FlyWalt Posted May 16, 2023 Report Share Posted May 16, 2023 Good afternoon, Our engine was overhauled about 9 months ago. In that time I have put about 40 hours on her. I have noticed that once cruise power is set, Usually 75% AT 12,500 feet, I am getting MP variances by as much as .8 inches. And it will cycle back and forth. Does anyone have any thoughts on where to look here? 1 Quote Link to comment Share on other sites More sharing options...
carusoam Posted May 17, 2023 Report Share Posted May 17, 2023 There was a discussion regarding lubrication around here… earlier today. MP controllers are the first thing to consider… they have a few moving parts that get exhaust temperature hot… There is a particular lubricant for this… called mouse milk… Use early and often… Simple and effective… start there, and see where to go next… PP thoughts only, not a mechanic… Best regards, -a- Quote Link to comment Share on other sites More sharing options...
Z W Posted May 17, 2023 Report Share Posted May 17, 2023 How fast is it "cycling"? On a long cross-country, that amount of variation is very normal over time as you pass through changing atmospheric conditions, especially up over 12,000 feet. You might even notice it corresponds with altimeter changes given to you by ATC. You have to move the throttle in and out to keep your settings the same. Something I think happens on all aircraft, really, but you notice it a lot more on a turbo which is already finicky to manage, traveling at 170+ knots over the ground for hours with not much to do but stare at the gauges and out the window. If it's sitting there oscillating constantly, that would be another issue. Quote Link to comment Share on other sites More sharing options...
FlyWalt Posted May 19, 2023 Author Report Share Posted May 19, 2023 On 5/17/2023 at 7:19 AM, Z W said: If it's sitting there oscillating constantly, that would be another issue. When returning home yesterday, I was cruising at 11,500 feet and had a setting of 31.5 and 2400 rpm. The MP was cycling between 31.7 and 30.5. It seemed to be every 3 to 4 minutes. Quote Link to comment Share on other sites More sharing options...
FlyWalt Posted May 20, 2023 Author Report Share Posted May 20, 2023 Well after talking to the shop that overhauled my turbo last year, they feel like it is a failing pressure relief valve. And have offered to take care of it. Quote Link to comment Share on other sites More sharing options...
Fly Boomer Posted May 20, 2023 Report Share Posted May 20, 2023 2 minutes ago, FlyWalt said: Well after talking to the shop that overhauled my turbo last year, they feel like it is a failing pressure relief valve. And have offered to take care of it. That's good support from a year ago! Who did the work? Quote Link to comment Share on other sites More sharing options...
FlyWalt Posted May 20, 2023 Author Report Share Posted May 20, 2023 Main Turbo in Visalia, Ca. They could not be more helpful and knowledgeable. Quote Link to comment Share on other sites More sharing options...
Fly Boomer Posted May 21, 2023 Report Share Posted May 21, 2023 2 hours ago, FlyWalt said: Main Turbo in Visalia, Ca. They could not be more helpful and knowledgeable. That must be the place to go. Thanks. Quote Link to comment Share on other sites More sharing options...
kortopates Posted May 21, 2023 Report Share Posted May 21, 2023 Does it maintain redline MAP at takeoff okay? If so i would be very skeptical of it being a pressure relief valve.Do you have Merlyn installed and/or running LOP? Those are more probable causes IMO - a sticking controller or too deep LOP for mixture or ignition.That said, Gary (Main Turbo) is a real stand up guy.Sent from my iPhone using Tapatalk Quote Link to comment Share on other sites More sharing options...
FlyWalt Posted May 21, 2023 Author Report Share Posted May 21, 2023 12 hours ago, kortopates said: Does it maintain redline MAP at takeoff okay? If so i would be very skeptical of it being a pressure relief valve. Do you have Merlyn installed and/or running LOP? Those are more probable causes IMO - a sticking controller or too deep LOP for mixture or ignition. Good morning. Redline on this engine is 40 inches. I usually set it at 38 to 39 for take off and she seems to hold just fine. Neither intercooler nor an automatic wastegate installed. And, as per my engine builder's recommendation, I run ROP all the time. I enrichen it back about 100 degrees south of peak TIT. Quote Link to comment Share on other sites More sharing options...
kortopates Posted May 21, 2023 Report Share Posted May 21, 2023 14 minutes ago, FlyWalt said: Good morning. Redline on this engine is 40 inches. I usually set it at 38 to 39 for take off and she seems to hold just fine. Neither intercooler nor an automatic wastegate installed. And, as per my engine builder's recommendation, I run ROP all the time. I enrichen it back about 100 degrees south of peak TIT. Good Morning, If it doesn't leak at 38-39" it really hard to believe its leaking at 30" but without the Merlyn and running it ROP there isn't a whole lot of things it could be; so worth a shot. That said, there is no automatic waste-gate option for this engine but the Merlyn manual pneumatic wastegate is a very worthwhile upgrade over the fixed bolt. But its entirely manual. The aftercooler is really valuable if flown high. And of course this engine is flown LOP a lot resulting is less cooler CHTs and cleaner combustion; just has to be flown within proper limits and out of the red box. Let us know how the new relief valve works out. Quote Link to comment Share on other sites More sharing options...
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