[NSRCA-discussion] [Bulk] Re: 120 AC issues UPDATE

Tue Jul 15 12:04:28 AKDT 2008

OS 160's don't have cams. 

From: nsrca-discussion-bounces at lists.nsrca.org
[mailto:nsrca-discussion-bounces at lists.nsrca.org] On Behalf Of Dave Harmon
Sent: Tuesday, July 15, 2008 11:18 AM
To: 'General pattern discussion'
Subject: Re: [NSRCA-discussion] [Bulk] Re: 120 AC issues UPDATE

At least the YS cylinder liners don't peel.

Within the past couple of months Hobby Services replaced my new OS 91 that
had the cam peel.

This thing was new and only had 6 flights. They acknowledged that this was
still a serious problem and not just some 'issue'.

We all live in a glass house.

Regards

Dave Harmon
NSRCA 586
K6XYZ[at]sbcglobal[dot]net
Sperry, Ok. 

-----Original Message-----
From: nsrca-discussion-bounces at lists.nsrca.org
[mailto:nsrca-discussion-bounces at lists.nsrca.org] On Behalf Of Gene Maurice
Sent: Tuesday, July 15, 2008 9:11 AM
To: 'General pattern discussion'
Subject: [Bulk] Re: [NSRCA-discussion] 120 AC issues UPDATE

This is the reason I went from YS to OS 6 years ago; way too much stuff to
go wrong :<)

Gene Maurice

Plano, TX

AMA 3408 NSRCA 877

PACSS.sgmservice.com

gene.maurice at sgmservice.com

From: nsrca-discussion-bounces at lists.nsrca.org
[mailto:nsrca-discussion-bounces at lists.nsrca.org] On Behalf Of Anthony
Abdullah
Sent: Tuesday, July 15, 2008 8:42 AM
To: General pattern discussion
Subject: Re: [NSRCA-discussion] 120 AC issues UPDATE

I don't know if someone suggested this or not, but I had a similar problem
with a 120FZ and it turned out to be a bad head shim.

Good luck with it

Michael Cohen <precisionaero at hotmail.com> wrote:

Surging after 5 minutes or so wound up being caused by a worn piston for me
way back when.  Once the engine heats up, it allowed the piston to wobble
causing a mid range surging that limited max power.  If you can get your
hands on a "slug" piston, without all the weight saving machining done to
the skirt, you would be better off, but a lighter piston will be OK, it just
won't last as long.  Of course, when changing out the piston, use a new
piston ring.  

  _____  

Date: Mon, 14 Jul 2008 20:15:47 -0400
From: schale at optonline.net
To: nsrca-discussion at lists.nsrca.org
Subject: Re: [NSRCA-discussion] 120 AC issues UPDATE

I want to thank everyone for their suggestions.  Too many possibilities :)
First thing I did was to change the liner and the exhaust.  Replaced tank
internals.  Decided to run it on the ground at home and save a trip to the
field.
After 5 minutes or so flying issue was reproduced.  Motor started surging
and would not go to full throttle from idle.  Needle valve setting didn't
seem to matter.  Switch to 30% heli fuel no difference.
Changed both check valves no change.  Took the motor out again swapped the
original liner back in and checked the regulator.  
-Bingo the edges of the silicone diaphragm are frayed.  Replaced the entire
regulator unit with one from an un-run 120AC (thanks Norm S.) figured that
had to be the cause.
No change still surging and no power after heating up.  The motor still
turns free, no binding so although I will try a different piston and front
bearing I do not believe that to be the issue.
APC 14x12 used for all of today's tests.
I think I will put a well used but last time ran fine 120 in it and try to
diagnose this motor on the test stand..  I'll see if the same issue crops up
with a different motor.

Stuart C.

William C. Harden wrote: 

I ran an APC 15 X 10 on my YS120 AC engine with 30% nitro (Cool Power).  

Bill

  _____  

From: nsrca-discussion-bounces at lists.nsrca.org
[mailto:nsrca-discussion-bounces at lists.nsrca.org] On Behalf Of Stuart Chale
Sent: Sunday, July 13, 2008 9:52 PM
To: General pattern discussion
Subject: Re: [NSRCA-discussion] 120 AC issues

Various props from 13.5x14 to 15x8
I would think the 13.5x14 would be under propped so shouldn't have been an
issue.
Stuart

Paul LaChance wrote: 

Here is a stupid question, but what size prop are you running?  Is the
engine fully broken in?  Just a thought.  Had similar issues with a 170 DZ.

Paul

----- Original Message ----- 

From: Ken <mailto:KTHOMPSON56 at satx.rr.com>  Thompson 

To: General pattern discussion <mailto:nsrca-discussion at lists.nsrca.org>  

Sent: Sunday, July 13, 2008 7:55 PM

Subject: Re: [NSRCA-discussion] 120 AC issues

Stuart, 

I had the same problem with a 91AC a few years ago, like Ron, it turned out
to be the front bearing.

----- Original Message ----- 

From: ronclark51 at comcast.net 

To: General pattern discussion <mailto:nsrca-discussion at lists.nsrca.org>  

Sent: Sunday, July 13, 2008 8:46 AM

Subject: Re: [NSRCA-discussion] 120 AC issues

Stuart,

I've had the same problem before. It was the front bearing. The bearing
heats up the front of the motor, then the regulator, vaporizing the fuel.
Better known as vapor lock.

Ron....................

-------------- Original message -------------- 
From: Stuart Chale <schale at optonline.net> 
I wouldn't have thought about the pipe.  I should have another.
Thanks,
Stuart

RUDDERCABL at aol.com wrote: 

In a message dated 7/12/2008 11:33:24 PM Eastern Daylight Time,
schale at optonline.net writes:

I'll have to pull it a part again and see if I see anything with the sleeve.
Anyone else have any thoughts?
Thanks,
Stu

Sure do.

Try a different pipe. I know a flyer who had this same problem some years
ago, not with an AC though. He tried everything and the problem kept
hounding him. Turned out that the pipe was plugging up when it heated up and
restricting the exhuast flow. 

Robert

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