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Date: Sat, 23 Jul 2005 22:21:40 -0500
From: Charlie England <ceengland@bellsouth.net>
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Lycoming debugging test - -HELP!
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kevin lane wrote:

> I realize that this isn't exactly the right forum, but you guys seem 
> to have excellent debugging skills.  my local RV group is totally 
> worthless ("I find the carnauba wax doesn't show fingerprints as much 
> as the....")(except Mike!)  the on-field mechanics are sick of me 
> coming by.
>     my O-320 RV-6A is having RAG (rpm attention getter) problems.  it 
> runs fine until about 300' on take-off, then the rpm's drop to like 
> 1700 (from 2200).  switching mags to electronic ignition(Rose) makes 
> no difference.  mixture no diff.  pulling the throttle it will seem to 
> run fine at 1700rpm.  I have 4 new cyls that I am attempting to break 
> in.  ground run ups can only go like 2 minutes before CHT's exceed 400 
> degrees.  I discovered I can get the rpm drop on the ground if I run 
> it a minute or so full power.  cht's will typically approach 415 
> degrees when the drop takes place.  I don't know if the temp is 
> significant or not, it does seem that way.  I have a brand new slick 
> left mag.  rose checked the electronic ignition and could find nothing 
> wrong, even put it in an oven to test.  I installed a new carb since 
> the old one showed signs of leakage (and I'm at whits end).  no 
> change.  my fuel pressure has been showing 8psi this last year, up 
> from 6 psi when originally installed.(no idea why)  I installed a 
> pressure regulator in-line which works like a charm.  I can dial 
> whatever pressure I like.  2 psi makes no difference.  I bypassed the 
> mechanical fuel pump and ran it just on the facet electric.  2 psi, no 
> difference. I discovered that you can run the carb for maybe 30 secs 
> with no fuel pressure while it burns off the bowl gas. premier engines 
> suggested induction leak making the engine run lean.  no leaks 
> detected cold or hot engine. (pressurized intake with vacuum, sprayed 
> soapy water)
>     if the engine didn't run right to start with then many 
> explanations would hold.  but it runs fine for several minutes.  it 
> runs the same under mag or electronic ignition both before and after 
> the problem kicks in.  everyone really wants to blame the rose 
> ignition, but I'm not seeing any connection.  with such a quick run-up 
> my oil temp barely registers, so I doubt parts are seizing.  I have 
> new mineral oil in it for breakin right now.  there is a bit of MMO in 
> the fuel too I believe, left over from a mechanics "what the hell" 
> attempt from way back.  my cyls are all new, rebuilts, so no valve 
> problems.  I checked the push rod lengths when I reinstalled them.  
> the engine isn't missing when the problems occurs, it simply won't run 
> faster and it seems to prefer the throttle pulled back to match the 
> rpm it is putting out.  I can't figure out any more lean mixture 
> scenarios to try.  the new carb runs just like the old one did.  I 
> recently replaced the mag harness with a much newer, used one.  I 
> tested it and it was fine.  the plugs are all new, but again, no diff 
> between mag and elec ignition.  if I flip the ignition to R and shut 
> off the elect ig then the engine quits as would be expected, no wiring 
> problems.
>     fuel, spark, air, timing, that's all there is.  this damn lycoming 
> lawn mower has me stumped.  my engine has been running fine up until 
> this (hey, we all have "cracked" cylinders, get out your microscope 
> and look!).  you guys have any ideas?
> Kevin Lane  Portland, OR
> e-mail-> n3773@comcast.net <mailto:n3773@comcast.net>
>
>     ----- Original
>
Does it run rough when rpm sags or just drop in rpm while running 
smooth? If it runs rough I wouldn't completely write off a sticking valve.

I have a vague memory about issues with Lyc hydraulic lifters pumping up 
& not being able to do the proper leakdown thing to set zero lash if 
they are compressed too much in their static state (pushrods too long). 
The new cyl's might be slightly shorter than the old ones, rocker shafts 
slightly shorter, etc.

If your egt's don't change odds are the mixture isn't changing. Do all 4 
cht's go up?

Long shot:  Do the new cylinders have 'choke' in their bore? I don't 
know if small Lycs have choke or not but a friend had a problem with an 
O-470 years ago when the rebuilder gapped the rings in the bottom of the 
cyl instead of the top. It caused cyl head temps to go way high as the 
engine heated up. What does the engine feel like if you pull the prop 
through when cold vs immediately after seeing the problem & shutting down?

Charlie