Shop our Airplanes Products Drone Products Sales
Thread Tools
Old Sep 07, 2012, 07:40 PM
JBG7676 is offline
Find More Posts by JBG7676
Registered User
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.
Sign up now
to remove ads between posts
Old Sep 07, 2012, 09:23 PM
seair is offline
Find More Posts by seair
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.
Old Sep 08, 2012, 09:18 AM
JBG7676 is offline
Find More Posts by JBG7676
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?
Old Sep 08, 2012, 09:42 AM
whitewolf is offline
Find More Posts by whitewolf
Registered User
What fuel, prop and rpm?
Old Sep 08, 2012, 04:38 PM
landeck is offline
Find More Posts by landeck
Registered User
Hobby Services has always done a good job on my engines.

Bruce
Old Sep 09, 2012, 05:47 AM
epoxyearl is offline
Find More Posts by epoxyearl
Bellanca Kruesmaster
epoxyearl's Avatar
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.
RCG Plus Member
Latest blog entry: New Builders are appearing.
Old Sep 09, 2012, 06:37 AM
TimBle is offline
Find More Posts by TimBle
Registered User
Plug?
Old Sep 09, 2012, 08:46 AM
TomCrump is offline
Find More Posts by TomCrump
ARFs Are Me
TomCrump's Avatar
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.
Old Sep 09, 2012, 10:40 AM
JBG7676 is offline
Find More Posts by JBG7676
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!
Old Sep 09, 2012, 02:37 PM
FlyingBrick50 is offline
Find More Posts by FlyingBrick50
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.
Old Sep 09, 2012, 06:46 PM
706jim is offline
Find More Posts by 706jim
Registered User
Running too lean can cause this.
Old Sep 10, 2012, 05:11 PM
Gary Cee is offline
Find More Posts by Gary Cee
Smart to be kind without cruel
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 .
RCG Plus Member
Old Sep 11, 2012, 07:17 AM
JBG7676 is offline
Find More Posts by JBG7676
Registered User
Will do, engine will be at Hobby services Wednesday
Old Sep 21, 2012, 07:27 AM
JBG7676 is offline
Find More Posts by JBG7676
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.
Old Sep 21, 2012, 11:59 AM
shooboy is offline
Find More Posts by shooboy
Registered User
$95 ? Ouch......


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Sold OS 70 Surpass Dunedinflyer Aircraft - Fuel - Engines and Accessories (FS/W) 2 Jul 16, 2012 05:58 PM
For Sale OS Max 70 Surpass Four Stroke Grumpy Monkey Aircraft - Fuel - Engines and Accessories (FS/W) 0 Jul 08, 2012 08:05 PM
Sold New OS Max 70 Surpass Four Stroke Mounted But Never Run LCS Aircraft - Fuel - Engines and Accessories (FS/W) 2 Jul 06, 2012 10:34 PM
Sold OS Max 70 Surpass Four Stroke with 8 Flights LCS Aircraft - Fuel - Engines and Accessories (FS/W) 0 Jul 06, 2012 09:07 PM
Sold OS FS 48 Surpass fourstroke engine hobbylink1 Aircraft - Fuel - Engines and Accessories (FS/W) 0 Jan 23, 2009 01:38 PM