# Any information on Zenoah G50?

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#### Built2Fly

##### Well-Known Member
I recently acquired a project coming with Zenoah G50 engines. It's a nice looking oppose twin 2-stroke engine, that looked similar to a Hirth F23. However, I have since been struggling to find information on this engine, such as the repair manual, connection diagram, and torque setting of various nuts, etc.

The Tennessee Prop website has a bit information (Tennessee Propellers, Inc.), so I hope initially. But they are not responding to the emails, and their phone number has been disconnected when I called them.

I also tried to email the Zenoah company in Japan. And their initial response is that they have a list of engines (for model airplanes), and G50 is not one on their list (of current or discontinued). I don't have too much hope for more info.

So back to the wonderful forum here, does anyone have a copy of the repair manual, connection diagram, and torque settings for tightening the bolts? Thanks a lot.

Picture from Tennessee Propeller website

#### TFF

##### Well-Known Member
They make decent model engines. One of those has not been made in twenty years and I’m sure they don’t want to know about old products not supported.

#### proppastie

##### Well-Known Member
Log Member
Probably get torque spec. from any motorcycle over haul manual.

#### Built2Fly

##### Well-Known Member
Probably get torque spec. from any motorcycle over haul manual.
Good idea. I will check those manuals.

#### proppastie

##### Well-Known Member
Log Member
I did a google search and had a bunch of hit for this engine.

#### Built2Fly

##### Well-Known Member
I did a google search and had a bunch of hit for this engine.
Do you mind sharing the links you found? I could not find much useful information besides the Tennessee Prop website. It is interesting that their email/phone are disconnected, but the website remains up. There is also a now defunct east Tennessee BBS where people talked about this engine. But that BBS has gone quiet for more than 10 years.

Any information would be very much appreciated.

Log Member

#### Built2Fly

##### Well-Known Member
Thanks. That's not too much different from what I have been seeing last few days.

I am thinking that as I am working along, I would setup a website as a place to keep all the information I found ("found" as acquired on Internet from searching and reading) and discovered ("discovered" as figured out from trial and error through working on the actual unit). I will share everything here in case someone would need this in the future.

#### Planenut25

##### New Member
Flyingiants.com contact "Antique " aka Ralph Cunningham, he can tell you everything you want to know about that engine.

#### Built2Fly

##### Well-Known Member
Flyingiants.com contact "Antique " aka Ralph Cunningham, he can tell you everything you want to know about that engine.
Thanks for the info.

The flyinggiants.com seems to be a RC model airplane group. I know that Zenoah still making model airplane engines these days. I have contacted Zenoah (the Japanese company). But they seem have complete disowned the older models such as the G50 I have. It is not even in their discontinued list, and the person who responded has not even heard of it.

I will keep digging, and may try finding Ralph's number and giving him a call. But I don't have a lot of hope.

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#### TFF

##### Well-Known Member
What kind of info are you looking for?
You should be able to figure out how worn out it is with compression checks and pressure testing the case. Obviously you are not going to find spare parts unless very lucky, so anything needed is going to need to be whittled by you. It actually sounds like a fun challenge. Just let reason call how far you should go with this engine. I have a friend who rebuilt an OX-5, just make sure it’s worth it.

#### sigrana

##### Well-Known Member
I recently acquired a project coming with Zenoah G50 engines. It's a nice looking oppose twin 2-stroke engine, that looked similar to a Hirth F23. However, I have since been struggling to find information on this engine, such as the repair manual, connection diagram, and torque setting of various nuts, etc.

The Tennessee Prop website has a bit information (Tennessee Propellers, Inc.), so I hope initially. But they are not responding to the emails, and their phone number has been disconnected when I called them.

I also tried to email the Zenoah company in Japan. And their initial response is that they have a list of engines (for model airplanes), and G50 is not one on their list (of current or discontinued). I don't have too much hope for more info.

So back to the wonderful forum here, does anyone have a copy of the repair manual, connection diagram, and torque settings for tightening the bolts? Thanks a lot.

Picture from Tennessee Propeller website
The present Zenoah company is only involved with RC model engines and is completely separate from the original Zenoah KOMATSU. The single (G25 fan cooled) and twin (G50 fan cooled) two stroke engines were manufactured in a comparatively small shed, inside the Komatsu big industrial factory.
I had two fan cooled G50 and for their times they were excellent engines, very light and long lasting. I am as well a tuned exhaust specialist and I designed and built fully tuned and silenced exhaust systems for the G50. The power at the same rpm increased by 20%, with the engine running much cooler than with the factory can and the consumption was much lower, with 10 lt/hour at cruise (4700 rpm). The maximum power of the G50 with my exhaust was 56 hp @ 5800 rpm, instead of the 43 hp at the same rpm with the factory can.
The free air version of the G50 engine only developes 35 hp and it is better not to push it and to create two ram-air ducts, reaching about 20 mm from the propeller blades, to help cooling it.
Komatsu stopped producing the engine in the early '80s and it was then possible to still order them BUT ONLY 150 UNITS AT THE TIME, which was obvioujsly excessive for us ultralight flyers. I am attaching the .Gif of the engine and my own designed and built two seat trike on which I used the G50, which gave me hours and hours of rewarding flying time.
You may as well check with New and used engines . They have some and they might be able to tell you more about your G50.

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#### Built2Fly

##### Well-Known Member
The present Zenoah company is only involved with RC model engines and is completely separate from the original Zenoah KOMATSU. The single (G25 fan cooled) and twin (G50 fan cooled) two stroke engines were manufactured in a comparatively small shed, inside the Komatsu big industrial factory.
I had two fan cooled G50 and for their times they were excellent engines, very light and long lasting. I am as well a tuned exhaust specialist and I designed and built fully tuned and silenced exhaust systems for the G50. The power at the same rpm increased by 20%, with the engine running much cooler than with the factory can and the consumption was much lower, with 10 lt/hour at cruise (4700 rpm). The maximum power of the G50 with my exhaust was 56 hp @ 5800 rpm, instead of the 43 hp at the same rpm with the factory can.
The free air version of the G50 engine only developes 35 hp and it is better not to push it and to create two ram-air ducts, reaching about 20 mm from the propeller blades, to help cooling it.
Komatsu stopped producing the engine in the early '80s and it was then possible to still order them BUT ONLY 150 UNITS AT THE TIME, which was obvioujsly excessive for us ultralight flyers. I am attaching the .Gif of the engine and my own designed and built two seat trike on which I used the G50, which gave me hours and hours of rewarding flying time.
You may as well check with New and used engines . They have some and they might be able to tell you more about your G50.
Very interesting information, Sigrana.

The project I acquired indeed have two G50s. One has apparently been used, and it is a free air cooled version. The other one looked has never been used. It comes with the red air duct (just like the Tennessee Prop pictures), and it is a fan cooled version. I was wondering why the fan version is needed. It is good to know that the free air version needs ram air ducts. I will see if I can add those once I get it running.

Are you still making/selling your tuned exhaust?

#### sigrana

##### Well-Known Member
Very interesting information, Sigrana.

The project I acquired indeed have two G50s. One has apparently been used, and it is a free air cooled version. The other one looked has never been used. It comes with the red air duct (just like the Tennessee Prop pictures), and it is a fan cooled version. I was wondering why the fan version is needed. It is good to know that the free air version needs ram air ducts. I will see if I can add those once I get it running.

Are you still making/selling your tuned exhaust?
I certainly do, but I have to tell you that I live in Melbourne, Australia, so the cost itself of sending to you the fully tuned and silenced system would be very high. What I can help you with is my full design, including the cone patterns, which I still have. I can send it to you by internet and it is about $120. Does your engine has the factory exhaust on it or not? Please let me know. #### Built2Fly ##### Well-Known Member I certainly do, but I have to tell you that I live in Melbourne, Australia, so the cost itself of sending to you the fully tuned and silenced system would be very high. What I can help you with is my full design, including the cone patterns, which I still have. I can send it to you by internet and it is about$120. Does your engine has the factory exhaust on it or not? Please let me know.
That would be interesting. Does it require sheet metal welding?

I do have one exhaust for my engines as shown below. I think that it is probably the factory stock exhaust.

#### sigrana

##### Well-Known Member
I think it is, because it looks like a Fischer pipe, which is working only at one specific and narrow range of rpm and it is not very efficient at all. What I would like to know is if the two into one (Y shaped) exhaust rounded leading pipe, connecting both cylinders exhaust ports, is there. That one is the one from which the design will start.
Yes, to build my exhaust system requires sheet metal welding, which can be performed with a MIG or TIG welder. It is not a long or difficult job and to roll the cones is not difficult either. I suggest to use 1/16" steel sheet, which is durable and easy to find.

#### Built2Fly

##### Well-Known Member
I think it is, because it looks like a Fischer pipe, which is working only at one specific and narrow range of rpm and it is not very efficient at all. What I would like to know is if the two into one (Y shaped) exhaust rounded leading pipe, connecting both cylinders exhaust ports, is there. That one is the one from which the design will start.
Yes, to build my exhaust system requires sheet metal welding, which can be performed with a MIG or TIG welder. It is not a long or difficult job and to roll the cones is not difficult either. I suggest to use 1/16" steel sheet, which is durable and easy to find.
Yes, I do have the Y piece. I guess I will need to learn some welding by that time. Will ping you when I am ready for that step. Thanks.

#### sigrana

##### Well-Known Member
Good. In the meantime, could you please measure the centre length of one side of the Y piece, plus the inner end diameter for me? Thank you in advance.
If you are not accustomed to weld (no offense) I would ask a welder tradesman to do it, because it is going to be easy for him and he will not charge you an arm and a leg.
May I ask what your application for this engine will be? My designs are tailored to the specific use, e.g. requiring more torque and less top end and viceversa, or more mid range etc.etc. Please let me know. You can also email me directly on msmprod@optusnet.com.au.

#### Built2Fly

##### Well-Known Member
Good. In the meantime, could you please measure the centre length of one side of the Y piece, plus the inner end diameter for me? Thank you in advance.
If you are not accustomed to weld (no offense) I would ask a welder tradesman to do it, because it is going to be easy for him and he will not charge you an arm and a leg.
May I ask what your application for this engine will be? My designs are tailored to the specific use, e.g. requiring more torque and less top end and viceversa, or more mid range etc.etc. Please let me know. You can also email me directly on msmprod@optusnet.com.au.View attachment 101782

It turns out that the two forks have slightly different length. You can see it from the picture above. The fork with a EGT sensor is a bit longer. I also measured from about the center of the ball joints, not the end. That is probably more relevant since you will need to calculate the cavity length for resonance.

By the way, I am wondering about how it is designed for a wider range than a narrow range stock? Is it using the overtones? I am just curious.

Please forgive me for using inches. All my measuring tape are in inches. 1 inch = 25.4 mm. I estimated that all these numbers have error of about 1/4 inch. If it needs to be more accurate than that, please let me know.

#### sigrana

##### Well-Known Member
Thank you for the measurements: I am fine with inches or mm: to me it does not make any difference. The total length of the leading pipe is towards the maximum advisable but that is fine and the slight difference between the two lead-ins is due to the position of the system, obviously to avoid being too close to some parts of the engine.
The design can be tailored as I indicated in my previous message and the tailoring involves different calculation and sizing of the various elements, but it does NOT involve overtones at all. The same happens for the muffler, which in my designs is part of the pipe, very efficient, quiet and not adding the usual weight and length as a separate silencer.
I still would like to know what your application will be: are you going to use it to drive an airprop? If so, keep in mind that the reduction drive of this engine is optimised to spin the propeller at a maximum of 2400-2500 rpm, which means that a two blade 66" or a three blade 60", both with ground-adjustable pitch, e.g. IVOPROP, will give the best performance.
In fact, when I used this engine I used a 60" Ivoprop ultralight ground-adjustable three blade propeller, which with my tuned system developed in eccess of 248 lb of static thrust and used to take up my trike and my sweet weight (17 stones) at 1000 feet per minute.