Kiwi Mk2 Engine

[rebush]

Vince: I'm not sure if it holds true for model engines, but given that information for a motorcycle I would leave the piston at 1 inch and hone the .003 out of the cylinder. If you dress the piston you're back to refitting the rings. Roger

 

[rebush]

Vince: I believe I misread the information. If you already have the rings sized to the piston then the .003 would come off the piston. I'm used to having a set piston size and making everything else fit them. Sorry for the confusion. Roger

 

[vcutajar]

Hi Roger

Actually I never knew pistons had different ODs. I always thought that they had one uniform OD. This is the first time I am turning a piston so I am religiously following the plans. I had a look at a different site where there was a build log of a different Westbury engine and the same thing was done with the clearances.

I suspect that if I make the piston with one uniform OD nothing untoward will happen. This engine will not run for long periods as it was designed but I do not want to take chances.

Vince

 

[moconnor]

Hello Vince,

The clearance in the ring land area is always greater than the piston to cylinder wall clearance (measured at 90 degrees to the piston pin on the skirt). This is done to keep the ring land area from expanding and scuffing the cylinder wall due the the higher temperature of the piston in this area because of its proximity to the combustion chamber.

Great job on this engine. I have been following along with keen interest.

Regards,
Mike

 

[vcutajar]

Hi Mike

Thanks for chipping in with that info.

As I might have said before, although not new to metal machining (self-taught), this is my first engine build and from a casting. The learning curve is steep but I am coping (with the help of the forum community) as long as I do not try to rush. So what might look obvious to somebody who has a couple of engines under his belt, it might not be obvious to somebody who is still green. Add to that the fact that castings are involved and there is always that fear that you might ruin it if you do not get it right.

So THANK YOU guys for your support and patience with us newbies. :bow: :bow: :bow:

Vince

 

[vcutajar]

This evening I have been mostly experimenting with some setups and cutting ops I need to do on the piston. I will be mostly following Westbury's instructions and some other info I found on another site (http://www.modelenginenews.org/projects/whippet/p6.html) which is also similar but explained better and with pictures.

I started off by measuring off the centre height of the lathe with a height gauge (photo 1). I put the height gauge away with the height locked in as I will need it further down the line.

Next I experimented, using a piece of aluminium bar, cutting the piston ring grooves. I used a parting tool with a 1/16" parting blade which I got earlier just for this job. The groove is a bit tight for my piston rings so I enlarged it slightly by moving the tool sideways. Perfect fit. Photo 2 shows the ring sitting in the groove.

Next I was going to fit the 4 jaw chuck to hold the piston casting in the lathe but I'd thought I would first give it a try with the 3 jaw chuck (photo 3). The OD of the piston runs nearly true but the ID is a bit wobbly. As I need to start with the skirt ID I will need to true it up as much as possible with the 4 jaw chuck.

 

[Charles Lamont]

The plans call for various clearances in the piston OD, namely

Top Land - 0.006"
Ring Belt - 0.004"
Skirt - 0.003"

Interesting. At 1" diameter, and with a thermal expansion coefficient for aluminium alloys of about 23 x 10-6, the 0.003" difference suggests an expected temperature difference between the crown and skirt of about 130oC.

 

[vcutajar]

Hi Charles

You got me there. I do not know what to say. Is this good or bad?

I have checked other Westbury engines using 1" pistons and he always specifies the same clearances. Oh well we'll find out eventually.

Vince

 

[vcutajar]

Started work on the piston casting. Replaced the 3 jaw chuck with the 4 jaw and trued up as much as possible the ID of the skirt. Took some skimming cuts on the ID to clean it up as much as possible (photo 1). Ended up about 0.2mm wider than the plans and still did not clean it up fully.

I then worked on the OD of the piston and left it a little oversize on purpose (photo 2). After that I reduced the length of the skirt to size. Don't ask how. It was too convoluted.

I then eyeballed the bosses horizontal as much as possible (photo 3). Then, using the height gauge I locked yesterday on the centre height of the lathe, I scribed two horizontal lines, one on each side of the piston (photo 4).

That's all for today. I was going to remove the piston from the chuck but had second thoughts and left it there.

 

[vcutajar]

Continued work on the piston.

Marked a line 12.7mm above the skirt (photo 1). This should be the correct place to drill the hole for the wrist pin. Put the piston in the 3 jaw chuck and cleaned up the top of the piston and also the thick OD of the piston (photo 2).

Now I need to increase the distance between the wrist pin bosses. Put the piston and clamped it in the vise and trued it up parallel to the mill table (photo 3). Using a long series 6mm end mill I milled the bosses to get a 9/16" distance between them (photo 4).

 

[vcutajar]

Some more progress on the piston.

Took my faithfull angle plate and scribed a line on it (photo 1). I then clamped the piston to the angle plate (skirt to plate) matching the lines on the piston to the lines on the angle plate (photo 2). Let me just say that it is not as easy as it sounds.

I then located the mark for the hole with a wobbler and centre drilled and drilled 5.5 mm the first hole. I then passed the centre drill through the same hole to mark the boss on the other side. Drilled again 5.5 mm and then reamed both holes 6mm (photo 3).

 

[vcutajar]

And here it is the piston hole finished.

 

[vcutajar]

I have been working on a mandrel to hold the piston with so that I can turn the OD of the piston, the face and the grooves for the ring. I have to remember not to remove it from the chuck before I am finished.

Photo 1 is showing the mandrel and photo 2 the piston on the mandrel.

 

[vcutajar]

Today I finished the piston with the correct clearances. Yesterday I had calculated all the diameters starting from a cylinder bore diameter of 25.43mm and today I did the same calculations to see if they were correct. During machining of the final diameters I got close to the diameter with the cutting tool and then sneaked up on the final diameter with 280 grit sand paper (photo 1). What I noticed during this build is that the material for the aluminium castings is very soft as compared to bar stock aluminium and a smooth finish is very difficult to get.

Photo 2 is showing the piston fitted to the conrod.

Photo 3 is a trial fit of the piston in the cylinder with the cylinder fitted to only half of crankcase to see if the conrod clears the surrounding metal. Also I wanted to see how far up the piston goes in the cylinder. I was a bit disappointed because it should be flush with the cylinder liner lip but instead it was sitting 1.2mm lower. Whilst I was fussing about how to get the piston higher it dawned on me that I had on purpose left the platform of the cylinder about 1mm higher than required to reduce the compression *bang*. Westbury had suggested this for an easier starting and more docile engine.

 

[metalmad]

Hi Vince
You look close now mate ;D
That crank assemble looks great :bow:
Pete

 

[Charles Lamont]

What I noticed during this build is that the material for the aluminium castings is very soft as compared to bar stock aluminium and a smooth finish is very difficult to get.

I am finding I have to be careful with the Seagull castings too. My findings so far are: don't use to much top-rake, go slowly (for aluminium), lubricate consistently. I don't have a coolant pump and found my usual system of neat cutting oil applied by washing-up-liquid-bottle-with-a-spout did not work well. So I tried a coating of RTD liquid. This is sticky enough to stay in place throughout the cut, and I have found it gives a good consistent, though not bright, finish. All the flat surfaces get lapped anyway. Other similar tapping compounds might be worth a try. YMMV.

 

[vcutajar]

Thanks Charles for the tip. Haven't thought of trying tapping compound. If I remember I'll give it a try.

Vince

 

[vcutajar]

Yesterday I made the wrist pin (photo 1). I still need to do two bottons out of soft metal to hold the wrist pin in place but I will make them after I case harden the wrist pin. I need to do some case hardening of some parts I already made but have been putting it off for some time now. I have never done this procedure so not sure how it will end up. I was thinking of getting this compound from Chronos (http://www.chronos.ltd.uk/acatalog/Engineering_Menu_Adhesives_439.html#aCHD3_2e_2e_2e). Has anybody used it?

Also yesterday I made an impromptu ring compressor out of steel tape used for packing and a jubilee clip (photo 2 & 3). Haven't tried it yet so do not know if it will actually work. I will find out when the time comes.

Today I machined the bottom rectangular base of the cylinder. I did not mill it to dimension but decided to do it to the shape of the crankcase cylinder platform so that the sides of the base would be flush to the crankcase. Photo 4 is showing the setup I used. That template I had made was used again. Good thing I made it.

 

[idahoan]

Hi Vince

I have case hardened quite a few small parts using Kasenit powder and have had great results with it. I usually hang the part from a piece of soft mechanics wire (bailing wire, Re-bar tie wire) or what ever you want to call it. Heat the part with a propane torch until it is a nice orange color then dredge it through the powder; then back into the flame and keep it at temp a little longer. Maybe 30 sec. to a minute then quench it in water; watch out for the splatter (I wear a full face shield).

When you quench your part all the gooey powder will solidify and come off in the water. A light buff with a wire wheel and oil is all that is needed to finish it up. If you do it correctly you should have a glass hard surface with a nice patina.

I would be willing to give the product in the link and try; hopefully it will perform as well as Kasenit.

Your little engine is looking great by the way.

Dave

 

[vcutajar]

Thanks Dave for the advice.

As it is just a Kasenit replacement and not the original Kasenit, I was wondering if it did the job properly. A quick search on the internet and I did not find any reviews on it.

Vince