On 23 May 2007 08:09:20 -0700, "Robert M. Gary"
wrote:

I have a mid time (1000 SFNEW) IO-360 Lycoming engine.
Recently oil consumption has increased from about 1 quart/10 hours to
about 1 quart/ 5 hours. For a long time we've collected oil on the
bottom #1 plug but it seems like its worse now.

What is the pattern of oil consumption? How often do you change your
oil? Assuming a 50 hr change interval, a "loose" engine is going to
burn as much oil in the last 10 hours as it did in the first
40-typically.

In addition, we've had high aluminum levels in our oil samples for
several years but now showing high iron and other harder metals.
Blackstone is saying that our oil sample indicates high blow by and
seems to show that a piston pin plug is now rubbing on the cylinder.

Please bear in mind that one of the two piston pin plugs on each
piston pin is going to be in contact with the cylinder wall during
normal operations.

The piston pin "floats" in the small end of the rod and in the piston.
The piston pin plugs "float" in the piston pin bore in the piston.

If you can tell me why in some cases they "rub" harder on the cylinder
wall, you are ahead of Lycoming, they are still trying to figure it
out.

The oil filter is still showing only a small amount of metal. The IA
at the A&P school says the amount of metal in the filter is expected
for any midtime engine, not excessive. Since the last couple of
Blackstone reports have indicated the pin plug may now be rubbing on a
cylinder we've been doing a boroscope every 10-20 hours of flight.
However, the boroscope is still coming up with nothing (we have
Nitrite cylinders and the cross hatching still looks great).
Compressions were all very high (enough that the A&P is always a bit
suprised to see them so high all around for a midtime engine)

Again, the piston pin plug is a relatively soft alloy, it may transfer
to the cylinder wall like a crayon, but it is not going to disturb the
material of the cylinder wall.

So, I'm wondering where I should go from here.

1) How can I tell if the oil from #1 is coming past the valves or the
rings?

It is more likely to be coming from the valve guides at 1000 hours.

2) Is there any reason to believe the oil in #1 cylinder and the oil
analysis issues are related?

No idea. Only way to know for sure is to tear down the engine and
physically inspect all the components.

3) Other than the oil usage in #1 I really have nothing to suggest one
cylinder over the other for making metal in the oil sample. Should I
just address the oil in the #1 cylinder and ignore the sample report
until there are other signs (filter, boroscope, etc)? Or, should I
just start pulling all cylinders (I'm told its about 10 hours of labor
per cylinder ) until I find a busted pin plug?

Better than half of "typical" Lycoming engines will have excessive
valve guide clearance after 1000 hours of operation. Unless an
increase in oil consumption is noted, a "wet" plug is found, or the
e-valve starts leaking, it is not a notable occurence. Heard of the
"wobble test"?

4) I spoke with Lycoming. Although they didn't have any suggestions on
how to determine which cylinder has the bad pin plug, they did mention
that if we find the issue before there is much scraping on the
cylinder we should be able to simply put the cylinder back on (and
avoid sending it to a cylinder shop, saving lots of $$$). So basically
the sooner I find this, the less expensive it will be (well, I guess
if I have to pull 4 cylinders before I find it, it might not be less
expensive).

Lycoming has a history of telling people that you can slide a cylinder
off and on and "save money". Speaking from personal experience, if you
remove a cylinder partially, and re-use it without a hone job and a
new ring set, it is likely to pump oil (increased blow-by). You will
have disturbed the working relationship between the rings and the
cylinder wall, and in-service rings often "sack" or loose some of the
spring tension that hold them "out" against the cylinder.

Not sure how gambling on another R/R, where you will be doing the job
properly (hone & ring set) is "less inexpensive". On most engine
installations, getting all the garbage out of the way (and putting it
all back on) is a much larger share of the labor cost than the actual
cylinder R/Repair.

5) If I find a pin plug broken what should I do? Several A&Ps have
told me that pin plugs just work loose on Lycoming engines and I
should just replace the busted one and forget it. Others have said I
should do something to the engine to prevent the next plug from
working loose (not sure what).

There is nothing to "work loose". There are two types of pin plugs in
service. One locates on the piston pin bore in the piston, the other
locates on the inner "hollow" in the piston pin itself. They can wear
slightly and be "loose", but show no other signs/symptoms, and have no
real affect on engine performance/engine life. They also can in
service begin to rub excessively on the cylinder wall, with no other
apparent faults. They can have the radiused end that butt into the
cylinder wall worn flat, and still not be "loose" in either the piston
or pin bore.

Piston pin metal is relatively easily identified in this case by hairs
in the suction screen or oil filter element.

TC