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

[nj111]

Yes it's a float carb by E T Westbury. I learnt so much making the Kiwi, including piston rings (Trimble method), making a camshaft grinder, honing accurate bores, getting small valves to seat properly etc. I tried to do a lost wax casting for the head, but I didn't source the correct wax and so it was a disaster. Eventually I milled the head but made sure all the fins were tapered in thickness. The toolpath options for CNC milling were pretty limited to me around 17 years ago but with some handwork it was a pleasing result. The second set of crankcase castings you see above went to the late Ron Chernich at MEN, who liked to have plenty of castings in stock under the bench! Sadly, Ron never did get to make a start on those. Nick

 

[a41capt]

Yes it's a float carb by E T Westbury. I learnt so much making the Kiwi, including piston rings (Trimble method), making a camshaft grinder, honing accurate bores, getting small valves to seat properly etc. I tried to do a lost wax casting for the head, but I didn't source the correct wax and so it was a disaster. Eventually I milled the head but made sure all the fins were tapered in thickness. The toolpath options for CNC milling were pretty limited to me around 17 years ago but with some handwork it was a pleasing result. The second set of crankcase castings you see above went to the late Ron Chernich at MEN, who liked to have plenty of castings in stock under the bench! Sadly, Ron never did get to make a start on those. Nick

Thanks Nick, excellent info! You’re right, every engine built provides so much education and grey matter expenditure that I feel like I’m in a Master’s degree program all over again!

Yours is some very beautiful work, and shows just what can be accomplished through motivation and persistence!

Thanks again,
John

 

[MrMetric]

Those castings are really nice, nj. In fact, I don't think I've seen many that I would consider to be nicer. Out of curiosity, what alloy of aluminum did you use for this? Or was it just melted aluminum from your junk pile? I know 356 is very common in die casting, but I don't know if people use that (or another specific alloy) for sand casting.

 

[nj111]

I cut some of these up and recycled them into Kiwi crankcases! The camshafts run in them on BMW straight six engines (from the 80's and 90's). There was a BMW dismantler next door and he had loads! Generally for work like this I would advise to use something from a previous casting.

 

[MrMetric]

View attachment 122726
I cut some of these up and recycled them into Kiwi crankcases! The camshafts run in them on BMW straight six engines (from the 80's and 90's). There was a BMW dismantler next door and he had loads! Generally for work like this I would advise to use something from a previous casting.

Thanks nj111. I agree that it is a good practice to use old, high quality, castings as stock. I do have to wonder if that still applies with modern castings tough. My association with that life is now over, so I really haven't kept up. But the auto industry seems to have moved far more "exotic" over the last few decades. Have the alloys done the same, to the point where you cannot recycle them as easily/safely?

 

[nj111]

I'd be inclined to agree with you. Fortunately we only cast small parts for this hobby so its usually possible to source something old that's damaged or worn out! The biggest problem I had was caused by myself overheating the alloy, it then absorbs hydrogen and the castings are full of holes and porosity. Once I had figured that out, and also plunged a tablet into the molten alloy to expel gasses and refine the grain I started to get really good results, but there were many poor results initially!

 

[MrMetric]

Yeah, de-gassing is a critical step in minimizing porosity.

 

[Eccentric]

Here I have attached the 3D models I created for the KIWI MKII crankcase. I have included both the STL files and the IGS files. These are enough to 3D print and to machine the engine case.

If you open them you will see I took a lot of liberties and redesigned the parts for ease of machining. They all can be made with a ¼” flat end mill with a .75” cut length. I have radiused the parts for this end mill and have made other modifications, for example the timing cover is more than .75” deep, but if you look at my model, I have the depth below .7” .020” inside so the tool does not hit the side wall as it goes deeper. I also used a ¼” ball end mill and a ¼” chamfer bit, but these were for cosmetics.

I have also included all of the Fusion360 CAM files for the crankcase front. You should be able to load them up in the free version of Fusion360 and see how I created all of the tool paths. I machine the backside (inside) of the crankcase front first. These are all of the critical dimension, the pocket for the ball bearing, the crankshaft and the pocket that is indexed for the precise placement of the cylinder sleeve. Then I flip it over and use the hole in the center to set the X=0 and Y=0 and ensure the axis are true horizontal and vertical. The features on the front of the case are less critical, but you do want the screw and the crankshaft to hit the center of the bosses.

Feel free to use these for your personal use, I can't imagine they would be of any commercial value.

 

[MrMetric]

Thank you! I really want to try printing them for fun. I've got a 3d printer, but I really haven't used it. This will be fun.

 

[Eccentric]

Call me crazy, but I had so much fun making the crankshaft, that I decided to make another one. I did three things different that I hope will result in a better crank. 1.) I heat relieved the cold rolled steel blank 2.) I milled the center web instead of using the lathe, and 3). I placed a piece of steel in the web to prevent flexing of the crank at the offset crank pin before I turned the main shafts.

I am using a small kiln made from firebrick. I heated the blank to a dull red, then slowly turned down the heat. I had additional firebricks at each end to hold in the heat, then let is cool slowly over several hours.

I used the mill to cut out the center web section. My lathe is small and I can only feed out a small amount of the tool at a time and it is difficult to get a smooth continuous edge. The milled finish is much better.

So far so good. The crank pin came out well, still need to do some polish work here.

I locked this “precision” steel block into the web, if it is too big it will actually spread the web and if it is too small it doesn’t do any good and the whole shaft will flex under the cutting pressure. I had to tweak my original crank by whapping the crank web with a hammer to straighten it.

I am going to put the crankcase and crank aside for awhile and work on the cylinder sleeve, cylinder and cylinder head. They will come out of the aluminum and cast iron sitting next to the engine. I am going to turn the sleeve first, I think I will use the 4 jaw for additional clamping force. Probably use the drill press and mill to remove the majority of the material from the sleeve before boring.

 

[nj111]

I recall making two crankshafts for my Kiwi to get one really nice one. In fact, I pretty much made two kiwi's to get one good one!

 

[Eccentric]

Today I have fabricated the blanks for the cylinder sleeve and the cylinder itself. I have ordered a ½” boring bar to machine the internal bores, wanted one that was really rigid. While I am waiting for the Amazon driver, I have started working on the fly cutter to cut the tiny teeth in the timing gears. The spur gear is 1” in diameter with 40 teeth and the pinion is ½” in diameter with 20 teeth.

Here I am milling the starter hole in the cast iron rod that will become the sleeve. In hind sight I should have milled out more material. I milled the hole to a .6” diameter thinking that would be enough for the ½” boring bar, but milling goes so much quicker than boring. Boring can get quite tedious. I’ll resist the boring pun.

Here are the blanks for the sleeve and the cylinder.

Using info readily available on the internet, I have created the profile for an 40DP involute cutter, as the spur gear is 1” in diameter and has 40 teeth.

This is the generation of the tool path using a 1/8” end mill to shape the end of an 01 tool steel, 3/16” cutter blank. After I mill the shape, I will grind relief, then heat treat, temper and sharpen.

Milling

This is my heat treat/temper kit. I warm the fly cutter in a low flame and dip it in boric acid a couple of times until I have a good build up. The I turn up the MMAP torch full and heat the tip to a bright red, then plunge it into the vegetable oil. I then go into the kitchen and use the wife’s tea kettle to boil up some water and rinse off the boric acid. It prevents the black scale from forming during heat treat. Then I again use a light flame heating the rod away from the tip and watch the color change from a light straw to a bit darker straw at which point I again plunge it into the vegetable oil. Finally, I take it to the sharpening stones and finish up with an Arkansas stone to a bright polish.

The result – a DP40 involute gear cutter. It is tiny, it will be interesting to see how this thing holds up, it could fracture before I finish a gear. We’ll see. Oh, and my boring bars showed up.

 

[Eccentric]

I got to get a little machining in this afternoon working on the cylinder sleeve. My new boring bar works like a dream, I have a consistent 1.000” bore all the way through. It is 2.125” tall with a 1/16” lip at the top and a 1/16” wall. From that big ole cast iron rod, this is all that is left. Well, not really true, the rest of it is covering my lathe, workbench and workshop in a fine gritty dusty mess.

 

[Eccentric]

Today was spent at the lathe working on the cylinder. I didn’t have any issues, aluminum is nice to machine after a day of machining cast iron. I mean, I like the way cast iron machines, but aluminum cleanup is a breeze. I have a white board right next to my lathe and as I approach the critical internal bore ID, I write down both the lathe cross slide indicator position and the bore measurement. This helps me visualize where I am so I don’t overshoot. The math is dead easy of course, but I have messed it up too many times. SA as they say in the Air Force – Situational Awareness. I aimed for an interference fit of .001” with the sleeve. For the outside features, I did all of the math and marked out where they fell on the cylinder blank using Dykem. The machining was pretty straight forward, no super critical dimension except the overall length, but I like to hit the numbers on the print; it is good practice. I did take a little liberty and free hand machined the fins to give them a taper to the outside. I machined them square, then turned the tool in the tool post about 10 degrees one way, then the other machining the sides of the fins.

2.25" aluminum round blank

Cylinder and Sleeve

I need to mill and thread four holes in the top of the cylinder for the cylinder head to mount and I need to mill the bottom of the cylinder into a square with four holes to attach to the crankcase. Finally, of course, I need to press in the sleeve. I am having fun with this project. Next I will do some CAD work on the cylinder head and start researching the fabrication of the cast iron rings.

 

[Eccentric]

Today was a light machining day, but I did the work required to mate the cylinder and the crankcase.

When I machined the two crankcase halves, I put a square feature at the top that I could indicate off of to exactly find the position of the cylinder sleeve so it is centered over the crank. Here the cylinder sleeve mating hole is being machined centered on this square index hole.

Here the sleeve hole is complete with the slot for the connecting rod. I machined the hole to exactly 1.125" diameter, then had to go back and open it up .001" becasue the sleeve didn't quite slip into the hole.

Machining the bottom of the cylinder. I made a mistake when I designed the crankcase, I intended the pad that the cylinder sits on at the top of the crankcase to be 1.875" square, but I made it 1.875" by 1.375". So instead of remaking the crankcase, I am going with it and making the base of the cylinder rectangular as well. The cylinder sleeve extends below the bottom of the cylinder and into the crankcase by .3125" and there is just enough sealing area at the base, I think it will be OK.

Here is the result so far. The cylinder is resting on the crankcase and the sleeve has been pressed in. I have spot drilled the holes at the top of the cylinder for the threaded holes to mount the cylinder head. That will be the next project, back to the computer for a bit to model up the cylinder head. I bought my little 10mm spark plug so I can have its actual dimensions in the model.

 

[CFLBob]

Interesting build.

I've heard of using steel liners, but never looked into details, in particular if they're bonded in place or not. Is that .001" press fit all you're doing? Is that good vs. temperature?

 

[Eccentric]

Bob,

I use an interference fit for the sleeve to the cylinder then add wicking Loctite 609 which has good thermal properties. Also, the sleeve is completely retained by the cylinder head which bears down on it when tightened. We don’t push these engines very hard so using a cast iron sleeve in an aluminum cylinder works fine.



Cast iron is the perfect material for cylinder walls and piston rings. It is great for high temperature environments, is low friction and has great wear properties. When I was a kid engine blocks were cast iron. But it is heavy. I think the primary reason for using aluminum in engine blocks was weight which is of paramount importance in aircraft and also race cars and to some degree cars designed for fuel economy. Aluminum has better thermal conductivity, three times better, than cast iron. Aluminum is easier to machine and is less expensive. So, the two material lend themselves to different areas of the engine. In my application the aluminum when shaped with lots of surface area on the fins, is better at getting the heat transferred to the surrounding air so works well in the cylinder.



You are absolutely correct about the different coefficient of expansion between the two metals, aluminum expands more at a given high temperature and this can cause problems in engines using cast iron sleeves. Using a sleeve adds parts and much more machining to the finished cylinder assembly. Sleeving adds complexity without improving the functionality of our model engines as infrequently as they are run.



My motivation for picking a single cylinder engine with a sleeve was to gain experience, to ease myself into building a twin cylinder engine, one that will require the skills to make cast iron sleeves and rings.

Bob—thanks for the comment, sorry I rambled on. There is not much dialog or feedback in this forum and it is fun to hear from a fellow engine builder, it is reassuring to know that folks are out there.



--Greg

 

[Kasey]

Bob,

I use an interference fit for the sleeve to the cylinder then add wicking Loctite 609 which has good thermal properties. Also, the sleeve is completely retained by the cylinder head which bears down on it when tightened. We don’t push these engines very hard so using a cast iron sleeve in an aluminum cylinder works fine.



Cast iron is the perfect material for cylinder walls and piston rings. It is great for high temperature environments, is low friction and has great wear properties. When I was a kid engine blocks were cast iron. But it is heavy. I think the primary reason for using aluminum in engine blocks was weight which is of paramount importance in aircraft and also race cars and to some degree cars designed for fuel economy. Aluminum has better thermal conductivity, three times better, than cast iron. Aluminum is easier to machine and is less expensive. So, the two material lend themselves to different areas of the engine. In my application the aluminum when shaped with lots of surface area on the fins, is better at getting the heat transferred to the surrounding air so works well in the cylinder.



You are absolutely correct about the different coefficient of expansion between the two metals, aluminum expands more at a given high temperature and this can cause problems in engines using cast iron sleeves. Using a sleeve adds parts and much more machining to the finished cylinder assembly. Sleeving adds complexity without improving the functionality of our model engines as infrequently as they are run.



My motivation for picking a single cylinder engine with a sleeve was to gain experience, to ease myself into building a twin cylinder engine, one that will require the skills to make cast iron sleeves and rings.

Bob—thanks for the comment, sorry I rambled on. There is not much dialog or feedback in this forum and it is fun to hear from a fellow engine builder, it is reassuring to know that folks are out there.



--Dear Greg,
I agree with your last comment, and I have had only a few on my project of building a twin/flat four cylinder, two stoke engine based around a VICTA twin and single crankshaft, incorporating the split single concept in both. and using 2 of its 85 cc pistons/and old run-in polished rings in a new cast, and homed, alloy block. Using an available crankshaft can have its problems re.lubrication as I may be about to find out,, as I'm using fabricated alloy con rods themslelves as big end bearings first. I'll only go to slippers or rollers if necessary.
I've found a local hobby guile which is into foundry jobs to cast the cylinders in alloy. For sleeves,, if I need them, I may find some seamless tube to do the job as cutting ports may be easier than in cast iron. Currently, they are cast with the cylinders.
Good luck with your project. If you have a 3D printer it's an advantage to make the parts in plastic first.

 

[Charles Lamont]

Bob—thanks for the comment, sorry I rambled on. There is not much dialog or feedback in this forum and it is fun to hear from a fellow engine builder, it is

Well, I am watching, for one.

 

[Eccentric]

Kasey,

You might look into DOM steel tubing, it is supposed to be very dimensionally accurate and might make a good cylinder sleeve (not as good as cast iron ).

I feel silly becasue I 3D printed the crankcase, but not the cylinder, if I had I would have noticed the cylinder hole pattern didn't match the crankcase hole pattern.

Today I worked on the cylinder head, did the lathe work including the features on the bottom. I also worked on the piston, I think before I finish off the cylinder head (I still have some CAD cleanup on the finned top) I am going to make the connecting rod and piston. How cool is it going to be to see the piston go up and down in the cylinder when I spin the crankshaft?

Can you see where the head ends and the cylinder starts? Hint, look at the next photo

I have read different things regarding how tight a fit the piston is supposed to be in the cylinder, I decided to leave .005" difference between the piston OD and the cylinder ID. It falls into the cylinder and I can still get a 'pop' when I pull it out fast. I am looking forward to try my hand at piston rings. the rings will have across section of 1/16" X 1/16" and will expand into the 1" diameter cylinder.