Engine valve timing

Last weekend I finally found what problems I have been having.

Initially I did set up the valve timing according to the manual. and yes the engine ran quite nicely. But when it came to test runs and flying, it barely came of the ground. So we started looking into the problem.

I did find that I had my tappet clearance set wrong, I blame the manual for not being clear and myself for never worked on engines before. I got a bit more power, just enough for getting of the ground. But I need a lot more.

So Warren and I and later Wayne, started looking into the valve timing. And after I did a whole lot of measurements, mainly valve position against crank shaft position, with detailed position of the #1 and #2 cylinder valves, and just opening times for all other valves, I found:

  • The exhaust valves open very early, and as a consequence close early, and the same for mixture open and close times.
  • The time #1 exhaust valve is open is a lot longer then all the other ones, and the should be the same, so something is wrong with that one.

So I started changing the cam timing to get valve open and close times that make more sense. Its then when “the coin dropped“. The initial valve timing setting was wrong because the #1 exhaust valve has a timing problem. We expect a bigger cam roller for that one.

When increasing the tappet clearance on the #2 and #5 exhaust, after all had been set to reasonable timings, the exhaust valve closed at the time described in the manual, at TDC (top dead center).

Great, so the manual has been correct all the time. Its just the wrong #1 exhaust valve timing that changed everything.

So currently taking more of on the back of the engine to investigate this silly exhaust valve!!!!!

Symmetrical CAM timing

Today I have been modifying the cam timing, to make them symmetrical.
And guess what it seems to work.
Below is the “vernier adjustment” I think Wayne called it. by taking the 4 bolts out and re positioning it in the next 4 holes, there is a fractional angle change. And because the cam shaft is geared, rotating this ring once around , you have a whole new set of options, but all slightly shifted again.


But the most interesting thing is, when I was talking with Wayne again, and showed him the brass plate at the front of the engine:


he, Wayne said, why don’t you work backwards, now the engine is set up correctly, and set the tappet clearance to 35 thou and check if the exhaust closes when the cylinder gets to TDC.
And indeed that worked for cylinder #2 and #5 !!!!!!
So the instructions have been correct all the time.
So now I need to find out why that didn’t work with cylinder #1. That’s next weeks job.

Full steam ahead

After a bit of a break because my parents have been here on holiday,
FULL STEAM AHEAD again !!   🙂

Because the idea is to change the valve timing a bit and because there is something not right at the length the exhaust valve for the #1 cylinder is open, I have done another set of measurements for the #2 cylinder valves this time.


Below is the valve open timing shown at 6 thou:


And the valve position:



Just checked the time these two valves are open and they are identical. For the mixture valve its 274 deg and for the exhaust valve its 280 deg, so that’s good. The reason I am saying this is that when I did the measurements on the #1 valves, the exhaust valve was open longer then the inlet (mixture) valve. So when I open up the engine sometime soon, that will be one thing I want to have a look at. We ( Warren and I ) expect that the cam-roller for that valve is bigger then the other ones, but will see.
I also did a measurement to see when the 5 pistons reach the TDC position (Top Dead Center)




The reason I did these measurements (see results below) is this:

In a radial engine with one master rod to the #1 piston and 4 connecting rods (con rod) connecting the 4 pistons with the master rod, the #1 piston will make a nice movement, but the other 4 won’t be ideal, and will have a timing that slightly of the theoretical one of 72 deg between each piston.
Now one of the thoughts Warren had was to give each piston its own triggered timing pulse to optimize the ignition, but I don’t think that’s necessary now.

Very low error, so I am not going top worry about the ignition timing !!


While I was doing my measurements, a guy walked in and started asking questions. He wanted lots of figures, angles etc etc. I noticed straight away he knew what he was talking about.
This is Wayne Lindebaum, he has a hangar next to me with the opening the other way, maybe that’s why I never met him…..
Wayne has a business there, and one of the things is engines. Has been doing it “all his life”.


The valve timing instructions in my manual say to set the EVC (Exhaust Valve Close) time to the TDC (Top Dead Center), this is with a tappet clearance of 35 thou.
Now if you look in all the literature you can find on engines, you see that the EVC is past the TDC, and that the IVO (Inlet Valve Open) is before the TDC. Wayne called this the valve rocking point, where exhaust is closing and inlet is opening.

Wayne tells me to change the cam timing so that the exhaust closes later. Make it symmetrical around the TDC.
This means that the EVO (Exhaust Valve Open) will be later, which is what I want, and also the IVC (Inlet Valve Close) will be later, so that more fuel can be drawn into the cylinder.
I compared the TDC of all 5 pistons (see 5 measurements just above) with the IVO and EVC times I have measured earlier.

On average the CAM needs to be moved by 25 deg, to delay the valve movements. This is what I always wanted !!!  🙂
By doing this I should get what you see below. Yes I think it looks good.



Oh yes the other thing Wayne was saying is that the LSA (Lobe Separation Angle) that’s currently about 120 deg and maybe needs to be reduced a bit, possibly to 105 deg, is not changing that much. Moving the cam to make the valves rock around the TDC is going to double the power !!!

My parents

My parents are here at the moment and also one of their best friends, Piet Hubregtse, just for the day. One of his reasons for popping in was, you guest it, looking at the plane and the engine.
He is a mechanical engineer has been working on ships with big, I mean big engines most of his working career. He really liked seeing the Velie and could tell me about all the little details that “proved” to me that he knew what he was talking about 🙂
Also learned a few new things.
First was the rings in the piston, there are 3 rings, the top two look identical and are for sealing, knew that, but the 3rd one apparently is an oil scraper. Now if you look at one of my pictures with the pistons on it you will see that this ring is sort of a double ring. And because its the “lowest” ring I suppose that’s what it does, scrape the oil for the inside of the cylinder wall.
When looking at the fuel tank he also told me about condensation, and I sort of knew but this confirmed it. When not using the plane you need to keep the tank full or empty, but full is better I think. This way with changing temperatures during day and night, no air is sucked up (when its cooling down) getting moisture inside the tank. This will over time create condensation that will go down to the sump. So make sure you empty that before flying.
Apart from that he was just very impressed with the plane and engine. So it was great to have someone here liking what I am doing. I must be doing something right 🙂