Crazy four stroke question

[Clancy Arnold]

I have reviewed the owners manual and have many years experience working on car engines but I can not find the answer!

How does the lower end of the OS FS91 SII-P engine get lubricated?

The only thing I see is that there is a line from the lower crankcase to the intake manifold.  The only instruction in the manual is to put after run oil in the glow plug hole.

Clancy

[Bob Reeves]

Not positive about the OS but Saitos get lubed by what blows by the ring when they are running. Would put money on the OS being the same.

[Tim Wescott]

My understanding is that it depends on blow by.

[Clancy Arnold]

Thanks
I had not taken that into consideration.
I am not used to rings having that much blow by, but then I am used to pistons with three or four rings.

I was expecting something along the line of the crankcase filling with fuel/air mix during the compression stroke through the crankcase breather tube.
Clancy

[Dick Pacini]

I have pondered that too, but never asked the question.  After all, how can you have suck, squeeze, bang and blow without a crankcase full of oil?

[Rusty Pieper]

If your engine has a vent line running from the crankcase (behind the cam) to the intake manifold, make sure it doesn't get plugged.  That is how excess oil is removed from the crankcase. It goes back through the engine.  This is supposed to stop the excessive oil from being vented on the airplane.  I had one that the vent line plugged up and the engine case got so much oil in it it didn't want to run right. 

It is a good, powerful engine.  Enjoy

Rusty

[Matt Spencer]

Yep , NO Oil Control Ring .

[Jim Kraft]

They do get oiled from blowby. I have one of the original OS 60 FS engines with the open rockers, and it blows quite a bit of oil out of the crankcase breather. You do have to oil the rockers before a days flying, as they do not get oiled any other way. I also have one of the old original OS 90 FS engines, and it also blows out quite a bit of oil from the breather. The 90 is a very powerfull engine, and will swing a 16-6 prop. The 60 is a sweet runner, but not great on power, although it will swing a 14-6 very well. I also have an old Saito 90 twin that uses a vane pump in the rear to blow out excess oil, as it has both rods connected to the same crankpin, and therefore does not scavange the oil from crankcase pressure. It is actually more of a 2 cyl. radial than a twin. Saito makes them both ways.

[Clancy Arnold]

Thanks Jim
Should I oil them before each days flying or before each flight give them a drop or two?  I have several oils to choose from:  Marvel Mystery Oil, 3 in 1, Singer sewing machine oil, WD-40.  I use the Marvel Mystery Oil as an after run oil in all of my engines.

I fly the OS FS91 SII-P engine at 1/3 throttle most of the flight.  It is swinging a 15 x 6 prop and doing 7.5 second laps on 65 Ft. lines.

Is this a good idea, bad idea or recommendations?
Clancy

[Jim Kraft]

As far as the rockers on the OS 91, you should be fine as they are oiled up the pushrod tubes. I sure would use an after run oil in it, and my preference would be Marvel Air Tool oil, or Rislone. I have used both, and they both do well. I would not use WD-40 in any engine, as it has a bad habit of building up a residue on the cyl. walls that is real hard to clean off. I usually give mine a shot of rislone in the breather nipple after a days flying, and flip it a few times to distribute the oil. There are other after run oils that work well also, but my experience has been with these two.

The Rislone I use is the one in the quart bottle that is used as an additive, not the concentrate. Marvel Mystery oil is okay for short term, but no good for storage as it will dry out and leave your engine stuck with a red residue. Just about any air tool oil should work and not dry out.

[Clancy Arnold]

Thanks Jim
I will still give the rocker arms some oil before each day's flying.  I will use the 3 in 1 oil as it will wick into the small spaces.

This is not the first time I have heard about Marvel Mystery Oil drying out but the can I have is over 20 years old and even the spillage around the top of the can does not dry out.  I heard that they changed the formula some time back.  I have engines that were treated with Marvel Mystery Oil and have not been run in years that still turn over freely.  I guess that when this can runs out I will have to switch to Rislone!
Clancy

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