Things are finally starting to come together now.
After seemingly working for very little gain over the last few months, progress has leapt forward over the last few weeks. All of the preparation work is paying off.
One of the first tasks I undertook after my last post was to drill out the mounting holes for all of the myriad bolts and studs that go in this engine crankcase. The number of bolts and nuts in this model amount to quite a considerable cost. They are perhaps the most expensive part of the model, after 3D printing. I obtain almost all of my miniature nuts and bolts from Prime Miniatures.
When it came to the actual drilling, I did find one thing I forgot to add to the CAD model: drilling point markers (a small depression in the casting to centre the drill bit). I have them in some places, but not everywhere. One big omission was forgetting to put them in for the cylinder mounting bolts. There are 76 of them per engine, and I plan to build 2 engines, and possibly 3. 228 holes to be accurately marked out and drilled if the cylinders are to fit properly. Big mistake. Big. Huge!
To recover the situation a little I resorted to a CAD generated photoetch mask and created a drilling template. I have also gone back and updated the original CAD model and 3D print files, just in case I ever print them again.
Thankfully I had added drill points to the holes in the sump, though I had to drill very carefully as a number are very close to the edge of the casting. One disadvantage of cold casting is that the output is even more brittle than normal resin and it is very easy to break. you can however patch it with a cold cast mix dabbed on the offending area.
The photo above also shows the addition of the inlet and outlet pipes from the oil tank. They should have ‘in’ and ‘out’ actually embossed in the casting, but I was unaware of that when I had the 3D print made. I also had no idea how to do embossed text in CAD either for what it was worth. However, I have rectified both omissions and updated the model, so if I ever get it printed again they will be there.
Next was the addition of the oil suction pipe that runs from the front of the sump to the rear where the pump is. I’ve made it from brass tube, purely because that is what I had in stock of the right diameter. It will be copper plated and slightly aged eventually.
Having drilled all the holes (oh how easy it is to type that) I got down to painting some of the resin cast hardware in preparation for finally fitting the cylinders and their water jackets.
Fitting the cylinders and their jackets is quite complex. There are a lot of parts that all have to be finished accurately if it’s all to fit together properly. Each cylinder has to be exactly the same height and the bases sanded square, or gaps start appearing where they shouldn’t.
Finally, I got on to actually assembling something. An exciting moment in my life. For those who think I need to get out more, I know, but remember I am housebound.
The upper and lower halves of the crankcase are held together with some unusual bolts in a number of the pictures of museum engines that I’ve seen. I replicated them by drilling out the head of an M1.6 bolt and inserting a small 1mm peg, which itself was cross drilled 0.5mm. A short length of brass tube was added to form the body. the whole assembly was then darkened using burnishing fluid.
Then it was mounting the cylinders. As these are studs, it was necessary to cut the threaded parts off some M1.2 bolts and glue nuts on them. As before all the parts were darkened in burnishing fluid to give an aged appearance.
There then followed a lot of quite tedious trial-fit, glue, trial fit, glue…. etc. Did I mention it’s important to be accurate at this point?
A similar activity was carried out on the underside of the engine using M0.8 nuts and studs.
Yet more bolts. These things are expensive too you know!
Then came the moment when the first water jacket and cam cover went on. Up to now I had used Super Glue throughout, but as it has a habit of grabbing and setting suddenly I decided to fit the water jacket to the cylinders with 5 minute epoxy. This would give me enough time to make sure everything was in place an adjusted properly before it hardened.
In the end there were no great dramas fitting the water jackets, just a bit of cramp holding everything together while the glue set, especially as the first side took a lot longer than 5 minutes to cure. I must not have mixed it enough.
At last the model was starting to look a bit like the engines I’ve seen in photos. In fact it felt slightly surreal to see something I have created from nothing start to come to life. Throughout my life as a designer it’s always been like that for me. The feeling of “Did I really do that?” or more often “Good grief! It does actually work.” when you are confronted with real hardware.
Having added the big parts to the cylinder block I put it aside to cure properly and got on with the magnetos. These were given an undercoat of matt black enamel. The Bakelite parts were then masked off and the bodies sprayed in two metallic colours. One for the tin covers, and a darker one for the aluminium castings.
I’m not overwhelmed with the result if I am honest. I’m hoping that a bit of subtle weathering and staining can make them more realistic. The addition of ignition leads should also help.
On the subject of ignition leads, I made the guides that bolt to the water jackets out of brass tube with small brass P-clips soldered to them. As I couldn’t find any brass tube with the right scale wall thickness I reamed out each end of the tubes with drills 0.5mm less than the outer diameter. Having painted everything gloss black you can hardly tell. It took quite a bit of time and effort too!
The spark plugs come from RB Motion in the US. They are fabulous little things (the spark plugs), but it is up to you to paint them. As they are aluminium I started with a coat of etch primer before I added the gloss white. The ignition leads are 30 AWG, 0.05mm² silicone wires. The end pieces are just 1mm OD nickel/silver tube crushed in pliers at one end and drilled 0.7mm
In parallel with painting the magnetos I’ve also started to assemble the drives at the rear. The photoetch parts mentioned in my pervious post have been stained and glued in place, as well as what I assume are slipping clutches. These were originally cast on the magneto bodies, but I had second thoughts and cut them off to paint and assemble separately.
The advance and retard lever plate is also in place, but I haven’t got around to adding the adjustment lever yet.
One sorry tale amid the positivity concerned the inlet manifold. I did have the idea of making it highly polished, along with the cam covers and carb. To that end I polished one of my castings up with the intention of plating it.
Then a copper strike was plated on to ensure good adhesion of the bright nickel.
And the final result.
Which is good as far as it goes, but it way too blingy for my liking. I should’ve left it in the initial polished state. I was also faced with the problem of struggling to obtain pewter cam covers that matched accurately enough.
In the end I felt that it was more important that the overall look of the model was harmonious, so I went back to cold cast cam covers and manifold, both slightly polished. It isn’t the highly polished look I originally had in mind, but it does look convincing. In fact I’ve got my doubts now about the air filter…
So that’s where the model stands at the moment. Its sister model, which will be in burgundy rather than black, is on the back-burner for the moment as I want to pioneer all of the problems on this one first.
Hopefully next time the magnetos will be in place and I’ll have begun to make some progress with the transfer gearbox (remember this is a marine conversion of the engine for use in power boats).