Thread: Building A Billabong Engine From Castings

G’day All,
In a post a few months ago I mentioned that I had started doing work on building a model engine.
As it might be of interest to a few of the members here I thought I would start a thread on the build.

This is going to be a fairly long term project because I have a family, day job, and other things that occupy my time, however I will endeavour to keep it on track and post updates as progress is made.

The Billabong Engine (as it’s named) was designed by a mate of mine who made all of the patterns himself and had the castings done at Billman’s Foundry in Castlemaine. It was designed as a throttle governed low tension ignition petrol engine but I might tinker with this a little. I like the idea of making it hit and miss and possibly even gas fuelled but all this is a little down the track.

I actually started work on the engine back in April so the first few posts will cover the work done since then and may give the false appearance of rapid progress.

First job was to machine the bottom of the base casting which will become the reference surface.
As the base casting doesn’t have another surface parallel to the bottom, a fixture was made to support it for the initial machining rather than mess around with jacks and packers. The bottom was machined just enough to produce a clean, even surface which only required a couple of .02” passes to complete.

Photo 1: Base casting and support fixture.
Photo 2: Machining the base.
Photo 3: Job done.

The main bearing caps needed to be finished to final dimensions so the seats in the base casting could be machined to a matching snug fit.

The first cap was mounted in the vice with one side facing up and indicated in as even as possible before making a couple of clean up passes. The cap was then flipped over and positioned on a parallel so the other side could be machined flat and the width of the cap bought to size. This process was then repeated for the second bearing cap.

With the sides of both bearing caps now parallel they were clamped together in the vice so each end could be machined to bring the cap length to its final dimension of 2.625”.

Both caps were then mounted together with the bottom facing up and the shoulders bridged across a couple of parallels so they could be machined to bring them to a height such that they would sit aesthetically on the base while leaving enough meat to bore later on for the crank bearing.

Finally they were flipped over and positioned on a parallel so the top of the oiler boss could be machined flat before removing them to mark out the hole positions for the retaining bolts and oiler.
Each cap was then returned to the vice and bridged across a couple of parallels so as to allow clearance for drilling.
Each retaining hole was spotted with a centre drill, pilot drilled to 4mm then counter-bored with a 16mm slot drill just enough to allow the mounting bolts to sit flat. The oiler hole was spotted then drilled to 4mm.

Unfortunately I didn’t take any photos of this process and apologise if this is a bit wordy.

Photo 1: Finished bearing caps.

Watching this with great interest. What size and type of cutter did you use? Asking as I'm new to the machining side of things.
Regards
Kryn

Back to work on the base casting where the next job was to machine the front which will mate with the cylinder.

The base was positioned square to the table then indicated in as close as possible so as to minimise the amount of material to be removed. I reckon the cast surface looks more authentic so rather than just machining the entire front perpendicular to the bottom I used a facing head to remove only the circular area required to mate with the cylinder. Because of the pattern draft, the machining resulted in a small shoulder which will act as a seat for the cylinder.

The clearance hole for the cylinder liner was first spotted with a centre drill before progressively drilling it out to 27mm (my largest drill bit) then boring. I soon realised it was going to take a long time to get to 2.25” taking 0.03” cuts and decided to try using a 2” hole saw to remove a large chunk of the material. I was not sure how well this would work but the cast iron cut like butter with a spindle speed of 60 rpm and I had a 2” hole cut in about five minutes as opposed to what was probably going to take an hour or more of boring. This done the hole was finished bored to the required diameter.

Without disturbing the base, the main bearing seats were machined next in order to maintain alignment with the cylinder mounting face. The caps were then positioned and the holes for the retaining studs spotted through the 4mm pilot holes in the bearing caps. Again, I didn’t take any photos of this bit.

Photo 1: First cut on the cylinder mounting face.
Photo 2: Cutting cylinder liner clearance hole the quick way.
Photo 3: Base showing main bearing seats.
Photo 4: Base with bearing caps fitted.

G'day Kryn,
It's an 80mm six insert 90 degree face mill. It works really well for this sort of thing.
Ideally I should have made a finishing pass with a fly cutter but I don't have one so that wasn't going to happen.
I know I could have used the boring head but to be honest the finish from the face mill is actually very good.
Thanks for your interest.
Cheers,
Greg.

This looks very interesting ! I'll have to keep a close eye on this thread.

With everything that could be done on the base casting finished it was time to move on to the cylinder. This required a little bit of thought as to what would be the best way to proceed.
Ideally most of the work on the cylinder would have been done in the lathe but I was not comfortable with the idea of hanging the 3kg+ casting unsupported from the four jaw of my little Hercus. So the mill was again pressed into service and the boring and facing head utilised.

The facing head was mounted in the horizontal spindle and the cylinder casting supported on a pair of matched v-blocks then clamped so the base mating surface (crank end) could be machined as the primary reference. It was indicated in as close as possible and about .100” removed to get a clean mating surface.

The cylinder was then flipped to a vertical position so the reference surface could be clamped directly to the table and the head mating surface machined down so as to bring the total cylinder length to the required 5.5” using the facing head in the vertical spindle, sorry no photos of this part.

The cylinder now needed to be bored to be a press fit with the cylinder liner at each end of the water jacket. The crank end was to be 2.25” and the head end 0.100” smaller to facilitate the liner installation.
My original plan was to support the cylinder reference surface on a pair of parallels which would allow clearance from the table then bore the cylinder for the liner. As soon as I started to clamp things down though I realised that this setup wasn’t going to work as it left me no means of measuring the crank end bore. I know I could have bored them both to the smaller dimension then flipped the cylinder and finished the larger one but I wanted to machine both in the same setup to guarantee concentricity.

Another small problem was that the mould core must have shifted slightly during the casting process as the void for the water jacket was about 0.180” off centre but a bit of measuring confirmed that there was enough meat in the casting to allow this to be corrected.

The cylinder was again supported on the v-blocks and the tilting table on the mill proved its worth here. The cast surface of the cylinder made repeatability virtually impossible so the cylinder was first indicated in to the X plane then clamped down. The table tilt locks were then slightly loosened and a few judicious taps allowed the Z plane to be quickly aligned and the table locked down. The whole thing was then roughly aligned to the spindle by using the boring head to swing a tool over the circumference of the cylinder flange while adjusting in the X and Z until it made even contact.

The crank end was bored to the required 2.25” diameter using the shortest boring bar for the head, unfortunately the longest boring bar is a bit too short to reach through to bore the head end so I will have to come up with an alternative. One option is to use a 16mm insert boring bar but as this is 8” long I’m a bit concerned about chatter.
I will take a few cuts with it and see how it goes.

Photo 1: Facing the crank end of the cylinder action shot.
Photo 2: The final facing cut on the crank end of the cylinder (the reference face)
Photo 3: A shot showing how the cylinder casting was clamped down.
Photo 4: Clamped on it's side again after facing the head end. The non-concentricity of the void is now quite visible.
Photo 5: Marked out to verify there is enough meat to bring the bore back on centre.
Photo 6: Boring the crank end action shot.
Photo 7: The crank end bored on size.

Nice job, was the bore still "on size" once the clamps were released? I would expect some ovality.

G'day Techo and thanks.
The cylinder is still clamped to the table so I can't answer your question yet.
The walls of the cylinder are around 0.500" thick and the clamps are only tightened enough to hold it securely.
I would be surprised if there was much distortion due to the clamping, at least anything that my measuring gear could detect but when it comes off I'll check it and get back to you.
Cheers,
Greg.

I've been slack with this posting business but there has been some progress on the engine.
Boring the head end of the cylinder using the 16mm insert bar actually worked better than I expected. I started off taking 0.015” cuts which were only partial contact due to the non-concentricity and they cut fine with little chatter. I continued the 15 thou cuts once the tool was cutting for the entire circumference until the bore was close to size then took a few spring cuts to allow the bar to equalise and the chatter marginally increased but was still acceptable. The final cuts were made by in 0.004” increments taking a primary cut advancing the tool, a spring cut withdrawing the tool, then a final spring cut advancing the tool. This seemed to work well and although a bit tedious it allowed me to sneak up on the final size and finish up spot on. The small amount of chatter left a slight pattern on the surface but a bit of a rub with fine emery cleaned this up and I’m pretty happy with the final finish.

Next operation was to clean up the water jacket which was also off centre due to the shifted core. This was a fairly straight forward operation using the longest boring bar for the head. First boring roughly to size with the HSS cutter in the 90° end then clean up the end faces with the tool in the 45° end then a couple of light finishing passes across the length to bring to size.

I had previously made up a bushing which allowed me to use 10mm shank lathe insert tools in the boring head and this was used to trim the cylinder flange. This was a straight forward job but there was only about 1/8" clearance between the boring head and the mill table which looked pretty scary. With the flange down to the correct size the cylinder was mounted on the rotary table and the six cylinder mounting stud holes drilled.

I took some measurements of the bores after removing the cylinder from the table and couldn't detect any variations or loss of concentricity caused by the clamping forces.
That's about all that can be done with the cylinder for now so its on to the cylinder liner.

Photo 1: Adaptor bushing to hold 10mm shank lathe insert tools.
Photo 2: Cylinder on the rotary table ready to drill stud holes.
Photo 3: Finished stud pattern.

I have also posted a short video showing some of the cylinder machining steps:
https://www.youtube.com/watch?v=TMMy729ColE

Also well worth a read is the story of how Len designed and built this engine which can be found on his website:
http://members.iinet.net.au/~hoppi/M...ongEngine.html

The casting I have for the cylinder liner is one that Len cast himself. He was not sure of it's quality or if it might have some inclusions or porosity but we figured it was worth giving it a crack. Once again the core must have shifted a little during the pour and the void was a bit off centre. More measurements and head scratching to determine the best approach then the casting was mounted vertically on the mill table using vee blocks on an angle plate to get vertical in the X plane then a square to get it close enough in the Y plane, this with about 1/8" clearance from the table.

First off the top end was machined flat then the top 1.5" of the bore was machined out using a short boring bar until a complete circumference was cut. This was repeated on the outside surface of the liner so I would have something to indicate off if needed. Next the bottom 1.5" of the bore was machined using the 16mm insert bar, again until a full circumference was cut. Finally flip the liner upside down then mount on the angle plate with the machined end flat on the table, I couldn't get a 0.002" feeler gauge between the liner and the table so I was happy with that. quick couple of passes and that was about it for the mill work. These surfaces will be used as references for machining the outside of the liner to final dimensions in the lathe. Unfortunately I didn't get any photos of this work, my brain was hurting just getting things set up and cut.

To hold the casting in the lathe I made an expanding mandrel for the spindle end and a simple tight fit plug mandrel for the tail stock end which will let me swing the casting between centres.

That pretty much brings things up to date, I plan to get stuck into the lathe work next and will do another update after that.

Photo 1 & 2: Cylinder liner after machining reference surfaces on the mill.
Photo 3: Mandrels to hold cylinder liner in the lathe.
Photo 4: Mandrels installed in the liner.
Photo 5: mounted between centres and ready to go.

Thanks for reading,
Cheers,
Greg.

I finished machining the cylinder liner about three weeks ago, I just haven't got around to putting a post together until now.
Working on the liner involved machining to different classes of fit on different sections. There were two LN1 interference locational fits and two LC2 clearance locational fits (refer to photo2).
Len's casting turned out to be very good with no porosity inclusions or voids, it machined well and I'm very happy with the final result.
The mandrels worked perfectly and didn't budge even during the initial heavy interrupted cuts.
It would have been nice if the driven end mandrel had been about half an inch longer to allow a bit more access between the drive dog and the end of the liner but as I made it using a bit of scrap I had to hand, it was what it was.
In the end the final cuts were so light I could machine the driven end without the drive dog anyway so all was good.
Note that the final bore is still to be machined but this will be done later when the cylinder has been mounted on the crank case.

The LN1 sections are 0.0005" oversize on a 2.150" and 2.250" nominal diameter.
The LC2 sections are 0.001" undersize on a 2.400" and 2.250" nominal diameter.

Photo 1: Work in progress, all the heavy cuts are done and working on rough machining to size.
Photo 2: Finished liner.

Cheers,
Greg.

Very interesting, will be keeping an eye on your WIP.

Thanks for sharing, I like the way you are showing all your special little fittings and fixtures, I too have spent many hours making jigs and holders designed to do one thing for a few minutes... once!