High CHT's on Takeoff

[jimosborn]

Guys & gals;

 

There's a wonderful article by John Deakin posted on AvWeb in his "Pelican's Perch #18" titled "Mixture Magic" that deals with the entire combustion subject - fuel, timing etc.  It's a hugely important tutorial for pilots all.  Among other essential learning it contains a  graph depicting what happens to cylinder materials when overheated - sobering stuff for those routinely seeing temps above 400^oF. 

 

Enjoy the class!   http://www.avweb.com/news/pelican/182084-1.html

 

Cheers!

[kurtsnyder]

I should clarify that I get the very high CHT temps on #3 and #4 cyls. The front 2 run just fine. The Insight G2 has a probe diagnostic page and all the probes are working just fine.

[BigTex]

All,

 

It looks like we lost some a portion of this thread that had my engine analysis link so I re-posted it:

 

https://savvyanalysis.com/flight/216933/0b4ebb0e-2468-4037-8762-e9c41a73f705

 

Jim and a few other folks thought that my timing might be off was well as a slight induction leak on #3.  So based on this analysis I had my mechanic check and the timing and as it turns on the time was set to 17-18 degrees!  He's adjusting the timings this weekend.  It will be interesting what kind of change I'll see.  Couldn't find the leak but we'll do some additional testing in that area once we get the time issue corrected.

 

Thanks for all who provided input.

[jimosborn]

Gary, it will indeed be interesting to see the difference after re-timing.  Do you know if your A&P is using a digital timing device?  I ask because those are infinitely more accurate than other methods, particularly so is using the fairly new and simpler to use Rite-Systems kit  --   http://www.ritesystem.net/index.htm

 

Too, 17^o & 18^o BTC is quite retarded from 25^o factory specs, thus I'd expect to see much higher EGTs and lower CHTs than yours show  -  exactly opposite of what I thought was going on in your situation - therefore my specific curiosity about how timing is being measured.  Regardless of method, if you've not seen it done before and have opportunity to be there, it will be quite educational to observe the mag timing exercise in process.

 

Cheers!

[BigTex]

I actually wasn't there when he checked the timing but I'll have to ask what he used.

[jimosborn]

Gary, have you had a chance to fly and evaluate your CHT situation since re-timing, including a JPI download?

 

Cheers!

[BigTex]

Long story short...  My mechanic went to time the mags but discovered that the prior A&P that installed the mags after an IRAN didn't index them correctly so we had to pull them.  In the process of pulling the mags we noticed that my right mag was missing 4 of the 5 bolts and the 5th bolt was just about to fall out.  Not good.  After some investigation it looks like the prior A&P had challenges installing the mag so he disassembled it and installed it in parts.  After reassembling the mag, he never tightened up the bolts.  If it wasn't for the prop governor angle bracket, the mag would of completely come apart!  Just when you think you've seen everything, this happens.

 

Right now my mag is at a mag shopped being IRAN'ed.  I hope to have the plane back in the air next weekend. 

[jimosborn]

Holy Mackerel, that's incredible.... just jaw dropping incredible!  No wonder you and we who've weighed in on the subject have been scratching heads!  Does makes me feel a little better for sermonizing about a possible timing issue though.

 

Sounds like your A&P is a whole bunch smarter than the so-called mechanic who did the mags earlier.  Hope the entire CHT issue is then resolved, and we're looking forward to hearing the results.

 

Cheers!

[KSMooniac]

Wow.

[jimosborn]

Gary, any news on your CHT issue after getting the mag problem straightened out?

 

Cheers!

[BigTex]

Hi Jim, Mag issues are resolved. The engine is running better than it ever has. Still working on the #3 EGT issue. My mechanic seems to think it my be a plug issue. Since all of the plugs got some age on them, I'm taking this opportunity to install some fine wire plugs to see how the work out. I've also replaced som old baffling around the front of the doghouse. It was allowing airflow to go over the top of the doghouse. The end result is that I'm still seeing high CHTs on takeoff. I'll post more engine data after I finish up with the plug swap out.

[jimosborn]

Glad to hear the mag issues are resolved, Gary, and that she's running better than ever.  I sure expected some noticeable CHT improvement with proper timing though.  Not sure how much difference changing the plugs will make but from my own experience with leaking baffles I suspect replacing the front doghouse baffling will yield a remarkable improvement in CHT..... chip, chip, chip away!

 

Do keep us informed of your progress; inquiring minds and all that! 

Cheers!