FL-70 loss of power
06-01-2008, 05:08 PM
#1
Thread Starter
FL-70 loss of power
Hi Bax,
Hope you can help me out with this problem, as you've helped me many times in the past.
I have an FL-70 running on CoolPower with 15% nitro and turning a 13x6 APC grey prop. For some reason, I cannot get it to put out the power like it did just a month ago. I have it in an Excelleron 50 and just a month ago it had unlimited vertical, and take offs were short. This model has stock soft mounts which came loose slowly, robbing the power. I did not know the mounts were loosening, but I sure noticed that gradually the plane was struggling to get off the ground and vertical disappeared. When I finally discovered the loosening and softening soft mounts, I dumped the soft mounts and built hardwood rails on top of the existing rails to make the engine mount solid. Anyway, today, the plane was better but still struggled somewhat, and I put a friend's tach to it and found it running only 8600rpm max, which I backed down to about 8200 rpm for flying. It just hasn't got the pep it had originally (I did not tach it before today). I did check the glow plug, it was fine, but I changed anyway and got the same lackluster performance. I should mention that I logically (to me) tried to lean the engine more when power gradually decreased over time as the soft mounts loosened and softened. I also tried a 12.5x6 and 12x7 prop before going back to the 13x6 prop and hard mounts today. What can you suggest to reobtain that fantastic performance the engine had a month ago with short take off runs and unlimited vertical? Thanks Bax. Jon
Hope you can help me out with this problem, as you've helped me many times in the past.
I have an FL-70 running on CoolPower with 15% nitro and turning a 13x6 APC grey prop. For some reason, I cannot get it to put out the power like it did just a month ago. I have it in an Excelleron 50 and just a month ago it had unlimited vertical, and take offs were short. This model has stock soft mounts which came loose slowly, robbing the power. I did not know the mounts were loosening, but I sure noticed that gradually the plane was struggling to get off the ground and vertical disappeared. When I finally discovered the loosening and softening soft mounts, I dumped the soft mounts and built hardwood rails on top of the existing rails to make the engine mount solid. Anyway, today, the plane was better but still struggled somewhat, and I put a friend's tach to it and found it running only 8600rpm max, which I backed down to about 8200 rpm for flying. It just hasn't got the pep it had originally (I did not tach it before today). I did check the glow plug, it was fine, but I changed anyway and got the same lackluster performance. I should mention that I logically (to me) tried to lean the engine more when power gradually decreased over time as the soft mounts loosened and softened. I also tried a 12.5x6 and 12x7 prop before going back to the 13x6 prop and hard mounts today. What can you suggest to reobtain that fantastic performance the engine had a month ago with short take off runs and unlimited vertical? Thanks Bax. Jon
06-02-2008, 09:54 AM
#3
My Feedback: (11)
RE: FL-70 loss of power
Your engine will need a teardown to see what its problem might be. Because you leaned it as the power went down, you very likely ran the engine too lean at one point and possibly got it too hot. This could cause a bad fit between the piston and cylinder liner. In either case, you've lost compression when the engine gets warmed-up and that means power. You'll either need a new ring or new valves.
06-02-2008, 10:06 AM
#4
Thread Starter
RE: FL-70 loss of power
Thanks for the quick response Bax. Could you ballpark me the cost of either job if I send the engine to you? Sounds expensive. I need to weigh that against just getting a replacement. Thanks again.
06-02-2008, 10:46 AM
#5
Senior Member
Join Date: Mar 2006
Location: Kershaw, SC
Posts: 838
Likes: 0
Received 0 Likes
on
0 Posts
RE: FL-70 loss of power
ORIGINAL: Bax
Your engine will need a teardown to see what its problem might be. Because you leaned it as the power went down, you very likely ran the engine too lean at one point and possibly got it too hot. This would cause the ring to lose tension or a valve to warp. In either case, you've lost compression when the engine gets warmed-up and that means power. You'll either need a new ring or new valves.
Your engine will need a teardown to see what its problem might be. Because you leaned it as the power went down, you very likely ran the engine too lean at one point and possibly got it too hot. This would cause the ring to lose tension or a valve to warp. In either case, you've lost compression when the engine gets warmed-up and that means power. You'll either need a new ring or new valves.
06-03-2008, 10:37 PM
#7
Thread Starter
RE: FL-70 loss of power
My son suggested that it might be worth pulling the valve cover off to see if the valves have proper gaps. Worth a try before replacing or sending the engine in for repair. Opened it up, and one rocker had a huge gap of more than 1/16th inch! We narrowed it down with a calibrated piece of paper (best we had :P). My guess is the vibrations allowed by the soft mount caused that rocker nut and set screw to loosen, leading to substantial power loss. I'm anxious to see if I get my original power and performance back this weekend!!! That would be great. Jon
06-07-2008, 09:49 PM
#9
Thread Starter
RE: FL-70 loss of power
Our feeler gage was copy paper which my son said was 3/1000th of an inch thick or so. I got to fly the Excelleron 50 with the FL-70 on it today, with the valve lash reset per copy paper, haha. It ran like a champ, like it did originally. Take off run was short again, with lots of torque, and the plane had unlimited vertical again! Needless to say, I am real happy that the fix was this simple and that I did not actually overheat and ruin the engine. Whew, looking forward to flying it more tomorrow/Sunday. Jon
