2,550-2600 RPM max after changing plug wires

[Skates97]

I don't know that it is related, but it seems like the only thing that was changed on the plane. I was previously getting an even 2,700 rpm at full power on take-off. After finding that one of the plug wires had one of the small nuts that hold the plug wire in was sheared off and just basically sitting there I replaced the plug wires last Saturday. The new plug wires are the Slick Harness by Champion Part #08-05287.

After replacing them I am only seeing 2,550 and sometimes 2,600 rpm at full power on take-off. Maybe it's not related, but that was the only thing that was changed. Ideas?

[AaronDC8402]

Does it sound like you're only getting 2600 rpm? I'm wondering if you're still getting the same rpm, but the tach is indicating differently. Is your tach mechanical or an electrical pickup?

The prop governor wouldn't have changed with a plug wire change. If the rpms are really lower than they used to be, it seems like you're not making as much power as you were.

 

[aaronk25]

Is level max cruise speed the same?


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[Skates97]

I don't think it sounds any different, however I only had about 5 hours in the plane before changing the plug wires so not much to go off of. It is a mechanical tach so may not be entirely accurate, but it was reading 2,700 on the nose before on take-off. I would back it down to 2,600 shortly after take-off for climb out.

I can't say for max cruise speed, again not enough time in the plane prior to changing the wires and we were just working maneuvers, short hops, and pattern stuff previously so nothing to compare it to. 

Edited January 15, 2017 by Skates97

[Shadrach]

https://www.hobbyzone.com/hangar9/all/han156.html?gclid=CObIxbOuw9ECFZyEswod3tIBBQ

under $30 and highly accurate. 

[carusoam]

Things to consider, ways to consider it...

1) is it an instrument problem or is it really only turning <2600rpm? (Ross' device or an iPhone sound/rpm should tell)

2) is it producing full power, and the gov isn't working?

3) is the gov set to max rpm, and the engine isn't working?

4) what is MP at full throttle?  (Hint of full power)

5) what are the CHTs and EGTs saying? (Hint of plug wire not working properly)

6) is the prop against the stops? (Hint of the gov working properly)

7) is the sound and acceleration the same? (The rpm change alone is in the range of 5% less power, 2700 rpm is quite loud compared to 2550)

I'm not a big fan of taking something flying that isn't behaving in a known way.  If something is failing slowly, it may not be done yet.  I'm still only a PP, not a mechanic...

Best regards,

-a-

Edited January 15, 2017 by carusoam

[Yetti]

The various phone apps that use sound to measure RPM are pretty accurate.  May download one and try it.   You could use it with fast taxi's down the runway without really catching flight.

[Piloto]

Check the mag timing. This could had changed when the cables were replaced.

José

[bradp]

Physically twist your mags to make sure they are not loose. If they are loose replace the hardware and re time.


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[ShermAv8tor]

https://www.hobbyzone.com/hangar9/all/han156.html?gclid=CObIxbOuw9ECFZyEswod3tIBBQ
under $30 and highly accurate. 

Will this read through the windshield from inside cockpit or does it have be outside to read? I borrowed one awhile back, but don't remember brand, etc, I had to stick my hand out pilot side window and point at prop to get it to read…hang on tight!!


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[Yetti]

the optical will work through the plexiglass windscreen....

[Skates97]

2 hours ago, Piloto said:

Check the mag timing. This could had changed when the cables were replaced.

José

 

39 minutes ago, bradp said:

Physically twist your mags to make sure they are not loose. If they are loose replace the hardware and re time.


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Thank you for all the ideas. I will check on these. I'm also going to pull the plugs, check them, and hook the wires back up and test it out. If it is still reading low I'll move on from there.

I don't think it is an issue of the tach reading incorrectly because it was reading 2,700 prior to changing the plug wires. I'm not sure how changing them would suddenly make the tach inaccurate. 

[carusoam]

Richard,

The oddity of the situation is something changed unexpectedly...

1) a timing change is usually a less visible but more serious power change.  It shows in performance, EGT, and CHTs... not usually an rpm change... the seriousness is because it may be a loose mag that (at worst) can fall off and bleed a lot of oil...

2) if a plug were not working because of a broken new wire, it would show up during the run-up.

3) downloading data from a JPI would indicate intermittent problems.

4) what is the chance that an ignition wire is mis wired or grounding out...?

The list of things to check is probably a good thing to take to your mechanic to review the normal things that have been done to the unusual thing that may be happening...

PP thoughts only, not a mechanic...

Best regards,

-a-

[Skates97]

Thank you, always appreciate the ideas and things to look for. I have one of those digital tachs coming, you have to love Amazon prime, $23 and free two day shipping. It arrives on Tuesday. Now I have to find the time to get out there this week to hopefully have it resolved so I can go flying next Saturday. 

https://www.amazon.com/gp/product/B0006N72U2/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1

Edited January 16, 2017 by Skates97

[211º]

https://www.hobbyzone.com/hangar9/all/han156.html?gclid=CObIxbOuw9ECFZyEswod3tIBBQ
under $30 and highly accurate. 

Wow, and much less expensive than the unit that is available at pilots shops. I think I paid over $150 for mine.


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[Shadrach]

8 hours ago, ShermAv8tor said:

 

Will this read through the windshield from inside cockpit or does it have be outside to read? I borrowed one awhile back, but don't remember brand, etc, I had to stick my hand out pilot side window and point at prop to get it to read…hang on tight!!


Sent from my iPhone using Tapatalk

 

It works fine through plexi. It can be a little spotty in low or flat light when it's overcast. Other than that, it's a lot of bang for the buck!

[Skates97]

So last night I pulled the plugs and took a look at them. Some of them had some deposits in them that I cleaned out with a pick. The bottom plug in the #2 cylinder had some oil in it. It had a compression of 79/80 at annual at the beginning of December so I don't think it's rings. I have been reading on here about possible valve issues that can cause the oil, but the plug also had some deposits in it so perhaps it was just not firing well and burning off the oil. I don't have anything to test the resistance of the plugs, but from the looks of them I am thinking that I need to put new plugs in anyway.

Cleaned the plugs and reinstalled. It was quiet at the airport so I made a few full power runs down the runway, pulling power just before reaching take-off speed and rolling out. Still not showing 2,700rpm. I have the digital tach that is supposed to be delivered today but won't be able to check that until Saturday.

I had another question. In the Cherokee's I flew when you pushed the throttle all the way in it would actually go "all the way in." On this plane it stops and there is still another 1/4"-1/2" of shaft showing, like it could go in farther but it just won't. Is there a set screw or an adjustment somewhere that controls where the cable stops? Just thinking out loud here (with very little experience...) but I wonder if it is just not allowing the throttle to open all the way. If it had that extra 1/4"-1/2" that might be the 100-150rpm I'm missing. I've also read a couple old threads here about throttle cable failures and want to make sure this isn't a sign of impending failure somewhere down the road.

[N6758N]

28 minutes ago, Skates97 said:

So last night I pulled the plugs and took a look at them. Some of them had some deposits in them that I cleaned out with a pick. The bottom plug in the #2 cylinder had some oil in it. It had a compression of 79/80 at annual at the beginning of December so I don't think it's rings. I have been reading on here about possible valve issues that can cause the oil, but the plug also had some deposits in it so perhaps it was just not firing well and burning off the oil. I don't have anything to test the resistance of the plugs, but from the looks of them I am thinking that I need to put new plugs in anyway.

Cleaned the plugs and reinstalled. It was quiet at the airport so I made a few full power runs down the runway, pulling power just before reaching take-off speed and rolling out. Still not showing 2,700rpm. I have the digital tach that is supposed to be delivered today but won't be able to check that until Saturday.

I had another question. In the Cherokee's I flew when you pushed the throttle all the way in it would actually go "all the way in." On this plane it stops and there is still another 1/4"-1/2" of shaft showing, like it could go in farther but it just won't. Is there a set screw or an adjustment somewhere that controls where the cable stops? Just thinking out loud here (with very little experience...) but I wonder if it is just not allowing the throttle to open all the way. If it had that extra 1/4"-1/2" that might be the 100-150rpm I'm missing. I've also read a couple old threads here about throttle cable failures and want to make sure this isn't a sign of impending failure somewhere down the road.

Depending on how your throttle cable is rigged, it will not necessarily hit the stop in the panel. Proper rigging of the throttle should have the arm on the carburetor hitting the forward stop BEFORE the throttle in the cockpit hits the panel.  This way you always know you are making contact with the fully open position on the carb. I usually set mine up so it is about 1/4" away from the panel when it hits the forward stop on the carb. Take off the right hand cheek cowl on the plane and with the throttle inside pushed all the way forward, check to see if the stop on the carburetor is making good contact with the forward stop. It should be on the right side of the carb looking from the pilots seat. If you are unsure then ask a friend to move the throttle while you look at the carb. The mixture arm is the one at the back of the carb. I had a similar issue with my C with the mixture arm. It was moving inside the plane but it had broken inside the cable housing so at the carb end nothing was happening. 

I would also do the same exact thing for the prop control. The governor is located at the back of the engine and should be spring loaded to max rpm, however a poorly rigged system or slipped prop cable could hinder this. 

[carusoam]

Checking the The control cables sound like a good idea...

1) The throttle knob controls MP.  What is the MP you were seeing while doing the fast taxi tests? It only controls rpm when below a certain power output.  Look at the full travel under the cowl.

2) The prop knob controls rpm. Check to see if the prop control is not going all the way in.  Prop control cables have been known to fall apart.  Look at the full travel under the cowl.

3) Sence you was in there, Look at the mixture knob too under the cowl....

4) I like to see a few things prior to committing to flight... Just prior to AS Alive. 

- MP, high 20s - air intake is good.

- FF, high 20s - fuel is being delivered.

- Rpm, 2700 - engine is producing power.

 

 

Use caution, after the plane starts rolling, instrument scanning is secondary to keeping the plane aligned with the center line....

Try to not be distracted in the classic sense...

Best regards,

-a-

Terry beat me to the post button! 

Edited January 17, 2017 by carusoam

[DXB]

27 minutes ago, Skates97 said:

So last night I pulled the plugs and took a look at them. Some of them had some deposits in them that I cleaned out with a pick. The bottom plug in the #2 cylinder had some oil in it. It had a compression of 79/80 at annual at the beginning of December so I don't think it's rings. I have been reading on here about possible valve issues that can cause the oil, but the plug also had some deposits in it so perhaps it was just not firing well and burning off the oil. I don't have anything to test the resistance of the plugs, but from the looks of them I am thinking that I need to put new plugs in anyway.

Cleaned the plugs and reinstalled. It was quiet at the airport so I made a few full power runs down the runway, pulling power just before reaching take-off speed and rolling out. Still not showing 2,700rpm. I have the digital tach that is supposed to be delivered today but won't be able to check that until Saturday.

I had another question. In the Cherokee's I flew when you pushed the throttle all the way in it would actually go "all the way in." On this plane it stops and there is still another 1/4"-1/2" of shaft showing, like it could go in farther but it just won't. Is there a set screw or an adjustment somewhere that controls where the cable stops? Just thinking out loud here (with very little experience...) but I wonder if it is just not allowing the throttle to open all the way. If it had that extra 1/4"-1/2" that might be the 100-150rpm I'm missing. I've also read a couple old threads here about throttle cable failures and want to make sure this isn't a sign of impending failure somewhere down the road.

I wouldn't stress about oil on one bottom plug for now if it's the first time you've seen it. Just recheck at next oil change, maybe scope the valves then. I won't try to explain the myriad of causes for this per my understanding, as there are much more knowledgeable folks here.

Your throttle cable is likely fine - just make sure it moves the lever on the carb from full open to full closed. If not, have A&P adjust.

[carusoam]

Keep in mind...

Compression rings and oil control rings do different jobs... good compression doesn't always mean there isn't a problem with a broken or worn oil ring...

The oil ring is the one closest to the bottom of the piston.

Best regards,

-a-

[N6758N]

2 minutes ago, carusoam said:

Keep in mind...

Compression rings and oil control rings do different jobs... good compression doesn't always mean there isn't a problem with a broken or worn oil ring...

The oil ring is the one closest to the bottom of the piston.

Best regards,

-a-

True Anthony. However I do not think that is the culprit here. Really sounds like a propeller/propeller control issue. Ever tried to take off without having the prop pushed in? THe results are exactly what he is describing. 

[carusoam]

T,

Richard had mentioned the lead balls and oil as a possibility, and that his compressions were good at the annual.  I agree with your statement.

 

For the second part of the Have I ever question...

yes, for two solid years my rpm was stuck on 2500 rpm. The STC for 2700 rpm was the solution... 

 

Clarifying for Richard...

For checking on things that affect the engine's output...

1) fuel - FF

2) air - MP

3) spark - EGTs 

4) 10-20% of the HP comes with full rpm - RPM .......(a huge factor for T/O and climb)

5) ignition/magneto timing - CHTs

 

There is a lot pointing towards the prop control.  Terry gave the great detail of what to look for.

Best regard,

-a-

Edited January 17, 2017 by carusoam

[N6758N]

1 minute ago, carusoam said:

T,

Richard had mentioned the lead balls and oil as a possibility, and that his compressions were good at the annual.  

 

For the second part of the Have I ever question...

yes, for two solid years my rpm was stuck on 2500 rpm. The STC for 2700 rpm was the solution... 

 

Clarifying for Richard...

For checking on things that affect the engine's output...

1) fuel - FF

2) air - MP

3) spark - EGTs 

4) 10-20% of the HP comes with full rpm - RPM .......(a huge factor for T/O and climb)

5) ignition/magneto timing - CHTs

 

There is a lot pointing towards the prop control.  Terry gave the great detail of what to look for.

Best regard,

-a-

Wasn't thinking of your O when I posted that now was I, haha! I'm sure you would agree that life is so much better at 2,700RPM!

[Skates97]

Anthony, Terry, thanks for the ideas. It gives me a direction to go in. I'm going to put new plugs in later this week and will take a look at the travel of the control cables while I have the cowl off. Plus by that point I will be able to check the rpm's with the digital tach as well.

The MooneySpace education continues...