| Gents-
Seems like we have this resolved. Thank you to all who responded, especially George Braly. For reference:
I was loath to run the CHT's above 390. I was worried that I had some bad setup somewhere (timing, fuel flow, MAP, baffling) that was causing higher temps than I was comfortable flying with. The guys at BPA (backed up by the TCM manual and aircraft operating handbook) say that continuous operation below 420 degrees is just fine. Not forever, but breaking in an engine in the summer means that higher than normal operating temps (I was used to 360-380 max in a full power climb) are ok. Quote "if you stay below 420 you are not hurting a thing, and in fact we want those higher temps and pressures during break in to seal the rings good".
That assumes of course that some other bad combustion and/or timing events are not happening. I did find out that the engine was timed a bit too far advanced. The motor was built with 7.5 : 1 compression pistons, and we retimed the motor twice with 2 different methods to make sure each mag was at 24 degrees BTDC (indications were that they were about 26 AND 25). I found out from George B that if you have your motor built with 8.5:1 pistons, 21.5 degrees BTDC is the correct timing.
After assuring that the timing was correct and all baffling was tight, flew again today. Full power WOT/ROP climb all the way to FL220 with max CHT recorded as 398 (see attached photo 1). At level off, motor was fine, cooled down nicely and ran strong at lower power settings and when LOP. A follow up call with BPA guys confirms this is totally acceptable. Thoughts?
Last question for guys that have IV-P's - see attached photo of cyl 5 and 6 with silicone on the front of the fins. Do you guys recommend this? I have 2 local mechanics (neither IV-P owners, which is why I am going to the source) that adamantly disagree, one says its horrible and the other says its necessary. Can you respond with pictures? I have all of the other recommended IV-P mods but am not sure about this one. I will accept any and all photos of IV-P baffling that you want to send to me direct. Greatly appreciated to compare my setup with you experts out there.
Again thanks for the responses that got me thru the break-in insanity. Plan is to tweak a few settings (MAP, max RPM, min oil pressure), and do a full up GAMI test tomorrow….
Bob Rickard
On Jun 25, 2012, at 7:27 AM, George Braly wrote: >> soon as throttle pushed in, cyl's 5 and 6 climb at about 1 degree per second - power always retarded not to exceed 390 and cool down in the 350-360 range before trying to push up power again.<< Bob, When I read that statement - - I stopped what I was doing (preparing a presentation for the ASTM in connection with the approval of the G100UL™ avgas ) - - In order to follow up. THIS IS IMPORTANT: There are VERY FEW THINGS IN AN AIRCRAFT PISTON ENGINE THAT CAN CAUSE AN OPERATING CYLINDER CHT TO SUDDENLY BEGIN TO INCREASE AT A RATE OF 1 DEGREE / SECOND ( 360 TO 390 IN 30 SECONDS, FOR EXAMPLE ) - - - except: 1) Outright pre-ignition; or, 2) Simulated outright-pre-ignition due to improperly advanced timing. MERE DETONATION - - EVEN MEDIUM TO HEAVY DETONATION - - will not do that. Amazingly, if you have caught and limited the CHT rise and managed that at levels under about 420 dF, as you appear to have done - - then you have likely NOT done any harm to the cylinders. But a borescope is in order. And change the spark plugs in those two cylinders. The plugs can be damaged from those kinds of combustion events. I have a lot of old and a lot of more recent data that documents all of the statements made, above. If you will forward to me the engine data downloads from those flights I will try to take a look at them and I can tell you what was going on. Call me if you want to. I might have some suggestions for you to allow you to proceed to get your aircraft flying again comfortably. However - - getting me the engine download data is the most important thing you can do. Regards, George <image003.jpg> George W. Braly Head of Engineering GAMI toll-free: 888-359-4264 ph: 580-436-4833 x1009 cell:580-421-5645 fx: 580-436-6622 On Jun 20, 2012, at 7:15 PM, Bob Rickard wrote: IV-P non turbine Fellow Pilots: First flight - one pattern only - Max MAP was set too low, low fuel flow - fixed. Next flight - 10 minutes - Cylinders 5 and 6 temps run away hot at 38.5 MAP and 45gph. Must retard throttle to less than 25gph (25ish MAP) to keep under control. Third flight - after checking baffling for hours and scratching head - same deal. Fly for 1 hour full rich at low power settings. Motor very smooth and happy at low settings, but as soon as throttle pushed in, cyl's 5 and 6 climb at about 1 degree per second - power always retarded not to exceed 390 and cool down in the 350-360 range before trying to push up power again. Fourth flight - today - a 2.3. Takeoff WOT and full rich. Can't get above 3000' agl before having to pull power for cal 5 and 6. Pull power to 25gph/25 MAP/Full rich and slowly climb to 10.5k MSL. Fly there for a while, cylinders all look great in the 340-350 range. After an hour, try full power climb, have to stop within 1500' of climb. So then I leveled out, and set my typical speed cruise LOP mode to try something different - 34MAP, 2500 RPM, 18-19 gph. Motor is very happy. All EGT's normal (actually less than previous engine by almost 100 deg), CHT's all between 340-365. I climb with this setting to 16.5 and cruise for another hour, no problem. Return to base, set full rich/2700 rpm, and land normally. At retarded power settings in the pattern, motor stays cool and happy. So what to look at? New motor mounts make the engine sit noticeably lower in the cowl, and we are checking the rear baffling to make sure there is a good seal, but would that affect the front 2 cylinders (5 and 6)? Every other indication (including the other 4 cylinder temps) are totally normal. Any other suggestions out there to look for? Appreciate your experience
Bob Rickard
President, Rickard Consulting Group, Inc.
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