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kitfox812
04-12-2009, 12:32 PM
I am in denial but I think I am in trouble. I just turned over 345 trouble free hours on my 912ULS when I had a new noise last week. Kind of a slight rattling noise that comes and goes. Could not find anything loose and the engine ran fine at all speeds. Today I ran it without the cowl off and hear a definite but slight rattling,knocking sound at 2150 rpm on warm up. It goes away at 2000 and 2200 and on up. I am still flying but since I don't like off airport landings, I have to ask if anyone has any ideas.
....Please say its OK...
Oil usage is nill and has been changed on schedule since new. Average fuel consumption is 3.7 and always non-ethanol 91 octane.
The cost and loss of flying time is going to be grim. I don't even know where to get it fixed if I have to.

thanks in advance
Rich L

Slyfox
04-12-2009, 12:36 PM
what kind of prop

kitfox812
04-12-2009, 01:25 PM
Powerfin 3-blade 71"

DesertFox4
04-12-2009, 03:51 PM
Rich , The 912 series has a stellar rep. so lets check all the easy things first. I'll assume you checked all exhaust fittings for the rattle or new rubbing marks anywhere on the inside of your cowlings.
Lets take a look at the baffle inside the muffler next. When everything is quiet tap the muffler with a rubber hammer carefully and see if it rattles. I had mine come loose on my 912 years back and it made a weird noise but not at all rpms. If it has come loose you may need a new muffler or like me you may be able to remove the baffle one small piece at a time by breaking it up with a long needle nose pliers through the exhaust pipe inlets but of course you'd have to remove the muffler to do it. Not a great fix and very tedious but it got me flying again and seemed not to affect performance at all. Just a slightly different exhaust note.

allbee already mentioned checking the prop.

I would think if it was a gearbox problem you'd hear something different sounding when you turn the prop by hand or feel extra gear "slop" while hand propping. Do you have a slipper clutch in your gearbox?

Good luck and keep us posted.

kitfox812
04-20-2009, 06:12 PM
First I want to thank you all for the ideas to make me think in another direction and Im not gonna say that box thing.
I found the tab on the lower cowling which slides over the radiator in a KF-7 had somehow become weak and was not fitting as firm as it did in the beginning. I had put rubber tape under it but the fit had loosened to the point where it ratteled againsed the radiator. I am going to add a peice of fiberglass to the tab and put a thicker peice of rubber in between. It was scary but the Rotax is still running great.

thanks again for all of your input

Rich

DesertFox4
04-20-2009, 06:42 PM
That is good news Rich. Good catch. Glad it was not serious. :)

n85ae
04-21-2009, 11:51 AM
I had a very subtle whirring noise with my IO-240B, and wasn't even sure
I was hearing a noise. Til one night it turned into a loud screeching sound,
which then went away. That definetly get's the heart started. It was a vac
pump eating itself.

So definetly don't ignore those little noises.

Jeff

Pilot4Life
04-22-2009, 05:35 AM
Jeff,
In the intrest of finding just the right engine, I've seriously considered the IO-240 due to it being 100hp. I am 6"2', 215 lbs. If I were to take my brother up with me, I'd need to extra umph. I am looking to see if there's a good engine research site or forum that can help with the decision. Also, was the IO-240 your first engine for yours? I am still 2+ years out from engine installation. I need to do a couple things first, like, "Oh, I don't know?" BUY A KITFOX. It's still a year or two out, due to deployments, but I'd like to start researching now and have a good knowledge base when the time comes. Thanks in advance for your reply.

n85ae
04-22-2009, 11:21 AM
Chris -

I have an IO-240B, and I like it. However, I also like the O-200, and
the 912's, so I'd hate to say use this or that engine. I'd say the O-200
is probably the least complicated, most reliable of the bunch. However
the 240B has more power, oh BUT the 912 is a lot lighter, and lighter is
good in a Kitfox. Plus there's lot's of 912's out there, and most people
I know really like them.

My 240B in flight spends most of it's life around 2000 rpm, and I get
really good fuel consumption (around 4 gph). Solo with half tanks of
fuel it's pretty much the takeoff/climb king at the airport. You really
don't need the power for other than takeoff.

Full power the IO-240B pulls the plane up to 140, which is NOT a
comfortable speed for the Kitfox, 120 is generally the fastest cruise
speed I use and feels a lot less like a runaway freight train.

The 240B can be grumpy to start in the winter if it's cold. In fact
I have a second battery that I occasionally set on the CP side floor
and connect in with jumper cables for the initial start on cold days.

None are bulletproof, I lost my 240B once when the engine driven pump
failed so you CAN become a glider pilot with any of them. The Continental
continuous-flow fuel injection system does not work well on a boost pump
having less than 30 psi pressure, so at least in my case the pump I had
at the time didn't do anything (it was the original Facet from Systar) I
now have a (very expensive) Weldon pump, which hopefully if I ever
lose a pump again will keep it running.

I probably prefer Continental engines, but they're very expensive.

Jeff