Hi, I'm wondering if there are any problems with mounting an engine inverted on a plane. I'm building an Ultra Sport 40 Plus right now and I'm trying to decide if i should mount the engine inverted like the plans say or if I should mount it the normal way or sideways. Are there any problems with an inverted engine? I know they are harder to start, but if the glow plug is on the bottom of the cylinder will the oil build up on the glow plug and kill the engine when it's at idle? Also, what is an idle bar? I've heard of glow plugs with idle bars and I've been told they are designed to keep the oil from building up on the filament of the plug. Should I get some of these plugs if I mount the engine inverted on my Ultra Sport? Thanks!

Properly set up, an inverted engine performs as well as any other mounting. Tank location and idle adjustments are more critical though. You do run the risk of fluid lock (excess fluid in the combustion chamber) due to over choking or bad fuel tank placement which could cause you to damage (usually bent or broken crank rod) if you try to use and electric starter with fluid lock. A side mount is often the easier to handle, will tolerate some slight missadjustment of needle valves and is easier to get proper tank placement relative to the carburator center line. Attaching the glow plug clip can also be a problem in inverted mounting unless you instal a remote connector.

Fox idlebar plug on the left
Fox Miracle plug, good for fourstrokes and most large twostrokes.
Fox standard plug good for most two strokes.

So after the engine is running and tuned correctly, there shouldn't be much of a problem?

Going to agree with Rodney here. Tank location is number one. You need to lower the tank. Many people invert engines and leave the tank in its original position which is now far above the carb line which makes it a royal nightmare to tune the engine.

I have several inverted engines where as i changed all this and I have no problems at all. I dremel out the bulkhead to lower the tank but strengthen around the sides to compensate with epoxy and such

Given the choice, the sideways mount will always give the fewest problems.
True....if everything is OK, the inverted engine will run fine.

FBD.

I recommend not to have an inverted application.I have one and lots of problem.Try to use sideways.

To prevent any hazzles with an inverted engine, I usually start the first engine run of the day RIGHT SIDE UP ! The rest of the day it starts fine. If it give you fits....Turn it over and fire it up !!
Ugo

My thirty-five years of experience indicates sideways mount is preferable to all others. With the right set up inverted will allow reliable opertion, but it takes more set up care.