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Honda GX 31 four stroke thoughts....

Old 03-22-2008, 09:34 PM
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Default RE: Honda GX 31 four stroke thoughts....

John, go to the gas/glow thread and look from around page maybe 45-49, there are pics posted there.
Old 03-22-2008, 11:50 PM
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Default RE: Honda GX 31 four stroke thoughts....

I LOVE this engine.
Thanks for selling it to me.

The problem isn't what am I going to put it on, it's deciding what not to put it on.

The likely canadates are 540 edge, +100" Mr. Mulligan, 120 Ultra Stick.

I'm running a G-62 on the Mr. Mulligan now. I'll probally take it off and put the Echo on it.
I've decided to buy another plane that is already set up for a G-62.
And the plugs will stick out the sides of the cowl on the 540.

It looks like I won't get the muffler welded until Monday for the Partner saw motor.
It would go nicely on the 540.

It hand starts very nicely. Close choke turn it over 5 times. Flip it over, it spitters.
Take the choke off flip it 2 more times and it running.
I don't even bother with the electric starter anymore.
Old 03-23-2008, 10:12 AM
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Default RE: Honda GX 31 four stroke thoughts....

Forgot about the Partner. Sounds like it too turned out nice. Pictures???
Old 03-27-2008, 10:24 AM
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Default RE: Honda GX 31 four stroke thoughts....

Planepounder, sorry if I'm being redundant but when you say 30% nitro, do you mean 30% of your gas/glow mix is glow fuel and if so what glow fuel are you using or do you mean you are using 30-10 or something else glow fuel in your gas? Maybe I missed something.
Old 03-28-2008, 08:16 PM
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jerry dotson
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Default RE: Honda GX 31 four stroke thoughts....

AV8TOR,
I have a GX 31 on a 1/4 scale Fleet biplane that weighs 20 #. C-H ignition. It flies it OK but no power house... all acrobatics will lose altitude. I have 18-6(7600 RPM), 18-8(6800),18-10(6200), and 20-6(5600). All will fly it but the 18-8 is best all around. The 18-6 climbs best. I don't keep flight logs but guess it to have flown over 100 hours. The most dependable engine I ever had. It has never quit me. Stock carb. Mine starts like this.....choke flip it switch off 4 times, switch on, fires up most times on the first flip. Then let it warm up 2 or 3 minutes and it will take throttle. Be careful about nose over. I bent my crankshaft but managed to straighten it. It was a "Classic" nylon something or other. I use all wood props now hoping if I nose it over again it will break the prop instead.

Jerry
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Old 03-28-2008, 08:45 PM
  #31  
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Default RE: Honda GX 31 four stroke thoughts....

Wow, what a nice looking airplane. Great work, and thanks for the update. I bet it sounds, well, at least somewhat like it should, (scale).

It never ceases to amaze me when I see photos of grass flying fields/strips. Here in the desert southwest, "grass" is only something that... well, you know... []

Thanks again for the update on the Honda GX 31 and the really nice pic!
AV8TOR
Old 03-30-2008, 08:38 PM
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Default RE: Honda GX 31 four stroke thoughts....

JOHNF, been away from the thread awhile so this may be a too late answer. I am running 30% nitro heli fuel mixed in the normal gas/glow ratios (66% gas 33%glow). Heli fuel aint cheap, but I have it around since I have helis. The 4 stroke just sips fuel so I doubt the actual fuel cost is any more than a 2 stroke. The added nitro really wakes up the 4 stroke!
Old 03-31-2008, 12:25 AM
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Default RE: Honda GX 31 four stroke thoughts....

planepounder, Not too late and thanks for the reply.
Old 03-31-2008, 07:35 AM
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Default RE: Honda GX 31 four stroke thoughts....

Does a glow/gas mix deteriorate the seals in the carburetor?
Old 03-31-2008, 11:24 AM
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Default RE: Honda GX 31 four stroke thoughts....

There have issues with Zama Carbs. but not Walbro.

We run the carb dry before storage.
Some use ATF, tranny fluid, as an after run oil in the carb.
Old 04-09-2008, 10:41 AM
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Default RE: Honda GX 31 four stroke thoughts....

Hi Av8tor, Did the nitro wake up the Honda or are we doomed to re locating the wrist pin hole?
thanks, motorhd
Old 04-09-2008, 11:03 AM
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Default RE: Honda GX 31 four stroke thoughts....

Haven't gotten around to it yet. Since it's a Zama carb that's on it at the moment, I need to fit it with a Walbro to try the Gas/Glow fuel in it. I would run it again on gasoline to get a new baseline, and then try the Gas/Glow fuel. If I had a source for nitro, I would probably just dope some gasoline and try it in the Zama carb, but I don't. I'm not in too much of a rush, as it is going on an SR Batteries giant Eindekker. The plans for that plane are on the bench, but as yet no pieces have glued themselves together yet.....

AV8TOR
Old 04-10-2008, 06:28 AM
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Default RE: Honda GX 31 four stroke thoughts....

Hey AV8TOR

I want to see you make a flat twin! Call it a GX62! That will get you more power!

Rich

P.S. You would be a God if you could make a radial!!!
Old 04-10-2008, 10:50 AM
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Default RE: Honda GX 31 four stroke thoughts....

Actually, I have a twin 60cc engine to convert. It is out of an old Echo chainsaw and they are very hard to find. I'll finish converting it one of these days...

AV8TOR
Old 04-10-2008, 11:51 AM
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Default RE: Honda GX 31 four stroke thoughts....

I meant out of the Honda!
Old 09-29-2015, 09:12 PM
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I hope it is not too late to bump this thread. I have a GX31 Honda stripped on the bench. I would certainly like to raise the compression ratio, rather than use nitro as I have no experience with exotic fuels.
I have a 39 mm piston order from ebay which has a higher compression height. It has 13 mm gudgeon (wrist pin) in it, so I would have to sleeve it down to 8mm to suit the Honda.
Any comments or assistance would be most welcome.
This is my first engine conversion. It will be to power a tug plane for aerotow. I'm a glider flyer.
Old 09-30-2015, 07:02 AM
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Hey Jim,

I received your PM's and I'm sorry I haven't answered yet. I am recovering from major back surgery and am very limited in how long I can sit at the computer. I will try to answer soon.

AV8TOR
Old 09-30-2015, 08:43 AM
  #43  
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Hi Aviator,
Take it easy and slow with your recuperation. That is serious intervention that you have undergone; sorry to hear that.
This project of mine is a long term one anyway; there is no hurry at all with this it and our rainy season is almost upon us again for another summer. It is good enough for now to know that I have made contact and that we can communicate sometime in the future about this subject.

All the best,

Jim.
Old 10-28-2016, 12:07 AM
  #44  
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The aftermarket piston that I found on ebay is not suitable. The skirt would be too low and cannot be shortened etc.
So, I will talk to my engine rebuilder buddy to explore the option of plugging the gudgeon pin hole and re-boring it .025 inch lower. I figure I can manage the first part of the job; the plugging up of it with aluminium bar. I will machine it oversize and heat shrink the piston onto it.
Then I will give it to my buddy to take into the workshop and do the boring of the new pin hole at the lower position.
We figure on doing it in one piece, then dremelling out the middle to accommodate the crank small end.
But.............
First of all, I need to ensure there is sufficient room between the valves and the top of the piston. Does anyone already have some knowledge of this dimension?
Old 10-28-2016, 07:29 AM
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Originally Posted by av8tor1977
Hi,

Been playing with my converted Honda GX 31 four stroke. Using a spring over the pump diaphragm in the carb and an external pulse line from the manifold to the carb pump cover, I got a WT type two stroke carb to work. I made an adapter that necks down from the outlet throat of that carb to the inlet diameter of the engine, added a velocity stack, and it works very well. I converted the engine to electronic ignition, and made a straight stack exhaust outlet. With these mods and all dialed in, it turns an 18 x 8 wood prop at just shy of 7000 rpms. This isn't bad considering, but as always, I WANT MORE!

I haven't bothered to look it up, but the stock compression ratio must be horribly low. It is so low that it is almost difficult to tell which is the compression stroke when turning the prop over. It also won't even think about hand starting, though it takes off the second you touch an electric starter to it. It is so low, that I just now pulled off the valve cover and checked the valve clearances, thinking they might have tightened up and the valves weren't sealing well, but no such luck.

So that got me to thinking about the options for a low compression 4 stroke:

1. Raise the compression!! (Not likely with this engine design.)
2. Supercharge. (This engine is a great candidate for forced induction, but I'm not going to make a blower!)
3. Turbocharge. (See above!)
4. Nitro. Hmmm, now that is something I am thinking about.....

Anyone else playing with their Honda GX 31??

AV8TOR
Bob Decortin on Jims R/C Boat Dock messed around with Hondas and got a little more out of them.His screen name is the same as his name,He also has a site http://rcboatworld.yuku.com/forums/1...n#.WBNtW_krJQJ where there was Honda discussions.
Old 10-29-2016, 01:48 AM
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AV8TOR,

If you are on deck again and still reading this thread, can you provide me with any drawings you may have for the machining of a prop hub for this engine please? Or just basic dimensions.
Old 10-29-2016, 12:09 PM
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Oh man, that was a long time ago! Sorry but I don't have any info on the prop hub anymore, and I sold the engine along with the giant Eindekker it was on.

AV8TOR
Old 10-29-2016, 12:19 PM
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Originally Posted by av8tor1977
Oh man, that was a long time ago! Sorry but I don't have any info on the prop hub anymore, and I sold the engine along with the giant Eindekker it was on.

AV8TOR
Ok, that is understandable. I have an engineer flying buddy who will be happy to design me a prop hub. He drew up the one I made for my big Stihl engine recently.

Jim.
Old 10-29-2016, 02:03 PM
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One thing is, I converted it to electronic ignition. As such, I probably used my "lazy trick" of coring out the center of the magneto, trued it up in the lathe, then just made a simple screw on prop hub to screw on against the magneto center. I then make a collar to hold the magnet for the ignition that goes over that magneto center, and is held with a set screw for timing adjustment.

I like doing this as it is easier than setting up the lathe for a custom taper cut, plus that magneto core is keyed to the crankshaft. This prevents ignition timing changes should the prop hub slip or shift a bit during use.

Unless you run a timing sensor off the camshaft somehow on a four stroke, you will have a wasted, extra spark occurring on the exhaust stroke, but that is not a problem in any way.

AV8TOR
Old 10-29-2016, 04:27 PM
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Originally Posted by av8tor1977
One thing is, I converted it to electronic ignition.
I am planning on doing that too for sure.
As such, I probably used my "lazy trick" of coring out the center of the magneto, trued it up in the lathe, then just made a simple screw on prop hub to screw on against the magneto center. ....
I have wondered about doing that. Seems a good idea. How does the prop hub "screw on against the magneto centre"? Do you use a centreing spigot and six axial countersunk machine screws? Placed 30 degrees different to the six prop retaining bolts?
I then make a collar to hold the magnet for the ignition that goes over that magneto center, and is held with a set screw for timing adjustment.

.......................................AV8TOR
Got that bit. Very good! Thanks again.

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