Had a discussion about my 2500 hour engine with my IA

[jetdriven]

When you back the throttle off of full, the economizer circuit closes and leans it out. There is actually a separate passage with extra fuel for full throttle operation you cannot get any other way.

[cbarry]

In addition to your mechanic, I believe I would ask the owner/s who put the 2500+ hrs. on it for their thoughts on how to treat the engine. They would seem to be a good source--if they're available.

[BigTex]

When you back the throttle off of full, the economizer circuit closes and leans it out. There is actually a separate passage with extra fuel for full throttle operation you cannot get any other way.

I hear yeah but the gains from the economizer isn't enough to compensate for the poor baffling and cowling of the early C's.

[RobertGary1]

I don't think I would consider flying without an engine monitor. If I hadn't installed installed an engine monitor in my Mooney I would have been in a field last year.

 

-Robert

[ryoder]

Robert what happened amd how did the engine monitor help?

[Tony__L]

"Time in service" is what TBO is based on, which someone said earlier was "flight time". However, a tach only approximates flight time.  On the ground the tach adds up hours much slower. IE you taxi 15 minutes per flight but it only adds 5 mins to tach time. Then you fly two hours. Anyways, the tach time, assuming you have the right hour recording ratio, is pretty close to actual time in service.

 

Ours has a 2300 RPM tach installed in 1982. It then ran some 4,000 hours, counting 10% too much time, and it was reading a further 10% too high. I discovered this after a few long flights where the tach time recorded more than the hobbs meter. The correct tach recording speed is 2566 RPM.  After I discovered this, I installed a new 2566 RPM tach, I made a log entry, and poof, subtracted 600 hours from the AFTT.

 

In short, tach time approximates "time in service" IF the tach reads accurately, and IF it is the correct part number with the right recording speed.

 

 

I have a similar issue at hand and I am trying to figure this out for my own plane.  Generally, on shorter flights (1 to 1.5 hrs and less) I find that the tach is about 10-15% over reading on the clock.  On longer flights this comes down a bit but still over reads.  Seeing that I tend to fly at low power settings (24/2400 and less depending on altitude) I would expect that on longer trips (anything over 1.5 hrs) that the tach should in fact be lower than the flight time.  I do not have a hobbs meter in the plane.

 

My plane is in for annual maintenance at the moment and we are trying to look into this issue.  From what we can figure out it would seem that the tach in the plane could be the original equipment, we think this only because the hours on the tach equates closely to the air frame time.  However, we cannot find an actual spec for the tach.  I was hoping that some of the folk on this forum could assist in perhaps figuring out at what RPM my specific tach is supposed to be accurate.  The details as gleaned from the back of the instrument are as follows:

 

“Patented Made in USA.”

“A.C. DIV.G.M.C”

“FLINT, MICH”

“64.121.10”

“91103’ ( this is not clear at all)

 

My plane is a 1967 M20F Executive.  Is there a resource that would tell me what tach should be installed in the plane and what the spec of that tach are?  Knowing this and the specs of the tach above I will then be able to compare them and see if I must just live with the situation as it is or rectify it.

 

Any assistance would be great!

 

Tony

[Awqward]

My 87J does not have a tach time meter...it has a Hobbs which starts counting at start up until shutdown....I log it for interest but I use the FAR part 1 definition of Time in Service by recording actual time off the surface of the earth...

"Time in service, with respect to maintenance time records, means the time from the moment an aircraft leaves the surface of the earth until it touches it at the next point of landing."

[N601RX]

I have a 67F also. If I remember correctly it uses the 2566rpm tach also. If your not sure if the tach is reading correctly there is an Iphone app call Engine RPM that works off engine sound.  I've found that it always matches my JPI exactly.                                                                                                                                                                         

[AndyFromCB]

When you back the throttle off of full, the economizer circuit closes and leans it out. There is actually a separate passage with extra fuel for full throttle operation you cannot get any other way.

 

Does Bravo have it too? I've noticed my CHTs are actually higher at cruise climb than full throttle…Full throttle being 38/2550 and cruise climb being 34/2400, same as max cruise…I quit doing cruise climbs, instead I'll just climb at 130indicated, full throttle and never see a CHT over 380...

[RobertGary1]

You're fortunate your insurance company agrees to cover you. Typically I'm told they don't go much over 10% of hours on overhaul. I have to declare my smoh hours each year at renewal.

[jetdriven]

That's interesting, as our insurance company doesn't ask that. The aircraft simply must be airworthy (annual inspection etc) and the pilot qualified.

[AndyFromCB]

You're fortunate your insurance company agrees to cover you. Typically I'm told they don't go much over 10% of hours on overhaul. I have to declare my smoh hours each year at renewal.

 

NationAir does on their universal application but then they write with individual companies, so I have no idea whether Global or AIG use the number or not in their underwriting.

[garytex]

Ryoder:

Wow,2500 hrs, that's great. You must be doing something right.

On condition ops past tbo requires monitoring of the condition of the engine. So you pay attention to all that you can. It would follow that you would do oil analysis, cut open the filter, monitor spark plugs condition and type of fouling, track oil use, maybe wobble test valves. An engine monitor will speak volumes and, downloaded and checked for the incipient valve burning plateau/drop/plateau trace warn you before the lip cracks off. Bore scopes do the same.

The other aspect is assuming a questioning & pensive attitude. What's this stain of oil/exhaust/gas on the windshield/inside cowl/belly or anywhereon the engine. Has the vibration of the engine changed? How it starts, and how the prop stops. Know the reason for anything anomalous, especially concerning the cylinders, as they and the accessories will go first. Sadly I haven always understood what an engine is saying till after it broke. I just didn't understand the failure modes well enough to put 2 & 2 together. More knowledge is always better. (And saves money at the mechanics' shop)

And mags are never on condition, service every 500 hrs. Or prepare to get to know the trees better than you would care to. Speaking of trees, a smart old fart taught me to avoid flying over hostile ground, and it's not that hard or that much further to do so. IFR can also mean 'I follow roads' thru desserts, mountains, and continuous swamps or trees.

Gary

[Hank]

You're fortunate your insurance company agrees to cover you. Typically I'm told they don't go much over 10% of hours on overhaul. I have to declare my smoh hours each year at renewal.

My two previous and now current insurance companies have never asked anything about aircraft times. Lots of pilot times, though--total, retract, hp, make & model, instrument, actual, training received, etc.

For the plane, it's not much more than N#, make & model, hull value and deductibles for motion/non-motion.

[ryoder]

garytex I agree with you on the hostile ground avoidance. I don't fly over trees at low altitude. I tend to treat them as open water or worse. As for the mags I do plan on getting them overhauled soon. I found a guy who does them with removal and installation for a great price. I am probably going to wait for the part 23 changes and get a Garmin or Dynon with everything built in for 4k including pfd, map, com, transponder, and engine data. The transponder is remote but is operated by the efis. That is what all the light sports use now and it's a low cost and light weight system.

[aaronk25]

garytex I agree with you on the hostile ground avoidance. I don't fly over trees at low altitude. I tend to treat them as open water or worse. As for the mags I do plan on getting them overhauled soon. I found a guy who does them with removal and installation for a great price. I am probably going to wait for the part 23 changes and get a Garmin or Dynon with everything built in for 4k including pfd, map, com, transponder, and engine data. The transponder is remote but is operated by the efis. That is what all the light sports use now and it's a low cost and light weight system.

Don't hold your breath waiting for part 23....I was looking forward to it for 2 years and our huge gov. is to big to respond in the allocated time. What a joke.....this was gonna be the best thing for aviation since the wright bros.