High CHT, 470 degrees +.

[takair]

Any chance you have a Standby vacuum system that takes vacuum off cylinder 4?

[cliffy]

I looked at all the responses here and didn't see any that addressed the spark plugs  ( I could have missed it)

Have you ever tried a different pair of spark plugs?  Have you ever tested the ignition leads for shorts or opens? 

Even new plugs can come with problems.  I'm thinking ignition problems with high a high BMEP setting (high power related)  Maybe a hot spot on one plug causing slight preignition?

I'm really thinking cylinder specific instead of carb specific unless the carb maybe has something diverting the airflow. How about the AD on the old 2 piece venturi that came apart sometimes? Has that been checked? 

I didn't notice if you have actually taken the intake tube off and looked at all that stuff very carefully?  Cracks in the rim of the intake tube where it seats against the head?  Really look it over good off the engine?

Can you remove the intake tube and then bolt it back on without the connector rubber tube and see if it will tighten up and seat properly.   With a gasket in place!

If it does,  after a good internal cleaning try a new gasket and re attach the intake tube for another try.  How about a new rubber coupling at the same time to try?

I'm into doing the easy and cheaper stuff first.  

Edited April 11, 2020 by cliffy

[ragedracer1977]

3 hours ago, takair said:

Any chance you have a Standby vacuum system that takes vacuum off cylinder 4?

No.

[ragedracer1977]

1 hour ago, cliffy said:

I looked at all the responses here and didn't see any that addressed the spark plugs  ( I could have missed it)

Have you ever tried a different pair of spark plugs?  Have you ever tested the ignition leads for shorts or opens? 

Even new plugs can come with problems.  I'm thinking ignition problems with high a high BMEP setting (high power related)  Maybe a hot spot on one plug causing slight preignition?

I'm really thinking cylinder specific instead of carb specific unless the carb maybe has something diverting the airflow. How about the AD on the old 2 piece venturi that came apart sometimes? Has that been checked? 

I didn't notice if you have actually taken the intake tube off and looked at all that stuff very carefully?  Cracks in the rim of the intake tube where it seats against the head?  Really look it over good off the engine?

Can you remove the intake tube and then bolt it back on without the connector rubber tube and see if it will tighten up and seat properly.   With a gasket in place!

If it does,  after a good internal cleaning try a new gasket and re attach the intake tube for another try.  How about a new rubber coupling at the same time to try?

I'm into doing the easy and cheaper stuff first.  

Replacing spark plugs was the first thing I did when this started.  Didn’t help.  Then I installed the surefly and new fine wires.  Didn’t help. 
 

I thought I addressed this earlier in the thread, but maybe I didn’t.  I pulled all the intake tubes and oil return lines.  New gaskets and new connector tubes on all 4 intake tubes, and new rubber connectors on the return lines.  Didn’t help.

I have to assume the AD was taken care of sometime in the last 57 years.  

Edited April 11, 2020 by ragedracer1977

[cliffy]

Well damn Back to square one.  Last item just might be the carb. 

If its not what then? Cam?

[carusoam]

Hmmm...

One thing that would indicate everything else working properly.... including the cam...

• T/O distance and...
• initial climb as a second piece of back-up data...

an app like CloudAhoy and a WAAS source can measure T/O to the foot... and climb rate...

and... CloudAhoy is free this month for lots of great performance capturing skills... a corona special.

 

If you don’t want to fly the plane... a stop watch to capture a 0 to 60 kias run should work...

end with a practiced abort...

Everything is still indicating that the engine is safe to fly... if not that is a different discussion...

PP thoughts only

Best regards,

-a-

[ArtVandelay]

Well damn Back to square one.  Last item just might be the carb. 
If its not what then? Cam?

The cam intake nodes are shared between 3&4 cylinders, so if both were acting up that would be a good guess (I had a similar problem). I don’t know if a partially opening exhaust valve could cause this, but can’t you pull the valve cover and manually turn the engine over to check the valve travel?

[PTK]

Unless I missed something what I have distilled from this thread is that the op has a ff and distribution issue. The distribution issue is most likely a consequence of the low ff through the tired carb. The carb is older and overdue for an oh or maybe replacement. @ragedracer1977 have you tried to increase the ff a little on the carb? Is that possible? Seems to me it can’t hurt to try and see how the temps react? You'd be surprised the difference in temps even 1gph can make! I fly the IO360 and don’t have any carb experience but 15.5 on TO seems low to me. I typically see 19.5 gph WOT full rich @ sl. Just thinking out loud. 

[ragedracer1977]

6 hours ago, carusoam said:

Hmmm...

One thing that would indicate everything else working properly.... including the cam...

• T/O distance and...
• initial climb as a second piece of back-up data...

an app like CloudAhoy and a WAAS source can measure T/O to the foot... and climb rate...

and... CloudAhoy is free this month for lots of great performance capturing skills... a corona special.

 

If you don’t want to fly the plane... a stop watch to capture a 0 to 60 kias run should work...

end with a practiced abort...

Everything is still indicating that the engine is safe to fly... if not that is a different discussion...

PP thoughts only

Best regards,

-a-

Takeoff roll was 886' on the last flight. Quick extrapolation from the POH says that's probably a little faster than expected. Accelerated to 100 knots before reaching 100' agl.  Climbed at 105-108 knots. 

Edited April 11, 2020 by ragedracer1977

[carusoam]

Fantastic data, Brice!

Man those M20Cs rock! 

Did you get a climb rate with that as well? (Compare to book value)

Best regards,

-a-

[ragedracer1977]

25 minutes ago, carusoam said:

Fantastic data, Brice!

Man those M20Cs rock! 

Did you get a climb rate with that as well? (Compare to book value)

Best regards,

-a-

Book or better.  7-900 fpm through 6500

[carusoam]

We need to find a carb OHer to ask some pertinent questions to...

Do we know any?

Best regards,

-a-

[Skates97]

Here you go Brice, the numbers and info from my double carb replacement experience.

 

[ragedracer1977]

13 minutes ago, Skates97 said:

Here you go Brice, the numbers and info from my double carb replacement experience.

 

Excellent!

[Guest]

8 hours ago, PTK said:

Unless I missed something what I have distilled from this thread is that the op has a ff and distribution issue. The distribution issue is most likely a consequence of the low ff through the tired carb. The carb is older and overdue for an oh or maybe replacement. @ragedracer1977 have you tried to increase the ff a little on the carb? Is that possible? Seems to me it can’t hurt to try and see how the temps react? You'd be surprised the difference in temps even 1gph can make! I fly the IO360 and don’t have any carb experience but 15.5 on TO seems low to me. I typically see 19.5 gph WOT full rich @ sl. Just thinking out loud. 

The only field adjustments to a carburetor are idle mixture and idle speed.  Once the mixture control is at full rich there is nothing more that an operator can do to increase fuel flow.

Clarence

Edited April 11, 2020 by M20Doc

[orionflt]

Just brought my plane down to Virginia today. Took a few picks of my temps in cruise. 
didn’t get any pics during climb out because it was too bumpy, but my max CHT was around 330 on # 3. 
Oat was around 50 on the ground and 32 at 4500 ft. Had everything pulled back to keep out of the yellow because of the constant chop. 
the first pic was just after TOC. The second was about 20 min into the flight. 
 

[carusoam]

@ragedracer1977 Brian posted a set of M20C data to your thread...

Just a Note to let you know...   

-a-

[ragedracer1977]

50 minutes ago, orionflt said:

Just brought my plane down to Virginia today. Took a few picks of my temps in cruise. 
didn’t get any pics during climb out because it was too bumpy, but my max CHT was around 330 on # 3. 
Oat was around 50 on the ground and 32 at 4500 ft. Had everything pulled back to keep out of the yellow because of the constant chop. 
the first pic was just after TOC. The second was about 20 min into the flight. 
 

Can you upload your data to savvy?

Here's an interesting data point.  And I have no idea what to make of it. It was considerably warmer here, 30 degrees or so, but my carb temp was really low.  When I applied take off power, it dropped from 70+ degrees to 40 almost instantly, and then continued to drop down into the 20's. Even lower later.  

Look what happens when I turn on carb heat.  EGT drops and so does CHT.  In one example (I only have 2 short samples, #4 was pretty stable, carb heat on, then off.  After I turned it off, it started climbing. 

Does anyone else have any data points on carb temp? Seems a little strange that mine would be so cold. I don't know what would cause that, it's strange

 

Edited April 12, 2020 by ragedracer1977

[orionflt]

I will grab a usb and download it tomorrow. 
 

Brian

[carusoam]

One of the recommendations above was to see if carb heat system was working properly...

I didn’t expect it to show up as anything would be getting colder... but...

carb heat automatically cuts back on the Lbs/hr of air getting through the carb with the change in air density... it draws in less gasoline as well...

with a result similar to pulling back the throttle...

So... less fire in the same amount of time, less heat input to the engine, no change in cooling... resulting in lower CHT and EGT...

Carb heat also draws air through a much more restricted passage... really cutting back on the CFM that is available....

When flying around at MGTW... beneath clouds... high rh air has a tendency generate carb ice... and more restriction to air flow...

The interesting oddity... the EGTs get reorganized by the carb heat and haven’t settled back in over a minute...  a very strong sign of the carb having something to do with the main challenge... just a sign, not a smoking gun, unfortunately...

carbs naturally can cause freezing temps with OATs in the 90s...add in high rh... they become natural ice makers...

I know @Hank has some M20C carb heat with carb temp gauge experience...

PP thoughts only, not a mechanic...

Best regards,

-a-

[mark21m20c]

Breaking in engine on m20c and getting high temp (480 on 3 and 4 ) first 1000 feet after take off . CHT go back to normal range after accelerating. Sea level airport and 70 degrees. Would this be considered normal for engine break in?

Thank You

 

[bfreelove]

I noticed in one of the photos you posted the rear lower cylinder baffles appears to have a small gap between the baffle "wrap" and the cylinder fins.  In my experience this area can be  sensitive to small adjustments.  The baffle there needs to stay tight to keep force all of the cooling air to stay in contact with the fins. Especially on the exhaust side.  Beyond that, try to find every single leak and fill it with RTV etc.  It doesn't take very many small leaks to lower the overall cooling efficiency.  

Also you can measure the lower baffle openings (front to back) to make sure that the middle inter cylinder baffle is evenly spaced between the two.  The size of the opening is critical to good cooling. 

Edited April 12, 2020 by bfreelove

[ragedracer1977]

46 minutes ago, bfreelove said:

I noticed in one of the photos you posted the rear lower cylinder baffles appears to have a small gap between the baffle "wrap" and the cylinder fins.  In my experience this area can be  sensitive to small adjustments.  The baffle there needs to stay tight to keep force all of the cooling air to stay in contact with the fins. Especially on the exhaust side.  Beyond that, try to find every single leak and fill it with RTV etc.  It doesn't take very many small leaks to lower the overall cooling efficiency.  

Also you can measure the lower baffle openings (front to back) to make sure that the middle inter cylinder baffle is evenly spaced between the two.  The size of the opening is critical to good cooling. 

I’ll take a look at that, thanks!

[ragedracer1977]

3 hours ago, carusoam said:

 

The interesting oddity... the EGTs get reorganized by the carb heat and haven’t settled back in over a minute...  a very strong sign of the carb having something to do with the main challenge... just a sign, not a smoking gun, unfortunately...

PP thoughts only, not a mechanic...

Best regards,

-a-

Interesting, right? In the longer example, even CHTs swapped.

[Oscar Avalle]

On 4/9/2020 at 10:49 AM, Skates97 said:

If you're going to replace the carb you want to use the 10-4164-1, it is the richer of the carbs.

 

It is a carb issue that the Mooney's have. I keep meaning to write up a post about my carb replacement journey, I'll try and start a thread on it tonight with all the data/info(work has been crazy cutting down on my MS during the day time...)

In a nut-shell...

There is the 10-3878, 10-3878M, and 10-4164. The "M" is just a modified 3878 which makes it the same FF as the 4164. I went back and forth on emails with Marvel-Shcebler and got some good information out of them. They had the specs from the bench test on my the 3878 that went in my plane in October which they tested at 16.7 GPH but I only saw 14.5-15 GPH resulting in much higher CHT's than I previously had. I have the JPI data from before the carb replacement, which apparently was a "M" despite nothing in the log books, the data with the 3878 that was put in last October, and the data from the 4164 that was put in last month. Some interesting numbers and how the FF on the different carbs acts as well as effect on EGT and CHT. More to come in a different thread, don't want to totally sidetrack this thread as I'm not sure that is Brice's problem?

At least that was my problem and I got that right 80% of my problem disappeared.