Reader Dave Fletcher recently sent an email concerning the failure
of the camshaft in his Lycoming IO-360 engine. He was concerned about
pre-oilers, Ney Nozzles, CamGuard and other oil additives.
This is a subject that both
engines expert Paul McBride and I have addressed before, but I thought I would try to add a little background to the debate.
To understand the problem with Lycoming
camshaft wear, one needs to look at the physical layout of the Lycoming
engine. The camshaft is on top of the crankshaft as opposed to
Continental engines with the camshaft below the crank. When most
aircraft sit idle, air enters the cowl openings at the top of the
engine, so the top is affected by ambient air temperatures before the
rest of the engine. During the day, the crankcase is warmed up and
filled with warm humid air. In the evening and at night, the engine
cools down and moisture collects in the oil.
As more and more water collects, the air in the crankcase becomes
more humid, so in the evenings the cam cools faster than the rest of the
crankcase. Once the cam cools below the dew point of the air in the
crankcase, moisture drops out on the cam. Over time, this water causes
rust to form on the cam and lifter surface. When the engine is finally
started, the rust acts like a lapping compound to start wear on these
surfaces. It is important to realize that the majority of cam and lifter
wear starts in the first revolution of the cam.
The problem with pre-oilers is that oil comes out the cam bearings
and lifter barrels, but no oil gets onto the cam and lifter interface
for that first revolution. Even the Ney Nozzles promise oil to the
lifter interface within one revolution. The pre-oilers get oil to all
bearing surfaces quicker, but have little or no effect on that critical
first revolution.
So do additives help prevent cam and lifter wear? They may help. The
reports on CamGuard vary from a marginal effect to a complete cure for
the problem. However, there are a host of other additives that have no
beneficial effect and are a complete waste of money, and many of them
are not FAA approved.
So what is the answer to preventing cam and lifter wear? The biggest
thing you need to do is have dry oil. To do that you need to make sure
your oil temperature is high enough to boil the water that is condensed
into your oil. To do this, I recommend that all plane owners remove
their oil sending unit, put it in a container with oil, water or even
chicken soup, and place the container on a heat source. With a good
thermometer, make sure the container is heated to 180°F. Then check your
gauge. I recommend making a paint mark on the gauge so you can easily
reference where 180° is when flying.
Now go fly and check your gauge. If after a half hour or so your oil
temperature is not up to 180°, take steps to raise it up. If it is well
over 200° during a level cruise, you may need to lower it. The reason
for this is that as oil goes through your engine, the highest
instantaneous oil temperature is usually about 50° higher than oil
entering the engine temperature. At 180° the oil will see 230° in the
engine, which will boil off the moisture. If you operate at 230° during
level flight, the oil is getting to 280°, which can lead to problems.
So what is the bottom line? I have found that Lycoming engines that
operate with a “true” oil temp of 180-200° and are flown regularly
almost never have cam and lifter problems. If you live in a humid
climate and operate with an oil temp well below 160° and do not fly
regularly, then the chances are pretty good that you may have a problem.
If you are not going to fly for a period of time, like over the winter,
change the oil and add a quart of preservative oil that meets
Mil-C-6529C Type II specification.
Pre-oilers, additives, brand and grade of oil, etc., fall into the
great gray area of maybe they will work or maybe not, but why depend on
them when you have an almost sure thing.
