Today we had another fast taxi and managed to get of the ground for the first time  WOOOHOOOOOOO !!!!   🙂

But and there is one big thing, stopping us from flying higher at the moment.

There is still not enough power !!!

Every time its a little thing here and a little thing there to improve on, so what’s next.

One of the things Warren and I quickly tried, was making a plenum chamber hanging underneath the carburetor. There is a lot of pulsating air going past the carburetor. We were thinking that that could influence its performance.
Warren had seen it in the past.
But no, that’s not it.
This plenum chamber smooths and equalizes the air going into the carburetor.
Below you see the tin with holes hanging under the carb 🙂



When I set the tappet clearance to the right settings last time, where the exhaust valve closing time is used as a reference, I noticed that the exhaust is opening very early.
I know that the exhaust opens before the piston get to the BDC  (Bottom Dead Center) but this one starts opening before the piston is even half way down.

So Warren and I decided to “dive” into this and see what can be done about it. Next weekend I am going to plot the valve position of both valves against the crankshaft position.

To give you another look at the internals of the engine, here are two important pictures…….


Left: 3 cam lobe’s, and the interesting thing is that all 3 are used to open both exhaust and inlet valves.

Right: the 10 valve lifters for the 5 inlet and 5 exhaust valves


Now if you look careful, well its not to hard to see, there is a different spacing between the valve lifters. The pair for each cylinder have a bigger spacing. The bottom 2 that you see here are for cylinder #1. The angle between them is about 40.3 deg I think, just measuring from the screen. I measured all 5 and then averaged it.

Now as you can see in the photo with the 3 cam lubes, the cam “shaft” is geared down. It needs to make 1 revolution for every 6 crank shaft revolutions, that way every 2 revolutions of the crank shaft, one lube goes past the inlet and exhaust valve once.
Now I think this is how this works….. If the cam shaft would go at normal speed, and there was only one lube on it, the 40.3 deg I measured is the real LSA (Lobe Separation Angle).   But in this case here, the lube is moving 3 times slower, so the 40.3 deg is not 40.3, but really 40.3 * 6 = 241.8 deg.
According to Warren that is on the high side, and less deg would easily improve the performance.

_1396161734Now to make the angle smaller may look a hard to achieve, but Warren had this idea. All we need to do is move the rollers a few mm towards each other. We can make 10 new steel pins see photo to the right and drill the roller pin a few mm off center.

Another way to change the timing is to use the original steel pin with roller, and make a new brass guide, with the hole off center or even on an angle.
This last option is something I have seen done on other Velie engines today, So that looks very promising, and also something others have done/tried.


OK this is all talk for now. First I am going to map the valve movement against the crank shaft angle and talk with a CAM specialist here in town, see what he says about decreasing the LSA, or just the whole job of increasing the power output  🙂

Yes we are flying


Yes we are flying !!!   🙂


Not high though, still more work to be done on the engine and maybe the propeller….

The engine is now running at about 1700rpm, but that’s not enough.

After the 3 short flights today here in Rangiora (NZRT), Warren and I started measuring the valve timing, and came to the conclusion that there is something wrong….

The exhaust starts opening tooooo early in the power cycle, when the piston is not even halfway down. So maybe there is a way to change that and not loose all that power.

So coming weekend I am going to measure and draw a nice graph with the valve timing and see what is wrong.

Correct tappet clearance

Last Sunday I changed the clearance on all valve tappets to .015″ as they were set wrong, ooops !!!


Today I tried running the engine but died after 1/2 second every time.

Came back today did another check on fuel level in carb, check a little nut on priming valve and tried starting again.

THIS TIME it started perfect as it has the last we while. Turns out that the mixture control push cable was screwed into the carb at a different position, so the mixture had to be pushed further forward. I fixed that now.

When running at full power, I get now more then 1700 rpm, so that sounds promising.
Pat from Rangiora Aircraft Engineering was there as well and checked the speed with his optical tacho, and his was indicating the same as mine so good as well !
He thought the engine sounded really nice

Also checked the mixture at different speeds and apart from full throttle, all other throttle settings, the mixture lever is in the same position for the correct mixture setting, as it should be.
At full throttle where the mixture is slightly rich, I suppose the mixture lever needs to stay where it is, but I do still notice that when the mixture is leaned off, it goes faster again.

So all looking good, and waiting for calmer weather and my test pilot.

Compression test

Today we did a compression test to see if there is something wrong, as we still don’t get enough power, see last high speed taxi on 29 Dec 2015.

So we found that all 5 cylinders were good really, the differential pressure was better then 70 / 80 psi.

But after talking about the problems and “going backwards and forward” as we didn’t understand the low power, we started looking at the valve tappet clearance, as that’s quite big, and I did set that at .035″ as stated in the manual, but !!!!

I didn’t see the last sentence in that chapter that said, to set the clearance of all valves at .015″
Turns out the .035″ was just an intermediate value, and they all need to be a lot smaller; .015″

So I am quietly positive that this will give us a lot more power.
Currently the exhaust valve closes to fast, so not all exhaust gasses have been driven out,
and the mixture inlet opens to late so it doesn’t get enough air/fuel mixture. Surely this will result in less power.

So in the next few days hopefully good news !!!!   🙂