Stuart S50, my first engine build

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Oct 7, 2023
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Brighouse. Yorkshire, UK
After a lot of prevaricating I bit the bullet and bought a set of castings. Obviously the cheapest, simplest one I could find and its been on my dining table for a while now. I've looked over the bits and the drawing and pondered which bit to start with, if I should do the easy looking bits first or go for the bit where I ruin the whole thing and abandon the project.
There are lots of people on YouTube who have built this model and that's the perfect excuse to sit and watch videos rather than stand in the cold workshop. Hopefully spring is around the corner and things will get warmer.
Starting at the bottom, making something that the other finished bits can be mounted on appeared to be a theme on the YouTube community so that seemed a reasonable place to start.
The first thing that struck me is that there are no starting points for the dimensions, all are referenced to an axis that is yet to be determined and a centreline between two unmachined linear features on the casting. OK, I can find the centre of the "main bearing cap" that's part of the casting and the bore is dimensioned from a wobbly bottom surface. The bottom surface was flattened on my belt sander enough that the casting can sit flat on the mill table. But the bore has to be square to the cylinder centreline or bad things will happen.
I decided that I needed to fasten the base casting to something that can have datums machined in. Mntg plate.jpg

A lump of hot rolled steel was found under the bench, where I keep things like this. Then it got machined to a kind of half decent looking bit of jig tooling.Machined plate.jpg

The plan is to drill and tap holes in the ends to allow it to be bolted to 1-2-3 blocks and clamped on a vertical orientation with a good degree of accuracy.
123 block.jpg

The next bit involves more head scratching as the three tiny M3 screws are all that holds the part I'm about to ruin to the fixture. These were fitted into holes which were marked in the castings with little dimples. Unless these are shrinkage artifacts and nothing to do with the hole position? Well they're drilled now and the M3 hex head screws ae very close to the side of the casting. I think socket heads may be required.
Tight fit.jpgWork around.jpg

I saw a couple of guys on the videos remove the fake bolts that are cast into the base casting to replace them with real bolts to improve the look of the finished article. I might chop these off, spot face and drill them and then use the holes to add more fixings to secure the lump and then fill the holes later using nuts and bolts to pretty it up.