Rotax 582 Alternative Possibility

[TFF]

My words meant to say, own the best maintained 582 and not hot rod it. OR change the plane to handle a 4 stroke. There is one of those Pulsars a airport over from mine. He probably flew it today. He has had it a long time like twenty years.

Last week I took a part to a local machine shop guy. We will call him semi famous. He showed me a motorcycle he made. He has made a few and had F1 guys ride them in races. This one was probably 25 years old. Had some big snowmobile engine on it. I think it was flipped so the output was up and it went though a gear reduction then into a regular gearbox to the rear wheel. Looks like a Delorean because the frame was bent sheet Stainless. The only thing he did not make was the wheels and forks and gears. That is the kind of person who can make a off use engine work. The kind of person who just wants to solve a problem. He is not an airplane guy but he made 600 exhausts for Rutan to sell to the EZ builders back in the day.

The more stuff us computer designed, the less they have to piggyback castings. Making something modern fit is not as easy as it once was for more universal components.

As for helicopters, it’s four stroke or turbine. And for me I’m staying away from the smaller ones. A friend had his turbine helicycle quit while during a fast taxi. Successful auto but he was done. Me, got to be bigger than a R22.

 

[koyama]

My words meant to say, own the best maintained 582 and not hot rod it. OR change the plane to handle a 4 stroke.

That is how I understood it. I was just using your quote to clarify that if reliability is the goal, building a one-off engine is not likely the right approach. I was getting the hint from other posts that the reason for not wanting a 2-stroke 582 was at least partially reliability. There are many reasons for not wanting a 582, but if reliability is one of them, the idea of using a one-off conversion is not the right path to go. (Maybe I could have used another quote or worded it better.)
Just my 2 cents worth on that one.

 

[Yellowhammer]

What ratio and oil you use?

I have never flown behind a 582 yet. The Pulsar I am building calls for one. What is the best set up in you opinion ( oil and what not) ?

 

[Yellowhammer]

The only 4-stroke engine I have found that matches the weight and power of a Rotax 582 is the Weber MPE 750.
If you look at this engine in detail it is obvious why. They did every trick in the book to get the weight down and the power up. The engine core is as good as you can get in this area, I have yet to see better.

https://weberpower.com/mpe.html

They are difficult but possible to keep within 10 pounds of the 582.
They make ~63 HP when they are setup in the lightest possible configuration. You can get more, but you will go over weight. There is also a turbo available, so you can get well into the ~90 HP range even at altitude!
As far as the reliability of the engine goes, it is hard to say. There are too many things that enter the picture.
The top problem I found right off, is that in the chain of gears that drive the water pump, there is a plastic gear. (Part 11 here https://weberpower.com/mpe-cooling-system-water-pump.html) Within the first week, the one I had failed. I made aluminum gears to replace them, this problem is cured.
When I buy used engines to convert, it is common to find bad rod bearings. Rod bearing failure is quite the thing with these. As it turns out, the failure is caused due to running too rich or misfire. The pistons are extremely short, there is no piston skirt to speak of on the sides. (Refer to the diagram here https://weberpower.com/mpe-crankcase-crankdrive.html) This means that the rod is unusually short as well. This combination allows raw fuel to get into the rod bearing and cause failure. Also, the oil gets thinned down as fuel mixes with it. This means that you have to be EXTREMELY careful with the software to never allow too much fuel into the cylinder under any conditions, especially on starting, or you will have a rod bearing failure for sure. One thing I did to help with this, is I installed a small electric oil pump to pressurize the oil system before starting. I also added a sensor to measure now much fuel is in the oil, as well as careful layout of the oil system to avoid bubbles or foam. (The engine is dry sump.) Since I made the software changes and added the pump, I have not had a rod bearing fail, or any other failure.
Also, the electronics are quite the problem. I would never use the stock computer, nor have I found any off the shelf solutions that work. You will either need to make your own computer or you will need to adapt a MegaSquirt.
MegaSquirt | Premier DIY EFI Controller
The earlier conversions I did were using their board design, but I quickly ran into limitations and started making my own board designs. The software can not be made to work without modification, due to the rod bearing fuel contamination issue, you will need to make changes to address this! (The pre-start code that over fuels the engine to start easier needs to be changed for sure!) There are also a few tweaks that can be made, especially to deal with RPM hunting and overshoot. This is easy because the actual throttle butterfly is controlled by the computer. (However, again, the off the shelf MegaSquirt software and hardware is not setup for controlling the throttle butterfly.) I also added some changes to deal with misfire to prevent extra fuel from building up in the cylinder.
If you are good with assembly language and making computers, this is a good way to go. If not, the 582 is likely better.
The MPE 750 project has proven to be a reliable engine, but only after 8 years of trial and error, 6 killed engines and nearly $5000 in fuel for running on a dyno in the process. If you are willing to go through something like this, this engine is the best option I have found to date to replace a 582.

Thank you sir for your helpful guidance. I am going to look at the link you posted right now