# Yamaha 701 PWC engines -- why not?

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#### Armilite

##### Banned
I did a search for posts and general web sources for PWC engines in airplanes. There is nothing here that I could find and precious little on the web. That probably means it doesn't work, but let's take a look at this option.

As I continue to research the engine options for a small plane build, I keep circling around the usual suspects and am routinely shut down by the usual ridiculous prices. I can buy a 350hp LS1 Corvette crate motor for less than a 50hp Hirth. It's ridiculous how much the word 'aviation' costs.

This frustration leads me to the larger world of engines outside those marketed for aviation. And while I'm not stoked about 2-strokes, I dislike the power/weight ratio of half VWs and the like. But, I trust the name Yamaha, having owned and ridden many of their motorcycles and PWCs over the years. As one of the most prolific engine manufactures on Earth, their merit is proven.

Enter the Yamaha 701 2cyl/2stroke
Stock horsepower is 63 to 73 depending on year of manufacture
with popular mods the hp is up to 80-85
Max HP achieved at around 6200RPM
Weight is 36kg/80lbs

Even the older but very similar 650 gets 50hp stock.
The newer 790 gets 90hp stock.

These of course, are liquid cooled/open loop systems, so we would need to convert to a closed loop and add the weight of a radiator and coolant. The advantage may be far better cooling than high output, air cooled 2-strokes are known for. I'd be happy with a little better.

We would also need a PRSU which adds some weight - common in 2-strokes.

To my mind, we have an engine with some of the same considerations as a Rotax 582, but we can get it rebuilt for $595 (plus core)..., a tenth what a rebuilt 582 costs. I'm certain I am wrong and that plenty of dialog exists to prove it, so please educate me so I can move past this 'too good to be true' flight of fancy. Thanks! ================================================== Andy the reason you don't see Jet Ski Engines being used, is there is many Good Used Rotax UL Engines Available, 277UL, 377UL, 447UL, 503UL, 532UL, 582UL, 618UL, and Rotax Rick offers the 670, all fairly Cheap, and also their Counterpart Snowmobile Engines even cheaper. You also have many of the Kawasaki 340/440's that were popular also cheap. Can you adapt a Jet Ski Engine, Yes. Can all Jet Ski Engines be used, probably not. I don't know about all Jet Ski Engines but the Kawasaki 440/550 used a Threaded PTO. They have a Big Boss around PTO just as some Kawasaki 340/440 Snowmobile Engine had, but not All. The Sled version used an Adapter Plate 3/4" Thick with a Rotax A Gear Drive. Never seen a B Drive Conversion on a Kawasaki. I have seen a Provision 8 Adapter Plate for the C & E Drive. Most Jet Ski Engines don't have Water Pumps, so would have to figure out a Solution for that. Will Fan Cooled/Free Air 440 Cylinders work on a 440 Jet Ski Case, maybe? You could run a Non-Provision Belt Drive like this, Small Pulley could be Threaded for PTO. The Arctic Cat Suzuki 340/440 were copies of the Kawasaki 340/440, so they are a good option. Last edited: #### Andy Garrett ##### Active Member I appreciate your thoughtful response Armilite. It's true that many good engines exist already set-up for aircraft with Rotax leading the pack. Affordable, however is a matter of perspective. The reason for looking for alternatives in PWC and sled motors, is the difference between thousands and hundreds. Yea, it will take more work and creative engineering, but the goal of this thread is to discover if the savings is worth that effort. Simply put, if I have to shell out$5k+ for an engine, I simply won't be flying. That's just reality--I didn't choose my career for the money.

Now, I fully realize that there are those reading this right now that are ready to start pounding on their keyboards with responses like, "welcome to aviation", or "how much is your life worth", and a half-dozen other predictable responses. I understand that sentiment, and won't fault anyone for embracing it and writing my exploration off as folly. But I'm not new to aviation and the value of my life is my own business. In the end, I'm an optimist and the people in this community are rather smart. I'm pretty sure that we can crack the code to making affordable engines work in aircraft. The bad news..., once we do, they probably won't be affordable anymore. Then the PWC and sled guys will hate us.

#### Turd Ferguson

##### Well-Known Member
This is what you need to find Andy - In the next town over from me someone is selling off their collection of vintage snowmobile parts. A pile of vintage snowmobile engines for $750. He's saying about 26 complete engines, so....rounded up that's ~$29 per engine.

#### Neal Scherm

##### Well-Known Member
Any modern car engine will perform at any chosen constant rpms that you choose within it's designated rpm band, i.e. from idle to red line.

The only troubles I have seen related to what people wrongly believe, is that most car's cooling systems are undersized for maximum continuous rpms, simply because they are almost never used like that, so manufacturers save a bit of cash by supplying the minimum amount of materials required to cover targeted usage.

For example, if you tow a boat or caravan at continuous high rpms up long hills, many find it a requirement to add extra electric fans and an oil cooler.

These myths tend to propagate in countries with restrictive speed limits, Europeans know well you can hold cars flat out down their (previously) open speed limits highways. Some are 140kmh now (90mph), but In Germany, you still can go flat, and they do.

I will have to stand on a local hill and show you what they do to Chinese commercial vehicles, and you will see why I am so impressed with their engines.

First thing the manufacturers do to the Police Interceptors is put in a bigger radiator and transmission oil cooler. Old VW's and Fords ran 3500 rpm all the time before an overdrive gear was added to the driveline. A '65 VW did a 36 hour non stop run at 3500 - 4000 rpm from Memphis, TN to Los Angeles, CA one fine August in 1981. ( Home trip after my Navy duty

#### proppastie

##### Well-Known Member
Log Member
This is what you need to find Andy - In the next town over from me someone is selling off their collection of vintage snowmobile parts. A pile of vintage snowmobile engines for $750. He's saying about 26 complete engines, so....rounded up that's ~$29 per engine.
any singles cylinder engines in that pile?....how about I send you $75 and you find one that turns over and you buy it for me. #### TFF ##### Well-Known Member Boy that’s a big fuel tank to go non stop. A4s or P3s? #### Rik- ##### Well-Known Member I appreciate your thoughtful response Armilite. It's true that many good engines exist already set-up for aircraft with Rotax leading the pack. Affordable, however is a matter of perspective. The reason for looking for alternatives in PWC and sled motors, is the difference between thousands and hundreds. Yea, it will take more work and creative engineering, but the goal of this thread is to discover if the savings is worth that effort. Simply put, if I have to shell out$5k+ for an engine, I simply won't be flying. That's just reality--I didn't choose my career for the money.

Now, I fully realize that there are those reading this right now that are ready to start pounding on their keyboards with responses like, "welcome to aviation", or "how much is your life worth", and a half-dozen other predictable responses. I understand that sentiment, and won't fault anyone for embracing it and writing my exploration off as folly. But I'm not new to aviation and the value of my life is my own business. In the end, I'm an optimist and the people in this community are rather smart. I'm pretty sure that we can crack the code to making affordable engines work in aircraft. The bad news..., once we do, they probably won't be affordable anymore. Then the PWC and sled guys will hate us.
I feel your pain. I've been saying this for years, the pink elephant in the room is the engine and yet everyone defends the cost of an aircraft engine.

Watercraft engines are just another engine that has the cylinder pressured design considerations taken care of as they are constantly under a load. There is no coasting down a hill nor drafting in the boating world. So I have no concerns as to their integrity.

The naysayers will point to an RPM issue but that is handled in boating as there is a reduction ratio in the outdrives. In aircraft you will merely need a belt drive to reduce the rpm to a more reasonable one for your propeller choice.

Possibly the only drawback to the marine engines is finding one small enough in the power output to satisfy your needs as most watercraft are HP hungry

#### Neal Scherm

##### Well-Known Member
Boy that’s a big fuel tank to go non stop. A4s or P3s?
I never shut it off cause the battery was bad LOL. Had a Johnny Jar and was trained to use it properly
P3's thank you very much ASWO out of Millington.

#### Turd Ferguson

any singles cylinder engines in that pile?....how about I send you $75 and you find one that turns over and you buy it for me. Right now he's in the "Selling as one lot" mindset. Have to give it a few weeks of no bites. #### cheapracer ##### Well-Known Member Log Member Right now he's in the "Selling as one lot" mindset. Have to give it a few weeks of no bites. Well at least he's not a "Not for sale, I'm going to do them up one day ...." type. Too many of them on the planet. #### Andy Garrett ##### Active Member That's a nice pile of engines there. Too bad they all seem air-cooled and of course, the certain damage of the elements. Air-cooled engines (including my 447) always seem to run hot on the back jug. The heating problems give some Rotax's such a narrow band of 'good' performance that it's too much like walking a tight-rope. #### crusty old aviator ##### Well-Known Member Remember the old Mosler Motors bumper sticker? “Friends don’t let friends fly two cycle.” #### GTX_Engines ##### Member Why don't we do Yamaha PWC engines? Where do I start...Look, it has been done, successfully. Once, maybe twice. As for Yamaha Genesis (YG) four stroke engine conversions there are literally hundreds by now. It takes a lot of work to convert a PWC or sled motor, no matter who you are. So why add to the myriad headaches and potential problems during construction with a motor that is liquid cooled and yet has no integrated cooling system? Gee, I dunno, maybe I have nothing better to do than make a conversion more time consuming, with many more headaches and higher costs involved. Yeah, ri-i-i-i-ght. Then there's the reliability thing. How many times have you actually watched a PWC on the water, and how many times have you watched sledders on the go? We are talking about a niche in aircraft power that is looking at re-purposed (read USED) engines. So think about this: Water craft are run flat out a LOT. There are simply no obstacles out on the water, other than other watercraft, and it's pretty boring pretty quick on a PWC all alone, driving around on a flat surface with no trees, hills, or narrow trails, so ya get your grinnies on the throttle. Sleds - yeah, that too, but not nearly so much, unless you are in Michigan and flying down a lake drag racing your buddies day in and day out. Talk to a typically sledder and he'll tell you his average speed over the life of the machine is about 35 mph - and the thing does 110 flat out. I built and started flying the first successful Yamaha 4-cylinder (YG4) conversion in 2012 on one of my Air Command gyroplanes. A friend of mine built the first Yamaha Genesis 3 cylinder (120HP) aircraft (Air Command gyrocopter) in 2008. He told me about the 150 HP YG4, and I agreed to leave the YG3 sales to him and struck out to sell YG4 kits. He no longer sells conversion kits for YG3's due to health reasons, so I picked that market up too from him. Last year I built the first successful YG2 80 HP kit for a guy in Louisiana who put it on a Quicksilver float plane. He sent me videos the first day he got it flying, and I posted them on Youtube for proof of concept to the public interested in replacing their aging Rotax headbangers with something far more reliable, far more powerful, about the same all-up weight, with maybe 1/10 of the maintenance at a slightly lower cost. It's kinda funny talking about the Edge Performance 300 HP Yamaha turbo monster on Steve Henry's Highlander. Here's why: It was my YG4 kit on Henry's plane that he flew to all those awards at Oshkosh '18, every STOL contest he entered all week long and Grand Champion of the show. This past year Oshkosh '19 Henry had built his next gen plane with that 300HP engine and he won...nothing. Nada. Zip. Zilch. Not even a lousy STOL drag race, so far as I know. Jason Busat won it with a punched-out (and stroked?) turbo 912. What's hilarious about that is that he blew his engine on the way to the show! That's right - his redone engines are so reliable that he had to land on some dirt back road en-route and put another one in his plane before he could continue on to Oshkosh and kick Steve Henry's ass. Things that make ya go, "Hmmm." As for me, well - I never got into this thing to spend$30,000 on some super-dee-duper one-off engine built in Europe. I got into it to find solutions for experimental aircraft power plants that would rival and even best Rotax's products, and iron grip on the market, at a fraction of the cost.

It certainly seems I dun that.

Now, do I want to do it with PWC engines? Oh, Hell no. I already weighed the pros and cons years ago, and came up with the winning combination. I don't need to tinker with PWC engines to know I made the right choice 8 years ago.

Happy trails, boys, I'm ridin off into the sunset now...

#### Andy Garrett

##### Active Member
I appreciate the input regarding the YG engines and the color commentary about Steve's most recent engine choice. I'm actually a fan of the tech you seem to be promoting, but after several searches and identifying your business as Mohawk Aero (I think), I finally got to your website. Unfortunately, it was not helpful. More forum searches indicate that the exact issues I had with navigating your business page date back to at least March 2019. It seems like the brief history you just shared in your post is about as much useful information as I can get after considerable effort, but I thank you anyway.
My guess is that the Genesis conversion is too powerful, too heavy, and far too expensive for my desired application, but I appreciate the insight.
This may indeed be a dry hole.