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Air Cooled Engine Repair, Heat and Debris

June 2, 2010

Engine repairs aren’t much fun. So here are a few simple tips for keeping your air cooled engines in top working order and avoiding air cooled engine repairs.

Proper Oil Prevents Lawn Mower Engine Repair

Air cooled engines (Lawnmower engines, Tiller engines, Pressure washer engines, Generator engines) are designed to operate in a temperature range higher than most automotive engines. Because of this they require motor oil blended for higher temperature. This is why it is not a good idea to just put any motor oil in the crankcase. Most engine manufacturers have specially blended oil with their company name on it that they recommend. This isn’t simply a way to make more money, there are definite advantages to using their oils.

Now I don’t mean that you can’t put Briggs and Stratton oil in a Tecumseh motor or vice versa. But it is preferable to make sure you use the blended oils designed for air cooled engines if you want the maximum longevity of your equipment. This is as true today as ever. Briggs and Stratton, Tecumseh, Onan, Kawasaki and Kohler all offer their own line of motor oil for use in their engines.

Modern Kohler engines are designed with hydraulic valve lifters and the use of Kohler’s 10W30 oil insures the lifters operate properly. In the early years of these hydraulic lifters, engines had many maintenance issues traced to the motor oil being used. Use of Kohler’s oil prevented these issues and still today, I recommend only using Kohler oil in a Kohler engine.

Importance of Proper Air Flow

Additionally air cooled engines are designed to operate in specific RPM ranges in order to produce maximum torque, horsepower and to maintain adequate air flow for cooling. Air cooled engines are dependent on air flow across the flywheel for their cooling. That is why the air cooled engine manufacturers specify that the unit be operated at wide open throttle for optimum performance. That is also why it is not advisable to operate the engine without the sheet metal covers and guards in place as they were shipped originally. The air is pulled in through the blower housing, spun by the flywheel fins and routed around the bore of the engine by the sheet metal guard to ensure proper air flow which cools the engine.

Allowing a large mass of grass clippings, dirt, mud or debris to build up around or under the sheet metal prevents proper air movement and will cause hot spots in the engine block. These hot spots will cause the bore to distort lowering compression, and allowing oil to flow improperly. All these issues will lower the life and performance of the engine.

Full Throttle Minimizes Small Engine Repairs

Another issue is the use of the throttle. In order for the engine to perform properly and cool properly it must operate at the manufacturer’s recommended RPM. The engines are governed to perform at wide open throttle, usually around 3600 rpm. At 3600 rpm, the air flow is sufficient to keep the engine operating in the required temperature range and at the optimum point in the power curve.

For this reason the operator should insure that the engine runs at wide open throttle during operation. Failure to run at wide open throttle allows the engine to overheat and this in turn causes the engine oil to be less effective. This is one of the main reasons that many modern engines have very little throttle control. They are set up from the factory to operate in a very small range of rpm. This insures the product and the engine give maximum performance with very little operator input.

At one time my father’s neighbor bought a brand new Snapper rear engine rider with a 12 Horsepower Briggs and Stratton engine on it. He was surely proud of his new mower and in his mind running it just slightly above idle speed would insure the mower outlived him. I was at my dad’s one day and the neighbor was mowing. Dad said that he imagined the new Snapper would be running after both he and the neighbor were long gone. I told him no, that the engine wasn’t running fast enough and that his neighbor would have issues within a season or two at the most.

In this case, Father didn’t know best. After only one season of use, the neighbor’s Snapper wouldn’t start. He brought it to me and I tore it down. There were hot spots in several places in the cylinder bore and the piston and rings and the cylinder head were black with burnt oil residue. The heat and oil buildup had caused the rings to stick in the piston allowing loss of compression. So the morale of the story is run the engine at wide open throttle and keep an eye out for buildup of debris that can create and obstacle to air flow.

Your Weedeater Too

The same rules apply to 2 cycle Weedeater engines. They are designed to run at high rpm. This insures cooling and maximum power. It also insures the cutting attachment operates in the specified range for best performance. There are a lot of people that run the line on their Weedeater heads too long thinking they are cutting a wider swath. In theory, yes you are cutting more area, but the engine has to lug along at significantly lower rpm than required to turn the load. This will cause premature failure of the engine due to heat. Today’s string trimmers are tools and like any good tool, it is up to the operator to use them correctly.

Simple Way to Avoid Air Cooled Engine Repair

Even though many people have the idea that since it is only a lawnmower or Weedeater, it is not necessary to take any special pains to keep them running. But as you can clearly see, they require maintenance and upkeep just like your automobile. They also need to be operated in specified ranges to insure optimum life and performance. This day and time, when every dollar counts, shouldn’t you take the necessary steps to insure that you got what you paid for.

Filed under: Lawn Mowers — Discount Online Parts @ 4:37 pm
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