[NSRCA-discussion] 120 AC issues UPDATE

Tue Jul 15 05:41:48 AKDT 2008

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:
      .hmmessage P  {  margin:0px;  padding:0px  }  body.hmmessage  {  FONT-SIZE: 10pt;  FONT-FAMILY:Tahoma  }    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: 
      .ExternalClass .EC_shape  {;}              .ExternalClass p.EC_MsoNormal, .ExternalClass li.EC_MsoNormal, .ExternalClass div.EC_MsoNormal  {margin-bottom:.0001pt;font-size:12.0pt;font-family:'Times New Roman';color:black;}  .ExternalClass a:link, .ExternalClass span.EC_MsoHyperlink  {color:blue;text-decoration:underline;}  .ExternalClass a:visited, .ExternalClass span.EC_MsoHyperlinkFollowed  {color:blue;text-decoration:underline;}  .ExternalClass p  {margin-right:0in;margin-left:0in;font-size:12.0pt;font-family:'Times New Roman';color:black;}  .ExternalClass pre  {margin-bottom:.0001pt;font-size:10.0pt;font-family:'Courier New';color:black;}  .ExternalClass span.EC_EmailStyle19  {font-family:Arial;color:navy;}  @page Section1  {size:8.5in 11.0in;}  .ExternalClass div.EC_Section1  {page:Section1;}          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 Thompson 

    To: General pattern discussion 

    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 

    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

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

  Get the scoop on last night's hottest shows and the live music scene in your area - Check out TourTracker.com!

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

_______________________________________________

NSRCA-discussion mailing list

NSRCA-discussion at lists.nsrca.org

http://lists.nsrca.org/mailman/listinfo/nsrca-discussion

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

  _______________________________________________
NSRCA-discussion mailing list
NSRCA-discussion at lists.nsrca.org
http://lists.nsrca.org/mailman/listinfo/nsrca-discussion

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

  _______________________________________________
NSRCA-discussion mailing list
NSRCA-discussion at lists.nsrca.org
http://lists.nsrca.org/mailman/listinfo/nsrca-discussion

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

_______________________________________________

NSRCA-discussion mailing list

NSRCA-discussion at lists.nsrca.org

http://lists.nsrca.org/mailman/listinfo/nsrca-discussion

---------------------------------
  _______________________________________________  NSRCA-discussion mailing list  NSRCA-discussion at lists.nsrca.org  http://lists.nsrca.org/mailman/listinfo/nsrca-discussion    

---------------------------------
  Need to know now? Get instant answers with Windows Live Messenger. IM on your terms. _______________________________________________
NSRCA-discussion mailing list
NSRCA-discussion at lists.nsrca.org
http://lists.nsrca.org/mailman/listinfo/nsrca-discussion
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.nsrca.org/pipermail/nsrca-discussion/attachments/20080715/7cbf00d5/attachment.html>