Loss of Power

[Tomtrotter]

I've recently noticed a loss of power, most noticeable in climb and cruise.  It seems I've lost 7 - 10 mph in cruise.  I had the prop overhauled last year, and I'm just coming out of annual now with strong compressions, no loss of oil.  1975 M20F, ~4,200 hrs on airframe, mid time engine.  Anyone else experience the same thing, and most importantly, what was cause and correction?

[gsengle]

Could be spalling lifters, which would be serious. Get it checked.

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[kmyfm20s]

Make sure you verify the RPM's. If it your governor was set to you tack and it is off you will not be getting the same power.

[Yetti]

summer and hot?

[Tomtrotter]

Thanks for responses.  RPM's, fuel and oil pressure all stable.  Lower climb and cruise is significantly worse than typical hot humid weather effect.  I'll ask mechanic to check lifters.  Other thoughts?

[N601RX]

If it happened immediately after the annual I would suspect the mag timing. You mentioned the rpm was stable, but is it correct. Phone apps are available to verify rpm. 

[Yetti]

Check compressions cold.  How many hours on the mags.  When were the spark plugs cleaned?

[Yetti]

flaps coming up all the way?  not that I would know how leaving them down would take about 7 knots off cruise

[Piloto]

If the climb rate looks normal your power is probably OK. Check the pitot tube for bugs. Also check the static alternate air source valve.

José

[aaronk25]

Hot temps do take off about 5kts....

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[Hank]

Summer is in full swing, and I'm now rotating at 75 mph instead of 70. Climb rate is down a little, but once I reach 6000-7000 feet, cruise speed is still there. High temps, high humidity = high density altitude in the ground! longer ground rolls! lower indicated airspeed.

If the speed loss was sudden, look for induction leaks. It won't apply to you, but my carb heat butterfly hinge broke and it defaulted to Full Open. Climb rate fell to just 200-300 fpm in the winter, and the cruise speed was anemic.mfixed her up, added a new cable, and now she's 10-12 mph faster than anytime since I bought her in 2007. Also spent two annuals patching up and reinforcing my doghouse. Now I'm even happier than I was before, but I didn't appreciate the bills . . . Now I just don't think about them as I watch the ASI wind up!

[AaronDC8402]

I would suspect an ignition issue also. Spark plugs are a good first place to look. Possibly mag timing or a failing mag. Have you tried doing a mag check just before shut down? I wonder how bad an idea it would be to do a mag check while cruising?

[Hector]

I would suspect an ignition issue also. Spark plugs are a good first place to look. Possibly mag timing or a failing mag. Have you tried doing a mag check just before shut down? I wonder how bad an idea it would be to do a mag check while cruising?

I had a p-lead go bad in flight resulting in the loss of the left mag. I noticed something was wrong when my engine started running a little rough. A quick mag check in flight revealed the problem when the engine quit when I switched to the left mag. Switch back to 'both' and the engine immediately came back although still running a little rough as expected. It was no big deal. Landed at a nearby airport and got the p-lead fixed and it was all good.

[carusoam]

Hector,

How did your pulse work during your well executed problem solving exercise?

 

Best regards,

-a-

[Tomtrotter]

Thanks again. Does anyone know what the alt static knob should look like in the normal (vs. alt) position? Should it be aligned with the tube, or perpendicular?

 

[carusoam]

Tom,  you may want to update your avatar.  It will keep you from typing what plane you have to get a more specific answer.

Alternate static is a valve that opens an alternate port inside the cabin...  Pull the knob out to activate the alternate source.  

The alternate source being inside the cabin is at a slightly lower pressure during flight.  It is usually drawing a slight vacuum.  It probably doesn't register any difference if you are stopped on the ground.

Did I answer your question properly?

The other thing to look for is the alternate air source.  This is the door that opens to allow air to enter the throttle body.  Important to be working when snow and ice have coated your air filter.

Make sure both knobs are completely working.  All the way out and all the way in.

Best regards,

-a-

[takair]

i would think loss of power would need to be compared to previous power settings.  Are you unable to get the same manifold pressure as previously or does it take more fuel flow to get there? If the RPM, MP and FF are still where they were previously, you might look for airframe differences.  Was the gear re-rigged at annual?  If so, we're the gear doors checked?  Are nose gear doors still closing?  Do you have a vacuum step...if so, does it still go up?  We're flaps or rigging adjusted?  Some good suggestions above too regarding pitot static.  Is ground speed down too?  Check what true airspeed is vs just indicated.  Just some ideas, hope some help.

[Hector]

Hector,

How did your pulse work during your well executed problem solving exercise?

 

Best regards,

-a-

I would by lying if the first words out of my mouth were not 'oh shit', but I was just as quickly relived when the engine immediately started as soon as I switched to both.

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