YS FZ120 rattle  
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All Forums >> Glow Engines, Gas Engines, Fuel & Mfg Support Forums >> Glow Engines >> YS FZ120 rattle
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YS FZ120 rattle - 4/20/2002 11:12:17 PM   
snsmith



Posts: 332
Joined: 1/11/2002
From: Greenville, SC, USA
Status: offline 		I have a new YS FZ120 on my Laser with almost a gallon through it now. After 4 tanks on the stand to break it in, I flew it for the first time today and noticed an occasional rattling sound on fly-bys that I'm not sure about, usually at high throttle settings, but not at idle.

I'm using the stock muffler, an APC 15x10 prop, OS F plug and 20/20 fuel. The engine's mounted on a Gator soft-mount and everything is still nice and tight after three flights. I checked the valve clearances after flying, and they were right at 0.1mm, but I tightened them up a bit anyway. I'm sure it's not too lean, as I peaked it with a tach at around 9200 and then richened it a quarter turn to about 8700 for flying. There was good smoke at all times. It's still not broken in fully, as there is little compression when turned over by hand (I'm assuming the ring hasn't seated fully, resulted in poor compression).

Any ideas? Is the rattle normal? What is the rattle likely to be? Is it underpropped? Other than the occasional rattle, it runs great with good power. Thanks!
       Post #: 1

UnderProped? - 4/21/2002 2:34:31 PM   
JohnW



Posts: 1688
Joined: 3/22/2002
From: Lincoln, NE, USA
Status: offline 		At first I instinctively was going to say "too lean" but you mentioned a good smoke trail. I'm a little worried about your static RPM. Don't think you have enough prop and you are getting too many RPMs. The rattle is probably valve float. I really don't know for sure... but I do know the rattle isn't normal. Try to keep your RPM under 8500 on the ground. I have a YS120FZ and use a APC 16x10... might try that prop.

Don't bother with the test stand break in. Engines often won't cool properly when static. Just fly it. I've had six YS engines and broke-in all off them in the air. Never had any problem doing it that way.

On the YS140/120 I typically set my high needle three clicks rich from peak. Might be the same as 1/4 turn... never checked that as I always just count the clicks.

Don't know what is up with your compression. You should have decent compression after just a few minutes of run time.

Great engine... enjoy.

(in reply to snsmith)
       Post #: 2

YS FZ120 rattle - 4/21/2002 5:49:47 PM   
snsmith



Posts: 332
Joined: 1/11/2002
From: Greenville, SC, USA
Status: offline 		Thanks for the input MonkeyBoy...it does seem to do it more at high throttle, so maybe it's unloading too much in the air. I was a little worried about being underpropped, but the instructions showed a 15x10-12 as the prop range.

Going bigger is a little risky due to prop clearance, but I have a 15x10 Menz prop that should load the engine a bit more and keep RPMs down. I'll give that a try and see if the rattle is still there.

I'm not too worried about the compression (yet) as it comes and goes when turning by hand. My FZ91s did the same thing...it took a couple of gallons to get good compression. The engine fires right up and pressurizes the tank and runs great (except for the occasional rattle).

(in reply to snsmith)
       Post #: 3

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