# 34-50 hp Engines

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#### mstull

##### Well-Known Member
Outboard engines are known for being compact, light, modern, and reliable. It should be a good engine to convert. Aren't they a bit expensive? Engine prices and parts prices, here in the USA, are so high, you'd do just as well buying a Rotax or other aviation engine that didn't need converting. A motorcycle engine might be a less expensive starting point. Are 2 stroke motorcycle engines still legal for street M/Cs in your country?

#### Peter V

##### Well-Known Member
Outboards are ideal. Gobs of torque at low revs. Big job to convert though. Motorcycle engines are good in terms of technology and weight, but they tend to need high revs and the engine designs focus more on horse power instead of torque, especially the smaller displacement ones.

#### AeroBaseSB

##### Member
Outboard engines are known for being compact, light, modern, and reliable. It should be a good engine to convert. Aren't they a bit expensive? Engine prices and parts prices, here in the USA, are so high, you'd do just as well buying a Rotax or other aviation engine that didn't need converting. A motorcycle engine might be a less expensive starting point. Are 2 stroke motorcycle engines still legal for street M/Cs in your country?
My choice of an outboard engine is because I have a current spare one which has been unused for quite sometime. Surprisingly parts for japanese outbard engines are cheap in the asian region although the price for the engine itself are a bit pricy. However they are not as expensive as a Rotax. and then again the service, maintenance and repair is simpler for an outboard engine. Currently without the modification being put in the engine weigh in the region of 40 to 45 Kgs. that is a good power to weight ratio for a 50 HP engine.

The engine I have is forced water cool 3 cyl, 697 cc, flyweel magneto CDI, electric start and 12V 11 A alternator built in. Full throtle speed range is 5150 to 5850 RPM.

My concern is on the Propeller RPM. I am not thinking of any requction for the set up and my calculation is trying to put a smaller dia prop and running at 4500RPM. The prop will be self made of either wood or fibre.

Our problem in Malaysia is the fact that most aero parts and material is not available.

Yes I have considered motorcycle or ATV engines. 2 stroke engines are still legal and available here. with a motorcycle or ATV engines I know that I dont have to worry very much about the reduction, cooling and exhaust system.

One other source of interest to me are the china built engines. In malaysia the motorcycle and ATV engines are getting to be more reliable. I am sure given the proper attention to its piston and sleves, more reliable end bearings and cap bearing, and replacing them with japs equivalent would certainly improve the reliability of this engines. I will post more site later of such engines which i have found on the internet.

rgds

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#### 1938PopularMechanics

##### Guest
Remember to look at www.GroupK.com if you ever wanna modify a "u$ed" engine. Their RAVE went SLOWER over 170psi. The newer Yamaha WaterCraft and SlowMobile'z have built-in gear reduction'z to keep the impeller and clutch or ? propeller ? to be SLOW enough. Turn the 4cyl 4stroke 12,000 rpm and ..... keep Prop SLOW enough ....... The new Kawasaki SuperCharged 250hp 1,500cc iz a STROKED Ninja 1200 ...... with WARRANTY .... My Father used a '82 KZ1100 air-cooled motorcycle engine and made it PROPELLER-Cooled. KOOL ...... ..... fan kooled. He designed it to have a 3-1 reduction straight off the crankshaft with welded-on extension ..... and the un-needed clutch and gear'z removed. Only about 375ish thrust at 8,000ish, for the 200 lb. engine including carb'z, exhaust and GearReduction ..... , I just called him and it iz with-out his adju$table Ivo-Prop .......

He built it ALL with center-line thrust, good Center of Gravity (doe$n't LEAN on Tail like MO$T do) , fiberglass over foam 13gallon_1quart dual-seat gastank and 6' tall-tail with 6' width and 2' depth made from BOTH fiberglass and a tin ver$ion. He now will$tick with FIBEDRGLASS-ONLY becau$e it iz EA$IER. Am I bragging TOOO much ??? He had THREE aluminum exhaust and ONE steel exhaust break over time, so now it it iz JUST straight-pipe ........ can't break that a$ea$ily, huh ??? we hope .....

It u$ed to be Kawasaki GREEN and HARD to find in unexpected set-down's in ANY field found. It iz NOW Hunter-$afety ORANGE ...... inca$e the timinig-advance$pring break'z again .... or ??? Be Prepared ..... for ANY -n- EVERY-THING .....

The PersonalWaterCraft using Ninja-Style Race-Bike engine's are getting wide-spread ..... with turbo-bogging and Super-Charging ..... under Warranty in the water, but ..... Go with 330hp race-gas mod'z in 'da AIR and ???

TOOO ri$ky for me in ME ..... I grew-up cra$hing ju$t for fun when I wa$ $till an UnDe$tructable-Kid. Pine-Tree'z do NOT feel like Soft-Wood ..... and water feel'z like cement over 50ish ..... Ice iz NICE, but Dirt HURT'z ..... winter racing had less grass to hide the rock'z .....

Imagine a TZ 750 of the PA$T ...... Kenny Robert'z GyroPlane ??? Imagine a "cra$hed" and "totalled" ,from ONLY scratched PAINT, bike engine being a 1,800cc or 1,900cc V-twin ....... Japane$e Harley in 'da$ky ??? or gear-reduction InLine-4 .....

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#### mstull

##### Well-Known Member
Peter,

That hose is made of very thin sheet metal that is formed and wound into a spiral. I doubt it would last long at all.

There are better hoses available:
http://www.hosecraftusa.com/group.php?grouptype=Mat&groupUID=25
They are VERY expensive, and would need custom adapters on the ends. I'm not too confident they'd last real long either.

Using an ordinary elbow with a ball joint on each end has proven effective.

#### PTAirco

##### Well-Known Member
Seriously - is it that hard to write like a normal person?? Z\$???

#### Peter V

##### Well-Known Member
The JC Whitney one is a pretty cheap and basic example.
If you were to spend some time investigating the options for your particular application you'd come across many different designs (there's a bunch here), as these things have been around for decades and are the standard way to alleviate stress in exhaust systems from vibration.
In any case, I'd rather live with the chance of an exhaust hose developing a leak than the potentially disastrous consequences of cracking in the rest of the system.

#### YGBSM

##### Member
Re: Ul engines

Yes, the Hirth is a nice engine, but so far nothing seems to be able to beat the 69 lbs weight of the MZ. The Hirth using a gearbox will weigh 89 lbs - that is 20 lbs of weight I'd rather put into the structure.

The Kawasaki 440 seems light enough but I can't seem to find anyone selling them or re-drives for them.
I don't know anything about this company, but they might have something some of you are looking for.
New and used engines

If you do deal with them, please let me know the outcome.

-----------------

#### mstull

##### Well-Known Member
J-Bird has been selling Kaw 440s and reduction drives for them for decades. He has an endless supply of Kaw 440 and 340 engines, along with everything you'll need to make them work. He advertises in most U/L and LSA magazines. He doesn't have much of a web page and doesn't communicate by Email. He does everything by phone. His number is 262-626-2611. I recommend the Micro-V drive on a fan cooled engine. Vortech just resells J-Bird's engines. You'll get about the same price either way.

#### YGBSM

##### Member
mstull:

Thanks for that info.

Now I wonder if there is a site where a person might obtain specs such as engine mount hole pattern, physical size, and performance like HP & torque, fuel consumption etc.

#### mstull

##### Well-Known Member
Most of the specs are in the snowmobile manual that the engines were used in... Arctic Cat and John Deere. The mounting bolt pattern is in J-Bird's little "catalog", if you use a magnifying glass to read them. If you write me privately with your Email address, I can send you a copy of the snowmobile manual. My Email address is below.

#### YGBSM

##### Member
I have found a complete Kawasaki EX500. I know this is a water cooled, 60HP 4 stroke and is a V-Twin with parallel cylinders. The red line is 11,000 RPM so running at 8000 (or less) should not be a problem.

According to specs found on the web, the estimated weight is 115 lbs. BUT at New and used engines it is listed at 60 lbs.

The person that has it owns a motorcycle shop and is also a certified aircraft mechanic.

He said that he could take all the gears out and leave only the output reduction I needed, which should save about 20 lbs.

I know that the engine would sit a little off the thrust line if the transmission is used to drive a prop. Or driving off the crank it would be on the thrust line.

My question is, does anyone have any experience or knowledge of any problems that using this engine would cause?

Also, what RPM can a 64" prop turn before going supersonic at the tip.

Thanks

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#### clanon

##### Well-Known Member
you'll need to take the gearbox apart(out) for weight and build the most efficient PSRU possible(cogged belt 98% and, over 4:1 reduction ratio) for a 64" keep it under 2500 rpm always.
use the ExtendedPropSelector program

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#### mstull

##### Well-Known Member
YGBSM

Be aware that it is necessary to include a flexible coupling/rubber cush drive in your reduction drive to absorb the engine's resonances/harmonics. I've always wondered if it might be possible to convert the existing clutch into a cush drive on a motorcycle engine with some custom machining. Chain drive motorcycles have that built into the rear wheel, behind the sprocket.

I don't think the engine has enough power for prop tip speed to become an issue. You'll want to de-rate the engine for reliability anyway.

#### Dana

##### Super Moderator
Staff member
Be aware that it is necessary to include a flexible coupling/rubber cush drive in your reduction drive to absorb the engine's resonances/harmonics. I've always wondered if it might be possible to convert the existing clutch into a cush drive on a motorcycle engine with some custom machining.
Quite possible... that's what I did on my Kawasaki conversion. I got rid of the clutch guts, and attached my prop shaft to the original clutch basket, which is driven off the primary 3.4:1 reduction gear via rubber bushings.

-Dana

When the chips are down, the buffalo is empty.

#### clanon

##### Well-Known Member
this saw it flying(video i mean) (i think is a trz 250 70hp@9500 or so)
Don't like PRSU though.
i'm testing my 250 belt driven ;when i'got thrust figures will upload data.

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#### PTAirco

##### Well-Known Member
Hm, that does look a little - agricultural....

#### clanon

##### Well-Known Member
Yet... it flies!
don't ask me for how long,though.

#### dino

##### Well-Known Member
HBA Supporter
Yes. Needs some cultivation.

Dino