Author: Gary Zilik <zilik@...> Time: Fri Dec 3, 2004 7:14 am PST Link
bmarvel@cox.net wrote:
> A few questions:
>
> 1. How many hours have you flown this engine?
The engine has ~700 hours since overhaul and ~500 hours since new
Millennium cylinders where installed. This is another story in itself.
> 2. Has this problem occurred periodically throughout its lifetime on
> your aircraft or is it relatively new?
The problem cropped up in July of this year. Previous to that there were
no problems.
> 3. If the latter, when did it start in terms of anything that you
> changed, adjusted or replaced on the engine or in the fuel system?
No changes were made previous to the episodes. After the July roughness
I pulled the cowl when we got home and checked it over pretty carefully.
The inlet ramp on #2 cyl was cracked and had lost a football shaped
chunk about 1.5 in^^2 in area. I repaired the hole using 500 mph tape
(aluminum tape used on Boeings) and intended to repair the baffle
properly at annual time. It turns out the 500 mph tape could not
withstand the heat and pressure of the cooling plenum and failed. After
removal of the baffle for repair it was noted that the football shaped
hole had also allowed the side of the baffle to push away from the
cylinder head when under pressure. I'm leaning towards the failed baffle
causing hot spots on the cylinder in question leading towards
detonation. I really think the baffle failure and the first roughness
episode came at the same time. The previouse episodes of roughness
always happend at higher altitudes where the engine cannot generate as
much power and enriching the mixture solved the problem. On the last
episode it was a coold day, high pressure in the area and full power.
Enrichening the mixture helped at first and then it slowley started
getting worse. Of course the cylinder in question was not the one my
single egt/cht is installed on and all readings were normal. So at this
point I have a strange looking piston and plug in number 2, failed
baffles on #2, leaned for cruse at 6000' 21 map 2500 rpm and I then
increased power for the chase. I think (i really don't remember) that I
violated the cardinal rule to increase the mixture before pushing in the
throttle. The roughness started soon after and then I pushed the mixture
in. As I said, it helped at first but only got worse from then on.
I thank everyone for the suggestions I have gotten so far. There are a
lot of great minds on the lists.
Gary
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