High CHT - Engine Stumper of the Week

[orionflt]

I know you said the mags were done 100 hrs ago and you checked the timing, but was the internal mag timing and E gap checked? most of the time when you get a mag back from a 500 hr everything is perfect but occasionally they mis time and or gap the mag. you may not even really notice it except it may hard start when hot, or even some of what you are seeing with your CHT's. when did you notice the CHT issues ... did it correspond to the time frame after the mags were done?... did it come on slowly and keep getting worse?

just a few things to think about

 

Brian 

[Bob - S50]

Look at the shape of the EGT curves in your latest test.  Notice that cylinders 2-4 all drop pretty steeply once they go LOP.  Number 1 cylinder goes almost flat.  That is, the EGT does not drop off as sharply as it should once you go LOP.  This mirrors the CHT shapes.  Also notice that number 1 is the coolest EGT until you reach the peak EGT area.

 

To me, that says, for some reason, #1 may be getting more fuel flow that the others and it continues to do so even after you go LOP.  It's almost as if you cannot shut off the fuel flow to #1 by leaning.  I don't know what would cause that.  Maybe a bad fuel distributor (spider)?

 

Maybe an A&P here would have an idea.

 

Bob

[N601RX]

The #1 egt not falling off like the the other three may by a spark plug problem in that cylinder. It may be firing fine when ROP, but is marginal when LOP.  Swap the 2 plugs from that cylinder with another cylinder and see if the problem follows.

[carusoam]

Brenden...

It is normal when all four do the same thing with a handful of degrees between them. Offset slightly by FF.

A perfect engine will overay all the data within a tight spread.

The 2011 EGT picture shows two different sets of data... A tale of two engines...

I'm unclear of what the X axis is actually representing. The data chart says 'setting'.

Is it in increments of 0.1 GPH? This is what I think is happening...

Could be time? Can't be GPH...

Notes indicate what a good GAMI spread is.

Did you not have a FF indicator in 2011?

Or am I just missing what you are showing?

I was expecting to see charts of EGT vs GPH And CHT vs GPH... (Like in 2014)

On the EGT chart they should peak in less than .5gph. Better if they are within .1 GPH....

What I understand....

Flying along level, constant power setting, ROP, you lean step wise through peak, into LoP...then you enrichen the mixture step wise, back towards ROP.

Each of the steps is actually a FF.

What is the FF of the first to peak?

What is the FF of the last to peak?

What did you consider peak? 1418 on the first cylinder to peak?

It really helps to put the data on the same type of graph with the same scale.

Cylinder 1&4 are behaving differently than 2&3...

CHT adds to the complexity because of variations in cooling as well as variations in heat generation(EGT)

The most interesting data is near peak with FF measured at 0.1 GPH...

The 2014 data goes from 8.5 to 9.5 GPH in four steps. It takes time at each step to equilibrate...

Overall, there are better ways to display the data for a clearer discussion. But you are onto something unusual...

Trying to help...

Best regards,

-a-

[Cruiser]

the only thing you have not checked (at least here) is the EGT/FF spread at peak for each cylinder. I would be interested to see the EGT/CHT traces for all cylinders as you lean from full rich through peak EGT and then LOP.  You can do this at 7000 or 8000 MSL without any issues.

 

CHT is the by product of internal combustion AND external cooling. If the above data appears normal, then it has to be an external cooling problem not an engine problem.

 

OK, I went back and saw the graphs in your post #21. You can see from the very beginning of the graph that both #1 and #4 are higher temperature than the others. The #1 cylinder has a baffle plate in front of the cylinder that extends up the front of the cylinder and is held in by two bolts, it is L shaped, reducing the height of this by ¼" can improve the cooling for #1, I don't know about #4 but I would be looking to improve the baffle/air flow for that cylinder also. Are all the cooling fins clear and free of debris and paint? Shine a light up from under and make sure all the cooling fins are open, not blocked

 

Where (which cylinder) is the OEM CHT probe and how is EI probe attached to that cylinder?