Saturday, 27 January 2018

200 hr service and more

I recently completed the 200 hr service on the UL engine.

I did everything myself except for the compression test as I don't have the gauges and fittings for that. I took it to Brinkley Aviation which is pretty handy as it's just 3 mins flying time south of Old Warden for the compression test.

I used Brinkley for the first annual inspection too - which I'm pleased to say G-FUUN passed "without comment". 

The results of the compression test were very encouraging with the following readings:

Cylinder #1 = 79

Cylinder #2 = 80

Cylinder #3 = 78

Cylinder #4 = 79

These are from an 80 psi pressure on the first gauge and so show almost no loss of compression despite 200 hours of use with 120 hours of that on AvGas.

Comparing the above figures - which was done on a hot engine BTW - to the ones from the same test performed at 110 hours at Oshkosh - on a cold engine.

Cylinder #1 = 75

Cylinder #2 = 75

Cylinder #3 = 73

Cylinder #4 = 75

Unlike a Lycoming or Continental the compression is at it's best when hot - just like an automotive engine.

The only slight worry is Cylinder #3 which shows a very small reduction in compression to the others. I put this down to the head gasket leak at 110 hours - but as you will see below in the photos the leak has since gone away.

I didn't have to do the compression test at 100 hours but as I was flying back across the Atlantic I wanted to make sure that the engine was not losing compression due to the AvGas usage.

If you did not already know - the UL engine does not like AvGas and will eventually lose compression due to the valve seats getting damaged from the lead deposits. Pete Wells has told me this happened to him after just 100 hours on one of his engines. He tries to run on MoGas as much as possible these days but it is impossible to do so all the time when you are flying away to other countries as he does.

I can't remember if I already talked about this but I used 'Decalin Runup' fuel additive on my Oshkosh trip as I was quite worried about the AvGas causing me problems as I knew it had to Pete already. This product seems to work and does what it says. It converts the lead into a Phosphate which is not as hard or damaging and tends to then get burnt up rather than deposit on engine parts.

I spoke with UL people in the USA and also to the Zenith agent there who has many hours on UL engines running on AvGas and he said they get 300 hrs on AvGas with Decalin before they see any compression loss.

The spark plugs certainly looked in good shape at Oshkosh when we took them out and the same goes for the latest set, although they had been running on MoGas for the last 20 hours or so which may have cleared them up anyway.

As you can see the fuel filters certainly needed replacing. There was quite a lot of debris in the coarse filter and the fine filter was blackened too.

The service went very well and there was nothing to cause any concern. 

However on my Oshkosh trip there were a few worrying things that happened.

The worst was a fault that developed just after Oshkosh when at 100% throttle the engine would intermittently go to idle. Not welcome when you are low over mountainous trees having just taken some pics of Mount Rushmore - which is when it first happened to me. As it was intermittent it recovered after a few seconds and later on I found that I could eliminate the problem by reducing the throttle to 90% setting.

After some thinking about it and then an email to Patrick at UL Power he agreed with me that it must be a fault of the Throttle Position Sensor. This TPS has two brushes of constantly varying thickness that send a 5 volt signal to the ECU at 100% throttle and a near to 0 volt (or actual 0 volt - not sure which) signal at idle. So if the brushes get damaged, where they are at the thinnest which is at the 100% setting, then they can cease to conduct properly and send the 5 volts to the ECU instead it 'sees' 0 volts and goes to idle.

UL Power have since given me a replacement throttle body and TPS (the two are calibrated together and must be replaced as a unit) which I have swapped out with the old unit. I've had no further problems since then. Patrick did say on investigation that the brushes were slightly damaged and then blamed the way the throttle was connected on me as the reason for the wear! This seems like a very poor component to fail at just 115 hours and not be able to cope with the vibrations of an aero engine environment. The TPS is a VW/Audi car part BTW. Pete has also had issues with the TPS and had to replace several of them too, so it's not just me.

Another issue was an oil leak from the front prop flange seal. See pics below. This resulted in a fine mist of oil being sprayed around the front part of the engine as it worked it's way out onto the flange and was spun off at high RPM. Once again UL Power have given me a replacement seal kit but I have not replaced it yet as the leak is very minor. 500mls loss over 70 hours flying on my return journey. Since I've got back it has not been as bad but I am keeping an eye on it and will replace it if it gets any worse.

The final problem was the Air filter which was found to be chaffing on the oil pipe which comes out of the top of the engine and heads to the breather. Not everyone will have this same identical oil pipe as I have but it is still something to be aware of. The US mechanic for UL Power which replaced the air filter positioned it so that the metal strip was touching the oil pipe fitting and the 15 hours or so I flew it before I noticed it was enough to cause the chaffing and wear on the pipe as you can see in the below photo. Make sure to position your air filter with the metal strip not touching anything.

Now to end on a positive.

The Oshkosh trip was a real test of the cowling and oil cooler mods. Would they work in all conditions?

I'm very pleased to say that they did and actually exceeded my expectations.

From the coldest ambient outside air temps of -20 degrees C (in the cruise at 12,000 ft over the Greenland ice cap) to the very hottest, heat soaked 40 degrees C days in the USA the oil and CHT's never came close to their limits.

On the 40 degrees C day with a heat soaked engine and with a full power climb for 10 minutes the oil only ever got to 102 degrees C - which is 18 degrees below the max. The hottest CHT's were 135 degrees C - which is 25 degrees below max continuous and 55 degrees below absolute Maximum.

On the -20 degrees C flight, in the cruise, the oil got down to 77 degrees C which is still 27 degrees above minimum and the coldest CHT's were also 77 degrees C which is also 27 degrees above the minimum.

So the cowl flap works very well, giving excellent control of the oil temp. The inlets, sealed plenums and outlets of the cowling also give excellent cooling of the engine. In fact I think I probably over-did it a bit with the size of the inlets and outlets on the cowling and could easily reduce them by 30% or so but as it is the engine does not require any 'heat management' other than setting the cowl flap position.

At Brinkley Aviation for the compression test.

Setting the air pressure to 80psi with the cylinder at top dead centre - then reading the second gauge to see what the difference is. Very pleased with the results of this.

Decalin RunUp fuel additive for use with AvGas to reduce the lead deposits. It seems to work.

Fuel fine filter showing a 'blackening' of the paper element.
Coarse fuel pre filter showing how much debris is in there after 200 hours. The outer (clean) side of the filter is shown on the left for contrast.

Very small evidence of cylinder head gasket leaks on 1 and 3. 3 has self-sealed itself over time and does not leak anything like it did at 25 hours. 2 and 4 show no signs of leaking.

Oil pipe chaffing from the air filter metal strip.
Witness mark on the metal strip shows where it was rubbing.
Plugs don't look too bad.

Oil weeping from the prop flange seal.

Cutaway of the prop flange seal. Photo taken at Friedrichshafen on the UL Power display stand.