Mooney Engine Baffling System, alternator and electrical pump for my M 20 C

[Oscar Avalle]

Questions and questions...

I had a nice flight today, but some little problems showed up and put me in a bad mood...

First my CHT on 3 got close to 490.... Then I leveled off and it went down to 434, but I could not get it below 430. The other CHTs, were below 400 in the 380 range. I feel that my engine baffling system is not working well, may be it is not sealing well. I took off the cowling and saw on the front right baffle a circular hole. I am not sure that this is right? and if there should not be something to close that hole.

So I was wondering if somebody could share with me a picture of the baffling system of the M20C, also know as the doghouse, in particular its upper part.

Second Also, while I was on my final approach, I turned my electrical boost pump on. It made a very load noise (fuel pressure seemed to be OK).

Last, but not least, my battery was not charging beyond 12.9 V. I guess I will need to adjust my regulator...

I am currently spending some time in Guatemala, there are only two Mooneys in the country, mine and one that has been parked in front of my hangar for at least 5 years, without being used...So, please if somebody could help me and provide me some advice that would be really appreciated.

[Steve65E-NC]

First: Your sudden problem with CHT on #3 may be a partially plugged injector. Fits what I have seen. I recommend having that injector pulled and cleaned with a soak in gun cleaner. You do not tell us the year so I do not know if you have the inner dog house over the engine. If before about 67, you probably do have the dog house, like my 65E. If so, I take a tube of high temp silicon, look from the inside with the outer cowling removed, make sure any seam openings in the sheet aluminum dog house are sealed (give it time to cure). I get concerned anytime my CHT gets over 400 for more than a minute or so.

Second: Check your aux pump fuel pressure with the engine off. I think they are all a littly noisy.

Third: Check your regulator voltage at the battery, or other heavy connection, with the engine running. My JPI always shows something less than does the battery. Probably varies with the load you have on that buss.

Steve 65E NC

[BigTex]

First: Your sudden problem with CHT on #3 may be a partially plugged injector. Fits what I have seen.

Unless Oscar's M20C has had the engine changed to fuel injection, he's likely running with an O-360A1D.

Oscar - Did you by chance notice what your EGT did on your #3 Cylinder during this time? EGT numbers are generally meaningless but can be a very good tool to troubleshoot problems if one changes drastically.

[Steve65E-NC]

Opps. My head got on automatic based on my own experience.

[jrwilson]

I have a C model also, 1963, and the cooling issue probably is the baffling, but I don't have a picture of the dog house. On the fuel pump, I changed my electric boost pump and it got quieter, so maybe time for one of those. It was relatively cheap, in the grand scheme of aviation things, $100 I think, and install was quick.

[Oscar Avalle]

Thank you for all your responses. Indeed mine is a m20c with a o360a1d. I just got 35 hours on my engine. EGT on number 3 has been high but has not changed...

The specific question that I still have is if the dohouses' upper right front baffle has a circular hole just above the coil of the upper spark plug of cylinder 1.

[BigTex]

I'm not sure how you can have a spike in CHT and not see a change in EGT as well. Maybe one of our A&P's out there can shed some light on that. You might want to swap CHT probes to see if the temp follows the probe.

[Oscar Avalle]

Gary, thank you for your feedback. This has not been a spike but cht 3 and EGT3 have been high since I got the engine back from overhaul. This AM I downloaded the information from my jpi and cht3 mad egt3 have been high but stable. That is why I believe that I have a "cooling problem".

Oscar

[carusoam]

What cooling ducts do you have at the back of the dog house?

I believe there are two that are aimed at the magnetos.

I think you might have one aimed at the vacuum pump?

Is it possible that the "extra" hole that you have is for a cooling duct.

Thinking out loud for you...

-a-

[Hank]

Oscar--

I'm going into annual this week. I'll take a doghouse photo for you unless the mechanics take it all apart first. That's usually my job, but it seems to vary year to year depending on how busy they are. Seems like I get to "assist" more every year.

[jlunseth]

I would be suspicious of other issues such as one plug not firing or a "hot spot" such as carbon causing a plug to glow red in turn causing pre-ignition. That temp just strikes me as being way too high for a baffle problem, although it could be I guess. But I would expect to see more than one cylinder running too hot if it was a baffle issue.

[Oscar Avalle]

Oscar--

I'm going into annual this week. I'll take a doghouse photo for you unless the mechanics take it all apart first. That's usually my job, but it seems to vary year to year depending on how busy they are. Seems like I get to "assist" more every year.

Thank you I will really appreciate getting the picture. I will ask to change the spark plugs on cylinder 3...

[jetdriven]

490 degrees is way, way over the limit for safe operations. If your redline is 500 then you are right there, any higher and you have to pull the cylinder off. I would check the ignition timing very carefully that it is not too advanced and check for air leaks in the baffling and in the induction system. Also, many of those carburetors have a main jet that is too small IE, too lean at ful throttle takeoff mixture. Vans RV guys ream that jet slightly larger for more full rich fuel flow. You cant legally do that, but perhaps there is an updated part number main jet you can install.

Also one thing further if you are using a lower spark plug washer thermocouple, they can read 80 degrees hotter than reality.

i would not fly it again until the problem is resolved.

[MooneyMitch]

As far as a hole in the top baffle cover over the spark plug area, there is a "bubble" cut out for each spark plug. But that bubble cut out is filled with a riveted convex type cover. Possibly the hole you are speaking of is a missing cover, creating an exposed opening. The diameter of the hole is approx. 2 inches or so. Hope that helps. If I could only download a photo for you. I will learn that soon, hopefully. :-(

[Oscar Avalle]

Thank you. Indeed that is the hole i am referein too. Oscar

[Oscar Avalle]

Just to close the discussion, i adjusted the opening of my fixed cowflaps to 1.5 inchea and the cht on cyl 3 went down feom the high 400 to about 408 in cruise and 470 on take off on a hot day. So problem solved...

[jetdriven]

If you are seeing 470 on takeoff then your problem is not solved. That cylinder might last 100 hours. Keep working on the problem. It is about to get a whole lot more expensive.

[Oscar Avalle]

If you are seeing 470 on takeoff then your problem is not solved. That cylinder might last 100 hours. Keep working on the problem. It is about to get a whole lot more expensive.

Suggestions please.... what else could it be?

[jetdriven]

Did you do all these?

I would check the ignition timing very carefully that it is not too advanced and check for air leaks in the baffling and in the induction system. Also, many of those carburetors have a main jet that is too small IE, too lean at full throttle takeoff mixture. Vans RV guys ream that jet slightly larger for more full rich fuel flow. You cant legally do that, but perhaps there is an updated part number main jet you can install.

For example, our engine will run 40 degrees hotter CHT with the timing at 25 instead 23 degrees.

[Oscar Avalle]

Byron,

Thank you and I really apologize for my frustration. I checked the airflow, I checked the baffling and the induction system... I checked compression in Cyl 3... I did not check the carburator. But your comment on the timing actually called my attention. I went through my LASAR ignition documentation and I read that the LASAR ignition advances timing and thus increases the CHT temperature by 25 to 30 degrees, in particular above 5000 feet... Considering that my field elevation is 4960 feet and that the OAT was 27 degrees celsius (DA around 7000 feet). So may be that could be the problem.

[jetdriven]

That LASAR ignition MUST be set by a special box, a regular buzz-box won't do it. A friend of mine got a new Lycoming engine, from the factory, set to 40 degrees timing. There is a way to disable the advance and have it run as a standard set of magnetos. I would definately look into this ASAP. Running 470 CHTs on takeoff, that engine wont last a year.

[N201MKTurbo]

Considering that cylinder 3 is where the stock EGT and CHT sensors are installed, and that any aftermarket scanner usually has a somewhat different installation on cylinder 3, I would check your thermocouples. I have all my CHTs in the thermowells except #3 which is a ring under the stock sensor. I dislike the rings under the sparkplugs, they are hard to install and get damaged easily and make lousy spark plug waswhers.

[Oscar Avalle]

During my last three flights chts on cyl 3 have been going down. I am now At 454 at 27 celcius. The other cylinders are just doing great.

[rbridges]

as someone just said, I'd also check the sensor. It could be wrong.