Single Cylinder 4-stroke machined from bar stock - Westbury's Kiwi Mk II

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Eccentric

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I am going to be machining Edgar Westbury’s Kiwi Mk II from bar stock. I thank Model Engineer Magazine for making the articles free to download. They were printed 60 years ago! I have captured the design in CAD and have made some modifications to ease my fabrication. I will not be using BA hardware, I moved the engine mount to the bottom of the engine so it will stand on its own and made lots of small modifications to suit CNC machining. I am starting with the front crankcase half, which will be machined in two operations, one from the back and one from the front, both using a ¼” flat end mill. I used my 3D printer to print the parts and identify errors in my CAD model, of which there were a few. I then used Fusion 360 to create the tool paths for my CNC router. My CNC router is home made mostly from MDF and performs surprisingly well.
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Brian Rupnow

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Eccentric--Very interesting. I was thinking about a single cylinder vertical 4 stroke this morning. I am suffering from 'machining burn out' right now, and trying not to start something new until January is over. If I do go ahead with one, it will all be manual machining. Good Luck!!---Brian
 

Eccentric

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Thanks Brian, I have digested most everything you have writen on the Webster as it was my first choice for an engine to build. I compiled a multipaged document of notes and recommendations. But I eventually decided I wanted to make an enclosed crankshaft engine with conventional valves, seats and lifters for the experience. I know you like Viton rings, but I am considering trying my hand at making my own cast iron rings, again for the experience. I ultimately would like to build a multi cylinder engine, but am working on building my machining skills. I spent today machining the front side of the crankcase front. I am pleased with the important dimensions, but I think the surface finish could be better. This is when I wish I had a bead blaster, but I don't have room in my little workshop and can't justify it for how little it would be used, but .... I will ream hole for the crankshaft bushing. I use fusion360 to generate my tool paths for the router. I am not sure what people are interested in seeing, the CAD design? the CAM and tool path programming? or just the odd shot of me making chips. If anyone is interested in building this engine, I am happy to supply any of my models or tool path files. The photos show the aluminum part compared to the 3D printed part I used for initial prototyping.

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CFLBob

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Eccentric - your project catches my eye because I see you and I in a similar place as far as our hardware goes. I have a CNC Grizzly CNC mill and a smaller, CNC Sherline mill, extended work envelope using A2ZCNC (now out of business) parts. I've just added a 3D printer for the same sort of uses, as well as making little aids for around the shop. The CNC process seems to make each part harder to do, because you make it at least twice - once in software then watch the machine make it - as opposed to walking up to the machine and turning cranks.

So I find this all interesting. I hadn't heard of this engine, but I'm sure there are thousands of designs I haven't heard of.

Having just gotten my Webster running, I think your preference for "enclosed crankshaft engine with conventional valves, seats and lifters" is a very good choice. It seems to me that the intake valve design on the Webster relying on the vacuum the engine generates is a weak spot. In terms of helping teach of us beginners how the piston compression should feel, it's a good choice, but comparing the solid action of the exhaust valve driven by a lifter and the action of the intake valve is a stark example of how much a lifter does for an engine. I suppose that's really educational for beginners, too.
 

Eccentric

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Bob,

I agree with your take on the CNC milling. I use mine as a standard Mill, with the monitor as a DRO, 90% of the time. But it does open up additional capabilities like this engine case I am making. I spent several days modeling the engine on the computer, and then a few hours on the machine making it. I don’t have the skill to machine it manually and with the CNC any shape is game. The alternative of machining the crankcase from a casting requires much more difficult and innovative fixturing on both a lathe and a mill. We all work with the equipment we have. I envy the guys that have, or have access to, massive production quality machine tools. If you are interested in using your CNC for something more complicated, I’d be happy to help with CAD modeling or CAM tool path creation; I enjoy working on the computer to support machining. Today I am machining the rear crankcase half. The internal cutouts are the same as the front, except the crank shaft is 5/16” when it exits the rear case as opposed to 3/8” for the front case half. Below are the plans and construction articles that Model Engineer has graciously made available for free download for the Kiwi MK2 Engine.

etw-kiwi-mk2-pt1.pdf (model-engineer.co.uk)
etw-kiwi-mk2-pt2.pdf (model-engineer.co.uk)
 

Eccentric

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More Machining today. Finished the mill work on the rear crankcase, reamed the holes and pressed in the bushings. I will wait to press in the ball bearings until I do more cleanup on the parts, don't want to get swarf in the balls. the third photo shows the plastic timing gear cover on the rear of the engine, this weekend I hope to machine an aluminum one. The square feature on the top of the engine will allow me to touch off and determine the center of the cylinder. I will then machine the cylinder sleeve hole, and the holes for the studs attaching the cylinder. I used a junky chamfer bit to cut the chamfer on the rear case, this will require some hand filing to fix. Then on to the crank shaft.
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Eccentric

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Finished the major machining on the rear timing cover and it is starting to look like a crank case. The first picture shows the timing cover with only the inside machined and mounted to the engine. The second picture shows all of the outside machined. You can see they don't exactly line up, fortunately this is just cosmetic as all of the critical machining was done from the inside such as the alignment of the spigot to the crank shaft and the relative position of the cam shaft to the crank shaft. Need to do the machining from the top, but I am not sure of the best order of operations for the cylinder sleeve (aluminum), sleeve (cast iron) and the crank case as they all need to fit together precisely. I guess you start with the most difficult operation, which for me is boring of the sleeve. Also, I would rather re-machine an aluminum cylinder than a cast iron sleeve. All of that machining will be done on the lathe. I will mount the crankcase base to the face plate and bore the cylinder sleeve hole into the crank case. Also, I think I want to lower the compression ratio. Westbury says, "The dimensions shown give the highest ratio recommended for general purposes". I am noodling on the best way to reduce the compression ratio, perhaps increase the volume of the combustion chamber milled into the bottom side of the cylinder head. An engine with a higher compression ratio has better efficiency and can produce more power at the high RPM range, an engine with lower compression starts easier, and is more forgiving of cam profiles and general play in the system due not less-than-perfect machining. They also run better at the slower RPM (I think). I could also just put a spacer between the head and cylinder, but then I have one more place to have issues with the sealing of the combustion chamber, but this would provide a less permanent solution. Decisions decisions.
 

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Mike Ginn

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Very impressive. work. I have been thinking of moving to 3D machining but don't have a suitable package. So far I been using Autocad 2D. Please can you advise which 3D package you use and which post processor you used for the GCode. At present I am using CAMBAM.
Many thanks
Mike
 

Jasonb

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You could also drop the compression ration by taking some material off the top of the piston, Provided you don't leave the top too thin you can start with it as drawn and then take a bit off if you feel the ratio is too high.

To help get the "cast look" to the crankcase think about doing a finish cut using either a ball ended cutter or one with a corner radius(convex) which will leave a small fillet on the internal corners. Also you can add draft angle when drawing the part and use a Ramp or Scallop finishing method with a small stepover to follow around the angled sides. Should then need minimal work with a needle file and abrasive paper to finish off. I used to like using "steep & shallow" in F360 but it's too expensive now that they have changed their pricing.

Your order of work sounds OK, make the liner and use that as a plug gauge for the hole in the top of the crankcase flange and also to gauge the bore on the sleeve and finally make piston to fit inside.
 

Eccentric

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Mike,

I understand the cost of CAD/CAM is hard to justify. I am lucky as I use Solidworks at work and my son has a license for Fusion360. I use Solidworks for CAD and Fusion360 for CAM. I thought that using Fusion360 for both CAD and CAM was free or inexpensive for the single hobby user for non-comercial purposes. I have also heard good thing about OnShape for CAD. You just can't beat Fusion360 for creating G-code for the CNC machine. My CNC router uses LinuxCNC, which is open source.

Jason,

I like the idea of modifying or simply using a second piston to adjust the compression ratio. That way I can 1.) put that concern off for later and 2.) build the cylinder and head to print. I will look into Step and Shallow in Fusion360, I have not used that technique. Thank you for the ideas to get the casting look.

Thank you for confirming my order of operations. I will work the crank shaft next, then turn to the cylinder sleeve.
 

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More Machining today. Finished the mill work on the rear crankcase, reamed the holes and pressed in the bushings. I will wait to press in the ball bearings until I do more cleanup on the parts, don't want to get swarf in the balls. the third photo shows the plastic timing gear cover on the rear of the engine, this weekend I hope to machine an aluminum one. The square feature on the top of the engine will allow me to touch off and determine the center of the cylinder. I will then machine the cylinder sleeve hole, and the holes for the studs attaching the cylinder. I used a junky chamfer bit to cut the chamfer on the rear case, this will require some hand filing to fix. Then on to the crank shaft. View attachment 122402View attachment 122403View attachment 122404, then m

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I have a question regarding the oil holes and channels on the crank. Will this be a forced oiling system so as to utilize the oil channels, or some type of wet sump and splash oiler? Not sure how it all goes together I guess.

thanks, and really excellent looking work so far!!!
John W
 

Eccentric

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I use a technique to locate holes that works very well for me. I use the 3D printer to print a drill guide, the darn thing is scary accurate. Here I am making a drill guide to place the two center drilled holes at each end of this chunk of cold rolled that will become the crankshaft. As you can see from the photos I use dowel pins to position the drill guide to the work piece. Then it is a simple matter of drilling the two holes on each end so I can turn on centers. The actual drilling is much simpler and I have better results getting the accuracy I want than scribing and punching the hole positions.
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Here you can see that I am at the extreme limit of what my little lathe can do. I have about 3/16” travel on my cross slide before the tool post hits the part, so I have to make a 3/16” deep cut, wind my cross slide back to the stop, adjust the tool, then take another cut. It takes forever and I have a hard time keeping the tool in the same position for each cut. I showed my wife and explained I need a bigger lathe, but she was not too sympathetic, she said, “it seems to work fine”.

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The crank pin is the hardest part machining the crankshaft for me, I polished with 320 grit, 600 grit and 1000 grit emery. I am uniformly ½ a thou over, so I’m going to call ‘er done. It is not perfect, the crank webs came out a little dodgy becasue of the way I have to reposition the tool as I cut in, and I should have put a radius on the edges of my cutter, I have pretty sharp corners where the crank pin meets the crank web and I have some stress risers there. Live 'n learn.


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Eccentric

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I have a question regarding the oil holes and channels on the crank. Will this be a forced oiling system so as to utilize the oil channels, or some type of wet sump and splash oiler? Not sure how it all goes together I guess.

thanks, and really excellent looking work so far!!!
John W
Yes I will use the oil holes and channels in the crank to lubricate the crank pin. It is a gravity feed system.
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Jasonb

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even with your sons license the Steep and shallow is now classed as a manufacturing extension and you have to pay per day or per Month, think it is something like $125 a month. It is/was a very easy way to do 3D milling but with a bit more effort the ramp and scallop can be used to give a fairly similar finish. This was one of the last pieces I did before loosing economical access to steep & shallow


And this is one of the first items I made with my CNC, a half crankcase.


I use Alibre for my drawing as I've had it a number of years and know my way around it so did not really want to change which makes F360 expensive if paying for both so I just use it's free CAM which I like a lot.
 

Vietti

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When I built Cole's 30 cc single cylinder 45 years ago I came up with a way to recover the oil in a total loss system like this one.
Somewhere I'd read about using a check valve to create negative pressure in the crankcase and prevent oil from being pushed out. I installed one in the only orifice open to me, the oil drain plug at the bottom, rear of the crankcase. I noticed that oil was pushed out as the one way valve operated so I ran a hose from the check valve back up to the side of drip oiler reservoir. Holes were drilled around the cap to allow the air to escape. Works really well. When its running you can see the oil moving up thru the clear hose.

Probably not an original idea but it worked for me.
 

Eccentric

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Finished one side of the crank shaft, here I am test fitting it into both the front and rear crankcase halves. In the first picture you can see the ball bearing mounted on the crankshaft, then it goes through a long oil barrier bushing. There is a hole in this bushing that allows oil to flow from a fitting on the front crankcase half and into the oil passage ways in the crank shaft.
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Back out to the shop and finish the other half of the crank shaft.
 

Eccentric

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Whew.. My crankshaft is going to be a keeper. It spins like a dream and no noticable end play. I had two issues with it, first the spacer I put between the crank web while I was machining the two main shafts was a bit loose and when I cranked down on the tail stock live center, it cause a little flex and the two sides of the crank shaft were not machined exactly colinear. when I spun the crankshaft in the crankcase, there was a discernable difference in the way it felt as I spun it with my fingers throughout a revolution. I set it up running in only one crankcase half and put a test indicator looking at the run out and sure enough the crank web sprung open ever so slighly. I placed one half of the crank web on an anvil and lightly tapped the other with a hammer until I got the dial indicator to run true. the second issue wasn't really an issue, but as I tightened down the two crankcase halves, the crankshaft got tight. the crankshaft runs on two ball bearings pressed into each half of the crankcase and the distance between the inner races was a few thou greater than the distance between the two shoulders on the crankshaft that ride on them. I put the crankshaft back in the lathe and just turned down the sholders a tad, it took three trips in and out of the lathe before I was happy with the end play and the crankshaft spins smooth as butter with the two crankcase halves bolted tight.

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nj111

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I shall follow with interest as I made a Kiwi over many years (actually decades!). It's a great little engine. But I wasn't happy with the commercial castings I had bought in 1976 so I started again around 2003 and this time made my own crankcase patterns. After months of casting failures I eventually learnt how to make nice castings but I failed to cast the head successfully so I milled it from the solid. At the time 3D CAD /CAM in the home workshop was more limiting than it is today but it came out quite well.

came out pretty good.
Kiwi finished 7.jpg

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crankcase  casting patterns 1.jpg
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Eccentric

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Your engine is beautiful, a real inspiration. Your castings really look nice and I hope my cylinder head comes out half as well as yours. I will continue to look back on those pictures as I build, that is what I am aming for. thanks.
 

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I shall follow with interest as I made a Kiwi over many years (actually decades!). It's a great little engine. But I wasn't happy with the commercial castings I had bought in 1976 so I started again around 2003 and this time made my own crankcase patterns. After months of casting failures I eventually learnt how to make nice castings but I failed to cast the head successfully so I milled it from the solid. At the time 3D CAD /CAM in the home workshop was more limiting than it is today but it came out quite well.

came out pretty good.View attachment 122685
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Does the Kiwi utilize a float type carb? Interesting looking carb, and exceptional work! Congratulations on a beautiful engine!

John W
 

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