Monday 3 February 2020

UL engine work

As explained in my post from August of last year, when I did my 400 hr service, there were a few outstanding maintenance items that I wanted to get done this Winter.

I managed to get organised a couple of weeks ago and flew up to Metal Seagulls (the UK, UL Power Agent) at Sleap airfield to get this done.

The two main items to fix were the leaking exhaust valve on Cyl 3 (with it's loss of compression) and the upgrade of the Throttle Position Sensor to the new 'Hall' Type sensor.

While I was up there, as my annual inspection was almost due, I got that done too. G-FUUN passed again without comment.

Then while we were waiting for parts to arrive back a Service Bulletin was issued regarding the Oil Thermostat failing. Good timing! The issue was the smaller of the two springs inside the Thermostat was breaking. The fix was a new grade of springs and those parts were supplied free in the UK by Metal Seagulls. 

Whilst I was taking the old thermostat springs out it was obvious that the small one had broken yet again - see pic. So that is a total of 3 failures for me with the oil thermostat. Hopefully the new springs will do the job and we won't have it fail again. I am lucky that my engine runs so cool I can actually still fly without the oil cooler working - it's certainly not a problem in the Winter although I would not want to fly without my cooler operating in the Summer.

Onto the two main issues.

The throttle sensor replacement was fairly straightforward. The biggest pain was removing my ECU as I have it located up under the footwell area of the safety cell so it's out with the instrument panel and then an awkward reach to undo the bolts. No matter, it is only the first time it's been out since it was put there and I don't envisage having to take it out ever again.

The ECU has to be removed because it has to be sent to Belgium to have it's firmware upgraded to 'talk' to the new throttle sensor type.

The whole throttle body was removed and replaced with the new body and sensor. There is also an intermediary connector to fit which converts the round plug of the new sensor into the 3 pin plug of the old connector. 

Of course the idle then needed adjusting once the engine was warmed up.

All seems well with it, although I did notice a hesitation from the engine when the throttle is moved rapidly. Slower movements are better. There was always a hesitation with the old style throttle when going from high idle to full power at take off but this new throttle seems to suffer from the brief hesitation at any setting change if done too rapidly.

Finally onto the Exhaust valve for Cyl number 3. There was a discussion with Jonathan about whether to repair or replace. In the end we decided to replace the whole head as the amount of labour involved to fix it ends up being almost the same as a new head. Also there was the problem of the leaking gasket on this head which had been there from new so it became a 'no-brainer' to replace the head to fix this issue at the same time.

All seems well so far. I need to fly it a bit more to let the head settle down but it seems to run well so far.

Hopefully we will have a good season of flying without any more issues. Fingers crossed.

At Metal Seagulls hangar for the work.
New Throttle Position Sensor, Made in the UK!
New parts. Throttle body and Hall type position sensor and the Oil Thermostat springs
The broken smaller spring from the Oil Thermostat

Detail view of the area where the leaking head gasket let combustion byproducts seep out.
General view of the old cylinder head from Number 3. 
 

Detail view of the Exhaust valve seat. It seems it was the valve rather than the seat that was damaged.

Exhaust valve showing evidence of damage and leak.
Jonathan cleaning up the gasket area before installing the new head.

General view of the piston and cylinder before the new head goes on.
New Cylinder head in place. Torqued down very carefully and progressively to ensure the gasket seals well and evenly.

The Metal Seagull...




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