Kiwi Mk2 Engine

[ProdEng]

That carb is a bit of a beast Vince, an awkward shape and lots of odd angles. I have a copy of the drawing in front of me else I wouldn't know what it was! Are you going to make the float chamber to go with it?

 

[vcutajar]

Jan

I am not sure about the float chamber yet. I would love to do it also but the aluminium casting is not really promising. I have measured it up a little and if I use the casting it would end up with a smaller diameter. Otherwise I will do it from barstock. Haven't decided yet.

Vince

 

[vcutajar]

Managed to do some more work on the carb. What was previously used as a mandrel was parted off and finished as the throttle body (photo 1). A shallow slot was milled to accomodate the handle (photo 2). This is not in the plans but I thought I would do it to give more support to the handle.

Next a thin (2mm) disk was parted off from the same material as the throttle body (photo 3). This was further machined to make the handle (photo 4). Photo 5 is a setup photo showing the handle and the throttle body. The handle is not fixed yet.

 

[vcutajar]

Using the casting chucking stub, the body of the carb was chucked up trying to keep the centre of the bore in the middle as much as possible. First both sides of the carb mounting flange were faced off (photo 1).

Next the drilling operation of the carb bore had to be done but before that a big decision had to be taken. Westbury states that if should be a maximum of 0.25" (6.35mm) diameter but then he says that for moderate speed and maximum flexibility in control, the bore can be reduced to 3/16" (4.76mm).

So I decided to do the bore 5mm. With the throttle body fixed in place, drilled and reamed for 5mm (photo 2) but did not go all the way to the chucking stub. I did not want to decrease the strenght of the stub for the next machining operation. Using the previously made taper d-bit the venturi of the carb was machined (photo 3). As you can see in the photo a piece of the d-bit chipped off. I guess it was too hard. Also a sizeable burr was produced on the casting. This was cleaned up and then the rest of the 5mm bore was drilled and reamed.

The last photo is the progress so far. I have left the carb in the chuck just in case I decide to open the bore up to 5.5 or 6mm. What do you people think? Should I increase the size of the bore?

 

[Charles Lamont]

I nearly asked about the reamer when you said 'hardened only'. Mild tempering will greatly increase the toughness of carbon steel tools without significantly reducing the hardness. I often heat until I can just detect a colour change, which puts the temper somewhere in the region of 220 C.

 

[Mainer]

Looking good, Vince! You may yet inspire me to get off my duff and get my Kiwi finished!

 

[ProdEng]

Vince, I would be inclined to leave the bore at 5mm. Easy starting and good slow running are a good trade for top end performane. If you are unhappy later, you can always open the bore up but putting metal back on is a bit more of a problem

 

[vcutajar]

Hi Steve. Long time no see. Would love to see your water cooled Kiwi when you finish it.

Charles, you are absolutely right. Thm: Lesson learnt - do not skip steps. I assumed that as the casting material was relatively soft I could get away with it. Problem is I forgot that I had changed the throttle body material from brass to phosphor bronze. :redface2: That is where the tool started to chip.

Jan I tend to agree with you.

 

[vcutajar]

Today the decision was taken to leave the carb bore at 5mm. The carb has been sitting in the chuck for the last couple of days in case I decided to open up the bore.

A mandrel was fashioned to the taper and bore of the chuck (photo 1). The carb was fiited on the mandrel and lightly tapped in with a plastic hammer (photo 2). I hope I can remove it later on.

Using a live centre the inlet O.D. was machined (photo 3). Then changing to a half dead centre the face of the inlet was machined (photo 4).

 

[vcutajar]

Now to give the carb inlet the bell mouth shape. Using a centre drill the inlet was openned up (photo 1). Next a countersink bit was used and this was used to half the depth of the previous operation (photo 2).

Then using a half round needle file the bell mouth shape was formed to a 12.5mm radius. Using sand paper and polishing it the final result is displayed in photo 3.

 

[idahoan]

HI Vince

That fussy little carby is coming along nicely; I'm enjoying watching how you are approaching the different setups and machining operations.

Dave

 

[vcutajar]

Thanks Dave

I am taking it real nice and slow as, as you said, it is a fussy little carby.

Vince

 

[vcutajar]

Drilled the two mounting holes on the carb flange using the flange brass template I had used on the cylinder head. The mounting flange was cleaned up and filed down to size. While I was at it I decided to clean up the whole of the carb body which I have been doing for the last two days.

 

[vcutajar]

I haven't done anything this week on the carb except soft soldering the handle to the throttle body. There were too many things diverting my attention from the Kiwi.

This weekend I found some time to play in the garage.

Before continuing work on the carb body I need to do the banjo connector and the fuel jet housing. These will determine how much more milling I need to do on the carb body.

Did the banjo connector first but was not in the mood of making it from one piece so I fabricated it from two pieces of brass. First I did the circular part which was simple work on the lathe (photo 1). Then I did the straight part on the lathe but drilled the through hole 0.5mm undersize (2mm).

Put the circular part in the vice and plunge drilled with a 5mm slot drill. I did not go all the way through the banjo. Applied some solder cream at the bottom on the plunged hole. Pressed in the other part of the banjo (photo 2) and applied heat to the part. I then started threading 6 x 0.75mm (photo 3). Unfortunately early in the threading process the part gave way. On inspection it was found that not enough heat was appled to melt and flow all the solder cream. I guess the vice jaws were sinking away all the heat. Some more cream applied and more heat applied. This time the joint was good because it survived the whole threading process. I then drilled the hole for the banjo 2.5mm which cleaned up the solder that might have gotten in the hole.

Photo 4 is the finished banjo connector. Now I need to source or make a brass locknut.

 

[vcutajar]

It's been 5 days since I did something on the Kiwi and I was getting withdrawal symptoms especially since tomorrow I will be going abroad for work. Some domestic appliances needed some TLC and as such did not have spare time to go to the garage.

Today I slipped into the garage for an hour to do a brass 6mm fine locknut. I actually made two of them. If I decide to make the float chamber I will need the other one.

 

[vcutajar]

Wow. It's been three weeks since I did something on the Kiwi mostly due to the fact that I have been abroad twice for work. It's good to be back and do some work on the engine.

Started work on the fuel jet body for the carb. Machined the front part of the jet on the lathe (photo 1) and then drilled the jet hole 0.7mm (photo 2).

 

[vcutajar]

Did some more work on the front part of the jet. I am noticing that the plans have some missing dimensions for the jet so I am guessimating some things.

First off I needed to make a 1/16" groove where the banjo will sit. So I used a 2.5mm drill which had the backside ground to a point to use as a tranfer punch, put the banjo in the jet housing, and with this transfer punch scratched the housing where the groove should be (photo 1).

I then cut the groove (photo 2) but the plans do not specify how deep the groove should be, so I made it to a depth of 0.75mm.

Then I drilled some 1.5mm holes in the groove. The plans do not specify how many so I drilled 4.

 

[vcutajar]

Some more work on the jet. Started working on the back part of the jet. Used a collet holder instead of the 3 jaw chuck. Machined and threaded the back part 6mm fine (photo 1). Then drilled, counterbored, countersunk and tapped 3mm the inside of the jet making sure the thread reaches the banjo groove.

The remaining photos show the finished fuel jet.

 

[vcutajar]

Did the gland nut for the back of the jet and then spent the rest of the time figuring out how to drill and tap the carb body for the jet. I think I worked it out but instead of drilling it at 45 deg I might do it at 40 deg.

 

[vcutajar]

Managed to drill and tap the carb body for the jet assaembly. Photo 1 is showning the setup I used to hold the carb. Photo 2 is setting it up at 40 deg angle. Inserted a 5mm rod in the carb air inlet and used this rod to measure the angle. Then drilled and tapped and milled the platform where the banjo will sit. This operation was done repeatedly in small increments until the tip of the jet just appeared in the carb air passage. Photo 3 showing the jet assembly screwed into the carb body.

Left the carb in the vise so that next time I will mill out the small defect in the casting that is evident in photo 3.