KIWI Mk2

I/C ENGINE BUILD

Part 6 By Vince Cutajar

I located the aluminium I used to machine the timing cover and bolted it to the rear casting with the timing cover in place. I bolted on the front casting and did a trial setup on the rotary table to see if I have enough headroom under the mill chuck. Well there is enough headroom but I did not like the setup. I needed to simplify it by removing the 1-2-3 blocks.

I simplified the setup on the rotary table by removing the 1-2-3 blocks. I put them there for two reasons. The first one was that the screws I was using where not flush to the aluminium and secondly because that I thought that if the drill passed through it would hit the rotary table. Well, both problems were solved. Bought new screws which fitted better the counterbore so the heads were flush and also realised that even if the drill went through it, it would still be in the centre of the rotary table hole.

I usually setup the rotary table using a MT2 taper tool (it is also used to hold things on the rotary table) that I made some time ago (next photo). I never bothered to check how accurate this method was, but out of curiosity I checked it with a dial and it was spot-on. I put the crankcase (with the aluminium plate) on the rotary table, and using the previously used homemade punch in a 10mm collet, I centred the crankcase and clamped it to the rotary table. I took the quill down into the crankcase and spotted the bottom part of the crankcase (where the hole needs to be drilled). Unbolted the front part off the crankcase and took it off and checked again that I am still lined up with the mark I just made.

Continued by centre drilling, drilling 6mm, 8mm and 9.8mm and then reaming 10mm. I did not use the drill chuck for these operations but used collets. Then I used 12mm, 15mm and 18mm slot drills to widen part of the hole for the bearing housing. Continued milling the bearing housing using an 8mm carbide end mill and the rotary table to get 18.995mm diameter for the ball race. It was a bit of a pain retracting the end mill and checking diameter but it was worth it.

Now for the moment of truth. Took it off the rotary table, inserted the bearing, assembled the cranckcase and checked if a 10mm silver steel bar would pass from one side to the other. It passed and it turns.

What a relief! I think I have passed what in my opinion was the biggest hurdle in this build. Now to go back to Westbury's instructions.

Decided on a trial setup for the next operation using V-blocks. It looked sound, and did some measurements and markings. The next operation was to mill the cylinder platform. It has to be parallel to the crankshaft and 1.5" (38.1mm) above the crankshaft centre line. Using the 10mm silver steel rod going through the crankcase supported on the V-blocks I marked the 38.1mm line. Put everything on the mill table and clamped everything (V-blocks and crankcase).
I milled the cylinder platform, but instead of 38.1mm above crankshaft centre line I did it 39.1mm above the centre line. Yesterday, I was re-reading Westbury's article and at one point he says: "The distance of the cylinder platform from the crankshaft centre influences the compression ratio, in conjunction with the dimensions of other components. Some constructors may wish to produce an engine to run under load at relatively low speed-not more than 2,000 to 3,000 r.p.m., for instance - and if so, the compression ratio may be reduced, either by leaving more metal on the platform surface, or by fitting packings under the cylinder platform, which is more adjustable but less positive.

“Low compression is recommended if the engine is to be used for driving a heavy boat such as a tug or cargo liner; the beginner may find it easier to deal with, as it promotes docility and easy starting, and all adjustments are less critical than when the compression is high."

Problem is that he does not say how much more metal to leave, so I left 1mm more. I can always bring it down to 38.1mm at a later stage.

After that operation was finished, I inverted the crankcase and making sure it was parallel to the table, I milled the engine bearers (supports).




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