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Old 01-11-2017, 06:09 PM
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Default Rotax C box EATS A BEARING after just 120hrs on YG4

Three years ago I posted on RFW that the Rotax C box, rated at only 6000kgf and designed for the 60-80 HP Rotax engines was not suitable for use with a Yamaha 140-150 HP engine putting out 90 PF torque at the shaft @ 8000+ RPM.

Certain "experts" on here said horse feathers, and cited claims of Soobies supposedly putting out 160HP and running a Rtx C with great, enduring success.

I ignored them and never installed a Rotax C on one of my YG4 kits.

Another fellow who flies trikes (not gyros) decided to ignore my advice, welcomed the encouragement of the others on here who didn't agree with me, and went into production with a gearbox adapter of his own design that looks great and which can only be used with a Rotax C gearbox.

Folks thought it was just sour grapes when I voiced my concerns about the use of such a small gearbox on such a high-performance engine, but that really doesn't matter.

One of the foremost experimental airplane builders, aviators, and kit dealers in the USA suffered a catastrophic failure of his Rotax C box installed (new) on a YG4 with a Skytrax adapter in his Highlander STOL after just 120 hours, last September.

His Rotax C gearbox ate the bearings.

When I realized the implications of this after a phone call with the builder this evening - recalling the timing of the Rotax halt of all outside sales of the Rotax C gearbox recently - it all made perfect sense:

This failure happened JUST PRIOR TO THE TIME WHEN ROTAX DECIDED TO STOP SELLING C BOXES FOR USE WITH ENGINES OTHER THAN THEIR OWN 2-CYCLE 582 AND 617 SERIES! I just had an epiphany and thought it might be worth sharing with ya'll on here.

And now you know...the REST of the story. Actually, make that "we".

I have a customer who wants to know if any of you want to buy his new Rotax C box, which is in my shop and was getting fitted for an Apex YG4i kit. That is, until tonight. That would have been my first Rotax C installation.

I know, right?

3:1, brand new, you can buy it with our adapter (YG4 or YG4i, or YG3, or YG2 80HP) and lifetime guaranteed GT4 RAM clutch.

We have a YG2 engine that just arrived. This will be our first YG2 kit. IT will be PERFECT for the little Rotax C box, guys. Seriously, c'mon! We can have the engine prepped and PSRU installed with GT4 clutch for um...$2400 engine, $1200 adapter, $550 GT4 RAM clutch, and whatever Steve wants for the PSRU, probably in the $1650-$1700 neighborhood, but i'll have to check back with Wild West Aircraft on that unit first before any commitments.
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Last edited by NoWingsAttached; 01-11-2017 at 09:11 PM.
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  #2  
Old 01-12-2017, 05:28 AM
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Mr Mills your sighting one failure and making a assumptions on Rotax descion. So buy your theory when the first Yamaha motor has a catistrofic failure they all will fail. I like the Yamaha motor and believe it will be a valuable asset in the future but it is not made for aircraft or the manor in witch you use it so by your theory it is not wise to use it. One failure does not invalidate the C Box for the use on The Yamaha it does suggest that others running that type of set up inspect there C Boxes and pool there findings. To yes you still sound like sour grapes and a self serving individual that is trying to sell his own idea with it out actually backing it up with a facts and data. And one failure is not sufficient unless you plane on making that also apply to any Yamaha failure? And yes I do agree we have a lot of self designated Experts on the forum. But that only make getting a different opinion about a consept from a person with experience. And rembe even Experts can be wrong more then once even. How many times have you givin your Expert opinion? Rember most of the people on this forum have read some of your other post.

Sincerely SWilliams

Last edited by swilliams; 01-12-2017 at 12:08 PM.
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  #3  
Old 01-12-2017, 05:42 AM
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Is the Yamaha engine designed to power a flying machine.

Why don't Yamaha offer this part themselves for the Yamaha engine.
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  #4  
Old 01-12-2017, 05:54 AM
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I believe Greg just wants to sell his own Gearbox and adapters and be the sole source of 4 cylinder yamaha sled conversions. I believe Greg wants Teals adapter off the market, simply because it is a cheaper and more elegant solution to getting a prop behind a yamaha 4 cylinder sled engine.

There are plenty of people using C box on much higher horsepower engines with success. Rotax 670's.... Yamaha 3 cylinders.... Yamaha and Kawasaki jet ski conversions.... Subaru.... Etc... My buddy Barry Thigpen has a 180+ hp Arctic Cat fuel injected 2 stroke sled engine flying on his Phantom UL, turning a big prop through a Rotax C box.

Call Ronnie Smith at South Mississippi light aircraft, the guys who make the RK400 clutch and ask them about the high horsepower applications their clutch and the Rotax C box has been successfully used on. Its alot of airboat people out there using the C box on HUGE engines no problems.



Or lets assume Greg is the true know it all expert and now pretty much everyone out there with a C box on anything larger than a 618 rotax, is doomed to suffer bearing failure and are likely to crash and burn. You been warned! LOL
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Old 01-12-2017, 05:56 AM
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Quote:
Originally Posted by Steve_UK View Post
Is the Yamaha engine designed to power a flying machine.

Why don't Yamaha offer this part themselves for the Yamaha engine.
No Yamaha designed these engines for use in snowmobiles. They have alot of common parts and design with the engines used in their Sport motorcycles, specifically the Yamaha R-1 / FZ-1.

They also recently came out with a side by side 4 wheel sport / race ATV, that is powered by a 3 cylinder engine that is nearly identical to the 3 cylinder sled engine alot of people have converted to aircraft use.
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Old 01-12-2017, 06:50 AM
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Most times if you over load a gearbox it runs hot and gears start to fail in a short time, I would suspect a Bering that wasn't good, I have had new bearings fail for no apparent reason in less than 10 hours, it just started flaking away, the replacement never had a problem , not everything is perfect every time so you shouldn't make drastic decisions because of one failure.
Norm
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Old 01-12-2017, 07:16 AM
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Greg,

Your accuracy in things said is greatly lacking.

(Now We Know, the Rest of the Story)
This is from the owner of Wild West Aircraft;


Re: Wild West Aircraft
Postby taildrgfun Ľ Wed Dec 07, 2016 10:09 am

I did have a bearing go bad in my gearbox but I think it may have been something I caused by not having the shaft shimmed exactly right when I changed the gears in the gearbox. I was also running a centrifugal clutch at the time it went bad because the engine would not start worth a darn with my big two blade prince prop. I put a new gearbox on it and I am trying a couple different propellers that have a lower mass moment of inertia and I am able to start the engine without the clutch. The prop that I am trying out now is a three blade 74 inch Kool prop. I am really impressed so far, it seems to perform as well as my two blade prince only it is much smoother and lighter and it is ground adjustable. I also have a new two blade 78 inch ground adjustable Kool prop that I am trying on my Rotax. If I like it on the Rotax I will have some made for the Yamaha's which turn the prop the other direction.

Steve Henry, Wild West Aircraft
(the Dead Stick Take-off Guy)
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  #8  
Old 01-12-2017, 08:18 AM
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Default Converting an engine for aircraft use.

One of the challenges of converting an engine not designed for aircraft use to aircraft use is to get it to turn the propeller at some reasonable speed.

Rotax has made many changes to their propeller speed reduction unit (PSRU) over the years because in my opinion it is not a simple engineering challenge. They have a room full of mechanical engineers to manage that challenge and make the changes.

The RK400 clutch seems a nice addition to a Rotax C box that is used on some other engine.

The success people have had using the Rotax C PSRU with back yard engine conversions is remarkable to me. It is not as simple as how much torque it can manage. There are lots of things that stress a PSRU.

A single bearing failure does not suggest to me that the Rotax C gearbox wonít work on a four cylinder Yamaha engine.

It is my observation that ball bearings usually fail from a lack of lubrication, trash in the oil, corrosion, a manufacturing defect or improper installation. In my opinion it is unlikely that the horsepower of the Yamaha engine had much to do with the bearing failure.

It appears to me that most of the PSRUs out there have not been properly tested. In my opinion a few hours flying around on a single article is not proper testing. They may work just fine. I donít like to be a test dummy.

If I were building a single place gyroplane I would use a Rotax four cylinder engine despite the cost to avoid the problems people appear to go through when converting an engine for aircraft use.

If I wanted more than 115 horsepower I would use a Lycoming or wait for the new higher horsepower Rotax to come out.

It doesnít matter to me that some people feel that is not cost effective. It only takes one engine failure at an inopportune time to pay for a life time supply of Rotax engines.

I like to fly more than I like to work on things and I want to minimize my chances or an unplanned engine stoppage.

If I expected to fly less than 50 hours a year and stay near the airport I might make different engine choices.

If I were going to use an engine converted for aircraft use; I would use an engine and PSRU from someone with lots of experience and many examples flying so other people would have gone through much of the pain before me and hopefully shared their experience to help me have less pain.

I admire people who make the choice to develop an engine conversion despite the challenges.

I feel for the people who believe what they read and are surprised when getting a conversion to work turns out to be more challenging than they expected and the results are less rewarding than they anticipated.
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  #9  
Old 01-12-2017, 08:26 AM
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Default Thank you for sharing the rest of the story Gerald!

Quote:
Originally Posted by Gman View Post
Greg,

Your accuracy in things said is greatly lacking.

(Now We Know, the Rest of the Story)
This is from the owner of Wild West Aircraft;


Re: Wild West Aircraft
Postby taildrgfun Ľ Wed Dec 07, 2016 10:09 am

I did have a bearing go bad in my gearbox but I think it may have been something I caused by not having the shaft shimmed exactly right when I changed the gears in the gearbox. I was also running a centrifugal clutch at the time it went bad because the engine would not start worth a darn with my big two blade prince prop. I put a new gearbox on it and I am trying a couple different propellers that have a lower mass moment of inertia and I am able to start the engine without the clutch. The prop that I am trying out now is a three blade 74 inch Kool prop. I am really impressed so far, it seems to perform as well as my two blade prince only it is much smoother and lighter and it is ground adjustable. I also have a new two blade 78 inch ground adjustable Kool prop that I am trying on my Rotax. If I like it on the Rotax I will have some made for the Yamaha's which turn the prop the other direction.

Steve Henry, Wild West Aircraft
(the Dead Stick Take-off Guy)
Knowledge is power and no knowledge is wasted.

You may have helped many to make a the decision that is best for them.
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  #10  
Old 01-12-2017, 12:25 PM
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Thanks to everyone for chiming in!
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www.MohawkAeroCraft.com info@MohawkAeroCraft.com
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Old 01-12-2017, 01:52 PM
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That is what a Forum is for.

It is not a personal pulpit, which is often exactly what you have treated this Forum as.

I will add in mitigation, that you also are sometimes civil and helpful.
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Old 01-13-2017, 12:11 AM
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Having a C box on the back of my 2.2 suby for some 4/ 5 thousand hours I know this much. You need a heavy flywheel to dampen the harmonics or whatever kills things. Even with the flywheel, I had the main bearing changed around the 400 hour mark, no longer. Never had a failure .
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Old 01-13-2017, 04:10 PM
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I may have missed it, which bearing on the 'C' gearbox failed?
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Old 01-13-2017, 06:53 PM
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Gerg, what say yee oh wise one?
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Old 01-13-2017, 06:56 PM
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Chopper Reid, 400 hours. Unacceptable. 😆
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