jetdriven Posted August 30, 2013 Report Posted August 30, 2013 Even after GAMIjectors, and after two rounds of tuning we have the smallest injector in #2 (F), and A, C, and Ein the other cylinders, the #2 cylinder is still much richer than the others, peaking about .8 GPH before the rest, and at LOP, it runs 100F leaner. Im starting to suspect its the flow divider.
OR75 Posted August 30, 2013 Report Posted August 30, 2013 question on the A3B6D to A3B6 conversion: how did the engine swap go ? was is really just a drop in replacement if you have that 1 bracket for the governor ? or was there other small items you had to change ? same fluid hoses ?
jetdriven Posted August 30, 2013 Report Posted August 30, 2013 It takes the governor arm bracket, the governor cable bracket, and different oil cooler hoses. IIRC thats all it was, but I posted a detailed writeup for all on here in one of the threads.
carusoam Posted August 31, 2013 Report Posted August 31, 2013 Byron is there a way to check the air flow into each cylinder? If there is a blockage to the richest cylinder, it would appear as running rich. If the intake valve has gotten a coating of LL goo on it, it's flow may be restricted. We have a tendency to watch fuel flow into each cylinder, but not the air flow as much. Thinking outside the box, in a chemical engineer sort of way. Ymmv... Best regards, -a-
bradp Posted May 2, 2014 Report Posted May 2, 2014 Hi all... The 77J is in for annual and mags are getting overhauled at 540 hrs. Engine model is an A3B6. Per the MSC timing was set at 20degrees, as per the data plate. I'm interested in at least considering setting 25 degrees advance. Per this thread it seems like this might be possible. Was the Lycoming documentation that may allow this just for the b6d to b6 conversion or for b6 in general? Please feel free to post or private message. Thanks for helping. Brad Sent from my SCH-I535 using Tapatalk
OR75 Posted May 3, 2014 Report Posted May 3, 2014 two candid questions: I understand that Lycoming somehow allows for the timing to be set at 25 .... but why do they recommend 20 ? what do you gain by setting the timing to 25 ?
carusoam Posted May 3, 2014 Report Posted May 3, 2014 Burning fuel takes time. If it didn't, it would be an explosion. Explosions are uncontrolled and would damage the engine... Timing that is furthest from TDC (25dbtdc) allows time for the flame front to spread. This maximizes the pressure that occurs on the down stroke. The cost is higher CHTs and increased probability of other things (like pinging). Engines are approved for timing settings. Some got 25 and others got 20. There are too many things going on with the engine to take on experiments that are not approved. It would likely get unusually expensive to go outside the approved range... Might be during the heat of summer or the cold of winter... Overall power increases as timing increases before TDC. until the pressure wave is too large before TDC, then power destroys the engine. That's my understanding, and it comes from my automotive background... Let me know if I missed something. Best regards, -a-
N201MKTurbo Posted May 3, 2014 Report Posted May 3, 2014 A lean mixture burns slower then a rich mixture. If you are running ROP. Set your timing to 20, if you are running LOP set it to 25. It will run much better.
hindsight2020 Posted May 3, 2014 Report Posted May 3, 2014 FWIW I went through a similar back and forth on my Arrow's -C1C. Early S/N were 25*, later they went to 20*. Mine was a 73 but got re-engined with a '79 Lyco that got stamped at 20. At annual the AP caught the last owner had it at 25*. I started sweating bullets about the performance loss. Got the airplane back and did a test flight. No change. Zip, zilch, nada. Cruises at the same true on the same fuel. I suspect my climb rate is infinitesimally less and the takeoff run will be equally so adjusting for condition. Not enough to warrant chasing rabbits for a re-timing. I also suspect that it will run rougher when attempting LOP at high altitudes. I was able to run the thing at 7gph around 12,500 without roughness, exactly the same as I was doing at 25*. The argument about starting easier I also didn't see. It should have been harder to start at 25* in the first place, but it hadn't been. So maybe on a dyno would see it, maybe at top end RPM and WOT you'd see it, maybe at super LOP you'd see it, but for nominal cruise power settings and your middle of the road takeoff climb, you probably won't know any different. Of course as with all these things, YMMV.
Recommended Posts