200cc 4stroke Bike engine for RC?? - RC Groups
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Jul 27, 2012, 06:29 AM
Caravan driver
wingnutzster's Avatar

200cc 4stroke Bike engine for RC??

Hi guys, so I am quite handy when it comes to airframes - any size and construction although I have a lot to learn about composites still. I am building my second homebuilt kit - an RV-7A QB this time and have been really thinking a lot about a giant scale RC project to take my mind off pounding rivets every now and then. My question in regarding an immaculate 200cc 4stroke motorcycle engine I have lying around - actually it is still fitted to an old bike I gave up on and was wondering whether it would be at all feasible to convert that for a large RC model?

As I said I am pretty confident in the airframe and design department but always relied on others when it came to powerplant so I would need guidance here for sure.

Here are the specs from the manufacturer:
Cylinders: One.
Capacity: 198cc.
Valvegear: SOHC with two overhead valves per cylinder.
Power: 8kW at 8000rpm.
Torque: 13Nm at 7000.
Induction: Shengwei PZ30 slide carburettor.
Ignition: Electronic.
Starting: Electric/Kick.

1. Can it be done, would the motor be worthwhile converting for a large RC project?

2. If so what type of airframe would best suit the particular power?

3.What size prop would best suit that size motor?

4. What is involved in converting a motor like this?

I have good knowledge of wood in aircraft structures so would be looking at a cost effective construction method using mostly commercial woods with wings cut from foam and veneered.

I am definately more partial to scale subjects and scale flying so not necessarily looking at unlimited vertical or competition performance, just want a machine that flies safely in a scale-like fashion. Any advice?
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Jul 27, 2012, 07:11 AM
Methanol, The Cool Fuel !
Gary Cee's Avatar
Being a unit construction engine where the transmission and engine casting are the same , you will have a lot of trimming to do. Once that is done , you will have to fabricate a prop hub and couple the PTO side of the crank to that hub . At this point , depending upon the PTO shaft form (probably a spline ) you may want to make a full floating output where the prop hub is mounted in bearings that are mounted in a housing . This will allow for a safety margin and take much stress away from the crank itself . If you try a direct drive , bear in mind that the motorcycle engine was not designed to handle large end thrust (axial) loads . The motorcycle may have one roller bearing on the PTO side and a radial ball bearing on the opposite side . The roller bearing is a pure radial bearing and the ball bearing is very limited in the axial direction . You may want to convert the bearing system to include angular contact ball bearings in order to handle the thrust loads .
In short , a bit of a project .
Jul 27, 2012, 07:15 AM
Registered User
earlwb's Avatar
Generally the motorcycle engines are too specialized to convert to airplane engines. The exception is engines such as the Harley Davidson motorcycle engine. So yes it is possible, but you'll have to machine a lot of parts for the conversion. What you have to do is pull the engine from the frame. Then you have to deal with the transmission or gear box and the clutch unit. The crankshaft stub is pretty short, so you would need a prop adapter. But the engine crankshaft bearings are roller bearings and designed for thrust loads, so you may have to make gears and a drive shaft to hook up the propeller to, The Harley engine airplane conversions use a gear reduction drive to a separate drive shaft that takes the thrust loads of the propeller. The other issue is the engine uses an oil sump and is not designed for aerobatics, so you cannot fly inverted or do certain other maneuvers with it. You also need to change out the float carbs for carbs better suited to airplanes too. Anyway the easiest engines to convert are those like the Harley engine where the engine is separate from the cltuch and transmission. Plus the engine has a dry sump with a separate oil tank. But even with those engines you have to use a gear or belt drive as the crankshaft cannot take the side thrust loads from a propeller pulling on it.
Jul 27, 2012, 07:24 AM
Caravan driver
wingnutzster's Avatar
I hear ya both, thanks it is as I suspected but took a chance. I don't have the time or patience with my kitbuild going on at the moment I think perhaps a 30cc project will be best and maybe in the future I get the knowledge or some other motivation and I do a 200cc - but as for this engine I think we need a dirt cart for the property!
Jul 27, 2012, 08:05 AM
Methanol, The Cool Fuel !
Gary Cee's Avatar
With the Harley of course the power to weight ratio is a limiting factor
Also some models have an extreme vibration level . The Moto Guzzi 90 degree v twin may be more suitable . The 90 degree V is inherently smoother running and the power to weight is quite good . The Guzzi was designed as a shaft drive powerplant and has a PTO shaft and mounting face that are easily adapted to drive a prop.

In fact the US government has used the Guzzi 750 cc V twin on UAVs with good results and the bigger Guzzis are used in man carrying planes .

Many years ago I was in an old Army Surplus store . Laying in the corner was a 4 cylinder inline crankcase minus cylinders and head . Still there were the rods , pistons , "Dixie" magneto and a casting on the front with the name "HEATH" cast proudly on the cover . The store owner agreed to sell it to me for $15 . That was a lot of money then as I was making $2/HR . I bought the bugger , took it home and parked it under the work bench . A few years later I was hanging out at the local Indian guru "Indian Wally's" shop and a character I didn't really like a lot came in . Said he needed a crankcase for a Henderson Four that he was restoring . I told him I had one in good shape . He asked "how much" ..bear in mind I didn't like this guy so I told him $250 (a month's pay) . He snapped it up but I kept the "Heath" drive unit figuring it would make a fine wall hanging with a propellor mounted .

It was about a month later I was talking to a fellow at the airfield who was building a Heath Parasol replica . I asked what he was doing about the drive adapter and he said he was measuring up one from a museum and about to have patterns made to cast a replica .
I asked him if he would rather use an original and he said for sure but there were none to be had . At that point I told him he just found one ..he too asked how much .
This one was free .

The Heath parasol used a few different engines and the Henderson Four was one of the best . "Heath" is the same company that after the war against the Nazis produced the Heathkit line of electronic kits in Benton Harbor Michigan . They also made R/C transmitter - receiver kits and photo tachs ,
Last edited by Gary Cee; Jul 27, 2012 at 08:22 AM.
Jul 27, 2012, 08:53 AM
Registered User
earlwb's Avatar
Good Story Gary Cee.
I always wanted to build and fly a Pietenpol or Heath parasol plane, but alas my time has passed for doing it now. But it has been fun to think about it all these years.
Jul 27, 2012, 09:07 AM
Methanol, The Cool Fuel !
Gary Cee's Avatar
Ya know I was just yankin ur chain on tha Harley stuff eh ?
Jul 27, 2012, 09:11 AM
Caravan driver
wingnutzster's Avatar
Great story man!
Jul 27, 2012, 09:16 AM
Registered User
A two stroke snowmobile motor would likely be lighter. A Rotax comes to mind. You may as well sit in it and fly it from the FPPV "First Persons Point of View" Don't crash it though.
Jul 27, 2012, 09:18 AM
Registered User
earlwb's Avatar
Originally Posted by Gary Cee
Ya know I was just yankin ur chain on tha Harley stuff eh ?
yeah, but in Europe the Motoguzzi ( http://www.aerotech-poland.com/index.php?go=6 ) is popular whereas here, the HD engine is popular in the homebuilt planes.

Jul 27, 2012, 11:18 AM
Hope to get out of life alive
kenh3497's Avatar
IMO the Hardly (yup I spelled it right) would be the worst possible engine to use in an aircraft. WAY to much vibration with power impulses also not being even. The Guzzi is a much better choice.

If I wanted a high performance 4C power plant I would look at the Yamaha snowmobile 4C engines. Relative light weight, tapered output shaft, fuel injected, dry sump and pretty darn reliable. Available in 2 ,3 and 4 cylinder models and there are super charger kits available if you feel the need.
Jul 27, 2012, 11:47 AM
Registered User
earlwb's Avatar
Yeah some of the Snowmobile engines may be much easier to convert.

The HD engines are easy to install dual plugs on them too. Yeah vibration isn't all that great I can agree with that. But it doesn't seem to be a issue in real life use though. They may be shock mounting the engines to minimize vibration, I don't know.
Lately for larger homebuilt planes the Subaru flat four engines seem to have a following now too.

I think I would just buy a large 200cc to 250cc RC airplane engine to use in a really big giant size RC plane. But then if I happened to have just the right engine on hand, it might fun to face the challenge of converting it.
Jul 27, 2012, 12:46 PM
Methanol, The Cool Fuel !
Gary Cee's Avatar
There ya go again , just like the bike a rubber band drive ! The geared shaft drive of the Guzzi spoiled me ! The Guzzi is also extremely easy to dual plug . I did the conversion on 3 of the Guzzis that I owned . There are many engines out there that convert well but the Guzzi seems a natural . (I admit a bias after 17 Guzzis and a few hundred thousand miles on them )
Aprilia has used Rotax based powerplants that could also serve well . With these engines however we are well beyond the 200cc of the subject .
The first thing I would generally consider is an engine with no gearbox attached .

There is a Wankel based rotary Kart engine out there that puts out an awesome 58 HP from a very small (noisy and thirsty) package . Could be fun if you could get the $5800 together !
Jul 27, 2012, 01:38 PM
Registered User
I TOBOR's Avatar
Earl, your experience is different, I can cruise at 80 and this 1200 is as smooth as silk, I can sqeeze my knee against the aircleaner and feel nothing. Some guys don't like the fact that fuel injection removed the shakes. I love it. With 79 foot pounds of torque at 3,500 and gear reduction it would a big prop.

PS, Gary, I much prefer the Carbon Fiber belt to a chain and its more effecient than a shaft..
Jul 27, 2012, 02:13 PM
Registered User
earlwb's Avatar
I have a Harley Sporster XL 1200 and the engine is mounted solidly to the frame, no rubber vibration dampeners. So above 60mph you start to get a good buzz off of it.

On some of the new bikes I think they added some kind of a vibration dampener to them. But they designed it to let the bike wiggle around at idle because it looks so good shaking the mirrors around and stuff.

The final drive belt is way so much better than the drive chains, as you don't have to do anything to it for something like 50,000 miles. But the drive shafts on the MotoGuzzi's is good too. But you have to check the gear oil level from time to time.

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