Do you need a pre-oiler?

Reader Edward Zeigler has some questions about pre-oilers. “”We see statements like “”70% of engine wear happens on start up.? So will a $3,000 pre-oiler pay for itself, and is it worth carrying around the extra weight of the system? Are there any scientific test results comparing engines with and without pre-oilers? And do the anti-scuff additives in Exxon and Shell multi-grade oils provide significant protection upon start up??


Reader Edward Zeigler has some questions about pre-oilers. “”We see statements like “”70% of engine wear happens on start up.? So will a $3,000 pre-oiler pay for itself, and is it worth carrying around the extra weight of the system? Are there any scientific test results comparing engines with and without pre-oilers? And do the anti-scuff additives in Exxon and Shell multi-grade oils provide significant protection upon start up??

While I have addressed the subject of pre-oilers before, Ed brought up several additional points. First is the subject of 70% of engine wear occurring on start up. This is kind of sorta true. The highest wear point in any four-stroke cycle engine is the interface between the cam and lifter. The maximum wear does occur in the first part of a revolution. So I guess the 70% figure could be right for this point only. The wear on the crankshaft and pistons is much less critical on start-up. To reduce the wear on the cam and lifter interface, it is necessary to totally flood the parts with oil.

Pre-oilers were first developed for use on radial engines during the war. Here the oil gallery was pressurized and oil flowed out the lifter bore onto the cam ring. Prior to the engine starting, there was oil on almost all of the cam and followers. Then when the engine was started, there was proper lubrication, and the wear was reduced. (The military published scientific data on these tests.)

The question is whether or not this experience can be translated to a current opposed piston aircraft engine. The answer is maybe. If you have a TCM engine, the pre-oiler may have a beneficial effect. In TCM engines the camshaft is located below the crankshaft. When the oil system is pressurized, oil flows out around the crankshaft journals and drips down on the cam. When the engine is started, there may be a coating of oil on the cam and lifter interface. However, TCM engines are not prone to cam and lifter failure.

If you have a Lycoming engine, the cam is located above the crankshaft in the engine. When you pressurize the oil gallery, oil drips out of the lifter bore, but does not fall on the cam and lifter interface. Therefore, just pressurizing the oil gallery does reduce the time for oil to get to all critical parts, but since oil probably does not reach the cam lifter interface, it will probably have little or no effect on cam and lifter wear. If you install a pre-oiler system that has an auxiliary oil gallery above the cam, then oil can be dripped onto the cam and lifter interface and I would expect a reduction in cam and lifter wear.

What about the effectiveness of anti-scuff additives in Exxon and Shell multi-grade oils? I would say that they are definitely maybe effective. If you fly your plane every week or two and the oil temperature is adequate, then the oils will be beneficial. However, if you fly only every month or so, the oil temp is well below 180?F and the plane is in a humid climate, then the oils probably will not be a total answer to the wear problem.

The key to long engine life is to fly your plane often, keep the oil temperature up to proper temperatures, and change the oil at least every four months. Remember, piston aircraft engines were built to fly, not sit. They are a bit like fish ? they don?t store well at temperatures above freezing.

Ben Visser is an aviation fuels and lubricants expert who spent 33 years with Shell Oil. He has been a private pilot since 1985. You can contact him at Visser@GeneralAviationNews.com.

Comments

  1. Dave Miller says:

    Does anyone build or sell a check valve for the pick up tube on continental oil system?

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