Engine Issue Fixed - #1 Cylinder Not Firing

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SlowFlight
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Engine Issue Fixed - #1 Cylinder Not Firing

Post by SlowFlight »

Pulled the plane out of the hangar weekend before last to stretch its legs after a month in the hangar (an an unusually wet one for Houston this time of year). At run up, I pushed the plane towards 2,000 and the #1 cylinder CHT dropped to about 150, the #1 EGT bar dropped off the screen, and the plane started running quite rough. Moved it to the maintenance hangar where we tried:

1. Cleaning the plugs (#1 was dirty)
2. Swapping the plugs (#1 was weak)
3. Testing the mag leads (fine)
3. Checking for stuck cylinders (none)
4. Replacing the seal on the intake manifold (Savvy suggested this, stuck cylinder, or classic "Lycoming morning sickness")
5. Cleaning the fuel injectors
5. Replaced the mag points and cleaned some rust out of the mags (mech. noted the charge was weakening with more power - I need to understand this better).

No luck. After each test, the #1 cylinder was ice cold. Scott Dodge (mechanic) then swapped a fuel hose around, ran the plane, and the #2 cylinder went cold while #1 fired up.

Clogged fuel hose was the culprit.

Extra credit: the engine is now running smoother than ever and getting 2720 - 2750 on takeoff. Maybe I'll be back to truing 150 on a regular basis now!

-tyson
-tyson

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Chris B
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Re: Engine Issue Fixed - #1 Cylinder Not Firing

Post by Chris B »

SlowFlight wrote:Scott Dodge (mechanic) then swapped a fuel hose around, ran the plane, and the #2 cylinder went cold while #1 fired up.

Clogged fuel hose was the culprit.
Hi Tyson -

Thanks for posting. By "fuel hose" do you mean the hard lines from the spider at the top of the engine to each injector? I didn't realize that these could clog, unless the fuel filter is defective. :scratch:
SlowFlight wrote:Extra credit: the engine is now running smoother than ever and getting 2720 - 2750 on takeoff. Maybe I'll be back to truing 150 on a regular basis now!
If the engine is actually running at 2750, you might want to get this tweaked. I don't know whether you have a Hartzell or MT prop, but 2750 is very close to Hartzell's spec for overspeed:

Image

103% is 2781, which is obviously close to 2750.

Additionally, overspeed is bad for the engine. Lycoming outlines their requirements in this mandatory service bulletin: link to PDF

The executive summary is that any engine overspeed >3 seconds must be logged and fixed. For <5% (2835), this is all that is required. >5% gets a thorough inspection. >10% (2970) and you tear down the engine. :shock:

OTOH, when I recently discussed this topic with my IA, he pointed out that until recently most tachometers were relatively inaccurate mechanical devices. So the specs probably have some slop.

Chris
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Re: Engine Issue Fixed - #1 Cylinder Not Firing

Post by SlowFlight »

Chris B wrote: Thanks for posting. By "fuel hose" do you mean the hard lines from the spider at the top of the engine to each injector? I didn't realize that these could clog, unless the fuel filter is defective. :scratch:
His comment was 'the hose from the fuel manifold to the cylinder'. Assume he meant 'fuel distributor' and will get clarification and ask about the fuel filter.
Chris B wrote: If the engine is actually running at 2750, you might want to get this tweaked. I don't know whether you have a Hartzell or MT prop, but 2750 is very close to Hartzell's spec for overspeed
MT prop. The spike above 2700 was momentary. I'll monitor on the next flight and if it spikes above that and stays, will report back and also follow up with mechanic. Thank you!
-tyson

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Re: Engine Issue Fixed - #1 Cylinder Not Firing

Post by rwtucker »

I hadn't given much thought to the accuracy of the tachs other than figuring the digital tachs would be the most accurate with full mechanical the least and hybrids in-between, I looked around a little and didn't see much. One post on Back Country Pilot had this:
I got frustrated by the inaccuracy of mechanical tachs . . . ordered an overhauled one . . . checked it with a stroboscopic tach checker and it was 50 rpm off . . . variable at different rpms . . . ordered a new one . . . (it) was 75 rpm off. The manufacturer stated that anything within 100 rpm was legal, and to just placard the tach with the error . . . I bought a Horizon tach . . . it is dead accurate. It has other features . . . a yellow light to warn that you're in the "5 minute" range and a red light that comes on if your overspeed.
Wonder why our G1000 doesn't warn us?

I don't know what dead accurate means in this context but it sounds like his digital tach tracked closely with the strobe-type tach which, if I recall, can be from 1-2% for the older units down to much less than 0.1% (essentially perfect). The Aircraft Spruce tach claims a "resolution" of 1 RPM which is more-or-less unrelated to accuracy (validity) or reliability (same RPM indication measures at multiple different times when the true RPM is the same).

So . . . if we get a 2750 RPM G1000 reading, what is true RPM? Don't know but a fairly safe worst case might be between 2695 & 2805. More likely, it is much closer than that.
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Re: Engine Issue Fixed - #1 Cylinder Not Firing

Post by SlowFlight »

2710 on takeoff today, steady. Engine sounds great.
-tyson

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