OS 70 Surpass Four Stroke doesn't sound right. - RC Groups
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Sep 07, 2012, 07:40 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
Last edited by JBG7676; Sep 07, 2012 at 08:18 PM.
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Sep 07, 2012, 09:23 PM
Registered User
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.
Sep 08, 2012, 09:18 AM
Registered User
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?
Sep 08, 2012, 09:42 AM
Registered User
What fuel, prop and rpm?
Sep 08, 2012, 04:38 PM
Registered User
Hobby Services has always done a good job on my engines.

Bruce
Sep 09, 2012, 05:47 AM
Bellanca Kruesair
epoxyearl's Avatar
Quote:
Originally Posted by JBG7676
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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Sep 09, 2012, 06:37 AM
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Plug?
Sep 09, 2012, 08:46 AM
ARFs Are Me
TomCrump's Avatar
Quote:
Originally Posted by epoxyearl
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.
Sep 09, 2012, 10:40 AM
Registered User
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!
Sep 09, 2012, 02:37 PM
AMA 959374

Knock


Rod knock, piston slap, all kinds of things can cause it to knock, curious what it was. Let us know will you.
Sep 09, 2012, 06:46 PM
Registered User
Running too lean can cause this.
Sep 10, 2012, 05:11 PM
Methanol, The Cool Fuel !
Gary Cee's Avatar
It is worthwhile to try grasping the prop while the engine is warm, rocking the prop to check for excessive bearing clearance .
Sep 11, 2012, 07:17 AM
Registered User
Will do, engine will be at Hobby services Wednesday
Sep 21, 2012, 07:27 AM
Registered User
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.
Sep 21, 2012, 11:59 AM
Registered User
$95 ? Ouch......


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