Two stroke engine orientation and durability

[amorrison]

In theory two stroke engines will operate in any orientation - how well does this work in practice?

 

[btrueblood]

I know my brother's old dirt bike will flood the cylinders with crankcase oil if the bike is inverted. I know this because I tested it, er, inadvertantly.

 

[hydrae]

Modern chain saws and abrasive wheel saws are run in any direction except upsidedown, where the fuel can leak out through the vent hole. The fuel pick up is filter on the end of a hose so it stays submerged.
Hydrae

 

[MikeHalloran]

My Troy-Bilt edger/trimmer has an inverted engine, with the spark plug on the bottom. The cylinder gets a pretty good load of liquid fuel in it while you're filling the tank. This happens even though I drain the tank and run the carburetor dry for storage.

That makes it hard to start, not because the ignition is weak, but because you're starting out with a wet plug, and a super- high compression ratio, so it's physically hard to pull the rope. Sometimes I have to prop it up, upside down, to let the fuel drain out of the cylinder, which makes it easier to pull the rope, but it's awkward because you're pulling the rope down.

It's not the kind of super- dumb design feature that I normally expect from a Troy-Bilt product.








Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA

 

[R1100S]

4-strokes can be made to run at any orientation as well. Look at aerobatic airplanes, pressurized oil return and fuel systems.

 

[richdubbya]

I think it has more to do with the carburetor orientation than the engine. One design aspect that should be followed is a downward sloping intake tract to the crankcase when starting so any excess liquid fuel is drained to the bottom of the crankcase rather than allowed on top of the piston. The gas and oil collect there until the engine is hot and loaded. This is the reason oil will drain to the top end if the engine is inverted.

 

[icrman]

All chain saws operate in any position. Well maybe not the ones from the 1940's.
The "diaphragm" carburetor solves the all position problem. And the fuel pick up freely falls into the various positions of fuel locations. I have seen the flooding problems in some engines, that is because of less turbulent areas of the crank case, and accumilation of oil in some areas. They seem to recover okay from the sudden over load. There isn't much leakage if any from the tank vent, I guess because of location and sizing. Since the fuel demands over ride the leakage.

 

[EddyC]

Old aircraft with radial piston engines collect oil in the cylinders at the bottom of the engine. The mechanics usually manually turn the prop a few revolutions to clear the oil out. Then when the pilot goes to start the engine, he/she lets the engine turn over a few times before switching on the ignition. After the ignition is switched on, the engine starts with a big cloud of blue smoke from the oil that collected in the cylinders.

 

[dunno]

Two stroke engines can operate in any orientation when they use a "pumper" carb ( as opposed to a float chamber)
like a Walbro or Tillotson, Zama etc.
These carbs are equipped with a small diaphragm pump and diaphragm operated metering valve, replacing the float chamber. The pump is operated by the pulses from the crankcase via a small gallery to the carb flange.
They are typically used in chainsaws, weedeaters, model aircraft, microlight aircraft etc., and so long as they use a "clunk" on the end of the fuel line inside the fuel tank, they always have a good fuel supply in any position.

There are seldom problems with these, and if there is a problem with fuel draining into the combustion chamber, then there must be a fault in the carb.

This type of layout has been successfully used since the fifties.

There is an increasing use of four strokes in these applications too, and there are various ways of getting around the more complicated issue of lubrication in these, - some brands have more successful ideas than others.

 

[rmw]

I have seen the old automotive Detriot Diesel 2 cycle engines in a variety of 'tilted' orientations, however, none as radical as 'up-side-down', since it still ultimately has an oil sump.

rmw

 

[patprimmer]

I believe that German WW11 fighter planes had there engines in with the crank at the top and the cylinder heads at the bottom.

Regards

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[skootaroo]

It's not all about diaphram carby's either, many rotax ultralight aircraft engines are mounted inverted with Bing float carby's you just turn them over.
Some report poor starting from oiled plugs when the engine has been left a while, but no running problems or bearings.