[NSRCA-discussion] OS 140RX rough and inconsistent idle

[Ed Miller]

Thanks to all that emailed suggestions for this problem.  To be honest I'm 
not sure what fixed it but my OS 140RX is back to idling as it should.  Upon 
disassembly I could find nothing wrong, no dirt in carb, bearings were 
smooth and wrist pin and conrod were fine.  What I did notice was what 
seemed to be a lot of varnish/carbon build up on the piston sides and 
cylinder liner, a result of the 2% castor I use in the oil mix of my fuel. 
So I cleaned off the varnish/carbon on the piston and liner ( Perf Spec 
AAC ).  Since the overwhelming responses felt it was a bearing issue, I 
removed the SS sealed Boca rear bearing and stock front bearing even though 
I could not see how they were the root cause of the problem and installed an 
OS EFI SS sealed rear bearing and a new stock OS front bearing.  All is back 
to normal now, 7700rpm with an APC Dave Lockhart 15.75x11 3 blade and a 
steady, reliable 1700rpm idle ( it will go lower but shakes the plane too 
much ) on S&W 20/16/2 fuel, OS F plug in center of Mintor head and OS 8 plug 
in angled plug position.  Back to practicing.............
Ed M.
----- Original Message ----- 
From: "Ed Miller" <edbon85 at charter.net>
To: "NSRCA Mailing List" <NSRCA-discussion at lists.nsrca.org>
Sent: Monday, June 26, 2006 6:17 AM
Subject: [NSRCA-discussion] OS 140RX rough and inconsistent idle


> Have an OS 140RX that has developed a rough and inconsistent idle. Engine
> runs perfectly except for idle. It has a Mintor head with either an OS F 
> or
> K&B 1L in center plug and an OS A5 in the angled plug position, a Perf 
> Spec
> AAC piston/liner assembly and a Boca sealed SS rear bearing. I have the 
> head
> mounted with angled plug towards the front or carb side of engine. Fuel is
> S&W 20 nitro, 16 synthetic and 2 castor. Engine has 7 gallons of fuel run
> through it. Prop is an APC 15.75 x 11 3 blade by Dave Lockhart.  The 
> lowest
> I can get the idle before it quits is 1900 ~ 2000 rpm and it is rough,
> sounds like it is firing every other revolution. Idle mixture screw is
> working, I can richen idle to point where engine will barely transition 
> from
> being rich and I can lean mixture so the transition is fine but engine 
> slows
> at idle like it is too rich. While it is slowing with either the idle
> mixture screw lean or rich, engine is rough, again like it often fires 
> every
> other revolution at times. I used to be able to reliably idle this engine 
> at
> 1300 rpm. I have a second OS 140RX set up exactly the same except it 
> doesn't
> have the AAC piston/liner and it runs/idles perfectly. Tried cleaning the
> carb/spray bar with no change. I once had a Super Tiger that exhibited
> similar characteristics due to a worn out con rod.  Is it possible the con
> rod on this OS could cause this issue ?? Any suggestions will be greatly
> appreciated.
> Ed M.
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