** = my reply
What I know is that there are an increasing number of valve guide problems with Continental cylinders, whether they’re on ‘new’ or overhauled engines. An increasing number of frustrated owners take their ‘new’ or overhauled engine to experts who have a process using Prussian Blue to get the correct print on the valve stem tip. Those experts are increasingly frustrated at the ‘quality’ of what they are seeing.
** Yes certainly some years ago there was massive TCM cylinder issues, closely followed by Superior and from memory a bit latter Lycoming too - but in recent years say last 4 or 5 nothing, but I am not current.
If you are drawing a distinction between before and after fitment and I got that wrong, well done! It proves nothing I say is true and there is no problem with quality control.
** Yes was confused as your fitment comment - yes all cylinder manufactures and engine manufactures have had quality issues over the years.
Is within tolerance too far? Errrm, I’ll make a wild guess and say within tolerance is not too far.
“In my honest opinion I believe you can not tell what you stated above, but that there is a change in indication most likely cause by timing adjustment”. It just goes to show that you have zero experience as a pilot flying behind these engines.
Out of maintenance the CHTs were 15C higher on climb-out than normal. That put CHTs above that magic number Lycoming got about right in the information I quoted earlier. A temperature I’d never been before. Mag check shows all plugs working but big differences between mags.
** I have not closely followed this thread but thought we were talking TCM IO520 - my fault but again not current with your engine.
The timing of one of the mags had been advanced too far (and out of tolerance - 25 degrees instead of 22). The engineer probably used a mechanical protractor rather than the accurate equipment used by the Timing Fairy to confirm the problem.
** Interested as to your knowing the 25 degrees and not 22, did they allow you to be present? Normally owners/pilots are not allowed to oversee such work in many places (that just an interest question). I personally have never seen a mechanical protractor in about 35 years and a number of countries. There was the plate on the pulley on the rear of IO520 TCM that had timing marks but that was removed years back. If it is a Lyco it would be the line on the fly wheel matched to the dot on the starter. This can be hard due propeller blade and cowling arrangements on some craft.
For your education, the reason advancing the timing increases CHT is because in reduces thetaPPP - i.e. brings the peak pressure point closer to top dead centre. A bit like leaning the mixture to 25C ROP.
** that can be changed by spark plug gap and E gap timing.
Yours is very small sample.
I’m talking about the experience across thousands of aircraft. Yours is a very small sample.
** Correct I have only worked on a thousand or so piston aircraft tail numbers
“Now if the nozzle has become blocked due to maintenance, it would be because the nozzle has been removed - just a random guess...”. Brilliant guess.
“Simply request at your expense to have the stainless fuel supply lines removed and cleaned when nozzles are removed...”. Spoken like a true engineer! Your fiddling (for which I’m paying) introduces the crud that causes the defect, and your solution is to ‘up-sell’ more fiddling.
I think I’ve mentioned this in other threads. I would offer various engineers many thousands of dollars not to inflict a range of counter-productive maintenance on my aircraft, if I weren’t committing what’s probably a crime under the civil aviation law. Bleeding money to reduce risk is better than bleeding money to buy risk.
** Think fuel nozzle cleaning on TCM was called up at 3 or 500 hour intervals - just apply to CASA for a dispensation. Will send bank details later.
Just as a matter of interest, have you ever seen any engine or engine component that’s ‘new’ or out of overhaul that’s had a defect? Just once? Or are you observing perfection?
** Yes plenty.
Have you ever made a mistake during maintenance that wasn’t picked up and ended up causing an in-air problem. Just once? Or have you achieved perfection?
** A reverse elevator trim due twisted cable - Darwin around 1995 on a C206 a nose gear issue on a 210. There are others but very minor.
I’ve made a number of mistakes during maintenance that weren’t picked up and ended up causing an in-air problem. When you’ve worked at it for a long time and you’re not perfect, it’s bound to happen occasionally. That’s why I know what really goes on inside maintenance hangars. But it’s also why I don’t rain down legal hellfire and brimstone every time one of these mistakes is made on my aircraft. I could do it, but I empathise with the people who’ve made the mistakes.
** I assume since 1985 counts as a long time?