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Old Sep 07, 2012, 06:40 PM
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Help!
OS 70 Surpass Four Stroke doesn't sound right.

Hey Guys,

I have a four stroke the was in the box awhile. It runs basically well but it has this intermittent knock. It almost sounds like something is loose or broken and I don't beieve it's getting full power. Any ideas? Thanks.

James
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Last edited by JBG7676; Sep 07, 2012 at 07:18 PM.
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Old Sep 07, 2012, 08:23 PM
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I thought the same regarding my .72. Came to find out the knocking was the clunk in the fuel tank.(thank goodness). Regarding reaching full power, mine doesn't ever sound like "full power". But it seems to have it when flying. You may want to try different props. The surest way is to use a tachometer.
If the specs in your manual are anything like mine, don't expect what it reads.
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Old Sep 08, 2012, 08:18 AM
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Thanks for responding. It's not the clunk. The engine makes the sound when it is on the bench.
Anyone have any experience sending engines back to OS Repair Service?
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Old Sep 08, 2012, 08:42 AM
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What fuel, prop and rpm?
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Old Sep 08, 2012, 03:38 PM
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Hobby Services has always done a good job on my engines.

Bruce
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Old Sep 09, 2012, 04:47 AM
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Quote:
Originally Posted by JBG7676 View Post
Thanks for responding. It's not the clunk. The engine makes the sound when it is on the bench.
Anyone have any experience sending engines back to OS Repair Service?
Do you mean you can hear the noise when hand
cranking on the work bench,or when running on a test stand?
If you hear it when it's not running,it's most likely the wrist pin or rod bearing.

If it's when running,try going a little richer and see if it gets quieter.Too lean,or too large a prop can cause a noise like preignition.
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Old Sep 09, 2012, 05:37 AM
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Plug?
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Old Sep 09, 2012, 07:46 AM
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Quote:
Originally Posted by epoxyearl View Post
Do you mean you can hear the noise when hand
cranking on the work bench,or when running on a test stand?
If you hear it when it's not running,it's most likely the wrist pin or rod bearing.

If it's when running,try going a little richer and see if it gets quieter.Too lean,or too large a prop can cause a noise like preignition.
My experience coincides with Earl. Open the needle a little, and see if the noise goes away.
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Old Sep 09, 2012, 09:40 AM
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I had a 12X7 prop, Fuel was wildcat 15%, but then I used S&W 20% which ran better I think it was the YS blend, i put a new plug in. I did not note the tach. It makes the noise running not by turning prop by hand. I did make it as rich a possible it did not change.
Thanks for the input, I just sent it to Hobby Services because I'm in the middle of moving and just want it fixed. I'll keep you posted incase anyone else has the same issue. Thanks for everything guys!
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Old Sep 09, 2012, 01:37 PM
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Knock

Rod knock, piston slap, all kinds of things can cause it to knock, curious what it was. Let us know will you.
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Old Sep 09, 2012, 05:46 PM
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Running too lean can cause this.
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Old Sep 10, 2012, 04:11 PM
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Get a methanol buzz .
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It is worthwhile to try grasping the prop while the engine is warm, rocking the prop to check for excessive bearing clearance .
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Old Sep 11, 2012, 06:17 AM
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Will do, engine will be at Hobby services Wednesday
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Old Sep 21, 2012, 06:27 AM
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Hey Guys,

Hobby Services received my engine on the 12th and had it dissassemled the same day. They found front and rear bearings to be rough/rusted and valves needed adjustment. The bearings are back ordered so I will not get it back for about two weeks. So far parts and labor $95.00. Ill let you posted on progress and results.
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Old Sep 21, 2012, 10:59 AM
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$95 ? Ouch......
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