markgrue Posted July 10, 2021 Report Posted July 10, 2021 I did the 500 hour inspection on my M20D/C today. I was surprised how much lead accumulated in the exhaust valve guides. I suppose because I have been doing a lot of short trips lately. It was a productive day none the less. Nice to see that most everything was in order. All of the black stuff in the picture is lead removed from the guides. Valves move nicely now though. Mark 2 Quote
Ragsf15e Posted July 10, 2021 Report Posted July 10, 2021 Interesting, I always heard climb/cruise should be hot enough to burn off or convert extra lead. Are you leaning real aggressively right after start and soon after landing? Quote
markgrue Posted July 10, 2021 Author Report Posted July 10, 2021 Just now, Ragsf15e said: Interesting, I always heard climb/cruise should be hot enough to burn off or convert extra lead. Are you leaning real aggressively right after start and soon after landing? Not so much on the ground. Perhaps that is a good point. I dont have but about 100 ft from the hangar to the runway though. Many times I have to run about 2000 rpm for a minute or so to get the oil warmed up enough for take off. I will have to try leaning on the ground. Mark Quote
carusoam Posted July 10, 2021 Report Posted July 10, 2021 Inside the valve guides… is a strange environment… Hot enough to coke the oil… and cold enough to allow for a lead collection… Cleaning the guides sound like a great idea… What 500hr inspection is this? A Lycoming one? +1 for leaning to the max while on the ground… PP thoughts only… Best regards, -a- Quote
Ragsf15e Posted July 10, 2021 Report Posted July 10, 2021 44 minutes ago, markgrue said: Not so much on the ground. Perhaps that is a good point. I dont have but about 100 ft from the hangar to the runway though. Many times I have to run about 2000 rpm for a minute or so to get the oil warmed up enough for take off. I will have to try leaning on the ground. Mark How did the plugs look? They are often the first evidence of running rich on the ground like flight school airplanes. I agree it doesn’t sound like you run it for a long time on the ground, but even for a short time, you should be very lean. Even if you run it up, you can likely stay pretty lean. You will have to richen a bit, but you can do the mag check lean. Since you’re at low power on the ground (even 2000 rpm), you can’t hurt the engine. Just start it, check for oil pressure, set 1000-1200 rpm, then immediately pull the mixture until it stumbles/dies. Push it in just barely far enough to idle smooth. In this condition, if you add power to taxi (or takeoff) it will stumble and likely die. Add a slight turn of mixture if you require more power for taxi, but strive to stay as lean as possible on the ground. Same after landing, as soon as you exit the runway, lean it aggressively. Good luck! 1 Quote
Hank Posted July 10, 2021 Report Posted July 10, 2021 ^^^^ Good advice from @Ragsf15e above. I generally lean my C about 3/4 travel towards ICO right after I start the engine, and enrichen for run-up. When landing, I generally lean again about the time I hit the brakes and know it's under control. 2 Quote
Boilermonkey Posted July 10, 2021 Report Posted July 10, 2021 I always lean on the ground, especially if you have to wait for your turn on the runway or an IFR clearance. ...but also watch to ensure you don't get too hot. ....and carb ice for the C model. I've seen carb ice effects on takeoff (aborted to) in a model c before. I've also seen detonation due to overheat on a Bravo on take off resulting in a crash. Quote
Guest Posted July 10, 2021 Report Posted July 10, 2021 This is the Lycoming SB covering this. https://www.lycoming.com/sites/default/files/Procedure to Determine Exhaust Value and Guide Condition.pdf Quote
markgrue Posted July 10, 2021 Author Report Posted July 10, 2021 10 hours ago, carusoam said: Inside the valve guides… is a strange environment… Hot enough to coke the oil… and cold enough to allow for a lead collection… Cleaning the guides sound like a great idea… What 500hr inspection is this? A Lycoming one? +1 for leaning to the max while on the ground… PP thoughts only… Best regards, -a- There is no formally defined 500 hour inspection but the lycoming service bulletin says clean the valve guides at 400 so I push that to 500 to coincide with the mag inspection and of course there is the normal 100 hour gear and control lube. Since I have lined up everything on my tach time to land on the 500 hour increments it just works out. For example this time is was at an even 2000 hours. next one at 2500 and so on. I just had to do the first one early at 1500 instead of 1643 where it would have landed. Since I fly usually about 200 hours a year it does not land on the annual anyway and there is enough to do then that I do not need to add valve guides and mags into it. By the way the service bulletin is Lycoming SB 388. Just the way I do it. Mark 1 1 Quote
markgrue Posted July 10, 2021 Author Report Posted July 10, 2021 9 hours ago, Ragsf15e said: How did the plugs look? They are often the first evidence of running rich on the ground like flight school airplanes. I agree it doesn’t sound like you run it for a long time on the ground, but even for a short time, you should be very lean. Even if you run it up, you can likely stay pretty lean. You will have to richen a bit, but you can do the mag check lean. Since you’re at low power on the ground (even 2000 rpm), you can’t hurt the engine. Just start it, check for oil pressure, set 1000-1200 rpm, then immediately pull the mixture until it stumbles/dies. Push it in just barely far enough to idle smooth. In this condition, if you add power to taxi (or takeoff) it will stumble and likely die. Add a slight turn of mixture if you require more power for taxi, but strive to stay as lean as possible on the ground. Same after landing, as soon as you exit the runway, lean it aggressively. Good luck! The plugs were a nice light tan color. I just replaced them about 150 hours ago at the last annual so they were firing well on the tester. I did clean a bit of lead out of them and test them while I had them out. I did not think to take a picture of them. I never considered that the bit I spend on the ground had much impact on the valve guide fouling but I do see the logic in your advice. I will have to make that a standard practice. Mark 2 Quote
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