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  #1  
Old 05-25-2018, 07:21 PM
plehrke's Avatar
plehrke plehrke is offline
 
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Default Do you rotate your injectors?

I heard years ago that at condition inspection you should clean and inspect your fuel injectors but always put them back in the same cylinder from where they were removed. I have been trying to find were I read or heard that years ago as I am starting to question if they should be rotated.
Do you always replace in same cylinder and why OR do you rotate in pattern OR put them back in any hole?
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  #2  
Old 05-25-2018, 08:03 PM
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airguy airguy is offline
 
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If you know for a fact that you don't have matched-flow injectors, then I guess it makes no difference if you move them around or not. If you've done the Gami-sizing and have specific injectors for each cylinder then you obviously don't want to move them around.
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  #3  
Old 05-26-2018, 09:03 AM
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FasGlas FasGlas is offline
 
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Moving the injectors around helps balance the cylinders. There are basically no two injectors exactly the same. Swap the hottest EGT with the coldest EGT, etc, until you find the closest matches.. Then they stay in those cylinders. Soak them in Hoppes #9 every annual and they come out like new.
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  #4  
Old 05-26-2018, 01:01 PM
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Quote:
Originally Posted by FasGlas View Post
Swap the hottest EGT with the coldest EGT, etc, until you find the closest matches..
No, you do not swap them to equalize indicated EGT. You substitute restrictor diameters until they all peak at the same time. The actual EGT values don't matter.

To the OP's question...there is no reason to rotate positions.
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  #5  
Old 05-26-2018, 01:28 PM
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Default Injector swapping

After burning a bunch of fuel, cowling and un-cowling the engine, spending a small fortune on different injector orifices from airflow performance, I would just die if someone swapped my injectors around.

I imagine if all the orifices were the same diameter it wouldn't matter.
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  #6  
Old 05-27-2018, 01:25 PM
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FasGlas FasGlas is offline
 
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Quote:
Originally Posted by DanH View Post
No, you do not swap them to equalize indicated EGT. You substitute restrictor diameters until they all peak at the same time. The actual EGT values don't matter.

To the OP's question...there is no reason to rotate positions.
Hmmm, Myself and most everyone one I know, for as long as I can remember, does this to get them as even (or peak) as possible. We don't move them after we get them where we want them. No two injectors flow exactly the same. But each to their own.
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  #7  
Old 05-27-2018, 04:18 PM
Timberwolf Timberwolf is offline
 
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Dan is correct. Called the GAMI test. Aiming to peak at the same fuel flow, regardless of what the actual egt temp is.

http://www.gami.com/gamijectors/leantest.php
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  #8  
Old 05-27-2018, 05:43 PM
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I like the ability to run lean of peak, so I did the GAMI process, bought 1 injector that was .0005 larger diameter for the hottest cylinder that wouldn’t come into line after methodical swapping and got everything to peak very close to the same fuel flow. After doing this, I asked an IA about the frequency of cleaning the injectors. His response was that the old recommendation was every annual, but after Cessna had some incidents due to crud getting into the injector mounting hole during the annual cleaning, the new recommendation was to monitor EGT’s and if there is an increased EGT noted on one cylinder, clean the injector and see if that helps, otherwise don’t remove the injectors.

Has anyone else seen/heard this advice?

Regarding differing sizes of injector opening: I’m not sure the variation of when the cylinders reach peak EGT is due to variations in injector hole size or simply variations in MANY things in the cylinder having the cumulative effect of different fuel/air flows and capacities. The solution is to vary the injector nozzle size, but it is not necessarily the cause. At least that is my understanding...

To the original question: I too would never change the position of the injectors because 1: I went to a lot of trouble to get them to peak within .1 gph of each other and 2: I have a known system with known characteristics and randomly changing the injectors will render that hard gained knowledge pointless. When something in the engine changes, I’ll know it and I’ll know that changing the position of the injectors didn’t cause it.
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Last edited by jjconstant : 05-27-2018 at 05:49 PM.
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  #9  
Old 05-27-2018, 07:24 PM
Lars Lars is offline
 
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I can't imagine why you would disturb something that's working fine. I believe history has shown that one likely way to have a problem where none existed previously is to take something apart and "inspect" it, just because someone thought it was a good idea. If CHTs and EGTs remain consistent, why mess with the injectors?
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  #10  
Old 05-27-2018, 07:52 PM
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Mike S Mike S is offline
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Quote:
Originally Posted by Lars View Post
I can't imagine why you would disturb something that's working fine. I believe history has shown that one likely way to have a problem where none existed previously is to take something apart and "inspect" it.

https://blog.aopa.org/aopa/2014/01/1...ington-effect/
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