After talking with Wayne last week, we decided that something was wrong with cylinder #4. We thought that a ring was probably broken but…
This is what I found. No broken ring ! 😊 But there was something else Wayne noticed. Above you see the new piston left and old one right.
The oil ring normally is a split ring with holes behind it. This is good for normal engines with the cylinders pointing up (normal in cars). But with engines with opposing cylinders and radial engines you need more oil “catching” as there is more oil splashing around. With my old piston (right) this is done with a big grove under the oil ring, and lots of holes. When the engine is running, the oil on the cylinder wall gets scraped off and “drips” back into the piston and then gets thrown back inside the engine.
With my new piston’s that extra oil catching mechanism is not there.
This means that
There is oil getting into the combustion chamber, and that’s not helping the combustion.
The film of oil prevents the rings from bedding in, as there isn’t good contact. This means the rings won’t seal as well as they could.
Plus I also might have gabs in my rings that are possibly a little too wide.
So I am going to make a little modification to my two bottom cylinders, #3 and #4.
And re-check the ring gabs 🙂
I keep on changing the reason why we think the engine is not performing anymore. This is after I put the new pistons in a couple of months ago…..
Today Rutger (my son) and I went back to the hangar after we dropped of the Bleriot on its trailer from the Omaka CF2017 trip just over a week ago.
We assembled the plane again. I took the opportunity to put some new foam in the gab between the root of the wing and the fuselage, and this time I used a electric bread knife to cut of the excess material. That looks 100% better then what I did last time (this was quite a few months ago) .
One thing I noticed immediately when I was pulling the Bleriot of the trailer is that it was dripping a lot of oil from one of the exhaust outlet’s. Something I have never seen before. I didn’t understand and stopped thinking about it as I was busy putting the plane together.
UNTIL, I was finished and was about to leave, when Wayne arrived at his hangar. He said he had been thinking about my engine, as you do when things aren’t right 🙂
He recons one of my piston rings is broken.
That’s when it clicked inside my head:
My previous thought about having problems with my exhaust didn’t make sense for one reason: “How is it possible that the engine was deteriorating over the days during the show”.
The oil was dripping from the exhaust right next to the cylinder #4 that had the really dirty spark plugs (note that cylinder #4 is at the bottom of the engine, so after stopping, it fills up with oil dripping down inside the engine)
Wayne did notice a few weeks back, that one cylinder did have less compression then the other ones. Probably this one.
I might not have been able to see the oil dripping out as this will only happen if the exhaust valve is open, and that depends on the prop position Not sure if it is but will check that next time.
So yes, I have one spare set of rings, so the next time I am going to the airport, I will start taking of that one cylinder, and hope that it has a broken piston ring. Hopefully it hasn’t damaged the inside of the cylinder. Wayne recons it should be OK, I mean, no damage…. Hope he is right.
I wonder if that ring, if it is broken, did break while running or maybe it got damaged at the time I put it in. Who knows.
Today the Bleriot didn’t come of the ground, but still thinking that the exhaust collector ring has a lot to do with that. Will hopefully find out soon !! 🙂
Taxing back with a bit of help, pushing and pulling the wing to steer into the right direction.
But the good thing is that my theory about the exhaust ring might well be correct. Today I found that all spark plugs are very clean, except the plugs for cylinder 4: see my previus post on the exhaust ring
Next to me in the big BP hangar, is a really nice little by-plane made by Louis McNair, his dad Robert and grand-dad Wallace:
What I want to talk about is what Wallace had to say !! 🙂
He has lot of knowledge of engines, so started talking about the optimum valve timing etc. Straight away we were checking mine 🙂
Exhaust closing about 20 or 30 deg past TDC, and mixture opening about 5 to 10 deg before TDC. Yes he was happy with that.
Talked about a few more things, and then the discussion switched to the exhaust collector ring.
What I have is basically a collector, picking up all the exhaust and spitting it out down below. All nice, BUT
The big problem engine people have is that when the piston get’s to TDC position (Top Dead Centre), the exhaust valve is still closing and the mixture is already opening (see above)
When a piston is in this position, and another cylinder is just pushing all the exhaust gas out, into the exhaust collector, you have the situation where “foreign” exhaust gas is entering another cylinder that is just about to start sucking up a fresh amount of mixture (Air and Fuel).
This action basically stops the mixture from entering its cylinder for a while, and even worse, this exhaust gas will stop it from burning properly I think….
So basically you need to make sure that each cylinder has a long enough exhaust pipe, to contain 2 exhaust cycles I think (calculated using volume, and speed, and …..) before they can be combined into one big exhaust pipe.
This of cause is very impractical, so on old engines you often see stubs on each cylinder. No common collector, just a short bit of pipe, and off it goes into the air.
Now to prove that my engine has the same problem, I made this Excel spreadsheet showing the exhaust and air intakes of all 5 cylinders. And yes theoretically I have this same problem. Not to bad for some of the cylinders because sometimes the distance from the exhausting cylinder to the cylinder getting mixture and the distance to the collector outlet make it unlikely that exhaust gas will go the wrong way. but there are definitely situations where it will go wrong:
You can see that at the TDC of every piston movement/ position, were the mixture valve is opening and the exhaust is still closing, another exhaust valve has already opened (exhaust valve is open before, during and a bit after the rising curve and the mixture is open just before, during and a bit after the falling curve).
And because that exhaust valve is opening early, the exhaust gas is already flowing out of that valve and into the collector ring.
So for every cylinder where a mixture valve is opening, another cylinder is already exhausting gas.
Not every combination will cause a problem as the opening exhaust valve could be on the other side of the collector ring somewhere.
Below is a list of cylinders with opening mixture vales and exhaust valves blowing exhaust gas into them:
Cylinder with exhaust valve blowing exhaust gas into:
Cylinder where the mixture valve is opening.
No problem as exhaust 3 is close to the exit of the ring
Possibly no problem as exhaust 5 is closer to the exit then exhaust 3
Possibly no problem as exhaust 2 is closer to the exit then exhaust 5
No problem as exhaust 4 is close to the exit of the ring
Could be a problem as half if the exhaust gas goes past exhaust 4
So maybe not such a problem having an exhaust ring but worth to try without the whole ring collector.
Just a comment on the Velie that was on the Bleriot picture I send to Jack in the US, that one had stubs !!!! See below 🙂
You can clearly see one stub on the left, in the shade two on the top right side by side for the top cylinder and the one to the right. And then there will be two at the bottom, but I can’t see them !! 🙂
I always thought that was, because it was cheaper and easier that way, but maybe there was more to it !!
Today I mounted the valve rocker covers, forgot yesterday…
Had help from Nigel Sheppard today. He also helped me last time (2 years ago) machining a bit of Alu for my stick.
This time we were talking about the air inlet of my SU carburetor. Currently there is nothing mounted to it.
So air basically goes from the big wide world, past these sharp edges into the carburetor. This creates lots of turbulence, and doesn’t help good carburation (mixing fuel and air).
So he was going to make a trumpet, or a bell curved piece of steel. Wasn’t going to be easy. He remembered that Wayne (I think his name was) from the Car Museum, next to the Aviation Heritage Centre used the same carburetor in his Jaguars, and might have something I could use.
So of I went to see him, and there he was talking with two other guys, we recognized me, and said, Oooo there’s the Bleriot man !! 🙂
Anyway, yes he had one I could have !!!!!!!!! Great 🙂
So went back to Nigel, who welded a mounting plate to it !!
Its on the carburetor now, looks great.
Might build a air box around it, with an air inlet facing forward later, to improve it even more.
At least this will improve the air flow a little. All little bits help !!!!
Today, Rutger and I spend about 4 hrs getting the Bleriot ready for the show. All went well !
Luckily we have this massive hangar to do it in. Very wet outside !!! But It looks like the weather is going to be on our side by the time the show starts !!! 🙂
Also, I am getting the feeling that I might have to start looking for a different propeller to get more performance, but will see later. Hopefully we find another thing we can tweak a bit, to squeeze a bit more power out of the Velie 🙂
So yes today I have been talking with a lot of people about my propeller. And the consensus is that I might need a bigger pitch, basically grabbing more air, as the engine itself is powerful enough to pull that through the air.
Would love to just try a prop, any prop, that fits my hub, and see what the difference is. But that hub is the big problem. This hub, mounted on the crank shaft, holding the prop is an old American style one. I would be lucky if I find one.
The bolt pattern is 4 5/8″ (117.475mm) diameter, 6 bolts. That gives you 2 5/16″ (58.7375mm) spacing between bolts!
Just in case someone is reading this: If you have one, let me know. Oh and yes it is a clockwise (from the cockpit) rotating prop !
I did get the name of a guy here in NZ who has been making lots of old style props for famous people, with tons of knowledge, so might start talking with him. He is Jeff Fox, lives on the North Island, around Auckland I think….