The Care & Feeding of a 2-Stroke Engine

[N523SK]

Hi, Everyone:

1. I'm a student pilot.
2. I bought an aircraft with one of the famous/infamous Rotax 670 motors (with the HO exhaust and the Ducati ignition) last year.
3. The motor was installed and configured in late 2018 by an A&P.
4. The previous owner only put approximately 15 hours on the motor before he lost interest in aviation.*
5. The airplane had been sitting, idle for most of 2019.
6. The only recent use that the airplane has gotten has been the 2-hour flight from Antelope, OK to Wichita, KS (STOL Creek Avaition) and the use that it got when Michael Busenitz performed the annual, made some tuning changes to the motor, and re-pitched the propeller.
7. The airplane has been in the hangar since I bought it.

* Some pilots that I spoke to during the inspection/purchase process expressed their opinion that maybe, that motor, in a pusher configuration, may have been too much for an inexperienced pilot such as the previous owner - But that's neither Here nor There. But it certainly indicates to me that I'll need to be very careful with this aircraft until I have more experience - much more experience!

Anyhow; I have questions about the care & feeding of this motor and 2-stroke motors in general:

• How to maintain it.
• How not to maintain it.
• How to operate it.
• How not to operate it.
• How to store it.
• How to take it out of storage and get it ready for the Season.

This might seem a little silly. But after reading the posts on this forum and others it's become clear to me that 2-stroke motors have their own unique set of needs. e.g.,

• I read somewhere that the 670 should only be operated at full-power to climb to altitude. And then it should be throttled-back to cruise because that motor isn't meant to be operated continuously at full-throttle.
• And another user on a different forum did quite an analysis on high-octane pump gas and how it ages; the pressure that's generated during compression (183 PSI with a 12.5:1 CR), and; considerations for living with the 12.5:1 CR (e.g., through the use of different cylinder heads).
• And another user somewhere wrote about the importance of closing the intake ports and the exhaust ports (by rotating the crank to TDC) in order to reduce the amount of ambient air that comes in through the exhaust port and flows through the crankcase.

Because this is all new to me and the airplane is going to be sitting for a while longer while I finish my training: I'd like to ask what steps should be taken...

1. to preserve the motor while I'm unable to operate it and then
2. to prepare the motor for use once I find a pilot friend to exercise that motor for me. Or once I complete my training and I'm ready to fly it myself! (Very few of my pilot friends fly LSA's. None of my pilot friends fly pushers. And none of them fly LSA pushers!)

TIA,
Eric P.
N523SK

 

[ultracruiser41]

California Power Systems has great Rotax technical information and parts.

 

[N523SK]

California Power Systems has great Rotax technical information and parts.

Thanks, Barry - I'll give 'em a call!

Eric P.
N523SK

 

[Sv.grainne]

I can only relate my experience with 2 stroke engines in a marine environment. Start and run the engine weekly if you can, use only fuel that contains no ethanol, ethanol attracts water and it will collect in the fuel system, use a fuel stabilization product like Stabil, mix in the fuel and run till you have it up in the fuel system. If you are going to leave the engine for a long period and can't run it consider fogging the intake with an oil emulsion to protect the internal metal components during the storage period.

Bobby

 

[N523SK]

I can only relate my experience with 2 stroke engines in a marine environment. Start and run the engine weekly if you can, use only fuel that contains no ethanol, ethanol attracts water and it will collect in the fuel system, use a fuel stabilization product like Stabil, mix in the fuel and run till you have it up in the fuel system. If you are going to leave the engine for a long period and can't run it consider fogging the intake with an oil emulsion to protect the internal metal components during the storage period.

Thanks, Bobby - I'd forgotten about the fact that ethanol will attract water! (So that's something that I'll be sure to record in my notebook!)

Also: I plan to create a sort of Fuel Management Plan so that I can avoid keeping fuel any longer than absolutely necessary because, as another user on a different forum wrote:

For Almost, All Rotax/Skidoo 2 Strokes, Detonation is the #1 Problem [because] they use High Compression Ratio's in most of their 2 Strokes... Fresh 91 Octane. Pump Gas can lose 2 Points in Octane in as little as 3 weeks... Atmospheric Pressure is 14.7 x 11.5cr = 169.05psi at Sea Level, and Good Fresh 91 Octane is Good for Max 175psi. So your Rotax Engine is on the Edge from suffering from Detonation. 100LL has a 5 Year Shelf Life. A 50/50 Blend of 100LL and 91 makes about 96 Octane. For a 670 92-95hp@6500rpm, a High HP Engine Pulling/Pushing a Heavier Airplane, I would use a minimum of 96+ Octane myself. Most Airports only carry 100LL, so that's what I would use.

But before I can do that: I should also figure out how to care for my Rotax 670 if I feed it 100LL or a diluted mixture of 100LL. Then I can decide whether or not I want the hassle of using high-octane pump gas!

Eric P.
N523SK

 

[N523SK]

And, in this post, GyroZprey shared this tidbit about Rotax motors and 100LL:

If you are going to use 100LL Avgas in a rotax engine you need a mineral or blended oil ...such as Shell sportplus4 .....if you are not a cross-country flier & know you will use MoGas 100% of the time ....synthetic is good!

However: The original post was about the turbocharged, 4-stroke Rotax 914 - So it might be completely irrelevant!

Eric P.
N523SK

 

[DavePA11]

Eric - Just make sure you are always prepared for engine out and can land safely during every phase of your flight. Be prepared for engine failure on take-off, cruise and landing. What is the model of the aircraft? I have witnessed many 2 cycle engine failures in ultralights and trikes so just assume it will happen at some point.

 

[digbar]

I doubt that this 2-stroke engine needs high-test gas. I fly two FW Challengers II, with Rotax 503s, and the most important things are to use good quality oil in the gas - I use Amsoil Saber 100:1, and to make sure to go easy on the throttle until she's warmed up. I sit at idle for 2 minutes before giving her gas to taxi, and warm her the rest of the way up at 3,400 or so at the end of the runway. My partners and my cardinal rule is - no takeoff power until 5 minutes have elapsed from startup.

The EAA website has a 1.5 hour webinar on why 2-stroke engines fail - based on the Rotax 503, and also has numerous short tips on 2-stroke engines. The EAA is the best $40 investment any flier can make.

 

[N523SK]

Thanks, Digbar - I'll look for that!

Wow - A quick search of the EAA site returns a list of a dozen videos about Care & Feeding of 2-stroke engines!

Thanks, again, Digbar!

Eric P.
Portland, Oregon

 

[N523SK]

I doubt that this 2-stroke engine needs high-test gas. I fly two FW Challengers II, with Rotax 503s, and the most important things are to use good quality oil in the gas - I use Amsoil Saber 100:1, and to make sure to go easy on the throttle until she's warmed up. I sit at idle for 2 minutes before giving her gas to taxi, and warm her the rest of the way up at 3,400 or so at the end of the runway. My partners and my cardinal rule is - no takeoff power until 5 minutes have elapsed from startup.

After watching Bryan Carpenter's video "Is your Two-stroke Engine about to Fail?": I'd say that correct loading is the most important thing. But there are a lot of important factors that go into the reliable operation of a 2-stroke motor!

The EAA website has a 1.5 hour webinar on why 2-stroke engines fail - based on the Rotax 503, and also has numerous short tips on 2-stroke engines. The EAA is the best $40 investment any flier can make.

IMO: Bryan Carpenter's video needs more specific guidance in the form of actionable tasks (e.g., How to correctly pitch a propeller). But it is definitely worth the Time and the Money - And I would recommend it to anyone that has an airplane outfitted with a 2-stroke motor!

HTH
Eric P.
Portland, Oregon

 

[N523SK]

...and to make sure to go easy on the throttle until she's warmed up. I sit at idle for 2 minutes before giving her gas to taxi, and warm her the rest of the way up at 3,400 or so at the end of the runway. My partners and my cardinal rule is - no takeoff power until 5 minutes have elapsed from startup.

Thanks, Digbar - Bryan Carpenter emphasizes that in the video "2 Stroke Cold Seizure"!

Eric P.
Portland, Oregon

 

[Rattler 1]

Give Rotax Rick a call. He has a web site and Has been helpful for me. He deals with a lot of 670's. Very willing to talk on the phone.