Static RPM Below Limit

ARFlyer

ARFlyer

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ARFlyer
Got a interesting issue on my new engine. Both flights this past weekend I noticed that I’m not producing at least 2250 RPM at full static power. At power application, the engine was only pulling about 2100 until I got the ram rise during the takeoff roll. It’s also climbing like a 150 and not a 180STC’d 172. I would maybe get 400/500FPM. At altitude, it’s closer to 200fpm during altitude changes.

The JPI data is also showing that the #4 Cyl Temp is running away from the pack on takeoff. The group is averaging about 370-380 while the #4 is going to 405-410. During climb it will slowly rejoin the others and then spike again. Kinda like a roller coaster. It’s setting off the CLD Alert for cooling above 50F/Min until cruise. Also during cruise LOP it is no longer staying below 400 unless I’m running the FF at around 11/12gph. About a month ago I could run it at book values 9.5/10gph with it sitting at about 380.

My other partners have also noticed a remarkable decrease in climb performance but they were chalking it up to high summer temps and density altitude.

What’s y’all’s thoughts?
 
Might help if we knew more background?

it sounds like a 172 with a ( insert STC holder here) conversion.

Prop ? Correct per STC?

Does the JPI also tell RPM?

Hand held may help here.

However; is seems you have low indication and low performance?

Never heard the 172/180 described as a dog!
 
ARFlyer said:
Got a interesting issue on my new engine. Both flights this past weekend I noticed that I’m not producing at least 2250 RPM at full static power. At power application, the engine was only pulling about 2100 until I got the ram rise during the takeoff roll. It’s also climbing like a 150 and not a 180STC’d 172. I would maybe get 400/500FPM. At altitude, it’s closer to 200fpm during altitude changes.

The JPI data is also showing that the #4 Cyl Temp is running away from the pack on takeoff. The group is averaging about 370-380 while the #4 is going to 405-410. During climb it will slowly rejoin the others and then spike again. Kinda like a roller coaster. It’s setting off the CLD Alert for cooling above 50F/Min until cruise. Also during cruise LOP it is no longer staying below 400 unless I’m running the FF at around 11/12gph. About a month ago I could run it at book values 9.5/10gph with it sitting at about 380.

My other partners have also noticed a remarkable decrease in climb performance but they were chalking it up to high summer temps and density altitude.

What’s y’all’s thoughts?
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Time to see your mechanic and have him check it out.

How many hours on the new motor?

Have you had a leakdown done on it?
 
Magman said:
Might help if we knew more background?

it sounds like a 172 with a ( insert STC holder here) conversion.

Prop ? Correct per STC?

Does the JPI also tell RPM?

Hand held may help here.

However; is seems you have low indication and low performance?

Never heard the 172/180 described as a dog!
Click to expand...

It’s a Air Plains 180 STC O-360-A4M. The JPI is a full JPI 900 Primary.

The prop is the oddball. It’s pitched at 63”. The STC at original install doesn’t show a limitation. Air Plains currently says it’s limited to 62” but that we brought the STC they didn’t have that limitation. I’ve been told both we do and don’t have to follow the current updated STC.

Gary Ward said:
Time to see your mechanic and have him check it out.

How many hours on the new motor?

Have you had a leakdown done on it?
Click to expand...

100TT

No not yet.
 
Last edited:
#4 exhaust valve damage?
Leaking induction hose on #4?

These are just guesses from a keyboard warrior.
 
Fuel flow. Mag timing. Restricted exhaust. Those are what I'd be looking at.
 
ARFlyer said:
Got a interesting issue on my new engine.
Click to expand...
Was this engine installed at the same time the STC was complied with or is this a different engine from a different vendor? Regardless it might be in your best interest to get the required static RPM set per the proper charts before any other work is performed.
 
Stewartb said:
Fuel flow. Mag timing. Restricted exhaust. Those are what I'd be looking at.
Click to expand...

Fuel flow is 14-15gph at full throttle.

Bell206 said:
Was this engine installed at the same time the STC was complied with or is this a different engine from a different vendor? Regardless it might be in your best interest to get the required static RPM set per the proper charts before any other work is performed.
Click to expand...

The engine is a Air Plains STC version from Lycoming. It replaced a previous engine converted to the Air Plains A4N. We’ve had the STC for about 20 years.

At engine break in and testing the static RPM was in the limitation range. It’s only in the last few weeks that we’ve noticed an issue.
 
ARFlyer said:
At engine break in and testing the static RPM was in the limitation range. It’s only in the last few weeks that we’ve noticed an issue.
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Sounds like something has loosened up since the initial check. May want to give the whole engine a once over.
 
Check your muffler. I’d drain the carb bowl and look for water, too.
 
After 100 hours, you may have a defective cam. Might borescope a cam lobe for abnormal wear and have Blackstone give you an oil analysis.
 
NordicDave said:
After 100 hours, you may have a defective cam. Might borescope a cam lobe for abnormal wear and have Blackstone give you an oil analysis.
Click to expand...

They showed a very high level of iron on our first sample at 50 hours. But the notes said that is normal during break in or from shafts/valves.
 
455 Bravo Uniform said:
Leaking induction hose on #4?
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That, or at the intake flange at the cylinder. Loose flange bolts or the gasket failed.

Other possibilty is one failing plug in that cylinder at high power settings.
 
Dan Thomas said:
That, or at the intake flange at the cylinder. Loose flange bolts or the gasket failed.

Other possibilty is one failing plug in that cylinder at high power settings.
Click to expand...

So we have checked everything and have found nothing wrong. It’s still only making 2200 at full
power. The A&P is baffled along with Lycoming.
 
Since no one has mentioned the obvious - has throttle or mixture linkage slipped preventing max. travel?
 
OP - I understand it once did make static rpm........?

If not and having checked ignition timing & the other obvious items listed above, in desperation you might check that the camshaft is properly indexed to the crankshaft by comparing the valve lap vs TDC on this engine, and on another similar engine. Twice I've seen factory assemblies put together one tooth off - by people that should know better.
 
SKEET duct instead of SCAT with the inner liner coming loose?
 
Collapsed Lifter would cause a little power loss.

Dry Lifter Clearance change?
 
nrpetersen said:
OP - I understand it once did make static rpm........?

If not and having checked ignition timing & the other obvious items listed above, in desperation you might check that the camshaft is properly indexed to the crankshaft by comparing the valve lap vs TDC on this engine, and on another similar engine. Twice I've seen factory assemblies put together one tooth off - by people that should know better.
Click to expand...

Last night the mechanic found during the timing check that the Right Mag is firing twice. Once at roughly 25° and another time forward. We think the mag point is bad or something else is majorly screwed up with the mag. We haven’t taken it apart as I want to be able to warranty the mag from Lycoming.

We also borescoped two cylinders and found nothing wrong. Everything looked beautiful.
 
Lycoming just called. They said the Right Mag is cross-firing which they have only ever seen maybe three times. They said that is 100% the cause of our power issues.

I surprised and happy it hasn’t damaged anything else. Crossing my fingers it stays that way.
 
ARFlyer said:
Lycoming just called. They said the Right Mag is cross-firing which they have only ever seen maybe three times. They said that is 100% the cause of our power issues.

I surprised and happy it hasn’t damaged anything else. Crossing my fingers it stays that way.
Click to expand...
I'd sure like to know the mechanism of that malfunction. Cross-firing implies arcing within the distributor. Firing twice is almost impossible, since the first spark drains the energy built up in the coil and it takes another half-turn of the rotor to build it again. In the O-360, that means the next cylinder.

Early firing could cause detonation. I hope it didn't. Lycoming might be on the hook for an engine. Was it a Slick mag?
 
Dan Thomas said:
I'd sure like to know the mechanism of that malfunction. Cross-firing implies arcing within the distributor. Firing twice is almost impossible, since the first spark drains the energy built up in the coil and it takes another half-turn of the rotor to build it again. In the O-360, that means the next cylinder.

Early firing could cause detonation. I hope it didn't. Lycoming might be on the hook for an engine. Was it a Slick mag?
Click to expand...

Slick Mag installed by the factory at manufacture.
 
Me thinks the number 3 is understated.

AD 82-23-01 refers a similar situation with the distributor contaminated with

filings from the contacts.

As Dan stated ; detonation is very likely.

The AD mentioned requires a check of the Dry Lifter Clearance and scoping.

The concern is DLC below limits.

Presumably the DLC check is for stretched exhaust valves.
 
Previous post related to Bendix.

Slick has a SB relating to loose distributor fingers that could act in the same way.
 
Magman said:
Previous post related to Bendix.

Slick has a SB relating to loose distributor fingers that could act in the same way.
Click to expand...

Ours is brand new S/N so it falls outside the range of the SB I found.
 
Dan Thomas said:
Slick might have found a new way to screw up. They are rather good at it.
Click to expand...

Air Power, Air Plains and Lycoming believe so. Lycoming said this issue is so rare that they want the mag to tear down. I need to check tomorrow with Aircraft Cert if they want the data as well for a SDR.
 
Self destructing carbon brushes redux?



Glad you checked S/N and not just figured “ new”.

The dealers have been sent selling mags with SBs outstanding at time of sale.

The Distributor Gear/ Finger costs about $150 (?) each to replace .

Slick did have an exchange program.
 
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