Pilot Dog Ship
Member
The issue:
Engine occasionally bogs down a bit, loosing 150 rpm, slight vibration and louder, irregular bark from exhaust. Same on all magneto positions.
Troubleshooting so far:
-plugs checked, none worn out, cracked, shorted, resistances all below 1500 ohms. Plugs serviced, gaps all okay, reinstalled: no change. All new plugs installed. No change.
-ignition harnesses replaced about fifty hours ago due age.
-magnetos Bendix with impulse on left, 190 hours since 500-hour shop visit. Impulse working and timing at spec.
Dismantled Bendix ignition switch. Worn but no signs of pitting, arcing, no carbon tracks. Cleaned metal surfaces and reassembled with dielectric grease, reinstalled: no change.
Fuel samples always clean, always 100LL and aircraft hangared. Carb bowl drain pulled and no debris or water drained out. Suspected a fuel flow issue but will turn up full static rpm for thirty seconds, albeit while intermittently trembling.
Always starts happily and easily, albeit with some mechanical clanking from left side of engine, which was built up in 1967 and has 2100TT. Last time cylinder was pulled, about 200 engine hours back, cam lobes and Followers visually inspected, not shiny any more, fish-scale appearance but no pitting or surface defect that catches a fingernail. Paper oil,filter always clean of ferrous metal, running Aeroshell W100Plus with Camguard.
When run at 1700, after ten seconds of smooth running, slowly gets rougher and rpm drops 125, no change on individual mag nor with leaning the mixture.
Exhaust valves checked for sticking, all free and slide/rotate without issue.four hundred hours since top overhaul.
Removed air filter, carb heat box; no change during brief ground run. Carburetor throat looks intact, venturi, jets all appear secure. During second last ground test, experienced triple the usual drop when selecting carb heat, left heat on,no subsequent rise, so heat off, rpm did not recover. So removed all that stuff to try again, no change.
Ground run with P-leads disconnected, eliminating ignition switch and P-leads, filters and wiring, feels and sounds better but still not as "happy" as four flights ago, when this started happening intermittently and for but a few seconds at higher power settings but not at lower power settings.
During today's ground tests, it would start running within 2-3 blades and run happily until running at 1700 for about ten seconds. Then it would start to bark out the exhaust, vibrate and loose about 125 rpm. Always turned up full static rpm but not willingly.
I'm still thinking the issue is heat related. The chances of two separate mags developing an internal issue simultaneously seems very remote.
Unlikely to be fuel flow related as it can turn up and sustain the required full-power rpm, albeit with random issues like this.
Tapped the exhaust piping, nothing loose internally anywhere.
Now, after three days of scratching my head, I don't have that much hair left to scratch...
Engine occasionally bogs down a bit, loosing 150 rpm, slight vibration and louder, irregular bark from exhaust. Same on all magneto positions.
Troubleshooting so far:
-plugs checked, none worn out, cracked, shorted, resistances all below 1500 ohms. Plugs serviced, gaps all okay, reinstalled: no change. All new plugs installed. No change.
-ignition harnesses replaced about fifty hours ago due age.
-magnetos Bendix with impulse on left, 190 hours since 500-hour shop visit. Impulse working and timing at spec.
Dismantled Bendix ignition switch. Worn but no signs of pitting, arcing, no carbon tracks. Cleaned metal surfaces and reassembled with dielectric grease, reinstalled: no change.
Fuel samples always clean, always 100LL and aircraft hangared. Carb bowl drain pulled and no debris or water drained out. Suspected a fuel flow issue but will turn up full static rpm for thirty seconds, albeit while intermittently trembling.
Always starts happily and easily, albeit with some mechanical clanking from left side of engine, which was built up in 1967 and has 2100TT. Last time cylinder was pulled, about 200 engine hours back, cam lobes and Followers visually inspected, not shiny any more, fish-scale appearance but no pitting or surface defect that catches a fingernail. Paper oil,filter always clean of ferrous metal, running Aeroshell W100Plus with Camguard.
When run at 1700, after ten seconds of smooth running, slowly gets rougher and rpm drops 125, no change on individual mag nor with leaning the mixture.
Exhaust valves checked for sticking, all free and slide/rotate without issue.four hundred hours since top overhaul.
Removed air filter, carb heat box; no change during brief ground run. Carburetor throat looks intact, venturi, jets all appear secure. During second last ground test, experienced triple the usual drop when selecting carb heat, left heat on,no subsequent rise, so heat off, rpm did not recover. So removed all that stuff to try again, no change.
Ground run with P-leads disconnected, eliminating ignition switch and P-leads, filters and wiring, feels and sounds better but still not as "happy" as four flights ago, when this started happening intermittently and for but a few seconds at higher power settings but not at lower power settings.
During today's ground tests, it would start running within 2-3 blades and run happily until running at 1700 for about ten seconds. Then it would start to bark out the exhaust, vibrate and loose about 125 rpm. Always turned up full static rpm but not willingly.
I'm still thinking the issue is heat related. The chances of two separate mags developing an internal issue simultaneously seems very remote.
Unlikely to be fuel flow related as it can turn up and sustain the required full-power rpm, albeit with random issues like this.
Tapped the exhaust piping, nothing loose internally anywhere.
Now, after three days of scratching my head, I don't have that much hair left to scratch...