KIWI Mk2 I/C ENGINE BUILD

Part 1 By Vince Cutajar

The Kiwi Mk2 designed by Edgar T Westbury was the choice for my first I/C engine build. I also took a decision to use castings which is also a first for me. I bought the kit from Hemingway Kits, which arrived here in Malta by Fedex nicely packed with each item individually bubble wrapped.

I thought I would start with something simple, namely the tappet guide which is a bronze casting. After checking the dimensions of the casting, I faced one side. As you can see I cheated a bit by scanning from the plans the tappet guide diagram, made it scale 1:1, glued it to the faced casting and used it as a template. Yes, I know, not very professional. I then drilled and tapped the edge holes 3mm and then drilled and reamed the middle holes (from where the tappets pass) 5mm.
And this is the casting faced drilled, tapped and reamed on one side.
First I marked the the tappet guide so that I could rough mill it before putting it on the rotary table. Rough milled it and then I attached it to a piece of flat aluminium using 3mm screws. Put it in the vice and then milled it some more.
Machined the circular section of the tappet guide to 14 mm diameter. Then milled down the height of the guide to the proper dimension. Took it off the rotary table and cleaned the side of the flange with a Dremel. Cleaned the whole part using 280 grit and then 400 grit sandpaper.

Final operation was to drill both 3mm tapped holes with a 3mm drill. To locate the hole under the chuck I screwed the 3mm tap in the tapped hole, locked the tap in the chuck and then fixed the tappet guide to the rotary table. Removed the tap from the chuck and inserted a 3mm drill.

Having finished the tappet guide, my next item in the build was going to be the tappets, and I noticed a mistake (I was warned to watch out for these). Actually it's not a mistake but a difference between the diagram of the tappet on the original 1960 magazine article and the diagram on the large plans. On the magazine, the bottom of the tappet, the cam follower is drawn as semicircular (having the same radius as the tappet guide), while on the plans, the same part is rectangular. I suspect that on the article it was semicircular more for aesthetic than practical reasons.

I was looking at the recess on the tappet where the pushrod fits and also the same recess on the rocker arm where the other side of the pushrod fits. They are both 3/32" and 1/8" deep but have a slight taper so that the pushrod does not bind at its maximum angularity.

I was thinking that instead of the taper I use a slightly wider recess like 3mm.

Finally came to the the conclusion that I need to try what happens if I use a slightly wider un-tapered hole (3mm ball nose mill). So decided to experiment on a scrap piece of steel and see what happens.

I drilled a 3mm hole in brass to the specified depth of 1/8" using a ball nose and tried the pushrod to see at what angle it touches the side of the hole. For sure the tappet will not be at this angle and I do not think the rocker will also need this angle. So unless I think of a better way I will use this method instead of the tapered hole.

I started work on the two tappets with a 12mm round section BMS and faced it. I then centre drilled the face and drilled the tappet hole with a 3mm ball nose end mill. I then reduced the 12mm section to 5mm. During the final cuts all the time checking with the tappet guide. Brought it down to a slip fit with 280 and 400 grit sandpaper. I then parted off the piece. Next operation will be on the mill with a dividing head to give the cam follower the rectangular section as per plans.
I then cleaned up the tappets and hand fitted the tappets in the tappet guide.























 

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