The Care & Feeding of 2-Stroke Motors

HomeBuiltAirplanes.com

Help Support HomeBuiltAirplanes.com:

bryancobb

Member
Joined
Jul 9, 2019
Messages
18
OK Fellas,
I had some more thoughts to put down here.

The 2-stroke engine is just a simple air pump. If it has ANY leaks, anywhere...it will not suck very well on the intake and it won't work hard after the power explosion occurs. When your Rotax is idling, spray WD-40 around close to crankcase joints, carb rubber mounts, and cylinder head to jug joints. If RPM increases, you have a leak. Fix it.

Another mistake many people make is the impulse line from the crankcase nipple to your diaphragm operated fuel pump. If that line is not very very firm tubing, the impulses inflate and suck the tube flat and never get a chance to do that to the fuel pump membrane. Your engine will probably starve for gas.

Want some insurance against engine failure because of lean-outs caused by something freaky, say a fuel line gets kinked in flight, or cracks due to age. Bing carburetors have an accessory most people call a choke. Well it's not a choke. Bing calls it an Enrichener. How about putting control cables from the two enricheners into the cockpit for use anytime you notice EGT's climbing. How's that for smart? If you notice rising EGT's and want to land and re-jet without seizing your engine, just use the lever to "enrichen" your cylinders until EGT's start decreasing.

My next post will cover RELIGIOUS DE-CARBONING.
 

bryancobb

Member
Joined
Jul 9, 2019
Messages
18
Every Rotax Engine's Maintenance Manual says you need to clean the carbon out of the piston rings at 50 hour intervals. Who wants to do that?? No One! Who should do it RELIGIOUSLY? Everyone. It's really easy, simple, and pretty quick, if you think it through, pay attention to details, and develop a habit of doing it. For Rotax to put that much importance on it, you simply cannot neglect to do it and expect your engine to be there for you when you need it.

The one thing that will destroy your engine BECAUSE you disassemble and de-carbon is if you allow a single needle bearing to be lost down in your crankcase without noticing. COUNT THEM VERY ACCURATELY AND KNOW WITH CERTAINTY that they are where they are suppose to be...around the wrist pins. If possible, do all disassembly and reassembly with your cylinders pointing downward. That way, needles fall out on your work table.

To assemble them...I line them up on a clean piece of glass like a watchband. I put a small amount of lithium grease on the needles to keep them from rolling away. I put a small amount of axle grease on the wristpin and roll the wristpin over the row of needles. The heavy grease will overpower the lithium grease and pick up all the needles off the glass like loading people on a Ferris Wheel. Then you can insert the whole affair into the piston and use a polyethylene milk jug washer to hold the needles in the piston as the pin is gently removed. Then the piston can be positioned on the rod and the pin can be carefully slid in without disturbing the needles.

A shoe string with rubbing compound is how I remove carbon from the ring grooves. Just "saw" it back and forth through the grooves. DO NOT be tempted to scrape the grooves with a hard tool or knife.

Clean buildup from underneath the crown of the pistons. Methylene Chloride paint stripper will soften stubborn buildup without harming aluminum.

When assembling, be careful to put gaskets in the right orientation. A tiny hole in a gasket that allows an air passage to be open to make something work ...will prevent your engine from running if it's in the wrong place.

The best thing about de-carboning is you get a chance to see how well you are doing at taking care of your engine by running it correctly. If you run your engine lean enough and at the right EGT's, and if you use a 50/50 synthetic-mineral blend oil, and run Marathon REC 90 no-ethanol gas, de-carboning at 50's will be quick and easy.
 

N523SK

Member
Joined
Apr 7, 2020
Messages
13
FWIW: There are at least another dozen videos available on 2-stroke operation and maintenance on the EAA site. I don't plan to watch all of them - But I'm going to at least give 'em a look to see what I can learn from them!

FWIW: I've actually watched quite a few of Bryan Carpenter's & Dick Koehler's videos over the past couple of weeks. These are a few of my favorites, so far:
  1. "Is your Two-stroke engine about to fail?" (Bryan Carpenter, Rainbow Aviation),
  2. "2 Stroke Cold Seizure" (Bryan Carpenter, Rainbow Aviation),
  3. "Inspect 2-stroke Engine for Carbon Deposits" (Bryan Carpenter, Rainbow Aviation), and
  4. "Borescope Demonstration" (Dick Koehler, EAA)
IMO: Bryan Carpenter's video "Is your Two-stroke Engine about to Fail?" 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 any/all of these videos to anyone that has an airplane outfitted with a 2-stroke motor!

HTH,
Eric P.
Portland, Oregon
 

cheapracer

Well-Known Member
Log Member
Joined
Sep 8, 2013
Messages
6,110
Location
Australian
Most 2 stroke work better on unleaded fuel, but again your factory manual will give you guidance.
Unleaded was an absolute gift for 2 strokes, resolved many a problem overnight.

Use Japanese spark plugs. My preference is for ND (Nippon Denso), proven over time, and I had more than half my Classic Motocross club on them eventually (air cooled 2 strokes), all were grateful for it. The others were all NGK.

Don't make the mistake many do of trying to lean off your oil mixture, follow Rotax's reccomendations.

The only issue you might have with your engine sitting for a year is side seals hardening, run it for 10 minutes or so and see how it idles. If it idles high and rough, it might be drawing air past the seals. TBH I doubt it only after a year though.
 

Armilite

Well-Known Member
Joined
Sep 5, 2011
Messages
3,281
Location
AMES, IA USA

Armilite

Well-Known Member
Joined
Sep 5, 2011
Messages
3,281
Location
AMES, IA USA
Another pilot in the Challenger Ultralight Facebook Group warned me that...




I'm puzzled by the comment about the Expoxy of composite fuel tanks (i.e., "which we do not use") because I believe that the 15-gallon fuel tank in my Challenger II is made of Fiberglass-Epoxy composite. But I'll verify that tomorrow... Or maybe someone here can shed some light on the 15-gallon QC tank?

Another pilot in the same Facebook Group added...



But I'm not sure what to make of that except to take it as a friendly suggestion that If I do burn 100LL in the Rotax: I should be sure to add Decalin to the fuel. But, IIRC, neither Armilite nor Rotax Rick mentioned Lead plating or Decalin - So it must not be that critical!

Notwithstanding all of that: Running 100LL sounds like the best possible solution...
  1. It's got a much higher octane rating.
  2. It's got a much longer shelf life.
  3. It runs cooler.
  4. It lacks ethanol so it won't absorb moisture; damage the fiberglass fuel tank, or; damage the fuel lines.
  5. It's ubiquitous.
  6. Running one fuel exclusively will reduce the possibility of human error.
What are The Community's thoughts about this strategy?

TIA,
Eric P.
N523SK
=========================================
If there is any Question with the Fuel Tank, I would just replace it, you can repurpose it, or Sell it. A new 12-gallon tank from CPS is like $108.

99% of the People here have not used 100LL in there 2 Stroke, and the few who have, have only used it marginally because that's all they could get at the time of there trip. Rotax for many Years said not to use 10% Ethanol Gas, not because the Engine couldn't Burn it, but because the Fuel System, (Fuel Line, Fuel Filters, Fuel Pumps and some Gas Tanks couldn't handle it. That was changed over 10 Years ago. They also said not to use 100LL, only reason was Lead Buildup, Yea, right maybe in 1000+ Hours, and People fell for it, they made Millions off People from Engines suffering from Detonation for 40 Years. Now Rotax says it's OK. Hirth says it's OK, Simonini Says it's OK, and yet People are Skeptical.

Your Thinking is right on! I added to your list. Only Bad thing is it Costs more than 91/93 Pump Gas, but Cost varies depending on where you live

Notwithstanding all of that: Running 100LL sounds like the best possible solution...
  1. It's got a much higher octane rating.
  2. It's got a much longer shelf life.
  3. It runs cooler.
  4. It lacks ethanol so it won't absorb moisture; damage the fiberglass fuel tank, or; damage the fuel lines.
  5. It's ubiquitous.
  6. Running one fuel exclusively will reduce the possibility of human error.
  7. It's all most Airports carry anyway. I Avg 20 out 21 Airports that only carry 100LL in a 50 mile Radius. Will you want to change your jetting for it, Yes.
100LL Avg Cost around the USA. 100LL around me, the lowest is $3.03 a Gallon. If you click on Green Box, More Nearby Places you will get an extensive list.

Ask yourself this, what does it Cost in Money to rebuild your Engine if it Fails before the 300hr TBO from Detonation & Time your Plane is down while it's being Fixed? If you burn 100LL and get 600hrs, or 900hrs, how much did you save on Rotax's Bogus 300hr TBO. Your Rotax uses the same Internal parts as a Hirth that has a 1000hr TBO. If you use a Good Oil & Ceramic Coated Pistons, you will also have less Decarbons to do, more down Time & Cost. You all will buy that $5 Cookie, Pancake dinner, but complain about Paying $3-$5 for a Gallon of 100LL Gas.
Ames Area 100LL.jpg100LL Avg Cost 6-28-20.jpg
 

n3puppy

Well-Known Member
Joined
Jun 25, 2019
Messages
138
=========================================
how much did you save on Rotax's Bogus 300hr TBO. Your Rotax uses the same Internal parts as a Hirth that has a 1000hr TBO.
Hirth and Rotax do not have the same internal parts and therefore different TBO recommendations. (Plus Hirth TBO is at only 75% power)

Specifically - Hirth uses Nickasil cylinders, Rotax uses replaceable iron sleeves.
Iron Sleeves wear out, so Rotax sells oversize pistons when they do. Even ceramic coated pistons still have piston rings that scrape (wear) the iron cylinder twice per revolution (up and down stroke)

The metal that gets scraped off the cylinder walls has to go someplace - like into the ring grooves and into the bearings

A lot of good information on inspection and rebuild procedures in the factory Maintenance manuals available at Flyrotax.com
I urge anyone contemplating their own maintenance to download/read them before they are gone (like the 277/377) Keep them handy for reference

https://rotax-docs.secure.force.com/DocumentsSearch/sfc/servlet.shepherd/version/download/0681H000005UbxnQAC?asPdf=false

https://rotax-docs.secure.force.com/DocumentsSearch/sfc/servlet.shepherd/version/download/068A0000001ttmFIAQ?asPdf=false
 
Last edited:

Armilite

Well-Known Member
Joined
Sep 5, 2011
Messages
3,281
Location
AMES, IA USA
Hirth and Rotax do not have the same internal parts and therefore different TBO recommendations. (Plus Hirth TBO is at only 75% power)

Specifically - Hirth uses Nickasil cylinders, Rotax uses replaceable iron sleeves.
Iron Sleeves wear out, so Rotax sells oversize pistons when they do. Even ceramic coated pistons still have piston rings that scrape (wear) the iron cylinder twice per revolution (up and down stroke)

The metal that gets scraped off the cylinder walls has to go someplace - like into the ring grooves and into the bearings

A lot of good information on inspection and rebuild procedures in the factory Maintenance manuals available at Flyrotax.com
I urge anyone contemplating their own maintenance to download/read them before they are gone (like the 277/377) Keep them handy for reference

https://rotax-docs.secure.force.com/DocumentsSearch/sfc/servlet.shepherd/version/download/0681H000005UbxnQAC?asPdf=false

https://rotax-docs.secure.force.com/DocumentsSearch/sfc/servlet.shepherd/version/download/068A0000001ttmFIAQ?asPdf=false
=====================================

Hirth & Rotax use the same 50:1 Oil Ratio, same rating for hp@6500rpm. Same Spec, Rods, Bearings, Pistons, Gaskets & Seals, Rings are different for the Nikasil Cylinder, but they don't Multiply the TBO! Nikasil Cylinders do FAIL from the same reason as an Iron Sleeve Cylinder does. Nikasil does lessen your chances of a Seizure, but not 100%, they can and Do still Seize. Rotax's don't run at 100% Power for their TBO either. Most people are smart enough to READ their Manual that says 2 min at Full Power only. There are some Rotax 503's and 582's out there with over 1300+ hrs with just a De-Carbon. Show me (1) Hirth making that 1000 hr TBO Claim! 1300/300 = 4.3 Rebuilds!

Your Question should be, How are they getting them 1300+ hrs with just a De-Carbon. Using a Good Conventional Oil (PENNZOIL® 2-CYCLE AIR-COOLED), Good Fresh 91 Octane Gas, and using Max 5800rpm for takeoff, then flying at 75% of that Power!
If they had today's Technology, Hirths Blue Max/Amsoil Saber and these Ceramic/Moly Coated Pistons, they would be getting 700+hrs before a De-Carbon might need to be done. PENNZOIL® 2-CYCLE AIR-COOLED only has a 175 ºF Flash Point, but I don't remember what they premixed it at 40/50:1. PENNZOIL® 2-CYCLE AIR-COOLED Oil was the recommended Oil by Rotax for many Years till these New Synthetics showed up.


Both Hirth & Rotax face the same problems, People, using Poor Gas, bad 2 stroke Oils, and doing poor maintenance. Since Hirth uses mainly 9.5cr in most of there Engines, they have fewer Detonation problems. But even Fresh 91 Octane in 3 weeks can drop to 89, and even lower over time.

When you have to finally Bore & Hone a Rotax Cylinder, 1300+ hrs, it Cost $40-$60, and can be done same day, when you have to Re-Nikasil a Hirth Cylinder it Cost $250+ and has to be sent out to the few Companies that do Nikasil, can take weeks.

You can change out a Sleeve, Bore & Hone it, but very few people in the World can Bore and Re-Nickel there own Cylinders. Since I use Good Oil and High Octane Gas, the only reason I would go to a Nikasil Cylinder is to Save Weight. A 277UL Fan Engine complete with Gear Drive & Exhaust (65lbs), 277UL Free Air probably (60lbs) vs the Hirth F-33 complete with a Belt Drive & Exhaust & Electric Start at (45lbs). The Belt Drive saves 3-4lbs but has a lower TBO with Belts($40+ea) needing to be replaced vs the Gear Drive 700hr TBO. A New B Gear Drive is $835 today!

Hirth has pushed using its own Bluemax Oil at 100:1 for many years. Just as Rotax Joe has pushed using Amsoil Saber Pro at 100:1 with his Ceramic/Moly Coated Pistons in his 582UL's with over 700+ hrs without a De-carbon.

Those manuals you posted don't include the 277/377. Only 447 to 582 Engines.
 

n3puppy

Well-Known Member
Joined
Jun 25, 2019
Messages
138
====================================
Those manuals you posted don't include the 277/377. Only 447 to 582 Engines.
Thank you for reiterating my post
" I urge anyone contemplating their own maintenance to download/read them before they are gone (like the 277/377) Keep them handy for Reference"

Some people may have missed it if they only glossed over the content without fully reading it
As time marches on, support literature for all the two strokes will disappear from the site - Just like the 277/377 info that has already been taken off.

It would be prudent to go to the site and download as much as is still available. Operators manuals. Install manuals, maintenance manuals etc.

That way don't have to rely on peoples fading memories for guidance on these old engines in the future.
 
Last edited:

Armilite

Well-Known Member
Joined
Sep 5, 2011
Messages
3,281
Location
AMES, IA USA
Top