OS .55 AX lost the pinch  
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All Forums >> Glow Engines, Gas Engines, Fuel & Mfg Support Forums >> Glow Engines >> OS .55 AX lost the pinch
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OS .55 AX lost the pinch - 11/20/2006 2:56:57 AM   
fc911c


 

Posts: 90
Joined: 6/23/2006
From: Greentown, PA, USA
Status: offline 		I broke in the engine on the bench his weekend after running a good half gallon. I noticed that the engine didn't seem to tight when new and now there is no pinch at TDC when cold. I broke in engine following directions. Any ideas what happened? Piston and liner look good.

fuel S&W 15% with 4 oz caster added for breakin
Prop APC 11X4

Thanks
Frank

< Message edited by fc911c -- 11/20/2006 3:05:47 AM >
       Post #: 1

RE: OS .55AX lost the pinch - 11/20/2006 3:09:12 AM   
alan0899


 

Posts: 2040
Joined: 4/17/2006
From: Cundletown, NSW, AUSTRALIA
Status: offline 		G'day Mate,
First off, not enough prop, start with a 12x6, & fly it, I bet it screamed with the 11x4, & you may have over reved it for too long.
As long as it has good compression, the lack of pinch, doesn't mean anything.
Don't use too much castor, as it will cause varnish build up, a small amount is ok, if you are a needle tweeker, to help with lean runs.

_____________________________

Good Flyin Mate. Keep Thyne Airspeed up, lest the ground arise & smite thee, Allan.

(in reply to fc911c)
       Post #: 2

RE: OS .55 AX lost the pinch - 11/20/2006 3:22:10 AM   
babenson


 

Posts: 65
Joined: 12/20/2004
From: Coppell, TX, USA
Status: offline 		How much did you spend on the .55? I just bought two OS .50 SX engines this year at $155.00 a pop. I just saw the new .55 on the OS site today.

(in reply to alan0899)
       Post #: 3

RE: OS .55AX lost the pinch - 11/20/2006 3:30:24 AM   
fc911c


 

Posts: 90
Joined: 6/23/2006
From: Greentown, PA, USA
Status: offline
quote:

ORIGINAL: alan0899

G'day Mate,
First off, not enough prop, start with a 12x6, & fly it, I bet it screamed with the 11x4, & you may have over reved it for too long.
As long as it has good compression, the lack of pinch, doesn't mean anything.
Don't use too much castor, as it will cause varnish build up, a small amount is ok, if you are a needle tweeker, to help with lean runs.


thanks for the quick responce

I am now running a 12X8 prop now, I does have compression , but feels a little soft. I think it was running around 14.800 when I tached it.

Why would running at that RPM cause that? Manual say 2,000-17,000 RPM could you explain?

I am running 21% oil after I ran the 2 first tanks with 23%.


Thanks
Frank

(in reply to alan0899)
       Post #: 4

RE: OS .55 AX lost the pinch - 11/20/2006 3:32:52 AM   
fc911c


 

Posts: 90
Joined: 6/23/2006
From: Greentown, PA, USA
Status: offline
quote:

ORIGINAL: babenson

How much did you spend on the .55? I just bought two OS .50 SX engines this year at $155.00 a pop. I just saw the new .55 on the OS site today.


149.00 at Tower

Thanks
Frank

(in reply to babenson)
       Post #: 5

RE: OS .55 AX lost the pinch - 11/20/2006 4:25:24 AM   
Rudeboy



Posts: 3256
Joined: 12/9/2002
From: Bejing, BELGIUM
Status: offline 		If it wasn't tight when new, it will not get any better over time. You'll just have to live with it... these things aren't hand fitted after all.

You will not hurt that engine by running it at 15000 rpm... lugging it down with a 12x8 on the other hand, doesn't sound too healthy. A 12x8 is a .90 size prop in my book.





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...I think it needs more power...

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RE: OS .55AX lost the pinch - 11/20/2006 4:26:58 AM   
alan0899


 

Posts: 2040
Joined: 4/17/2006
From: Cundletown, NSW, AUSTRALIA
Status: offline 		G'day Frank
If it starts & runs sweet, no problem, just because the maufacturer say it will rev to, whatever doesn't mean you can't damage the motor, if it is too lean, especially when new, I run between 18 & 20% Coolpower oil in all my motors, I don't use castor at all, I use 160FX, 61FX,2 x 46AX & FS120, put simply, don't run em lean, make sure, before you fly, that when the nose is raised, the motor pick up some revs, then it is rich enough to fly.
If it won't fly at this setting, then you need a bigger motor.
Enjoy.

_____________________________

Good Flyin Mate. Keep Thyne Airspeed up, lest the ground arise & smite thee, Allan.

(in reply to fc911c)
       Post #: 7

RE: OS .55 AX lost the pinch - 11/20/2006 4:35:03 AM   
alan0899


 

Posts: 2040
Joined: 4/17/2006
From: Cundletown, NSW, AUSTRALIA
Status: offline 		G'day Mate,
Get another book, that is a recomended prop for the 55 AX. I run one on my 61 FX.
If you ran a 12X8 on a 90, now that IS under propped.

_____________________________

Good Flyin Mate. Keep Thyne Airspeed up, lest the ground arise & smite thee, Allan.

(in reply to Rudeboy)
       Post #: 8

RE: OS .55 AX lost the pinch - 11/20/2006 8:46:47 AM   
DarZeelon



Posts: 7280
Joined: 4/9/2003
From: Rosh-Ha'Ayin, ISRAEL
Status: offline 		Frank,


If you ask Dub of Jett Engineering, he will tell you that for practical racing purposes, your engine has bitten the dust...

But for most people, if the engine puts out good power, idles well and starts easily; it is still good.


It just seems too soon for the pinch to be lost.
I have an engine with over 70 hours on it that still has a strong TDC pinch.


Don't do any break-in with less than 6" pitch. Cooling is impaired and reducing the diameter lessens the load without hampering the cooling. In this case, a 10x6 would load the engine like an 11x4.

_____________________________

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MVVS - Jett - Nelson - Bolly - Mejzlik

(in reply to alan0899)
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RE: OS .55AX lost the pinch - 11/20/2006 12:48:57 PM   
speedster 1919



Posts: 1476
Joined: 12/17/2004
From: Martinsville, IN, USA
Status: offline 		Are you sure your tach is working right? 12x8 is the perfect speed prop for a 90-91 size and at 14,800 to boot. I need to get rid of my 90's for a 55AX. I don't think an 11x8 would tach 14,800.

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Hey Buddy -That was the most spectacular crash I've ever seen , That rolling cart wheel with parts slinging out was cool...

(in reply to fc911c)
       Post #: 10

RE: OS .55 AX lost the pinch - 11/20/2006 12:57:58 PM   
speedster 1919



Posts: 1476
Joined: 12/17/2004
From: Martinsville, IN, USA
Status: offline 		ALAN you better get another book . OS website says 12x7 and 13x6 is the largest rec. prop not 12x8 and your 61FX is being held back with a 12x8 I bet a 12x7 and 12x6 would be a better match . OS has the breakin prop for a 61 at a 11x7

_____________________________

Hey Buddy -That was the most spectacular crash I've ever seen , That rolling cart wheel with parts slinging out was cool...

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       Post #: 11

RE: OS .55AX lost the pinch - 11/20/2006 1:31:17 PM   
Ed Cregger


 

Posts: 8076
Joined: 1/31/2002
From: Ringgold, GA, USA
Status: offline
quote:

ORIGINAL: alan0899

G'day Mate,
First off, not enough prop, start with a 12x6, & fly it, I bet it screamed with the 11x4, & you may have over reved it for too long.
As long as it has good compression, the lack of pinch, doesn't mean anything.
Don't use too much castor, as it will cause varnish build up, a small amount is ok, if you are a needle tweeker, to help with lean runs.



-----------------


Castor oil only turns to varnish when the engine is ran too lean, which is precisely when the benefits of castor oil are needed.

If you are seeing varnish build-up, you are running too lean.

An 11x4 is a prop suited for a .32 or weak .40. NOT a .55.


Ed Cregger

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"Flying models since the Fifties"

Saito Club Member #52

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RE: OS .55 AX lost the pinch - 11/20/2006 1:32:08 PM   
Kostas1



Posts: 1243
Joined: 12/19/2005
From: AthensAthens, GREECE
Status: offline 		Dar,
yesterday i tached my OS 65LA and can spin an MA 11x8 arround 12500.
What OS 55AX can do with the same prop?
Fuel was 10% heli.
Kostas

(in reply to DarZeelon)
       Post #: 13

RE: OS .55 AX lost the pinch - 11/20/2006 1:48:17 PM   
DarZeelon



Posts: 7280
Joined: 4/9/2003
From: Rosh-Ha'Ayin, ISRAEL
Status: offline 		Kostas,


I have not run this engine yet, but telling from the ~12K Guy was seeing on his engine, with a 13x4W, I would guess 12K is a good estimate for an 11x8 also.

_____________________________

Dar Zeelon - ISRAEL - ddzeelon@gmail.com
MVVS - Jett - Nelson - Bolly - Mejzlik

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       Post #: 14

RE: OS .55 AX lost the pinch - 11/20/2006 1:54:34 PM