating flange to the end of the plug threads. A plug with too long a reach will run "hot" and may cause the piston to contact the spark plug resulting in severe engine damage. A plug with too short a reach will run cold, causing misfire.

“Heat range” refers to the ability of the plug to transfer heat from the firing tip to the engine block and cooling system. A "hot" plug has a longer insulator, which slows heat transfer from tip to cooling system causing it to operate "hotter." A “cold" plug has a shorter insulator that allows rapid transfer of heat from the tip to the cooling system causing it operate "colder."

Engines running long periods at high speeds and under heavy loads normally require colder plugs; intermittent light-load or slow-speed operation requires a hotter plug for optimum performance. The heat range is normally indicated by numbers on the upper portion of the insulator. Numbering codes for heat range may differ among manufacturers. Plugs operating too cold tend to foul, but plugs running too hot may cause pre-ignition.

Replace badly fouled or burned plugs. Moderate deposits may be removed with a handheld wire brush or spark plug sandblasting machine. Note, however, that some engine manufacturers void the engine warranty if plugs are cleaned by sand-blasting. Dissolve wet, oily deposits in cleaning solvent, but do not use gasoline because of danger of fire or explosion. Lightly file the end of center electrodes and the underside of outer electrodes where spark contact is made so these surfaces are flat and clean. Reset the spark gap and clean or blow any metal filings from the plug.

Before reinstalling plugs, be sure old plug gaskets have been removed from plug sockets and new gaskets are installed on each plug (unless plugs have tapered seats that require no gasket). Tighten plugs to the torque recommended in the operator's manual, but avoid over-tightening, which can distort plugs and break the insulator or change the electrode gap.

Inspect spark plug wires and replace wires with cracked or extremely soft insulation. To help check wiring, start the engine in the dark, and watch for arcing or sparks along or between plug or coil wires and engine parts. Replace arcing wires.

To check spark polarity, hold the plug wire about 0.25 inch from the plug terminal and, with the engine running, insert an ordinary lead pencil in the gap formed. If the spark jumps around the pencil and feathers on the plug side, polarity is okay. If the spark appears to come from the plug, polarity is reversed, and the primary wires on the coil must be interchanged. Check the service manual for proper wire arrangement.

Distributor. The distributor controls spark-plug operation and spark timing. Pitted or badly burned breaker points can cause misfiring, hard starting or may prevent the engine from starting at all. Improper firing reduces fuel economy and power and, if severe, may damage the engine.

Refer to the service manual for specific instructions on servicing the distributor and do not permit untrained personnel to perform any tasks not covered in the operator's manual.

Before removing the distribute cap, clean the cap, wires and around the distributor to keep dirt from entering the distributor. Accumulation of dirt and moisture may cause formation of carbon paths on the outside of the distributor cap. Such paths mean electricity is flowing between the terminals or between terminals and ground, shorting out the system. If carbon paths are present, or if the cap is cracked or damaged, it should be replaced. The cap should also be replaced if the carbon button in the center is badly worn, chipped or broken. Be sure ventilation holes in the cap are open, too.

Remove and clean the rotor before inspecting it for cracks, damage or severe burning of the metal strip. Replace the rotor if it is damaged or badly worn. Check the distributor advance mechanism as directed in the service manual.

Inspect the contact surfaces of breaker points, and file them smooth with an ignition file if they’re not too badly pitted. Keep surfaces flat and parallel for even firing but do not try to remove all pits. Do not use emery cloth or sandpaper because particles from these may be imbedded in the points and cause burning or arcing. Replace badly pitted or burned points.

Burned points may be caused by oil or dirt on the contact surfaces, use of improper condenser, incorrect gap adjustment or poor alignment of breaker points.

Always replace the condenser (if used) when breaker points are replaced. Remove old breaker points, and clean and lubricate the cam that controls point movement. Use only special cam lubricant rather than grease, motor oil or petroleum jelly, which can melt and run off at high temperatures or become stiff in cold weather. Keep lubricant off points.

Install new points and condenser, and adjust the point gap as directed in the service manual. Be sure points have the proper gap (see service manual for specifications). If points are set too close they will burn quickly and become pitted. If the gap is too wide, the spark will be weak at high engine speeds. Improper gap also affects spark timing and engine performance. Recheck point gap after tightening screws to be sure the gap remains unchanged after locking points in place. Re-adjust points if necessary.

The cam angle, or dwell, must also be checked when breaker points are replaced. Dwell is the angle or number of degrees that the cam rotates from the time points close until they open again. Increasing dwell reduces point gap and vice versa. Too little dwell causes misfiring at high engine speed, but too much dwell causes points to burn.

Use a dwell meter to check dwell or cam angle, and adjust the distributor as necessary to obtain the angle specified in the service manual. If proper dwell and point gap cannot be obtained at the same time, look for a worn or bent distributor shaft or bushings, improper spring tension, use of the wrong breaker points, worn cam, or points not following the cam at high speeds.

Reassemble the distributor, making sure the rotor doesn't contact the condenser lead wire and possibly short the condenser, and check the coil wire for cracks or damaged insulation. Be sure connections are tight and that rubber nipples fit tightly over connections to keep out moisture. Replace damaged wires or rubber nipples.

To time the ignition system, locate timing marks on the flywheel or fan pulley and fixed marks on the engine. (Refer to the service manual if there is a problem in finding timing marks, and look for the specified timing adjustment—usually degrees "before top dead center" (BTDC) for the number-one piston.)

Connect the timing light to the number-one spark plug and to the battery or a ground, depending on the type of timing light used. Carefully follow instructions for the timing light. Start the engine and, with it running at the recommended speed, aim the timing light at the timing marks on the flywheel or pulley and on the engine.

Caution: Do not get hands, arms or timing light leads caught in the fan or drive belts. If the fixed and moving marks do not align exactly, loosen the clamp holding the distributor and slowly rotate the distributor back and forth until the marks are aligned. Tighten the distributor and remove the timing light from the engine. Recheck the engine idle speed because it will be affected by changing the timing.

The ignition coil normally requires no regular maintenance.

Ignition switch. Ignition switches seldom cause trouble. If current fails to flow to the coil and distributor, or the starter motor will not operate when the switch is activated and power is available from the battery, check for loose wires and replace the switch if it is bad.

The carburetor

The carburetor may be out of adjustment if the engine backfires, loses power and runs but misses. Follow adjustment instructions in the engine manual; remember that the specified sequence of operations is important. To adjust the carburetor, bring the engine to a normal operating temperature and speed. Turn the main adjusting needle in (clockwise) until the engine stumbles. Then, turn the needle out (counterclockwise) until it stumbles again. Note the number of turns between these two stumble points, and turn the needle until it's at the halfway point. Finally, put the engine under load. (If you are working on a mower, put the engine under load by engaging the blade.) If the engine stumbles, try nudging the needle in and out a little until the engine runs well under load. When making preliminary adjustments, turn the idle screw and power screw no more than finger-tight. Avoid over-tightening, which can damage the screw or its seat and prevent proper engine performance. Make the carburetor adjustments with the air filter in place, or the settings will not be accurate.

When adjusting the carburetor, make certain that the choke works freely and that it opens and closes fully when the choke lever is moved. Adjust the choke control linkage as necessary to ensure proper choke movement. Check throttle linkage for correct maximum and idle speed settings; don't guess. Use a tachometer to measure engine speed. A partially closed choke creates an overly rich air-fuel mixture that wastes fuel, reduces power output and causes the engine to smoke and foul the spark plugs. If the choke doesn't close, the engine may be hard to start.

Ensure smoother operation by draining dirt, water and old fuel from the fuel tank. Take the machine outside, away from any flames and drain the fuel into a container. Dispose of old fuel safely. Then clean the fuel filter (if one is used) and the vent in the fuel tank cap.

After many hours of operation, there may be a hard carbon buildup in and around the exhaust port on 2-cycle engines. This can reduce power and make the engine hard to start and keep running. Remove the muffler and clear carbon from the exhaust port with a wooden dowel or stick. Do not use a screwdriver or metal scraper that could damage the piston or cylinder.

Keep cooling systems cool

Keeping internal surfaces clean for maximum heat exchange is the key to good cooling system performance. However, hard water (high salts) can result in buildup of deposits that reduce cooling efficiency and may even damage the water pump and sealing surfaces.

The solution is to use good-quality permanent antifreeze all year, or antifreeze in winter months and a rust and corrosion inhibitor during the summer. Many engine manufacturers recommend mixing only distilled or deionized water with the antifreeze or coolant in your cooling system.

Do not keep the same antifreeze in the system for more than one season if the coolant appears dirty or rusty. However, replace the antifreeze after two seasons even it still appears clean, because the rust inhibitors and other protective components can deteriorate.

Use a hydrometer to check the protection level of antifreeze occasionally during cold weather and especially before entering the second season of use. Add more antifreeze as needed for the lowest expected temperatures.

Be sure you use coolant that meets standards defined in the owners manual, and always be sure to mix the coolant with water in correct proportions as set forth in label instructions. This is a critical point—do not assume that more coolant (higher concentration) is better.

  • Thermostat. Observe the temperature gauge during engine operation for unusually low or high temperatures. Replace the thermostat if the operating temperature is usually below the recommended level because running the engine too cold can cause damage. Remove dirt and chaff from the radiator if the engine overheats.
  • Radiator cap. Test the radiator cap at least once a year to be sure it holds the recommended pressure in the cooling system. This pressure raises the coolant boiling point and helps increase engine efficiency.
  • Routine inspection. Check the coolant level every day, and at least once a week inspect the fan belt for fraying, cracking or other damage. The belt should be tight enough to prevent slippage.

Keep hose clamps tight and watch for coolant leaks around gaskets and frost plugs. Regularly inspect hoses and replace any that have soft spots or that appear badly cracked. Lubricate the water pump at recommended intervals (if called for) in the operator’s manual.

If an engine persistently overheats, drain all coolant, flush the system with clean water and, if needed, put in a high-quality radiator cleaner. Be sure all drains are open when flushing the system, including the oil cooler, cab heater, engine block and radiator. Operate the engine for the recommended time, drain and fill the system again, and refill with clean softened water and antifreeze or rust inhibitor, depending on the season.

Exhaust gases leaking into cooling system can form acids in the coolant. If you think this could be occurring, start the engine when it is cold and, before it can warm, remove the radiator cap and watch for bubbles in the coolant. Coolant leaking into the combustion chamber or crankcase causes oil to foam or appear milky.

“Stop-leak” additives may be used to temporarily control minor leaks, but they cannot stop leaks in damaged head gaskets and similar major problems.

Technical credit: Kohler Co. Engine Division; John Deere & Co.

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