FP40 feels strange when crank turned
05-01-2007, 10:21 AM
#1
Thread Starter
FP40 feels strange when crank turned
Hello,
Have O.S. Max 40 FP that I've put probably three gallons or so of fuel through it. Throughout it's life have adjusted the needle so that it increases RPM when subjected to the pinch test. For sake of argument, assume there's been a lean run here or there, but by no means is it run lean with any regularity.
After flying it this weekend, upon shutdown, as I rotated the prop through a revolution, the engine no longer had a distinct compression feel at TDC and relatively easy to turn around the rest of the arc, but rather was stiff through a large portion of the prop rotation and less stiff through the rest. Tough to describe in words, but hope it makes some sense.
Any ideas?
Frank
Have O.S. Max 40 FP that I've put probably three gallons or so of fuel through it. Throughout it's life have adjusted the needle so that it increases RPM when subjected to the pinch test. For sake of argument, assume there's been a lean run here or there, but by no means is it run lean with any regularity.
After flying it this weekend, upon shutdown, as I rotated the prop through a revolution, the engine no longer had a distinct compression feel at TDC and relatively easy to turn around the rest of the arc, but rather was stiff through a large portion of the prop rotation and less stiff through the rest. Tough to describe in words, but hope it makes some sense.
Any ideas?
Frank
05-01-2007, 01:56 PM
#2
My Feedback: (11)
RE: FP40 feels strange when crank turned
Sounds like you may have a bent crank. That can be caused by a ground strike, crash, backfiring, an electric starter, and so on. If you remove the piston/rod assembly from the engine, and it turns over easily, and the the piston/rod assembly will easily slide up and down the cylinder liner when out of the engine, a bent rod is likely. If you look carefully at the rod, end-on, you may actually see the curvature. It can most certainly be measured, if you are careful.
05-01-2007, 09:47 PM
#3
Thread Starter
RE: FP40 feels strange when crank turned
Bill,
Thanks so very much. I disassembled the engine tonight and sure enough, there was a slight, yet discernable bend in the rod.
I really love the engine, got it used and I've put three gallons through it and until this, was going strong. Suspect I bent the rod when I hit it with electric starter after engine was overprimed accidentally (bright sunlight and couldn't see fuel flowing into carb).
Any other things to watch for to prevent a repeat?
Thanks again. BTW, like the engine so much I've got another one (new in box) for another project!
Frank
Thanks so very much. I disassembled the engine tonight and sure enough, there was a slight, yet discernable bend in the rod.
I really love the engine, got it used and I've put three gallons through it and until this, was going strong. Suspect I bent the rod when I hit it with electric starter after engine was overprimed accidentally (bright sunlight and couldn't see fuel flowing into carb).
Any other things to watch for to prevent a repeat?
Thanks again. BTW, like the engine so much I've got another one (new in box) for another project!
Frank
05-02-2007, 10:49 AM
#4
My Feedback: (11)
RE: FP40 feels strange when crank turned
To prevent hydraulic lock, which is what happens when the engine's over-primed, you must turn the engine over a few times by hand before applying the starter. We open the throttle to full, without the glowplug battery connected, and briskly flip the propeller several times. Once you can do that, you can retard the throttle, connect the glowplug battery, and then apply the starter to get the engine running.
