My new piston design

Going to meet a guy in town here at Proturn Engineering. He used to machine “blanks pistons”, but these days the “blank piston” company, Ross Pistons, is doing all the machining themselves, so Richard is doing the designs these days and sends them of to the States.

But before I was going to see him I thought, make my own design, and we will see what he things of it, but I would say its pretty close.

So what I have done, I made two spacers, 5.7mm thick and rolled a piece of Plasticine. Then I used the bottom of the cylinder that has the steel sleeve sticking out to cut my “Plasticine disk”


I put the disk on top of the piston, and marked the Piston pin orientation on it (solid line).

Then measured the distance from outside exhaust valve to outside mixture valve (left to right side). Cut that off, and made a 30 deg ramp going inward. That’s the angle the valves are positioned. This makes sure the valves keep the same clearance as what they have now!

Finally I marked the spark plugs position (dotted line) 30 deg from center line for piston pin. Looks like 30 deg was a handy angle when they were designing the cylinder about 90 years ago !!!  🙂 The spark plug doesn’t really protrude into the combustion chamber, but this way there is some room for the combustion to start. The shape might change a bit possibly.

So this is what I ended up with (see below)

Now all the off cuts, I made a nice round boll of and decided to calculate the volume. And instead of sticking that somewhere, I calculated if I make the “disk” 0.2 mm higher, then the volume decrease of the combustion chamber is what I need to get  a compression ratio of 1 – 7.

Looks nice and clean doesn’t it !!  Will be interesting what Richard will say about it.



Measuring combustion chamber for piston modification

Wayne told me to go and get Plasticine   🙂


Cutting it up, like cheese, and sliding it into the cylinder through the spark plug hole, smallest hole, see photo right).

I did cut up just a bit more than what would fit in the combustion chamber.



I fitted the spark plugs , and started compressing the cut up Plasticine, by pulling the propeller around. When it was almost at the TDC position, I couldn’t get any further, so that was good. I took one spark plug out and pulled the prop until the piston reached TDC.

This is the only bit of Plasticine that came out. Pretty good estimation !!  🙂



And on the right you can see what came out of the cylinder. Perfect !!!!

Now what ????

In this post , I calculated how much the combustion chamber needs to reduce in size. From 11.39 “cube to 8.35 “cube so that’s 3.04″cube.

With a cylinder bore = 4 1/8 ” that means the piston needs to go up by 3.04 / (Pi * (2 1/16)**2) = 0.22″ = 5.7mm.

I spoke with an engine guy today who is dealing with the same company in the States, Wayne told me about for making my new pistons. The only valuable information I got out of him was that need to make sure the valves and the spark plugs aren’t going to be interfering with this extra height (pretty obvious), so possibly need to create some voids for that, to keep the same clearance !!!


Don’t know how I am going to do that yet…..  But I will find something I suppose, just have to. And then pass on that information to a company who makes the pistons !!!

Next day, this is Sunday morning when I woke up, I realized how easy it was going to be. This what I will be doing:

With the same Plasticine, I will make a 5.7mm disk. The amount that the combustion chamber needs to reduce by.

Then I cut (on an angle) two bits exactly where the valves are, starting at 0 mm thickness on the outside edge, sloping up at the same angle how the valves are positioned.

Do something similar for the two spark plugs.

Then all material I have cut of, will have to be placed somewhere where its not interfering with valves or spark plugs, and all in a way so its nicely flowing. So when its finished it might look like this:


Lesson 29, First lesson in Kitfox KNZ

Had my first real lesson with Dave in the Kitfox : ZK-KNZ

This is a tail wheel plane a good step forward in my training program towards flying the Bleriot

I did quite a bit of ground handling  with a lot of steering using the brakes, and then after that flying…. Dave called it general handling. A bit of everything.

This plane is a hand full 🙂 Continuously controlling rudder and ailerons. When the plane is out of balance you can hear it, so yes all the time you need to keep the ball in the centre.

Dave says, if you can fly the Kitfox, you can fly any plane so that’s good !!

I had 1.4hrs on the clock today. First half was all about getting used to the plane, but after that it was getting better and better !! So yes feeling good abou this 🙂

Another run over the runway

Today was another day to see if anything has changed with the engine. The static run shows the same 1800 rpm, but in the air it looked like it was running faster then previously, just over 2000, Evan said afterwards.

We had a little incident, the stick (at the back of the Bleriot) snapped off after the landing. A little thing to repair, not hard !

But the good thing is that Evan want’s to do some more flying once the tail stick is fixed. Measuring how fast its climbing and maybe other measurements, so that’s promising !! But I still think I want to increase the compression a bit by putting new pistons in, increasing the power output…

Exhaust analyzer

Started to make adjustments to the SU needle last week, but its hard to see what’s happening, so I borrowed Wayne’s exhaust analyzer to check the mixture.

I Noticed that at lower rev’s it was running very rich and at high speed it was still lean I think. It’s a bit hard to say as the readings are very erratic, but I think that’s what it was.

So I adjusted the low speed mixture with a screw on the carb, and adjusted the needle a bit more to give me more fuel at higher speeds.

After installing the needle back in the SU carb, I was thinking “I don’t really know how far the piston goes up at full throttle, I need to find out somehow“.  This is so I know where to make the needle thinner, to get more fuel.

And that’s when Brian, showed up, he’s in our club. He loves photography, so with his massive tele-lens he made some great photos. Thanks Brian!!

SU piston 60{7d16e8204fe0e6723feb9d00795e42e38ac880e6f88f519e81a8ab927d02eaa1} up

As you can see the piston is up, about 60{7d16e8204fe0e6723feb9d00795e42e38ac880e6f88f519e81a8ab927d02eaa1} or so. This is at full speed !  🙂

Now if you do the calculations, the carb has an 2″ opening, the engine has an 1.5″ opening, that means that the carb needs to open 56{7d16e8204fe0e6723feb9d00795e42e38ac880e6f88f519e81a8ab927d02eaa1} to get all the mixture into the engine, so that’s looking good.

Just not sure yet if that’s a good thing or bad. Doesn’t matter I suppose for the fuel / air mixture ratio.

I think its still running a bit rich at low speed now and about 14{7d16e8204fe0e6723feb9d00795e42e38ac880e6f88f519e81a8ab927d02eaa1} at high speed which is what is required, so maybe that’s it.


Here is me looking at the rev counter and the exhaust analyzer:

Checking exhaust analyzer

So at the moment, the engine is running really nice, and people say it runs a lot nicer, so that must be good, just not sure if I have more power….

Starting to set the mixture ratio on the SU

After work I went to the airport to run the engine and try to set the mixture.
The engine started so easy !!! Great 🙂

After a idling for a five minutes, I started playing with the little pin that pushes up the piston for setting the idle speed mixture. If the engine slows down, the mixture is to lean, so you need to make it richer, with a little screw. If it speeds up it is to rich, so you need to lean it off.

In my case it was running to lean, so I started making it richer and richer, until I couldn’t go any further. Even at the highest setting it was still running to lean. So that’s the first finding……

Then at higher revs, while in the cockpit, you can make the mixture richer with the second control. For all speeds but hardly noticeable for the max speed, the engine was going faster when making the mixture richer……

So my conclusion is that I need a different “needle” that releases more fuel for all speeds. Going to see the guy tomorrow, and get one 🙂

Velie running very smooth with new SU carburetor

Spend most of the day today installing my “new” carburetor An “SU” for people that know about them 🙂

Two weeks ago Wayne with my help welded the pipe between the engine and the carburetor, and last weekend we modified it a bit to make it fit just perfect.

So today I bolted it to the bottom of the engine, connected the two controls, one for the throttle and one for the mixture control. This last one is only used for starting, to make the mixture richer.

After 4 hour, I rolled the Bleriot outside, pinned it down put the chocks in front of the mail landing gear and primed it. Maybe my first start is always failing because it scares me a little, but every other start, and I did half a dozen were all perfect. Almost like it starts even easier now.

Within no time I had people gathering around me, basically because it sounds so nice. They were all wondering were that nice sound came from 🙂  🙂

Turns out that with the new carb, the mixture is a lot better and more even and all cylinders fire, just nicely, where as in the past you could almost hear some miss fire….

Still working on the fine tuning of the mixture, to get that right, and hopefully that will give me the result we have been hoping for, more power. At least now I feel the carburetor is more reliable as its so simple, so that is a great step forward !!  🙂

Below a few seconds of one of the starts, still running at idle speed. VERY NICE.  Yes an old fashioned black and white video 🙂