Saturday, November 25, 2017

4th Annual Inspection

The RV has 227.0 hours on it and a few things started to indicate that some work had to be done. The engine had started to run a bit rougher than I remembered it from the first year. The vibrations were noticeable at all RPMs and even at idle.
The carburetors are supposed to get overhauled at 200 hours which felt overdone to me but I decided to do it as I could not explain the roughness other than by being carb-induced (the balance was fine last year).
Also, my oil temperature indication was going haywire since a few hours ago. In the middle of a cross country the indicator would erratically drop below 120degF which would make B*tching Betty call out "Engine Speed!" 3 times in a row for every drop below 120degF. As it would frequently go back to a more believable reading and then drop again one can imagine how annoying and distracting this can be. Thank Van's for the "Isolate" switch on the intercom which shuts off dear Betty and lets you focus on flying the aircraft.
I also wanted to use the occasion to finally stop the oil drain bolt from leaking by installing a quick drain valve using Loctite 243 to seal it.

And so another Annual begins!

The spark plugs (these were the Iridium version of the NGK plugs) had reached a hundred hours and they definitely didn't feel that great anymore during the ignition check, so I decided to replace them. As I still have a stack of standard NGKs I decided to put the regular type in to reduce my inventory.
The plugs that came out showed the usual rich pattern with the exception of the top aft plugs on both sides that showed a healthy light brown color. It escapes me how this could be possible but that's what I found.

I ordered more of the Iridium plugs as they really make a difference in the Rotax when they are new but I'll first use up the old stock that I have accumulated. 

The visual inspection of the engine looked good. A very slow leak on the bottom of the oil canister as I have grown used to but creating enough of an annoyance to make it onto the to-fix list. 

The temperatures all looked within tolerances with the voltage regulator still being a bit on the high side. Something I am planning to address next time around by adding a fiberglass laminated scoop in the tunnel to increase the air flow for cooling. 

VR abit higher than I'd like

No indication on either ignition module

The oil change didn't reveal anything abnormal. And after 4 years of flying I also removed the magnetic plug for the first time only to find a very small amount of shavings on it. Just as you'd expect from a Rotax.
I installed the oil quick drain valve with Loctite 243 as planned and safety wired it to ensure it could not open in flight.

So far no leaks, so I hope the inside of the cowling will stay clean from now on. 

Off came the carbs for he first time/. The air filters looked really good by the way. No cracks, no chafing, no dirt. I think these green ones will be staying with this engine. 

A little bit of build up on the intake side

I had not taken these off in the first years as nothing had pointed at any type of issue and I am a strong believer in leaving a system alone if it isn't broken but I was very curious what I would find inside this time.

Opening the bowl revealed that on theleft side I had a small piece of debris in the carb and I have no idea how it could have gotten through the system that far.

Nothing else was found that didn't belong there. The floats were removed and put on a scale and - WOW - what surprise! As I said, nothing had indicated an issue but when I put the floats on the scale it showed that one had drowned.

Drowned float

still good

I assume the carb never showed a problem because one floating float is enough to keep the bowl from overflowing. I never had an issue with fuel smell or fuel residue in drip pans below the carbs.

old parts coming out

Needle shows signs of wear

Viton valve and arm were replaced for good measure although the valve did not show signs of wear yet. The needle though did and so I replaced needle and jet hoping that this was the reason for my rough running engine.

The interior was cleaned, seals lubricated and put back together.

The way I did the overhaul was one side ata time so I would have an untouched carb to look at if I was in doubt how something would go back together. So the next day I installed the overhauled one and took off the remaining carb of the engine and did it again.
The right side carb also had one slightly sunk float!

Too heavy

Still within tolerance

No other findings on the right side carb, and doing the overhaul for the second time was a lot faster than the first time around. 

The engine test run revelaed that the roughness was gone. The engine was running very smooth, almost purring, with no indication of imbalance. The only thing that did change was the idle setting. You have to know that the way I removed the carbs from the engine was by removing all throttle and choke linkages from the carb so the balance settings would not get affected. So I was quite surprised to see the engine idling at 2200 RPM now, given that the throttle cable was in the very same position. Apparently the engine was running leaner now at idle which increased the RPMs. 
I opened the idle cable stops and readjusted the setting after the engine had heated up and set the idle to 1400 RPM which feels like the engine is just about to quit on its own. On final with forward movement the prop will turn easier and the engine will be ok with that low idle but it will allow me to slow down as much as possible.

The Skyview battery test next and it passed ok but it looked like it was just at the edge of failing. So I'll be prepared next year to swap it out with Dynon again. Probably do the test early on so I don't have to wait for shipping when I'm done with the mechanical part of the annual inspection.

Pretty low voltage close to end

The oil temp sensor was an interesting chapter. I tried to find a replacement from VDO to have one on hand in case it turns out that the temperature fluctuations I saw were caused by the sensor itself and not just by a bad connection. Don't get me wrong, the behavior strongly suggested a connection issue but I want to be ready in the case it did turn out to be the sensor anyway.
As I have documented on the forum, the cost of a Rotax temperature sensor for oil or CHT (p/n 965-531) is somewhere between $195 to $275 (as of 2017) which is completely ridiculous. VDO builds these for them and they usually run around $18-$25 when bought in an auto parts store. So to protect their business Rotax decided to use a thread on the sensor that was not commonly sold by VDO and so finding the correct type was a bit of a hassle. What you would be looking for from VDO is not one of their regular part numbers but a more complex internal ID system:: 323-801-010-001D, a.k.a. 801/10/1,  which should translate to 300 degF (150degC) NTC with a M10 x 1.5 threading and a flathead connector that allows a female spade connector to slide over it.  The regular VDO sensor in M10 (VDO #323-423) comes with a 1.0 pitch thread and will not fit on the Rotax.

Now back to my case of fluctuation. I removed the spade connector and found a very slight movement when tucking on the wire. So I decided to solder the wire in the crimp and add silicone on the connection between wire sleeve and crimp to help dampen the movement caused by vibrations.
The readings were a lot more solid on the ground where I had previously seen a ibt of a nervous 5 degree fluctuation up and down. Now it just sits there rock solid, so I have good hopes that this did indeed fix the problem and I won't be needing to replace the sensor.

This concluded the burning issue list items. A while back I had decided to finally add the carpet interior to my 12 as the interior noise on long flights was somewhat tiring and I hoped that the carpet could help with that - next to looking really nice of course.

Needed some custom trimming as I still have a sight gauge and my Moeller is not in the official spot as I added before Van's adapted this to their kit

It will be nice for the passenger to have something to rest their feet on

I did not install the carpet over the forward tunnel as this part gets very hot in the summer on take-off and I am worried that carpet would increase the interior heat to a damaging point.
The other part I did not install yet is the upper triangular piece that covers the area around the vents. I have a headset hook installed there that I 3D printed and I need to see how I can keep that with the carpet.
Next time at the hangar I will perform a dynamic propeller balance and hopefully notice that the interior is really quiet now.

I'll post a separate article about the prop balancing as I have a feeling this will be a longer story.

Also, after the balancing I am going to install a new battery as preventative maintenance. The 4 year old one got a bit tired in the winter before and I was getting worried about not being able to start the engine. Voltage dropped to 9V when cranking longer than usual and any small engine hiccup that would have delayed engine start could have left me with a dead battery on the ramp. IThis winter is really mild and so far no issue but I thought after stressing the old battery with a succession of engine starts for the balancing, I might just retire it before I get stranded somewhere on a cold morning.

I also forgot to take a full cockpit picture once all the carpet and seats were back in which I shall add after the next weekend.

On to another 11 months of fun flying!

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