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  #1  
Old 06-14-2019, 09:55 AM
lndwarrior lndwarrior is offline
 
Join Date: Mar 2015
Location: Cloverdale CA
Posts: 304
Default Suspicious performance after valve lash setting and new spark plugs

I realize this sounds a little weird. which is precisely why I'm posting.

Engine is a lycoming O-235 with adjustable warp drive prop. I did not change the prop pitch during the condition inspection, or even re torque, as I had recently done this.

During me recent condition inspection I replaced the very old Champion spark plugs with new Tempest UREM37BY plugs. I did not know the history on the plugs as they came with my used engine. Nor had they been properly tested other than with a generic ohm meter (yes, i know, not a good way of judging performance).

I also adjusted the valve lash. Some were off by quite a bit.

I didn't do anything else to the engine or controls that would affect engine performance.

Yesterday I did my post mx test flight.

Initially I was curious as to how the static rpm would be affected.

Density altitude was around 4500 feet at ground level.

Before the mx I would have expected to see right around 2300 to 2350 static rpm.

Yesterday, when I go to full throttle, the rpm runs right up to 2600 rpm and hold there for the take-off roll and climb out.

Prior to mx, in cruise, my wide open throttle rpm was about 2700 to 2750 max (engine rated for 2800 rpm).

Yesterday it went right past the max rpm to about 2850, when I immediately pulled it back.

So, one part of me is, "woohoo, lots more power!".

The other part of me is, "this just doesn't sound right for a spark plug change and a valve lash setting".

From my limited knowledge on aircraft engines such a big change in performance doesn't sound quite right. It makes me kind of suspicious... Am I missing something here?

And, yes, I will be re-pitching my prop.

TIA

Last edited by lndwarrior : 06-14-2019 at 10:05 AM.
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  #2  
Old 06-14-2019, 10:16 AM
William William is offline
 
Join Date: Nov 2006
Location: Tampa, Florida (KVDF)
Posts: 531
Default

When you say the valve lash was way off, how so? A open valve will definitely have a effect on performance.

Bill
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  #3  
Old 06-14-2019, 10:22 AM
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akschu akschu is offline
 
Join Date: May 2008
Location: Wenatchee
Posts: 393
Thumbs up

Can you come over to my place and do the same tune up on my rig? I could really use an extra 300 rpm.
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  #4  
Old 06-14-2019, 10:23 AM
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Mel Mel is offline
 
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Location: Dallas area
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Quote:
Originally Posted by William View Post
When you say the valve lash was way off, how so? A open valve will definitely have a effect on performance.
Bill
As also, will a valve not opening enough.
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  #5  
Old 06-14-2019, 11:47 AM
gasman gasman is offline
 
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Location: Sonoma County
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It may be that the prop was set to an out of tune motor. The prop is now under pitched for the extra power that the valve adjustment and the new plugs provided.

You can check this with a manifold pressure, RPM & power chart.
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  #6  
Old 06-14-2019, 12:56 PM
lndwarrior lndwarrior is offline
 
Join Date: Mar 2015
Location: Cloverdale CA
Posts: 304
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Quote:
Originally Posted by William View Post
When you say the valve lash was way off, how so? A open valve will definitely have a effect on performance.

Bill
Not really sure how far off they were. This was kind of new to me so I just started adjusting without first checking where they were currently set.

it's a learning curve...
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  #7  
Old 06-14-2019, 02:57 PM
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Toobuilder Toobuilder is offline
 
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Location: Mojave
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Quote:
Originally Posted by lndwarrior View Post
Not really sure how far off they were. This was kind of new to me so I just started adjusting without first checking where they were currently set.

it's a learning curve...
Ok, how about too tight, too loose or a mix?
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  #8  
Old 06-14-2019, 03:31 PM
lndwarrior lndwarrior is offline
 
Join Date: Mar 2015
Location: Cloverdale CA
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Quote:
Originally Posted by Toobuilder View Post
Ok, how about too tight, too loose or a mix?
it was a mix. some were too tight and dome were too loose.
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