# 2 stroke alternative ?

Discussion in '2-Stroke Aircaft Engines' started by MadProfessor8138, Jun 6, 2019.

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1. Jun 8, 2019

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Pictsidhe.......I understand what you're saying but we will probably end up agreeing to disagree on a few points.
1.Motorcycle engines are no more complex than any other engine....they are quite simple actually,just different than other engines.
2. Expecting peak power for long durations isn't ambitious at all....they are designed for it from the factory and will show no more signs of wear than any other engine.
3. Motorcycle engines dont see peak power for long durations:

Motocross....these engines are full throttle,engine braking down through the gears and then slammed full throttle...over and over through an entire race.
This is brutal on pistons,rods and cranks.

GP......streetbike is full throttle,engine braking down through the gears and then slammed full throttle....over and over through an entire race.
This is brutal on cranks,rods and pistons.

Enduro.....engine is held wide open for the entirety of the race....generally lasting many tanks of fuel and several hundreds of miles through blistering heat and very sandy conditions.

Hare & Hound scrambles.....see enduro.

Flat trackers....engine is held full throttle through the whole race.

To say that a motorcycle engine can't sustain peak power for long durations and will wear excessively if pushed hard just doesn't ring true with my 45 years of riding and racing streetbikes and dirtbikes.
I beat on my bikes like they are step-kids and I have never once experienced an engine failure or had to rebuild an engine.
Hell,most of the professional motocross and streetbike GP teams run entire seasons on one engine and never do anything more than general maintenance.......
Have I mentioned that the Japanese build great engines ???

Kevin

To prove a point......this is my 92 GSXR-750 Slingshot with a 907 big bore kit and some other work that SHOULD kill its dependability.
I've beat on this bike for almost 27 years and when I show up on River Road to make some money on the weekends everyone just quietly mutters "sh**********t"...and I've got to find a newbie to get someone to step up to the plate to get spanked.
This bike has had a hard life since 1992 and IS STILL GOING STRONG with almost 45k on the clock.

Have I mentioned that the Japanese build great engines ??????

Last edited: Jun 8, 2019
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2. Jun 8, 2019

### pictsidhe

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How many miles has your GSX-R spent at full power? 1000? You are a braver man than I. Fastest bike I've ever ridden (not owned) was a GSXR1100L (90). You only got a few seconds of full throttle at a time with that beast on British roads. 'Cruising' at somewhere around 160mph just can't be done for more than a few seconds. Something will get in your way. That bike won every stock production drag race that it entered, until the day that it slapped itself into the tarmac after a 1/4 mile wheelie on shot forks. The engine did look very good inside when I stripped it to replace the holed covers and check for other damage. Despite being raced often and ridden by assorted hooligans it certainly didn't spent much of it's life at full power.
Bike racing is full throttle, brake, corner, full throttle. Rinse and repeat until you finish (or fall off). It isn't sustained power for hours, like aircraft use. I've had numerous bikes. The little ones that I have been able to hold at high or even full throttle for a substantial fraction of their lives were by far the shortest lived. Japanese and European stuff.

Oh, if you want to entice more suckers, open up the valve clearances. This has two effects,
1. a small increase in power.
2. It makes your bike sound like utter crap. it was always fun watching a new guy line up next to Mark and sneer at him...

3. Jun 8, 2019

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Pictsidhe......you're absolutely correct,in the grand skeem of things my Slingshot hasn't spent more than a small portion of its life at full throttle.
But understand this....my bike is the exact same bike that was raced on the GP track back in 92 and won **** near everything that it ever entered.
They added a license plate,turn signals and put it on the showroom floor just to be able to say it was a production bike and qualify it for racing.
Kinda like Dodge did with the Superbird so it could be raced by Richard Petty.
Pull the plate and turn signals and wheel it to the starting line.......

The point is.....a constant power setting,no matter what that setting may be,is much easier on the engine than constant/ violent changes in rpm....provided the engine is capable of shedding the heat it generates.
I have 2 late 80's Yamaha YZ 490's that I race in motocross and enduros.....they are old,they are beasts and will still beat most any new bike out there.
The first bike is basically stock... still air cooled and geared a bit tall.
The second bike is set up with a rare liquid cooled head that I think was British design.
The liquid cooled bike is run in motocross and trail races....it handles slower speeds and less airflow better to shed heat.
The aircooled bike is ran in enduros where the top speeds are greater and it can take advantage of the increased airflow for cooling.
The enduro bike takes wide open throttle for many tanks of fuel and hundreds of miles each race and has never complained once........

The newer 4 strokes are as light,if not lighter,and put out the same hp as the 2 strokes now days.
A constant power setting for one of these engines,even if it is near max rpm,is nothing ............shed the heat and the engine will live forever.

Heres 2 quick examples.....
1. The 24 hour endurance races....they are full throttle for 24 hours and only stop to change tires,take on fuel and change out tired riders.
2. I think it was Evinrude back in the 60's that ran a boat at wide open throttle for something like 2 months....they wanted to hit 1 million miles at full throttle.
They never stopped the boat and changed drivers out and fueled while at top speed...the video clips are interesting to watch.

Engines love constant rpm........start changing rpm up or down and that is when the stress takes place in the engine.
Look at a turbine.....it will run forever at 150k rpm .....but panic slam one from low rpm to full power,for a missed approach,and I hope you have very deep pockets because stuff is going to break !!! And does break !!!!
Mandatory tear down ........

B/S,and like engines,live so long because they are set at a constant rpm....generally full throttle.
Operate that engine like a car.....increase rpm and decrease rpm to use it.....I promise that it's going to break in short order.
My bet is on a rod letting go........

Kevin

Last edited: Jun 8, 2019
4. Jun 8, 2019

### mcrae0104

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Yup. Bugatti 100P replica. Hayabusa.

5. Jun 8, 2019

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Bugatti......now there is one of my all time favorite aircraft.
That's not the replica that was destroyed in its second flight is it ?
Is this a new venture into the old classic design ?

Hayabusa 1300 is a good engine but it's heavy......but I think the Bugatti actually needs a fairly heavy engine for proper c/g.
Wasnt the original powered with dual v8's ?

Kevin

6. Jun 11, 2019 at 1:50 PM

### jbiplane

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They have 750cc version and possible a bit increase stroke. So it wil make 1600 cc 4 cylinder engine.

Very interesting looks Honda GX 690 cylinders. Lightheight cylinder + head integrated.

Last edited: Jun 11, 2019 at 7:02 PM
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7. Jun 13, 2019 at 12:07 AM

### mm4440

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Hi, magnesium straight 8s in the original.

8. Jun 13, 2019 at 12:13 AM

### mm4440

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9. Jun 13, 2019 at 12:14 AM

### mm4440

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His anyone worked with the newish Honda 690s? weights?

10. Jun 13, 2019 at 12:24 AM

### proppastie

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The 2 stroke motorcycles I owned were pretty simple......Also I thought Yamaha had an UL engine looked a lot like the single cylinder Rotax 277?

Also in terms of workmanship I was very impressed with the Jap bikes I owned in the 70's and 80's

11. Jun 13, 2019 at 4:34 AM

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Motorcycle engines actually are pretty simple...they are just different from other engines and people that have never worked on them tend to believe they are some complex and mystical creation that shouldn't be tampered with by mere mortals......lol

My reason for starting this thread is because after reading 29 pages of how to buy a cheap lawnmower v-twin engine and throw everything away except the cases and then put in a few thousand dollars worth of parts.....well,you still dont have the desired hp and the engine may or may not live a long life.
That cheap engine isn't so cheap in the end.....

I was just pointing out the fact that motocross engines for the past 10 or so years can be had in 4-stroke form,weigh the same as a 2-stroke and develop as much if not more hp than a 2-stroke....technology from the Japanese is awesome.

A 4-stroke that weighs 60-70 lbs,liquid cooled,electric start,,can take revs all day and puts out 45-55hp is in direct competition with 2-strokes.

The engine technology is there....has been for quite some time.
Have I mentioned that the Japanese spend $millions upon$ millions every year to ensure they have the newest and best technology in their engines ???
Now......if someone could figure out how to pull the clutch & gearbox and design a redrive for it..........

Kevin

As a side note.......the Japanese designed Yamaha RX1 snowmobile engine is a great conversion for aircraft....4-stroke,light weight,high hp and **** near bullet proof.

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12. Jun 13, 2019 at 2:39 PM

### pictsidhe

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Small japanese bike engines are built like Swiss watches. I was very impressed by a VF400 I had to strip. It was shot after 30k miles. It could not be repaired as the only engines that got parted also had shot cranks... My own plan for an industrial engines does not involve bolting on every possible mower racing part and keeping nothing but the cases. That is one individual, others here are taking a more standard approach. A modern bike engine has way more parts than an industrial. If we want decent life, we have to keep piston speed down. Usually to the level where an OHV 2 valve per cylinder engine breathes just fine. DOHC and 4 valves per cylinder is extra weight and complexity.
What does an RX-1 weigh?
Do you have any candidates for ultralight size?
The bike engines I've looked at have been on the heavy side for their hp.
Hotwings is looking at an 810 briggs for direct drive. They can be bought new for around $1000 on a good day. The long block is under 50lb. If he's clever about it, he can have a running direct drive engine with prop adaptor at around 60lb and over 30hp at 3000rpm, piston speed of 1445fpm, with maybe$500 of parts. What do you have from the bike world in the 30-40hp range at that weight and cost? We aren't looking for 150hp.

13. Jun 13, 2019 at 3:54 PM

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Pictsidhe......the Yamaha RX1 engine is just an example that I pointed out to show that engines can be converted with success.
The engine is pretty much bullet proof,4-stroke,electric start,low weight and high hp.
But of course it is too heavy for ultralight use.
It was merely pointed out as an example of technology.

If I read the context of your post correctly I'm going to agree to disagree with you on a few things.

Yes,motorcycle engines are built like Swiss,er,Japanese watches.....isn't every engine ?

If a VF400 engine was trashed within 30k miles it's because someone didn't know how to properly maintain the engine...nothing is idiot proof.
I know several bikes that have well over 150k miles on them and still run like new because they have been maintained.
My friends BMW has well over 300k on it and is the most dependable bike I've ever seen in my life.
Oil changes,plug changes and proper valve adjustments will do wonders for a motorcycle engine.

Rpm is not even a factor for the longevity of an engine,oiling and heat dissipation are the keys.
Each individual engine has a particular operating range that it was built for....be it high rpm or low rpm.
Take the Vanguard engine for example...it is designed for relatively low rpm.
Exceed that rpm by overriding the governor and all bets are off.
Don't run that engine at 3/4 - full rpm,where it is designed to run,while using it and I promise it's going to break a rod in short order.
Run it at the designed rpm's and you will have a happy engine with a long life.

Engines are engines....nothing more,nothing less.
They are a particular weight,run within a specified heat range,produce a specific rpm and torque....etc.
Keep the engine within it's designed parameters by using an appropriate redrive and you should have a very happy engine.
The redrive is the magic key...
Start trying to make the engine into something that it's not by replacing parts and exceeding it's designed limits....that's where the problems start.

As far as particular engines that might be a good candidate for conversion....well,just about any of the new 4-stroke motocross engines should work.
The YZ400F engine is about 60 pounds and produces around 55hp.
Strip the clutch and gearbox off of it and find an appropriate redrive and you're in business.
If close to 1 hp per pound on a 4-stroke doesn't do it for you,well..............

Kevin

14. Jun 13, 2019 at 3:59 PM

### Hot Wings

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Well, there goes the project down the Raptor path.......

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15. Jun 13, 2019 at 4:02 PM

### BBerson

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Motorcycle engines have been available since the Wrights flew in 1903. Curtis built motorcycles, yet chose direct drive low rpm purpose built aircraft engines for aircraft. There has never been a widespread use of motorcycle engines for aviation, because redrives are problematic.
The electric Zero motorcycle is getting some use now, but the battery is heavy.

16. Jun 13, 2019 at 4:20 PM

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