Honda GX160- 8.5cc

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Basil

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Thanks guys. I will be trying to replicate all the Honda detailing as close as possible. Fuel tank white, Red starter housing and fan cover. I have a friend that can do all of the Honda decals.
 

Basil

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The kill switch.
After working through a few designs and wanting to keep the assembly as least complicated as possible, this is what I came up with. The Zenoah system has two wires. The black is a standard short to ground ignition kill. This black wire will connect to the center contact and short to the brass fan housing when in the off position. I used a 1mm pin epoxied into the switch base running in a slot to limit the switch travel. Both the switch knob and base were machined on the CNC router. The assembly has 6 components including the 2.5mm stainless washer and oval headed allen screw. A delrin washer that backs up against the brass contact acts as an insulator and holds the switch snuggly in place.
I am always impressed with the machinability of Delrin and for me this just took it to another level. Needless to say it passed with flying colours.
 

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Basil

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Just a few pictures of the progress on the petrol tank. This will incorporate the ignition coil in the underside. The plugs were drawn up on Fusion and printed on resin printer, epoxied to a base and coated with Durabuild. Resin for moulds and parts is West Systems 105/206. After reading up on petrol compatibility with this resin I am happy that the petrol will not break down the resin over a limited time period. Apparently the increasing use of Ethanol can be problematic with fiberglass petrol tanks over time.
5 or 6 coats of #8 Mould release worked well. I use an old AC vacuum pump from my car repair days for vacuum bagging. I find regular plastic bags do a better job of conforming to contours better than specialize vacuum bag material.
I learned a valuable lesson on my first part ( Tank bottom). Do not use rattle can primer on moulds! Even with lots of coats of wax it breaks down from wax or epoxy? and bleeds through to the part. Quite the mess and touch and go whether the part was going to pop.
Cheers
 

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Basil

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If there is anything I have learned on this project so far it is that the time invested in drawing the items in CAD is time very well spent. This coupled with being able to 3D print the part so as to visually ponder over it is invaluable. I guess for the most part I am an the impatient machinist, I tend to want to rush out and start carving. CAD drawing time was for me is like having to make a complicated fixture just to hold a part one time. I usually would rather not and look for the quicker way out if possible.
Onto the Carburetor choices for this engine.
Build a float chambered carb or raise the carb up to the fuel level. The OS carb will fit within the confines of the air filter box with a little modification.
With the latter in mind the intake manifold will be dressed as a faux carb. All non structural components, faux float chamber, faux air intake etc can all be 3D printed.
For mockup I 3D printed the faux carb/intake manifold but this will be machined in aluminum as it is somewhat structural being that it must clamp the OS carb. The 3D printed air intake housing will have brass sleeves to take the clamping force when tightening the assembly
Plug cap and valve cover is also 3D printed. 👍
 

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Stefan-K

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Hi Basil
Congrats on a very well done, cool Looking and smooth running engine. I am more into building "Old Iron" Engines with big Flywheels, but i know how much work it is, even with the help of CAD and CNC to create an engine like this. My respect! 👍
 

Basil

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It's been a little bit tough getting time on the little GX160 at this time of year. Honda have had many fuel caps on this engine and the current one is probably the ugliest bit of chunkiness to date so I chose something to my liking from over the many production years. Fusion 360 and the new router to form. It has a 3/4" fine internal thread with a groove for venting. A male spigot was the next part to make. Had to order a gear up for the Myford and catch up on some threading on the lathe. Epoxied in the top section of the fuel tank., and forgot to take pictures of the whole procedure! The petrol tank is now epoxied together and has its stainless outlet tube which exits just under the fan shroud cover.
Moving on to the Faux carb. I had 3D printed this and done a mockup so it was pretty much make the same from aluminum with some detail work to make the bottom half look more like the original carb.
I decided to incorporate an air bleed in roughly the same position as the original idle mixture screw mainly with the thought of having some adjustment without removing the air filter housing, if it doesn't work I can always screw it all the way in. The OS carb had to be reduced in many areas but nothing that will change its function.
Non of the rattle can paint I used is petrol proof. Something I took for granted it would be. I have some 2 Pack clear in aerosol that hopefully will take care of that and not react with what is currently on there. Onwards and upwards 👍
 

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Bazzer

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It's been a little bit tough getting time on the little GX160 at this time of year. Honda have had many fuel caps on this engine and the current one is probably the ugliest bit of chunkiness to date so I chose something to my liking from over the many production years. Fusion 360 and the new router to form. It has a 3/4" fine internal thread with a groove for venting. A male spigot was the next part to make. Had to order a gear up for the Myford and catch up on some threading on the lathe. Epoxied in the top section of the fuel tank., and forgot to take pictures of the whole procedure! The petrol tank is now epoxied together and has its stainless outlet tube which exits just under the fan shroud cover.
Moving on to the Faux carb. I had 3D printed this and done a mockup so it was pretty much make the same from aluminum with some detail work to make the bottom half look more like the original carb.
I decided to incorporate an air bleed in roughly the same position as the original idle mixture screw mainly with the thought of having some adjustment without removing the air filter housing, if it doesn't work I can always screw it all the way in. The OS carb had to be reduced in many areas but nothing that will change its function.
Non of the rattle can paint I used is petrol proof. Something I took for granted it would be. I have some 2 Pack clear in aerosol that hopefully will take care of that and not react with what is currently on there. Onwards and upwards 👍
Brilliant.
 

Basil

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Thank you Bazzer.
Exhaust next. I have gone back and forth many times trying to come up with the best way to fabricate this item. Here is the route I chose.
After sketching up in Fusion I cut out some thin ply on the router and made a carboard mockup of the whole thing. Using card for the height spacer material and plywood I was able to check fit and trim the assembly until I was happy. I wanted to keep everything as compact as possible without running into the spark plug boot.
I loaded my router up and formed everything in brass at this point. The buildment will have a mixture of silver solder and 300c soft solder.
Next I will drill and solder in a perforated outlet pipe and add a couple of supports. The final design with incorporate a heat shield as per the original.
 

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Bazzer

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I will follow your project closely, I am a massive fan of Honda as an engine manufacturer, no company in the World covers the breadth of production that Honda and to such a high level.

Your GX160 model is a very fitting tribute to the small Honda engines.

I know a little about the 250cc six cylinder replicas and an associate of mine has one original 6 cylinder 297cc GP bike (which they ran in the 350cc class) and one replica of the same bike which I think were made by George Beal and JPX made the engines in France.

B.
 

Basil

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I'm getting very close to completing this engine. The exhaust heat shield being one of the last components to fabricate. It is made from 0.4 brass sheet.
I detailed the process I went through to form the top piece in the 3D section of this forum. Both sheet components were drawn up in Fusion 360 and cut out on the router. I decided not to stamp the recesses around the bolts for fear of ending up with wrinkles in the brass. I tried going through an annealing process a few times and no matter the temperature or cooling method the material did not soften up any more than when I initially received it. I machined up brass standoffs instead with a small locating ridge to locate in the top cap.
The heat shield assembly and exhaust will both be painted high temp black. Shame, I do like the brass look.
 

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Basil

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Having fun with a drag engraver!
I finally decided to bite the bullet and purchase one of these and give it a try. I wanted to add some serial numbers to the engine but due to the size of the lettering @1.8mm tall I was not sure how to go about this without it looking a real mess.
My main concern was that any side play in the floating styluss and its guide/holder would effect the performance at this letter size.
I must say though it performed very well. There was some slight rounding on some of the letters but this was easily taken care of by adding a little code to lift the tool and return it before a change in direction. I only had to do this on a couple of letters where the program had not incorporated this Z retract.
Very happy with the result.
Now onto the finishing decals.
 

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Basil

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After painting parts with regular rattle can from a car accessary shop I suddenly became aware of how this paint does not hold up to any solvents when I spilt some isopropyl alcohol. This is a petrol engine and even with the greatest of care I figured some would eventually find its way onto the paint.
Starting again, stripping everything and using 2K product from an automotive paint shop came to mind. I have gone this road when building Nitro powered RC models. Works great but expensive and you end up with lots of paint because usually it is only available in 1 liter tins.
First I thought I would try clear coating over what I already had.
The big negative on this is how the paint will react to another product being applied on top. I convinced myself I could not leave the paint as it was so with nothing to lose I gave some 2K rattle can clear coat a shot. I have never used the product before but in reviews it looked like this particular one came out on top. The hardener is in the can and you mix the 2 by pressing a pin on the underside. Maybe this is old news to many but new to me anyway.
Happy days! Amazing product and no paint reaction. I am going to give the clear a week to totally harden off before assembling the components to each other.
The transfers were done by a friend that builds exquisite miniature replicas of powerboats. Because white apparently cannot be printed on these transfers a thin vinyl backing gets applied first to the part then the water transfer float on. The 2K clear coat seals these in position.
I have included some photos of the modified Zenoa pull start internals.
The modification includes shortening the main spring, reducing the spool diameter and adding a new drive pin that engages with said spring.
Operation is;
The wavy washer under the screw sets up a slight drag when the reel is rotated by the cord, that lifts and engages the drive sprag to the engine. Both the engine starting and the return of the pull cord retracts and disengages the sprag. Magic!
 

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ajoeiam

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blank (like some others I've noticed)
After painting parts with regular rattle can from a car accessary shop I suddenly became aware of how this paint does not hold up to any solvents when I spilt some isopropyl alcohol. This is a petrol engine and even with the greatest of care I figured some would eventually find its way onto the paint.
Starting again, stripping everything and using 2K product from an automotive paint shop came to mind. I have gone this road when building Nitro powered RC models. Works great but expensive and you end up with lots of paint because usually it is only available in 1 liter tins.
First I thought I would try clear coating over what I already had.
The big negative on this is how the paint will react to another product being applied on top. I convinced myself I could not leave the paint as it was so with nothing to lose I gave some 2K rattle can clear coat a shot. I have never used the product before but in reviews it looked like this particular one came on top. The hardener is in the can and you mix the 2 by pressing a pin on the underside. Maybe this is old news to many but new to me anyway.
Happy days! Amazing product and no paint reaction. I am going to give the clear a week to totally harden off before assembling the components to each other.
The transfers were done by a friend that builds exquisite miniature replicas of powerboats. Because white apparently cannot be printed on these transfers a thin vinyl backing gets applied first to the part then the water transfer float on. The 2K clear coat seals these in position.
I have included some photos of the modified Zenoa internals.
The wavy washer under the screw sets up a slight drag when the reel is rotated by the cord, that lifts and engages the drive sprag to the engine. Both the engine starting and the return of the pull cord retracts and disengages the sprag. Magic!
Wow - - - methinks when you're all done that you might want to just build a full size GX 340 or 390 and then you're set - - - you'll have fantastic model and a great engine.

Serious beautiful work sir!!!!!!!!!!!
 
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