New Approach ?? Yamaha 120 gear box adapter

hibshman25

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I supplied a customer with an engine a few months ago and he shared with me his adapter for the Yamaha 120 engines. It's an aluminum adapter that replaces the oem recessed bearing holder on the pto end of the motor. The oem bearing gets transferred to the new adapter, and the adapter recesses into the case just as the oem one does and mounts with 4 bolts. The bolt size on the adapter was increased to handle the load, so the 4 tapped holes in the engine case need to be drilled and re tapped to the larger diameter. The adapter has a flange large enough to accept the rotax c gear box 8 bolt mounting pattern. The gear box serves as the template to drill these 8 holes. These 8 holes are not not pre drilled in adapter due to the fact that different builds require different orientations.

To make the the PTO connection between engine and gear box, a new pulley/hub is supplied with the adapter plate.

As of this morning the customer has 48 hours of flying time on this adapter combo and a rotax c box. If anyone is interested in this set up, he will sell the adapter and hub for $700. If anyone is interested feel free to contact me and I will provide contact info for the gentleman making them. I'm not aware of anything like this presently available so I wanted to share my findings.


First photo shows the oem bearing retainer
Second and third photo show the rotax c attached to engine
Fourth photo shows the adapter in rear, original rotax hub to left, and the new yamaha to rotax hub on right.
 

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RICK MARTIN

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Hey Travis,

Thanks for the info and photos. It's great to have another option. Granted, some guys might shy away because of the re-drilling and tapping, but it looks like a great piece of work.

Since you are such a great source for the engines, perhaps you or your supplier can get together and offer the drilling/tapping service if the customer can supply the orientation figures.

Just an idea,

All the best,
 

Jason O

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Rotax "C" box?

Rotax "C" box?

that gear box does not look like any Rotax gearbox I have ever seen. You sure its a rotax "C" gearbox?
 

NoWingsAttached

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That is an Air Trikes SPG4, same PSRU I am mounting on a RX1 YG4 right now, and not a Rotax C.

This YG3 adapter is not suitable for use on a gyrocopter. The entire rotating mass of the prop is held together on the engine by just 4 M8 screws threaded 10mm into the crankcase on a <4" diameter bolt pattern.

Would you attached your prop to its flange with just four, M8 screws threaded 10mm into an aluminum case on <4" centers, and turn it with a 120HP engine, then go out and try some hammerhead turns or other somewhat typical gyrocopter maneuvers that stress all attachment points for the prop far more than any other type of aircraft does?

If you say yes, and decide to go out and buy one of these adapters, then before you do just remove two of your prop bolts on your gyrocopter right now and go out and fly it around like that for a few months first to get used to the idea that you are nuts.

Have you ever seen any prop mounted to its flange with just four M8 screws (~ 5/16") for an engine with this much power? Oh, hell no.

Yeah, you MIGHT get away with this thing on a passive aircraft like a trike, but brother if you are flying a gyro and plan to kick it around a bit and have some good-ole gyrocopterin' fun I recommend you steer clear of this adapter.

I'd really rather see you at the next fly-in than read that your PSRU broke free from it's engine attachments...
 
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Viper22

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Looks like the SPG-3 - pictures is from the Air Trikes site
 

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gyro.pete

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adapter with the rotax c-box

adapter with the rotax c-box

I have this adapter mounted on my Yamaha 120 engine with the holes drilled for the Rotax C box. The adapter is not just a simple plate; it replaces the original recessed bearing holder and is actually inserted into the engine case. To install the adapter, first you need to loose the 2 M8 bolts at the bottom of the case, remove the original bearing/bearing holder, insert the new adapter with the bearing, tie the 4 M8 bolts on the adapter (threaded 20mm into the crankcase) and lastly tie the 2 M8 bolts at the bottom. The adapter, since it's inserted into the case is attached to the engine better than the rotax gearbox to the adapter. If something brakes it would be the rotax gearbox first not the adapter. The gearbox, however, works well with stronger engines than Yamaha 120 so I am pretty confident this configuration will work just fine.

I saw this adapter at Bensen days this year installed on the gyro with the rotax gearbox (first 2 pictures attached). The last picture shows the adapter installed on my Yamaha engine.

The gearbox in the first post of this thread looks great but the gear ratio is only 3:1 which is not quite enough for the larger prop and the engine that runs at 8500 RPM. The Rotax C box is available in ratio's with the 3.47:1 or even 4:1.
 

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hibshman25

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Hey Travis,

Thanks for the info and photos. It's great to have another option. Granted, some guys might shy away because of the re-drilling and tapping, but it looks like a great piece of work.

Since you are such a great source for the engines, perhaps you or your supplier can get together and offer the drilling/tapping service if the customer can supply the orientation figures.

Just an idea,

All the best,

I would certainly consider assisting. I could drill and re tap the holes in the engine so its ready to accept the adapter plate once the customer receives the engine.
 

hibshman25

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that gear box does not look like any Rotax gearbox I have ever seen. You sure its a rotax "C" gearbox?
I may have misunderstood my customer when he sent me the photos. Thanks to those that have correctly identified. Not trying to lead anyone astray.

Pete's post confirms that the adapter will indeed work with a rotax c.
 

NoWingsAttached

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I have this adapter mounted on my Yamaha 120 engine with the holes drilled for the Rotax C box. The adapter is not just a simple plate; it replaces the original recessed bearing holder and is actually inserted into the engine case. To install the adapter, first you need to loose the 2 M8 bolts at the bottom of the case, remove the original bearing/bearing holder, insert the new adapter with the bearing, tie the 4 M8 bolts on the adapter (threaded 20mm into the crankcase) and lastly tie the 2 M8 bolts at the bottom. The adapter, since it's inserted into the case is attached to the engine better than the rotax gearbox to the adapter. If something brakes it would be the rotax gearbox first not the adapter. The gearbox, however, works well with stronger engines than Yamaha 120 so I am pretty confident this configuration will work just fine.

I saw this adapter at Bensen days this year installed on the gyro with the rotax gearbox (first 2 pictures attached). The last picture shows the adapter installed on my Yamaha engine.

The gearbox in the first post of this thread looks great but the gear ratio is only 3:1 which is not quite enough for the larger prop and the engine that runs at 8500 RPM. The Rotax C box is available in ratio's with the 3.47:1 or even 4:1.
I'll try to keep an open mind, but I'm not convinced that 4 M8 bolts threaded 10mm into aluminum on a <4" diameter are enough to safely hold this thing together, recessed collar or not. If they do work I'll start making them too.

As to gear ratios, here is a link to a calculator tool to determine tip speeds.

http://www.warpdriveprops.com/propspd2.html

Using a 68" prop a 3.01:1 ratio is just fine for this engine, at 76% mach tip speed.

Using a 72" Prop you are still at 80%. With this prop and a 3.47 gear you are only at 70% Mach.

I can't see why you'd need a 4.0:1 ratio at all unless you get into an 82"-84" prop.
 
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Countach

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Is the 120 carburetor 3 cylinder PTO end the same as the 130 FI.
 

NoWingsAttached

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I have the Airtrikes SPG4 PSRU for this adapter for sale, ships from Savannah, GA - NOT CANADA...so you don't have to mess around with having to deal with Vassili's banking demands and spending more money on money conversion fees and customs, etc.

Price: $1895.00 USD plus shipping from Savannah, GA. 20 pounds shipping weight. Brand new, zero hours, never mounted, etc. Comes with the rubber 6-hole flex shaft coupling and the studs and bolts required to install it on the PSRU flange.

In stock, ships same day.
 

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gyro.pete

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I don't think there is enough material to support additional bolts in that 4" diameter wall. However, if you want to reinforce this setup, you can put an angle under the adapter and attach it to those 4 bolts (red arrows on the attached pic) at the bottom of the case and the adapter (red circles). I've seen other people using these 4 bolts on Yamaha 120 engine.
 

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helipaddy

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Its great to see people working on solutions for alternative engines to Rotax.

It looks like this setup has a a new longer yamaha-to-Rotax hub to fit the crank tapered end.

I thought one of the snags with this setup is the Engine/Prop vibration at low rpms and it really needs a clutch.

What if you wanted to fit a clutch??
 

DaveJaksha

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Hey, Peter
Do you have a contact email for the person that is making the Yamaha 120 adaptor you are using? Travis sent me a phone number, but no one is ever available to answer the phone.
Thanks,
Dave
 

hibshman25

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Hey, Peter
Do you have a contact email for the person that is making the Yamaha 120 adaptor you are using? Travis sent me a phone number, but no one is ever available to answer the phone.
Thanks,
Dave
Alexander lives in Georgia, but travels back home to to Russia from time to time to visit.
 

DaveJaksha

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Thanks, Travis.
That probably explains the phone call. I will be patient and periodically try the phone.

Dave
 

Supermotive

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Greenville
I supplied a customer with an engine a few months ago and he shared with me his adapter for the Yamaha 120 engines. It's an aluminum adapter that replaces the oem recessed bearing holder on the pto end of the motor. The oem bearing gets transferred to the new adapter, and the adapter recesses into the case just as the oem one does and mounts with 4 bolts. The bolt size on the adapter was increased to handle the load, so the 4 tapped holes in the engine case need to be drilled and re tapped to the larger diameter. The adapter has a flange large enough to accept the rotax c gear box 8 bolt mounting pattern. The gear box serves as the template to drill these 8 holes. These 8 holes are not not pre drilled in adapter due to the fact that different builds require different orientations.

To make the the PTO connection between engine and gear box, a new pulley/hub is supplied with the adapter plate.

As of this morning the customer has 48 hours of flying time on this adapter combo and a rotax c box. If anyone is interested in this set up, he will sell the adapter and hub for $700. If anyone is interested feel free to contact me and I will provide contact info for the gentleman making them. I'm not aware of anything like this presently available so I wanted to share my findings.


First photo shows the oem bearing retainer
Second and third photo show the rotax c attached to engine
Fourth photo shows the adapter in rear, original rotax hub to left, and the new yamaha to rotax hub on right.
Hello,

I am trying to adapt a Yamaha motor to a PSRU. Could you please share the information about the adapter supplier?
 
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