Cylinder 4 High EGT/CHT on Ground

I am breaking in my new IO-540 and on the fourth flight I noticed a spike in Cylinder 4 EGT after landing. To a lesser extent the CHT also climbed.

This is what the temps looked like at cruise (25"/2500rpm). Pretty normal except maybe for CHT 1 & 2 being higher - need to trim the dams a bit more. Note Cyl 4 CHT is consistently the lowest temp and EGT spread is minimal.



After landing the Cyl 4 EGT crept up significantly in relation to other cylinders and Cyl 4 CHT is now the highest.



What might explain this spread at ground power settings? What to check? I am thinking ignition or fuel injector blockage but am still pretty new to this.

The data logs for flights 1-3 do not show this spread (EGT or CHT ) for cruise power or ground power settings.

Before you trim anything I would look for a partial blockage in an injector or the flow divider. I had this exact scenario (but in a 4 cyl) and it was something in the flow divider.

Nova RV said:

Before you trim anything I would look for a partial blockage in an injector or the flow divider. I had this exact scenario (but in a 4 cyl) and it was something in the flow divider.

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Interesting. What did you end up doing to correct it?

Nova RV said:

Before you trim anything I would look for a partial blockage in an injector or the flow divider. I had this exact scenario (but in a 4 cyl) and it was something in the flow divider.

Click to expand...

+1 to do this.
Suggest you first do the shot glass test to measure flow to each cylinder. Did this on an IO-360 with the same problem to find one cylinder getting much less flow at idle. The root problem was a tiny spec of crud in the spider.

Carl

Carl Froehlich said:

+1 to do this.
Suggest you first do the shot glass test to measure flow to each cylinder. Did this on an IO-360 with the same problem to find one cylinder getting much less flow at idle. The root problem was a tiny spec of crud in the spider.

Carl

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Makes sense - will try that per the AFP manual.

Just out of curiosity did you see any issue while at cruise power?

bsvantho said:

Interesting. What did you end up doing to correct it?

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Flushed out the flow divider and it was good afterwards. Before you open the flow divider, do the flow test as Carl mentions and it will be clear if there is a partial blockage in that cylinder.

bsvantho said:

Makes sense - will try that per the AFP manual.

Just out of curiosity did you see any issue while at cruise power?

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No - just at idle or low power. The symptoms were similar to a sticking valve.

Carl

Great, seems like the culprit, will do some testing. Thanks for the guidance guys.

Flow test

Hi Guys,

Just out of interest

How do you do the flow test? What are the shot glasses for?

Best

Amer

Check out pages 70-71
https://airflowperformance.com/wp-content/uploads/2018/12/API-Installation-Service-Manual-9003.pdf

Nova RV said:

Check out pages 70-71
https://airflowperformance.com/wp-content/uploads/2018/12/API-Installation-Service-Manual-9003.pdf

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For a quick check of just the spider, you can disconnect the line at the injector (leave injectors installed) and put a shot glass under each disconnected line.

Carl

bsvantho said:

Makes sense - will try that per the AFP manual.

Just out of curiosity did you see any issue while at cruise power?

Click to expand...

Above 6~7 GPH, flow division is function of nozzle restrictor size. At that point the piston in the flow divider is raised enough to uncover high volume ports, allowing fuel to bypass the metering slots. Those slots control division at low flow rates. As noted, the slot feeding #4 probably has some trash in it. So lean cylinder when at 3 GPH (slot blocked), normal at 19 GPH (blocked slot bypassed).

Photos and illustrations pages 16 and 17 here:

https://www.danhorton.net/Articles/Bendix-and-Beyond (1).pdf

DanH said:

Above 6~7 GPH, flow division is function of nozzle restrictor size. At that point the piston in the flow divider is raised enough to uncover high volume ports, allowing fuel to bypass the metering slots. Those slots control division at low flow rates. As noted, the slot feeding #4 probably has some trash in it. So lean cylinder when at 3 GPH (slot blocked), normal at 19 GPH (blocked slot bypassed).

Photos and illustrations pages 16 and 17 here:

https://www.danhorton.net/Articles/Bendix-and-Beyond (1).pdf

Click to expand...

Did the shot glass test and sure enough almost nothing from No. 4 direct from the flow divider. The slot was restricted with a nearly invisible piece of debris. I am now intimitately familiar with the mechanics and geometry of the flow divider. It was a good learning experience. Did a run up, all is well after the cleaning.