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Cosworth V8 1:12 scale

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Steve Crow05/11/2020 17:01:37
260 forum posts
129 photos

This is the gear train for the cams. The camshafts rotate counter to the crank. The blue gears (EN1A) are driven or drive and the orange/yellow (brass/nickel silver) ones idle.


This is quite a bit simpler than the full-size engine, which has compound gears, but it does resemble it.

The gears are Mod 0.3 as I have a set of involute cutters. It would work in Mod 0.4 or 0.5 as well.

This is part of the build I'm looking forward to most.


Steve Crow15/11/2020 16:33:37
260 forum posts
129 photos

Now for the conrods.

These were cut from 2mm clockmakers brass in strips of 4.


They were then tapped 12BA.


I forgot to take photos of the clamping half but they were made the same way.

They were then separated with a jewellers saw.


I then screwed the two parts together, blended in the curves and tidied them up a bit. They were then drilled and reamed to 3mm.


These still need surface finishing.


Steve Crow15/11/2020 16:56:51
260 forum posts
129 photos

Before I went any further, I thought I'd test fit them on the crank.


A fiddly job attaching these but everything fits and moves nicely with minimum play. The middle one at the front looks like it isn't straight but that's the camera angle.


I then tried the whole assembly in its bearings in the block.


The conrods do foul the block in parts but this is because they are no liners or pistons in yet so the rods are rotating more than intended.


I've got to say that it doesn't look like the bottom end of a racing engine - more like some late Victorian marine engine. The thickness of the conrods is massively overscale. This is a consequence of using the smallest screws I had.

Even then, I had to turn down the heads to 1.8mm and dome them for clearance.

This is also the reason why there is only two bearings. There just wasn't space for other journals.

I'm happy to answer any questions or receive any criticism.

Anyway, will update as I make more parts.


Ady115/11/2020 18:57:47
4161 forum posts
588 photos

Looks great

With the scale of the work you are doing and the skill level you have reached it looks like you are at the edge of the normal tooling envelope

Alternatively the watchmaker industry may offer solutions and ideas

Bob Wild15/11/2020 22:50:44
50 forum posts
32 photos

Very impressed!!

Steve Crow27/11/2020 15:34:42
260 forum posts
129 photos

I made this gadget (mandrel?) to hold the cylinder heads while I milled it and drilled and counterbored the inclined valve holes.


It is basically a 18mm diameter brass bar with 4mm removed on the flat. The silver steel rod is 8mm so I can hold it in various tool holders and collets.


The idea behind this is that the 16 degree inclined valves converge at a point 5mm below deck height, the bottom of the cylinder head. If I axially centre a cutting tool, I can do all the operations just by rotating 16 degs. either way.

The above photo were taken after I'd used it, hence the square pattern of shallow holes where the drill (intentionally) broke through.

Here it is set up and the flats being milled.


It took me a long time to set this up. I had to clock it axially and make sure it was centred both ends. It seemed like hours with a little rubber hammer tapping things true before I was happy. This was done before I attached the workpiece.

After that it was drilled 1.6mm through, c/bored 2mm for the valve guides and c/bored 2.7mm for the springs.


This worked a treat. My Y-axis remained locked for the whole process.


Steve Crow28/11/2020 13:07:02
260 forum posts
129 photos

I made 3 cylinder heads, a left, a right and a universal.

The universal is going to be used as a test-bed for cutting the valve seats and a couple of other things. After that it will go back on the mandrel and will be a sacrificial holder for the cam carrier blanks when it comes to machining them.

There are 48 inclined holes here, that's 144 separate operations.


Here is the under side of the heads. The central holes were drilled at the same time as the holding down bolt holes.


Here is a close up. The web between the two valve holes is 0.1mm thick which I was a bit worried about as even the slightest variation from this between cylinders would be visible but everything came out alright.


A close up of the underside. The central hole is not for a miniature spark plug but a guide for the tool I'm going to make for cutting a recess.


All in all, I'm quite pleased with these. I can't find any errors so all the careful clocking and indexing paid off. Saying that, I'm glad it's over. It took me a whole day of dial-counting and double checking before drilling.


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