Long awaited engine ground run …

So after a hugely long wait .. the engine is back in … new valves, new pistons, liners, new rings, beefed up and drilled flywheel access to make it easier to check bolt torques regularly … sand blasted and repainted

The new prop on and wheels out of the hanger for a first hot start

I’d opted to leave the cowls off and the spinner off so that I could easily check engine oil temps and possible leaks and bolts.

Recorded each session from a side on iPad as I can see the engine from inside the cockpit …this was to prove useful

First start didnt start immediately as there was no fuel to the bowl. Then it burst into life …first test called for 1200 tick over for 2 minute ..all temp and pressures looked great except one CHT, Left one read minus …turned out to be wires switched ..only one mis wire in the full re wire 😊

Stopped after 2 minutes and removed all rocker covers in turn to check oil and temperature … all looked great

Let it cool down and 2nd run … let the oil come up to temp and then run a little longer … to get oil to 45-50’.. took a while as the engine was completely open so very cooled by the prop wash .. she had now had around 20 mins of run time and all was looking great … good pressure of 65 and temps all well within limits.

Still not going through the TOCA oil limiter .. so need to keep her at above 55’ for a little longer in 3rd run

3rd run started instantly following cool down … this run called for 1200 for 1 minute, then 1800 .. this being a block that would repeat and cool down between each

Then, at around 3 minutes into this run up , and just after I’d started to ease up to 1800 … all was sounding smooth then there was a loud crack .. it didn’t sound metallic but thoughts immediately went to the newly refurbished engine

As soon as the crack happened I hit both mags off ..stopping the engine immediately

I turned the engine very gently by hand and all sounded fine and smooth .. no obvious mechanical issues ..so I removed each of the rocker covers in turn to check valves were rising and falling .. all were .. so what was wrong ?

As I checked the last set of valves .. I removed the cover . Reached up to the prop tip to pull it through … and felt the tip was damaged. On farther investigation it looked like a bit of delaminating and a small strike on the hardened leading edge.

Not a clue what had caused it .. a taildragger prop is about 30” from the ground so highly unlikely to be a flicked up stone .. and we were on hard smooth concrete anyway

Watching the video back at that point and enlarging it and slowing it down .. you can see the problem ! As I’d left the spinner off for the ground tests I’d (stupidly) left the 6m hex bolt in the end of the spinner spigot

With successive runs this bolt had unwound .. and, as I approached the 1800 rpm test it reached the end of its thread and came out .. hitting the tip of he prop at prob something like 400mph

Now the task of trying to source another prop as soon as ….😔

4 thoughts on “Long awaited engine ground run …

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  1. Hi David, glad to hear the re-build is going well.
    Just out of interest, have you mic’d up the old parts to check wear levels, would be interesting to note the rate of wear relative to new, as would give a good indication of hourly life before inspection required in the future, relative to the existing service schedule.
    Kind Regards

  2. Hi Nigel – thanks for the comment and feedback – I believe my engine man did just that … but then, as he had the crankcase in half – to replace the through bolts with new improved versions with better heads, he advised that changing pistons and bores and rings was a sensible option .. almost zero timed the engine … certainly sounded more punchy on startup last week – or is that just (reduced bank balance) psychology 🙂

    1. Hi David,
      Ouch !!!. Just watched the video, have you checked that the bolt hasn’t hit any part of the aircraft on its way into orbit ?.
      In my Army days in the 70’s, I had a crown wheel bolt shear off whilst driving a Land Rover at about 50 mph, the bolt head punched through the differential casing, through the flooring, and through the canvas top, never to be seen again. The amazing thing about it, is that the differential didn’t seize up, although it didn’t sound too healthy,
      Which prop are you using by the way, I’ve heard that Hercules props are good, although I haven’t seen one in the flesh, so to speak, unless, of course, that is what you were using over here.
      Kind Regards

  3. Evening Nigel
    Yes ..I have been checking over every inch and still looking for the small missile .. suspect it will never be seen again … new prop due middle to end of next week.. so ready for continuing the engine pre checks then …
    The new prop will be my 3rd from Hercules … I visited Rupert at the factory at the beginning of this year to pick up my 30 minuter … feels a bit like Blackadder .. 30 mins being the run time before the bolt decided to end play for the day !

    The factory was amazing … love the wood and classic lines … new one will match the others … anti reflective black back with yellow colour matched tips

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