A-65 mechanic question

30 is fine though towards 40 is better,
but if you have less than that at anything above about 1500 revs and you're
not running sewing machine oil, you don't have enough to keep from scraping
bits of metal together on your cam or your bottom end.

It isn't the oil pressure that keeps metal bits apart, it's
the oil itself. Oil pressure is needed only to get the oil to the
places it has to go. If it's a light oil, less pressure will work, and
a heavier oil might need more pressure to keep it moving. My A-65
seldom sees more than 25 or 30 psi in cruise, and works just fine. If
the weather is really cold I'll use an automotive 15W40 oil in it to
keep it happy. Beware, though, of using an auto oil if the engine has
hundreds of hours of aero engine oil operation; the auto oil will
loosen a lot of accumulated crud in the case and that stuff will get
pumped all through the system or maybe plug up the screen.

Dan

egroups.com:

30 is fine though towards 40 is better,
but if you have less than that at anything above about 1500 revs and
you're not running sewing machine oil, you don't have enough to keep
from scraping bits of metal together on your cam or your bottom end.

It isn't the oil pressure that keeps metal bits apart, it's
the oil itself.


OK, fair enough for the Valve train, but the bottom end?

Oil pressure is needed only to get the oil to the
places it has to go. If it's a light oil, less pressure will work, and
a heavier oil might need more pressure to keep it moving. My A-65
seldom sees more than 25 or 30 psi in cruise, and works just fine. If
the weather is really cold I'll use an automotive 15W40 oil in it to
keep it happy. Beware, though, of using an auto oil if the engine has
hundreds of hours of aero engine oil operation; the auto oil will
loosen a lot of accumulated crud in the case and that stuff will get
pumped all through the system or maybe plug up the screen.


You've not been using AD aviation oil? That'll do the same thing if you've
been using straight mineral.


Bertie

You've not been using AD aviation oil? That'll do the same thing if you've
been using straight mineral.

I use AD for the rest of the time, but auto oils have more cleaners in
them.

Dan

egroups.com:

You've not been using AD aviation oil? That'll do the same thing if
you've been using straight mineral.

I use AD for the rest of the time, but auto oils have more cleaners
in
them.


OK, I still think you're wrong about oil pressure. Though I've had some
engines with gravity feed oilers, (which needed frequent overhaul, BTW) I
can't see a flim being sustained in a big end, for instance, without a
goodly pressure flowing constantly to it. IOW the oil would quickly squirt
out of the side of the bearing leaving it dry...




bertie

If there was a lot of bearing clearance in the mains, the rods
might run a little dry, for sure. The rods are fed oil through the
crank from the main bearings, and too little pressure might result in
most of it getting away at the main bearings. In some simpler engines
the oil is fed only into one end of the crank, and if the pressure is
low it will reach the first rod OK but can't fight centrifugal forces
back through crank axis to the next rod. I don't know of any aero
engines that are single-point fed, but there are plenty of industrial
engines like that.
The key to good rod and main bearing lubrication is
clearances as small as the manufacturer will allow, and this also
reduces oil consumption by keeping the cylinders as dry as possible.
(Cylinders are typically lubricated by oil flung off the main and rod
bearings.) The pistons and rings have relatively little pressure on
them and need very little oil. In any engine or compressor I've seen
that failed due to lack of lube, the bearings were always the first to
go.

Dan