Twisted: 400 hour service on UL Power engine

For the second 200 hr service I decided to visit the UK UL Power agents, Metal Seagulls, based at Sleap airfield.

Mostly because I wanted Jonathan Porter to look over the engine and also because I do not have the facility to do a compression test on the cylinders, which is called for as part of the 200hr scheduled service.

Jonathan is very knowledgeable and accommodating, readily sharing his wealth of knowledge in an open manner. We are really fortunate to have such a person as the agent for UL Power here in the UK.

We had also planned to look at the cylinder head gasket on number 3 as I had long suspected a slight leak from the head gasket and this certainly had evidence of it throughout its life with a 'spattering' of 'black stuff' (sticky by product of combustion) that continually leaked out and was spattered against the pushrod tubes and inner cowling since the very first 15 hour service up until now. As it turns out the 'black stuff' has reduced quite a lot recently and almost certainly has the effect over time of gumming up any leak to the point where it becomes a non-issue. So Jonathans conclusion was to leave it be.

The service went smoothly with only two issues.

The oil thermostat has failed again (stuck in the closed position so the oil cooler was not being used as part of the oil circuit). It last failed at 278 hours and was replaced with a new part. It failed this time after just another 100 hours at approx 380 hours. I noticed the oil temps again were not coming down as per usual in the cruise and stayed at 103 degrees. I noticed this about 10 hours ago. The oil thermostat has been replaced again (as a warranty item) and oil temps are back to their usual 90-92 degrees in the cruise which is optimal.

The second issue and a more major one is a leaking exhaust valve/seat on Cylinder number 3.

The compression test (done hot) gave these results:

Cylinder 1 - 78/80
Cylinder 2 - 78/80
Cylinder 3 - 69/80 (leaking exhaust valve/seat)
Cylinder 4 - 78/80

For comparison at 200 hrs they were all between 78 - 80 over 80.

An audible hissing could be heard from the exhaust when Cylinder 3 was being tested and putting your hand over the exhaust pipe you could feel and hear the difference, confirming that it was the exhaust valve/seat that was leaking.

This ties in with what Pete Wells was telling me recently - that the UL 260 cylinders are only good for approx 400 hours then they begin to fail. Especially at the exhaust valve/seat area.

So this is happening to me also despite me using the Decalin additive which helps to break down the lead in AvGas into a powder so it does not stick on the valve and damage the seat.

Lycomings and Continentals do not have this problem as they run much hotter CHT's and also they must have different metallurgy in the valve seats to cope with lead deposits. UL Power have made an aircraft engine which will not run reliably to TBO with AvGas - which is kind of ridiculous really...

There are many (most) places in the world where you have no option but to use AvGas so this is a gotcha for anyone expecting to run their aviation engine to TBO on aviation fuel.

Of the 400 hours that I have run this engine only approx 150 of those have been on AvGas (always using the Decalin additive). The rest on MoGas or UL91.

The other ongoing problem is the Throttle Position Sensor which has failed again. It first failed whilst I was in the USA at approx 120 hours. I replaced it with a new one when I got home at 188 hours. It failed again at 315 hours (approx 120 hours on from replacement - which seems to be the failure region/mode for this part).

This time I took apart the TPS and cleaned out all the Carbon dust from the contact face and also noticed that the ultra thin wires that make the contact were a little bent in places so straightened those out and bent the base of them slightly out so the contact was better. This worked fine for about another 70 hours or so until it started failing again. So I have pulled it apart and done the same procedure and it works ok now but I am looking to get rid of this and go for the Hall Sensor throttle option when I can afford the plane to be out of the air for more than a week. At the moment I am using it to commute to work so it would be a hassle to have it out of the air for so long.

The problem is that the ECU has to be removed and sent to Belgium for new firmware to be updated so this means at least a week lost to posting their and back not to mention the time fitting the new throttle sensor type and some wiring changes to accommodate it. (Not to mention the approx £600 cost!)

I plan to do this job and also get the valve seat on Cylinder 3 fixed in the Winter sometime when I can afford to be out of the air for a week or two.

The fact that UL Power no longer use this old style TPS and only make engines with a contactless Hall type sensor for the throttle now says it all. This was always a sub-standard component for aircraft use. I know of many other UL Power users that have had their TPS fail as well so it is not something unique to my installation.

I am also now using the UL recommended Teflon additive to the oil for aerobatic engines. See pic. This is UL Powers answer to the 'mysterious' seizure of the engine by oil starvation on G-JINX that Chris Burkett was flying during a display at Abingdon in May of 2017. UL's thinking being that the Teflon will continue to lubricate in the event of oil starvation. I would of course prefer that they got to the bottom of why the oil was not getting around the engine and why it seized in the first place rather than ad a 'sticking plaster' solution such as this. It is not cheap either at £36.40 per bottle! This adds quite a bit to the oil change cost each 50 hours.