PT20J

Since it seems repeatable, I would remove a spark plug from each cylinder and remove the rocker covers and compare the valve motion in all cylinders when rotated by hand.

FWIW, I have found a lot of errors in the dash numbers for vendor parts in Mooney IPCs. Mooney frequently seems to dispense with leading and trailing zeros and sometimes misplaces dashes

It’s probably a Cleveland part number. https://www.parker.com/literature/Aircraft Wheel & Brake Division/AWB Static Files for Literature/AWBPC0001.pdf

I bought some window trim from Bruce Jaegar. I ordered beige but he also had gray as I recall. It is different from the original. It is soft silicone rubber and I needed to glue it on the backside with some clear RTV, but I really like it because it doesn't get hard and shrink like the original. Bruce retired, but you could contact the company and see if they still have it available. https://www.jaegeraviation.com/home Another possibility if the Plane Plastics beading is a hard plastic would be to paint it with gray SEM Color Coat.

Looking at AWI's website, there are two M20 200 hp mufflers https://www.qaa.com/products/aircraft-exhaust-system/mooney/m-20-200-ball-rib https://www.qaa.com/products/aircraft-exhaust-system/mooney/m-20-200-slip-rib-m20j They have different tailpipes and different muffler part numbers because one uses ball joints on the risers and the M20J version has slip joints. If the ball joint riser muffler has a straight exit pipe, perhaps they made up the wrong part when they built yours.

The Mooney M20J SMM says to use a wash primer -- which I believe is a self etching primer -- before applying an epoxy primer. So, I assume that's what the factory did. I've got a lot of paint chipping off the leading edges of all surfaces and various flat rivet heads that are not smoking (Interestingly, the paint is adhering well on a few rivets that are smoking). My paint guy says he sees that a lot on Mooneys. I'm having it painted at Sunquest. They are highly rated and paint Caravans for FedEX and seaplanes for Kenmore Air among others. I'm beginning to understand why my paint job is going to cost north or $40K when others seem to get it done cheaper.

If you have a bob weight, then you don't have a M20J and so the M20J SMM does not apply.

All of the airplanes before the M20K had trim assist bungees. They function to bias the elevator neutral point in the direction of trim reducing the need for incidence change of the horizontal stabilizer to eliminate stick force at the trimmed airspeed. The K and after have a bob weight (to increase stick force per g) and a downspring that changes tension with stabilizer trim movement to perform the same function.

Agree with @GeeBee. The circuit breakers protect the wiring between the circuit breaker and the load. (Think where the circuit breakers are in your home). You always want the circuit breaker as close to the power source as possible. The panel/glareshield lights are controlled by a couple of transistors. The fast blow fuses between the collector and the lamps for each transistor protect the transistors (and also the wire to the lamps) in case there is a short at the lamps or wire to the lamps.

Would you expect this to happen with epoxy primer?

All the negativity probably ran @George Braly off of here (which would be too bad because I think we all need to keep open lines of communication until this is understood),but he’s continued to post on BT. He posted a drip-evaporate-drip test on one of his Beechcraft panels and said he will post a complete YouTube video of the test maybe later today. One interesting thing is that he was able to polish out the brown stains whereas others including @donkaye have been unable to do so. So, perhaps not all paint reacts the same to G100UL. Maybe the paint on George’s test panels is newer or something. I believe he said they were not original Beech paint.

Under part 91, there is no requirement to change oil ever.

Generally a propeller will have maximum efficiency at a particular advance ratio J=V/nD, where V = TAS, n = rpm and D = prop diameter. So, faster true airspeed requires higher rpm (and vice versa). But if you need to fly high (perhaps for wind, weather or terrain) in a normally aspirated airplane, you may need to run higher rpm than optimum just to generate the power required.

Here’s a drawing from the M20J IPC. All it does is create a direct path from the front of the cowling into the air intake on the fuel injector servo with a butterfly valve to open and close it.

But it wasn’t the same test. In one, the fuel was allowed to evaporate on the surface and the reapplied repeatedly simulating a seeping fuel tank. In the other, the painted part was continuously soaked in fuel. This difference might explain the different results. More investigation seems warranted.

I was a bit skeptical of the first video, but I'm actually impressed by the quality of the second video. This guy's like Jack Smith: He read posts by his critics on MS and other sites and took pains to address them in his discussion of his observations and methods and carefully makes his case. Some may not like his conclusions but I cannot fault his approach or methodology. I would like to see GAMI repeat his tests as he performed them. Others should also. If the results are repeatable then we will know something.

Fuel flow went up because the power increased. But, I think your experiment proved that the optimum is pretty broad. Good catch. Yep, typo.

I think time in service needs to be taken in context. The mechanic at a museum I used to volunteer at once offered that he had great job security because, "When they fly these old airplanes, they break. And, when they don't fly them, they break." The point being that machinery likes to be used. An aged hangar queen will likely not be problem free even if it has low time. That's why age as well as time in service and the logbooks showing evidence of good maintenance all need to be taken into consideration. Together they tell a story. Individually, they don't mean as much. There was a M20J that flew daily traffic watch in the San Francisco Bay area in the 1980's. Someone here used to own it, and it's still flying I believe. Top Gun maintained it back in the day. When it got to 10,000 hours, Tom Rouch called Mooney and asked if there was anything special to look for at such a high time and the factory told him they had never seen one with that much time and to let them know if he found anything interesting (he didn't).

Bob Kromer (former Mooney factory test pilot) has written that the M20J was optimized for 2500 rpm. Roy Lopresti did a lot of flight testing with a heavily instrumented airplane including a torque meter to measure actual engine power. I have no reason to doubt Bob's recollection. And when you say you are trying to pick the optimum rpm, you really have to determine what parameter you are trying to optimize: mpg or TAS. Or, maybe engine longevity? In reality, the slope of the curve (for whatever parameter you are trying to optimize) vs rpm is probably pretty flat in the vicinity of the maximum. In other words, the difference between 2500 and 2550 is probably negligible. A lot of people just go by what seems to produce the least vibration. The red box is a concept, not a hard rule. As the APS folks have pointed out, CHT is a proxy for cylinder stress. And as Mike Busch has pointed out that if you keep the CHTs under control you won't be in the red box. George Braly told me that he has never gotten any normally aspirated engine to detonate under any condition with a CHT of 400 deg F or below. He has gotten mild detonation at 430 deg F with elevated inlet air temp, 100LL at the low end of the allowable octane rating, sea level maximum MAP and mixture leaned to between peak EGT and 35 deg F ROP. So, you are not going to detonate an IO-360 unless you try really hard. Mike Busch told me that he cruises at fairly low powers (he guessed below 65%, but he doesn't calculate it so he doesn't know for sure). His rationale, and I quote, is, "I'm a longevity guy, not a speed guy," The airlines in the days of the radials cruised at around 55% BHP according to several flight manuals I looked at for the DC-3 and DC-6. All airplane performance calculations are based on the drag polar. Here is the actual M20J cruise drag polar I got from Lowell Foster when he was an engineer at Mooney many years ago: CD = 0.164 + 0.72CL2 A more fun way to determine the optimum parameters for your airplane though is to just do a bunch of flight testing.

Bruce's Custom Covers makes empennage covers.

You might be on to something. The bungees are the only part of the trim system that is not rigidly connected to the trim wheel. They should be lubed every annual. I might set the trim to the landing position and then check the elevator for anything that impedes its movement.

I wouldn’t read too much into those percentage ranges. Most likely, the amount of each component is much more tightly controlled. Companies blur the ranges intentionally to avoid disclosing the formula which is a trade secret.

No idea if this is the issue with the exhaust pipe wearing out, but they can get stressed by thermal expansion if you don’t keep the slip joints lubed and free. The “screens” within the muffler are usually called flame tubes or flame cones and they don’t seem to last long. Mine were completely gone on my J after about 500 hrs. As long as they are not restricting the exhaust flow, many mechanics just ignore them.

I don’t believe GAMI ever identified the chemical component of G100UL that leaves brown stains, but according to this source m-toluidine turns brown when exposed to air and light. https://pubchem.ncbi.nlm.nih.gov/compound/m-TOLUIDINE

I think maybe we pay too much attention to %power perhaps because we all learned in airplanes with power charts that showed %power and were admonished not to lean above a certain %power. But I question with modern instrumentation if %power really matters. I have a few MAP/rpm/ FF settings I use and I don’t ever think about %power.