*OS 120AX Bearing Noise*

*OS 120AX Bearing Noise*
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*OS 120AX Bearing Noise* - 10/1/2006 11:12:40 PM

Zippi

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From: Evansville, IN, USA
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I have my OS 120AX two stroke on a Seagull Laser 200 and it flys great with an APC 17X6 prop but the engine sounds really rough when it idles like a bearing is going out. I have less than two gallons of Byrons 10% fuel through it and I always run it a little on the rich side. Does anyone elses 120AX sound like this???

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RE: *OS 120AX Bearing Noise* - 10/2/2006 3:13:38 AM

w8ye

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Big glow two strokes often have a rattle that people are trying to fix.

Determine if the bearings are still good....
You need to feel of your crankshaft rotation for roughness or to see if you have any play (looseness)

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RE: *OS 120AX Bearing Noise* - 10/2/2006 12:53:23 PM

Flyer95

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From: STOCKHOLM Akersberga, SWEDEN
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The OS quiet muffler is very quiet but have a strange sound/ note at the lower throttle part. Both the 91FX and the 120AX had that strange sound at the lower part throttle. Some would think it is bad bearings and some say preignition, but it is not that. I tried a colder plug and rich idle settings and it would still sound the same. Now I have a quiet pipe on these engines and the sound is much cleaner like a twostroke is supposed to be and also much nicer

Bad bearings have a really wining and annoying sound and I have hard time to believe yours would get bad after only two gallons. Mine has more than two gallons thru it mostly at full throttle and the bearings are smooth as silk

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RE: *OS 120AX Bearing Noise* - 10/2/2006 11:44:27 PM

Zippi

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From: Evansville, IN, USA
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Thanks for the info guys.

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RE: *OS 120AX Bearing Noise* - 10/21/2006 1:40:53 PM

Oldbob

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From: georgetown, TX, USA
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Hay Zippi, I think your onto something. My 120AX also made a funny noise as I started to lean out the needle valves for optimum performance. To me it sounded like piston slap caused by early detonation. This can happen if the engine has too much compression or too much nitro. Since I am using Power Master 5% I don’t think it’s the nitro. I added a .005 shim to the head shims already in the engine and the noise is gone and the HS needle valve is much easer to adjust.

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Post #: 5

RE: *OS 120AX Bearing Noise* - 10/21/2006 1:49:31 PM

Hobbsy

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I ran my 1.20AX yesterday and it makes that same sound, so do my big Fox's and several other large two strokes, it's the nature of the beast.

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RE: *OS 120AX Bearing Noise* - 10/21/2006 8:08:53 PM

Oldbob

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From: georgetown, TX, USA
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Hobbsy, than why did the noise go away after I put the .005 shim in? Is what you are saying it’s the nature of the beast to be over compressed?

oldbob

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RE: *OS 120AX Bearing Noise* - 10/21/2006 8:34:28 PM

Hobbsy

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Back er down a notch or two there Bob, judging by all the others I have that do that it is the nature of the beast.

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RE: *OS 120AX Bearing Noise* - 10/22/2006 3:12:40 AM

Oldbob

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From: georgetown, TX, USA
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Hay Hobbsy, sorry, I did not mean to come off in a negative way. I just did not know your meaning by “the nature of the beast”. I hope we can move on.

If you add a .005 head shim, the beast will thank you for it.

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RE: *OS 120AX Bearing Noise* - 10/22/2006 4:11:36 AM

Hobbsy

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I run 5% Fox fuel in all my two strokes, it's surprising that they rattle on 5%, I checked the plug on the 1.20 today it is an OS #8. The odd thing is, it doesn't do it above half throttle.

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RE: *OS 120AX Bearing Noise* - 10/22/2006 5:34:39 AM

Oldbob

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From: georgetown, TX, USA
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Maybe you have the high-end needle valve set a little rich which cools the engine and retards ignition. In my case, I didn’t notice the rattle during the break-in runs, but after four or five tanks of fuel I started to lean the engine and the rattle was plainly noticeable.
To stop it I just richened the needle setting. Also the needle setting was very critical which is a sign that the engine may have too much compression. I have had this problem with a few other engines and by adding a head shim or two the rattle went away and a good needle setting was easier to obtain.

If you decide to add a head shim let us know the outcome.

oldbob

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RE: *OS 120AX Bearing Noise* - 10/22/2006 7:28:29 AM

DarZeelon

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quote:

ORIGINAL: Hobbsy

I run 5% Fox fuel in all my two-strokes, it's surprising that they rattle on 5%, I checked the plug on the 1.20 today it is an OS #8. The odd thing is, it doesn't do it above half throttle.

Dave,

Maybe going to 5% fuel is insufficient and it is necessary to change to a colder plug.

What boggles me is why OS supplies this engine with a #8, while their glow-plug page says under no uncertain terms, that it needs their A5 (or another COLD plug)...

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RE: *OS 120AX Bearing Noise* - 10/22/2006 12:23:26 PM

Hobbsy

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The 1.20 AX is a good strong engine, mine turns a 15x8 Graupner a couple of hundred rpm faster than my Webra 1.20 and that was a total surprise.

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RE: *OS 120AX Bearing Noise* - 10/22/2006 9:25:05 PM

XJet

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From: Tokoroa, NEW ZEALAND
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quote:

ORIGINAL: Oldbob

Hay Zippi, I think your onto something. My 120AX also made a funny noise as I started to lean out the needle valves for optimum performance. To me it sounded like piston slap caused by early detonation. This can happen if the engine has too much compression or too much nitro. Since I am using Power Master 5% I don’t think it’s the nitro. I added a .005 shim to the head shims already in the engine and the noise is gone and the HS needle valve is much easer to adjust.

May not be relevant but I fould this from the ST FAQ to be quite interesting.

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RE: *OS 120AX Bearing Noise* - 10/23/2006 3:07:13 PM

Oldbob

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From: georgetown, TX, USA
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Xjet, thanks for the link to the Super Tiger FAQ. Its interesting reading. I never knew that an exhaust system of an engine could cause a metal-to-metal sound. It’s hard for me to accept this as the cause of the noise in my engine. All I do know is that on my OS 120AX the metal-like rattle noise went away after I installed an additional .005 head shim. Maybe the head shim changed the sound of the exhaust system, or maybe the head shim decompressed the engine and stopped the piston from slapping the cylinder wall?? In either case I will leave the shim because the engine sounds more normal.

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Post #: 15

RE: *OS 120AX Bearing Noise* - 10/23/2006 5:38:08 PM

jaka

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From: Upplands Vasby, SWEDEN
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Hi!
It's more likely that the compression was to high to begin with and that adding a 0,1mm head shim fixed it.
I personally don't believe in the Super-Tigre's explanation. To me it's just over compression (or too much nitro or both) that makes this sound.

Regards!
Jan k

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