Hello all,

We've recently finished an engine/prop overhaul on the Twin, and installed an Insight G4 twin engine monitor. I've since been "analyzing" the data it logs, and trying to better tune my engines to make it smoother, more efficient, etc. I'm having trouble figuring out an issue with one engine's number 2 cylinder. I'll attach the graph of one flight where I was playing with the mixture and leaned it out several times, so the issue is very apparent. #2 cylinder ends up being about 50°F leaner than the other 3, so I end up needing about an extra .6 GPH total fuel flow for that engine in order to accommodate that lean cylinder. I have tried moving the richest injectors to that lean cylinder in different combinations, and it has little to no effect on the performance. It runs fine and the EGT's seem to be right in line with each other in all phases of flight so long as the mixture is 100°F+ rich of peak. It only shows up when I'm trying to lean it out to cruise settings. (usually shooting for 75° ROP) The injectors are the newer style 2-piece Bendix. I don't believe the flow divider could cause an issue like this, but am I assuming something I shouldn't?

EDIT: I should add that the issues I'm seeing are more pronounced on the older engine, not the one that was just overhauled. I'm only now seeing them because of the new addition of the engine monitor. The fresh overhaul is looking much more uniform, although not as perfect as I would like to end up with.

From SavvyAnalysis.com

Might look at cooling and especially after engines have been off the plane. How are the flexible baffles?

See page 4 of this blog for what I did in this regard. http://www.comancheflyer.com/forum2/vie ... les#p47838

Kristin Winter's baffles are the best I've seen.

How many degrees from peak should I reasonably expect to be able to achieve? I ask this in terms of the spread between degrees ROP or LOP from the first to the last cylinders to peak.

Check for an intake leak of any kind on the "lean" cyl (intake tube cracks, intake gasket, cracked cyl on the intake side gallery adjacent to the spark plug, degraded or cracking intake tube rubber coupling). I'm assuming it goes to peak first not just shows the hottest egt? Remember egt is very dependent on where the probe is in the stack. Referencing just the number of degrees of temp. is worthless. Referencing a number vs a zero point of peak is what needs to be done.

Zach

 

At WOT the effects of an intake leak would be less noticeable than when there is higher vacuum, so it could be the injector, but as you said you changed the lean for rich cyl and no change I don't think that is your issue (if the metered oriface isnt the issue, you could have a line obstruction or the flow divider could have an issue). You could rule the injector out by doing the baby food bottle test as outlined in the Lycoming and Bendix RSA manuals and see if the injectors are flowing at the same rate. Other than that, you may have a valve train issue and I would look hard for a burned exhaust valve or insufficient balance travel due to a bad lifter or worn cam on the intake side.

Zach