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Can't get past 2600 RPM


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Hello MooneySpace.  I'm looking for some help with the RPM on my plane.  We just overhauled the engine and replaced the governor with a new PCU5000 and can't get the engine past 2600 RPM.  Before the overhaul with the old engine and governor, we would get between 2650 and 2680 on takeoff.  My mechanic has adjusted on two different occasions and I'm not seeing any change in the RPM on takeoff.  I was under the understanding that the max RPM should be 2700.  Is this right?  Has anyone had a similar issue in the past?

Thanks!

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1 minute ago, bob865 said:

Hello MooneySpace.  I'm looking for some help with the RPM on my plane.  We just overhauled the engine and replaced the governor with a new PCU5000 and can't get the engine past 2600 RPM.  Before the overhaul with the old engine and governor, we would get between 2650 and 2680 on takeoff.  My mechanic has adjusted on two different occasions and I'm not seeing any change in the RPM on takeoff.  I was under the understanding that the max RPM should be 2700.  Is this right?  Has anyone had a similar issue in the past?

Thanks!

I had a similar issue after a prop IRAN.  I had to adjust the prop pitch (front of hub for scimitar prop) What prop do you have?  

My issue maybe slightly different: I made 2500-2600 static, I couldn't reach 2700 until after rotation and about 2-300' in flight.   

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A few notes to add to follow up to questions above......

No work was done to the prop.  It only had 300hrs on it at the time of overhaul with no issues before the work done so no work was done to the prop.

I trust the RPM reading as it's read on the new engine monitor installed during the work and verified with an external gauge.

It is not the low speed stop.  If I jam the throttle forward faster than the governor can govern, it will hit 2700.  However, it always hovers at 2600 otherwise.  I have seen it as high as 2630 during an established climb, but it's rare.

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37 minutes ago, bob865 said:

A few notes to add to follow up to questions above......

No work was done to the prop.  It only had 300hrs on it at the time of overhaul with no issues before the work done so no work was done to the prop.

I trust the RPM reading as it's read on the new engine monitor installed during the work and verified with an external gauge.

It is not the low speed stop.  If I jam the throttle forward faster than the governor can govern, it will hit 2700.  However, it always hovers at 2600 otherwise.  I have seen it as high as 2630 during an established climb, but it's rare.

It sounds like the governor stop needs to be adjusted.   If it hits 2700 and then pulls back, it is most likely the governor pulling it back off the stops.  There is a high-rpm adjustment on the governor.

 

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11 minutes ago, carusoam said:

Great details Bob!

Sounds like a gov adjustment coming...

Looking forward to the PCU adjustment Pirep!

Lots of PCUs in the field... never hear anything about them...  :)

Best regards,

-a-

The odd thing, however, is that the OP mentioned that his A&P has tried to adjust the governor TWICE.  Maybe the A&P doesn't know what he's doing, but I'm going to give him the benefit of doubt.

He hasn't touched the prop, has a NEW governor, BUT the engine was just overhauled.  I wonder what could have changed in the ENGINE?

Is it possible something is different with the crank, or the oil feed to the crank?

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Maybe it needs to be adjusted, but before doing that take a look at the prop cable and the travel. Always check off the simplest things first. I had a problem shortly after getting the plane where I wasn't getting 2,700 RPM. From this post in a thread I started follow on down to @M20Doc's suggestion and then the subsequent easy fix. The prop cable had slid up in the clamps and was not allowing it to hit the stop.

 

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7 minutes ago, Skates97 said:

Maybe it needs to be adjusted, but before doing that take a look at the prop cable and the travel. Always check off the simplest things first. I had a problem shortly after getting the plane where I wasn't getting 2,700 RPM. From this post in a thread I started follow on down to @M20Doc's suggestion and then the subsequent easy fix. The prop cable had slid up in the clamps and was not allowing it to hit the stop.

 

I'm going to bet you are correct!

Hopefully, the OP gets back to us when fixed.

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One other tidbit I learned here on Mooney space, the governor shouldn’t be “governing” your rpm during a static run or at the beginning of your takeoff roll.  A properly adjusted low pitch stop and a healthy engine are supposed to yield ~2680 rpm.  The governor is not increasing pitch or “pulling back” the rpm at all to hold that.
 

After the airspeed starts to build on takeoff roll, prop rpm would increase, but that’s where the governor brings it off the low pitch stop and keeps it ~2700 by increasing pitch.

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  • 2 weeks later...

Well, we did get an update on the governor late yesterday afternoon.  The most recent finding is that when the avionics were installed the lever hits the transponder and kept the prop lever from reaching the full "high rpm" position.  The cable was adjusted so now the "high RPM" position is slightly off of the transponder and she waiting on a test flight. Will report back with news.

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I wouldn’t assume your tach is reading correct. Mine wasn’t getting the full 2,700 rpm. So I went the simple route. I bought a tach that works through the windscreen. Sure enough.. my tach is reading 100 rpm low. I’m wondering if this is a common problem.. I’m not even worried about it any more. It would be nice to have it indicate exactly.

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1 hour ago, Yourpilotincommand said:

I wouldn’t assume your tach is reading correct. Mine wasn’t getting the full 2,700 rpm. So I went the simple route. I bought a tach that works through the windscreen. Sure enough.. my tach is reading 100 rpm low. I’m wondering if this is a common problem.. I’m not even worried about it any more. It would be nice to have it indicate exactly.

When I had the EDM830 installed I found that my mechanical tach read higher than actual. I don't remember the exact number but I think it was around 100, at 2700 on the mechanical it was actually only making about 2600 or so. 

Now with the 900 there's no more issue of the tachs not agreeing. :D

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On 10/30/2020 at 7:42 AM, Yourpilotincommand said:

I wouldn’t assume your tach is reading correct. Mine wasn’t getting the full 2,700 rpm. So I went the simple route. I bought a tach that works through the windscreen. Sure enough.. my tach is reading 100 rpm low. I’m wondering if this is a common problem.. I’m not even worried about it any more. It would be nice to have it indicate exactly.


The process to fix this is called calibration...

Your instrument shop can probably do this for you...

All mechanical instruments wear, corrode and/or get dirty or age... calibration skills are built into them at the factory...

PP thoughts only, not an instrument tech...

Best regards,

-a-

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On 10/30/2020 at 4:34 AM, bob865 said:

Well, we did get an update on the governor late yesterday afternoon.  The most recent finding is that when the avionics were installed the lever hits the transponder and kept the prop lever from reaching the full "high rpm" position.  The cable was adjusted so now the "high RPM" position is slightly off of the transponder and she waiting on a test flight. Will report back with news.

Hmmmm. Well that should probably take care of it. 

If the engine  won't make static rpm, there are only a few possibilities:

1. The tach is wrong

2. The governor is governing when it shouldn't be

3. The prop is set up wrong

4. The engine isn't putting out rated power

Skip

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Easy way to check your RPM without going to a A&P.  Be sure to do this during day light hours.  Artificial light impact the result. 

 

https://www.amazon.com/Hangar-Micro-Digital-Tachometer-HAN156/dp/B0006N72U2/ref=sr_1_3?crid=2IEWZ17EC2PX2&dchild=1&keywords=rc+tachometer&qid=1604181712&sprefix=rc+tach%2Caps%2C205&sr=8-3

 

 

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On 10/31/2020 at 1:07 PM, carusoam said:


The process to fix this is called calibration...

Your instrument shop can probably do this for you...

All mechanical instruments wear, corrode and/or get dirty or age... calibration skills are built into them at the factory...

PP thoughts only, not an instrument tech...

Best regards,

-a-

Can the tach be recalibrated? I didn’t realize that.. I’ll take a closer look at the back side of my tach for adjustments next time I have the top covers removed. Thanks! Chris

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15 minutes ago, Yourpilotincommand said:

Can the tach be recalibrated? I didn’t realize that.. I’ll take a closer look at the back side of my tach for adjustments next time I have the top covers removed. Thanks! Chris

Contact your instrument shop...

You might remove the tach from the panel...

Behind the plastic fascia... it is held in place with four screws...

Mine wore out the cable at the back... in a wild swing it knocked the needle from its mount... I sent the instrument in to be fixed...

They said they put the needle back on, and I should get a new cable...  :)

Note the location of the oil cup on the back of your tach...

See pics...

Also note the case and front are held together by a simple crimping mechanism... get the lens cleaned while you are at it...

Man, orienting pics just got even harder....

-a-

 

1530BF96-E917-44F5-9BE7-ED4B1C5914CC.jpeg

86B830D3-0954-4837-BB1A-20A6E19E72B8.jpeg

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So a quick update....the cable adjustment fixed it.  But now because of all of the attempts to get it to 2700, now it's over 2700 and we are working on dialing it in.  Had the suspicion that would be the case so grabbed the control quickly and never let it happen to avoid an overspeed.   Now we just have to get it dialed in.

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  • 2 weeks later...
On 10/19/2020 at 8:53 PM, bob865 said:

A few notes to add to follow up to questions above......

No work was done to the prop.  It only had 300hrs on it at the time of overhaul with no issues before the work done so no work was done to the prop.

I trust the RPM reading as it's read on the new engine monitor installed during the work and verified with an external gauge.

It is not the low speed stop.  If I jam the throttle forward faster than the governor can govern, it will hit 2700.  However, it always hovers at 2600 otherwise.  I have seen it as high as 2630 during an established climb, but it's rare.

Very interesting.  A&P told me that my tach was off by 80 rpm’s after my 2019 annual. Now that sounds like a bogus excuse....like he didn’t want to take the time to check low speed adjust.  

Also, i haven’t tried “jamming” the throttle as was taught (by my dad in 1970) to ease the throttle in and it’s become my habit.  I will try pushing a bit more rapidly....then if no luck, will talk to my current A&P about solutions.

 

@bob865

@Bob865 - even if the former A&P is correct and it is my tach, your input made me think rather than simply blindly go with what the “expert” said. 

Thanks!

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On 10/19/2020 at 8:19 PM, Bartman said:

My old and decrepit ship gauge reads 2600, but I downloaded the RPM app on my phone and it reads 2680. The JPI 900 is in my future upgrade list, but my recent engine rebuild consumed a lot of my funds. 

@Bartman, please enlighten me....RPM app for phone?

thx

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43 minutes ago, DJE22 said:

@Bartman, please enlighten me....RPM app for phone?

thx

They listen to the audio and find the frequency of the first harmonic.   A good one should provide a reasonable estimate, but, imho, are only good for a sanity check and are not something to calibrate or final check a tach with.    There are cheap optical tachs out there that are very reliable, though.

 

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