I'm in the midst of tracking down engine start issues. It's been getting progressively worse the past 3 months or so. I'm about 300 hours into a dual-mag overhaul and my money is on the impulse coupling. I tried to crank it yesterday and had to wait 30 minutes after I hit the starter duty cycle. My mechanic suggested a GPU start, which was successful and I flew it to him since he's at the airport across town.
I'm 700 hours since a factory overhaul and I'm suspicious of sticking valves as well. Cold starts will sputter like I've flooded it and it seemed unhappy for 30 seconds or so after the GPU start.
I'll post more when I know more, but I'm curious if anyone has had valve guides reamed. If so, did you do them all at once or try to track down the offending cylinder?
Bubba
Starting issues
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scottrsellers
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Re: Starting issues
The cold start sputter for 30 seconds sounds like potential sticky valve so worth pursuing the Mandatory SB 388C posted in this section. Lycoming recommends this wobble test be done every 400hrs and if your mechanic is familiar with the test it can be done in abbreviated fashion in about an hour so that the offending valve can be ID'd.
If there's a valve with inadequate movement it makes sense to ream others with inadequate movement as well.
If you're at 700hrs with no log entry for having performed 388C then it makes sense to do it.
If there's a valve with inadequate movement it makes sense to ream others with inadequate movement as well.
If you're at 700hrs with no log entry for having performed 388C then it makes sense to do it.
Re: Starting issues
My starting issues are now resolved and it was a weird one. The center jet for the #3 primer nozzle went AWOL. Only the back four cylinders have primer nozzles. #3 was getting most of the fuel from primer strokes flooding it badly while the other three were probably under primed. We don't know where the jet got off to but it's not in the cylinder.
Here is the faulty nozzle:
and the photo here is what it should look like: https://www.aircraftspruce.com/catalog/ ... 4022-1.php
Here is the faulty nozzle:
- IMG_4531.JPG (1.88 MiB) Viewed 181 times
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scottrsellers
- Posts: 246
- Joined: Tue Jun 11, 2024 1:53 pm
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Re: Starting issues
Good catch! Yes missing or broken or cracked primer lines can cause vibration at start as well.
This also makes the case to look for induction system leaks and to check torques on intake flange bolts any of which could contribute to vibration.
This also makes the case to look for induction system leaks and to check torques on intake flange bolts any of which could contribute to vibration.