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  #1  
Old 04-26-2012, 08:04 AM
LettersFromFlyoverCountry's Avatar
LettersFromFlyoverCountry LettersFromFlyoverCountry is offline
 
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Location: St. Paul, MN.
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Default Diagnosing engine performance

This is an extension of the thread on getting the paperwork in for an airworthiness inspection, which morphed into an analysis of engine ground testing. Makes sense to start a new thread.

On Alex Peterson's advice -- who said "take Paul Dye's advice" -- I tried to run the engine last night to 2000 until the CHT got close to 300.

I found I could not get the engine past 1900. I have to tach indications on the GRT EIS, one off the mag, and one off the Lightspeed EI.

So, here's the thing. I've gotten this far on the project, going slow and trying to conquer the strange land of things I don't know about, but i want to be VERY careful in approaching this situation because it just doesn't seem like proper place for a "I wonder what turning this screw will do?" method and that's pretty much what I would be doing.

So, I'm looking for resources to read on the step-by-step approach to analyzing what's going on here.

I'm assuming that step #1 is to check the throttle and mixture cable attachments to be sure they're extending the arms on the servo to their full travel.

After that, though, it gets a little murkier. If you're an A&P, what would be the logical progression of steps to take here.

By way of background, this is a TMX IO-360 M1B, it's a fixed-pitch propeller from Sensenich. It's a 72FM8S9-1-85 (standard). Sensenich information says the static RPM range LIMIT is 2050 to 2250.
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  #2  
Old 04-26-2012, 08:11 AM
gtmule gtmule is offline
 
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Assuming your tach indication is correct....

Is it a new engine? It may have low compression/power due to un-seated rings or something. Make sure you're not violating any break in instructions.

Assuming it's not a new engine:
Do a mag check to check for a funny drop or roughness on one or the other
Check the mixture and throttle cables
Beg or borrow a MP gauge and note that indication while doing the ground run
Check the compressions
Read the plugs when you pull them
Check mag timing and condtion

Report back
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  #3  
Old 04-26-2012, 08:17 AM
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Ron Lee Ron Lee is offline
 
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You are taking the correct approach to resolve what you think is a problem.

What is unknown is whether you do in fact have a problem. I have never run my RV-6A, Lycoming 0-360 with Catto three blade prop at full throttle on the ground while stationary.

The RPM at LIFTOFF is circa 2200-2250 RPM (full throttle). From that I would expect that not moving it would be less. It gets to around 2700 RPM at cruise speed and full throttle at suitable altitudes.

Thus, 1900 RPM on the ground...not moving...may be expected.
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  #4  
Old 04-26-2012, 08:19 AM
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Ironflight Ironflight is offline
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See if you can borrow an optical tach Bob - it is possible that youhave something mis-set in the EIS and are getting a false RPM reading (speaking from experience).

Paul
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  #5  
Old 04-26-2012, 08:52 AM
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LettersFromFlyoverCountry LettersFromFlyoverCountry is offline
 
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Tonight (after the Timberwolves game) I was going to take her out and do the "mercury vapor light" thing with the prop. I suppose that's not a completely accurate method. I'll look around for an optical tach.

(yes, new engine)
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  #6  
Old 04-26-2012, 09:17 AM
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Brantel Brantel is offline
 
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Bob,

Most avid model airplane guys have one of these. Hobby shops keep em as well.
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  #7  
Old 04-26-2012, 09:32 AM
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DanBaier DanBaier is offline
 
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Default Do the tach check

The good news is that if you tried to take off - with that RPM, you'd make it.

But, you should chase this down
- check the tach indication to be sure correct
(do this in low wind conditions)
- check the throttle / mixture linkage
(operate from cockpit and see if there is additional travel
possible at the carb.)
(does anything change if you move the mixture?)
- try a mag check

Watch the run times and temps on this as you troubleshoot.

Dan
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  #8  
Old 04-26-2012, 10:21 AM
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LettersFromFlyoverCountry LettersFromFlyoverCountry is offline
 
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Quote:
Originally Posted by Brantel View Post
Bob,

Most avid model airplane guys have one of these. Hobby shops keep em as well.
Cool, there's a big RC shop up where I meet my son (the other 'Wolves season ticketholder), I'll just go up a little early. Thanks!
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Blog: Letters From Flyover Country
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  #9  
Old 04-26-2012, 10:24 AM
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LettersFromFlyoverCountry LettersFromFlyoverCountry is offline
 
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Quote:
Originally Posted by DanBaier View Post
The good news is that if you tried to take off - with that RPM, you'd make it.

But, you should chase this down
- check the tach indication to be sure correct
(do this in low wind conditions)
- check the throttle / mixture linkage
(operate from cockpit and see if there is additional travel
possible at the carb.)
(does anything change if you move the mixture?)
- try a mag check

Watch the run times and temps on this as you troubleshoot.

Dan
Fuel injected. I'll get a second pair of eyes to watch the servo as I move the throttle/mix cables. Up to now, I just pushed full forward and got out to go look and everything seemed fine, but maybe that's not an efficient method.

I shut down the mag -- which kicks on the RPM reading from the Lightspeed -- and documented no change.

I did lean it a bit with mixture to see if there was a change but did not observe any. On the other hand, I was hearing "tic toc" in my head by then so I didn't fully lean it out. I wanted to get the engine shut down before the CHTs went much higher. Total run time was 3 minutes.
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Bob Collins
St. Paul, MN.
Blog: Letters From Flyover Country
RV-12iS Powerplant kit
N612EF Builder log (EAA Builder log)
Last article: "Gonna Finish This Sucker" (Kitplanes)
Waiting for the avionics kit (backordered: chip shortage)
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  #10  
Old 04-26-2012, 10:56 AM
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TomVal TomVal is offline
 
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Bob,

WRT EIS settings, review paragraphs:

7.6 Tach P/R – Setting for Correct Tachometer Readings
7.6.1 Tach – Connections to Magneto P-leads, Ignition Coils or Tach Outputs
7.7 TachSen

Also review Figure 7b. Other Tachometer Connections

However, as recommended, a good optical tach rpm check will eliminate tach output reading errors from your troubleshooting procedures.

Regards,
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Last edited by TomVal : 04-26-2012 at 11:16 AM.
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