Any comments on running an OS FS-70 II inverted?

I have heard differing opinions varying from absolutely never run any glow engines inverted, to it will cause no problems at all.

What is the real scoop?

It will cause no problems at all... thats my opinion. I've yet to read anything to convince me otherwise, and have seen it done too often with success to think anything else.

I am not an engine expert by any means however.

Nearly all my four strokes are mounted inverted...

Some care and special handling is required... You can easily hydraulic any engine inverted.

Properly tuned and operated you will have no problems at all...

Mav,
You must take care not to flood the engine when starting/ priming. Other than that, there are no negative issues with an inverted engine. 4cyl or otherwise.
David

Yeah, I know about hydraulic lock, but was just wondering about flame-outs due to fuel pooling in the head when idling.

Every inverted 4 stroke that I have used or seen has had a problem starting because the fuel pools in the glow plug area and makes it difficult to start unless you turn the aircraft upside down. I do not invert engines for this reason.

I think I have opened a can of worms! I already have differing answers. I guess I will just have to try it for myself and see.

I have an OS 70 S ll in a Texan inverted. It starts, and runs like a champ. You can flood it out if your not careful, but after a few starts, you will know just how much prime it needs.

Good luck, this is a great engine.

Rick

Thanks for the feedback guys. It is sounding like it will be OK if I be careful about flooding the engine when starting it.

I have also heard nothing but good about the OS FS-70 II.

We shall see soon. It is going inverted into a World Models P-51.

I inverted an OS Surpass 70 in a Global PT 19 with no problems at all. I even purchased an onboard glow lighter just in case but never had a need to install it.
As for starting it, I don't prime it at all, just put the glow driver on (used a remote set up) and crank it over with the electric starter.
Starts with little or no problems at all and I can't remember when I had a dead stick with it.

dj

I flew a Top Flite Spitfire with an inverted Saito .91 and it ran beautifully (I later put it on a World Mits. Zero). I read in an article either in RCM or MAN that 4 strokes actually run better than 2 strokes when inverted.

Sure - not a problem with any current engines-
also -most current stuff starts so easily that a glove and a flip against compression gets em going.
Starters are a double edged sword-you can bust a small engine -cramming them into a wet cylinder.
OS70 is my all time favorite four stroke . It simply is quality at it's best and dead reliable.IF you put the tank where is is supposed to be!
If you are new at the game - you may care to try this approach:
Fuel - use a heli blend -15-25% nitro-lotsa oil.
use only very hard wood or nylon filled props . NEVER use a plastic backplate spinner.
Make sure that the prop/spinner assy is tight -always . a piece of 600 grit sandpaper glued to back of spinner backplate is a good idea.-this is to prevent slip between the drive washer and the spinner backplate.
Use only a big nicad to start the engine .
Use OSF plug-
hook up fuel system so that you can easily check for fuel flow-an external loop may look goofy but it sure makes setup easy.
Always choke/hand flip cold engine -without glow attached , until the engine starts to feel loose -or a little wet.
Put engine to idle, choke off now -hook up glow .
carefully pull prop thru (remember the glove) - It should "bump".
give the prop a smart back flip - it should start.
I have had at least 4- 70 OS engines more OS 1.20s of all types and this procedure is 100%.

I built a Greatplanes P-51 and mounted a Saito 72 inverted and it just flew awesome. It is still flying fantastic. This plane was built for a friend and it is one of his favorites. It will hydro lock if you are not careful. It's just one of those things you have to get used to . He knows how to start the engine and very seldom gets hydro lock anymore. I highly recommend it....... as it is the only way to get some planes to look just right.

I have a 40 size ultimate bipe with an OS91 4/s. Zero problems.
I do like the OS 4 strokers, but my heart is with Saitos.
5

Hey Fivesquart. Is the Ultimate a Greatplanes Ultimate 40? I have one I have finished........ I put in a Super Tigre .51 with Slimline Pitts muffler. I have heard that a .91 four stroke is the answer to this plane. Thinking about changing it. I have not flown it or radioed it yet. Tex

Yeah TEX,
The 91 is the magic formula for this puppy.
Unless you have long eyes, verticle will make you shiver!
BTW Its FIVESQUARE. FiveQUARTS go in my silverado.

5

Sorry FIVESQUARE. Guess I got carried away with my T's. Thanks, Tex

I use a YS 91 inverted in my Sukhoi, and it runs great. I just wish someone made an inverted pitts muffler for the smaller four strokes.

I've had two four strokes mounted inverted with no problems at all. One was an OS .70 the other a Saito .90. It is very difficult to load up an inverted four stroke with fuel because on the exhaust stroke any excess fuel in the combustion chamber is exhausted out of the exhaust valve. They do not tend to load up because they are inverted. To the contrary, they are less prone to load up when inverted. Remember, this is a four stroke engine we are talking about, not a two stroke.

Check out the Bison mufflers. They do make mufflers for inveted engines and will custom build one for you a a reasonable price.