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  #1  
Old 08-08-2019, 08:48 PM
Tom @ N269CP Tom @ N269CP is offline
 
Join Date: Oct 2017
Location: Green Cove Springs, FL
Posts: 78
Default Workshop screw-up

I had a local service shop replace my left magneto early this week (Slick 4371 IC mag). On my first post-work flight I noticed the cyl # 1 EGT climb to possibly over 1450F with Cyl #1 CHT of 425F...other three cylinders were lower and comparable to each other...only the Cyl #1 temperatures spiked. During the left mag drop test the rpm dropped by about 120 rpm. The planes climb rate was definitely sluggish compared to normal climbout. I normally take off full rich as the plane has bags of power and it helps keep my CHT's below 400F.

Today the workshop checked the magneto timing which he found to be 30 deg BTC versus the Lycoming spec of 25 deg BTC. The discrepancy appears to have been caused by an internal mag timing error which the shop set while installing the mag, compounded by their not electronically confirming the advance....timing appears to have been set solely off the flywheel timing mark..which is wrong if the mag internal timing was wrong to begin with.

Static manifold pressure at my home airport is about 24.5"Hg. Takeoff RPM is 2650 rpm....this puts the takeoff power at somewhat over 75% (24/24).

My question for VAF is this: Could this 5 deg advance timing error have resulted in detonation during takeoff which may have caused the higher than expected EGT/CHT?

I'm hesitant to fly the plane until I better understand the potential for detonation damage...may have another shop borescope the cylinders Friday morning before flying it anywhere.

I would be grateful for any suggestions as to my next course of action. I'd rather be safe than sorry.
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Kind regards,

Tom
Machinery Engineer
==================================
RV-8 N269CP
O-360-A1A w/Hartzell CS prop on 100LL
Slick-IC+PMag ignitions
Steam gauges
EI UBG-16, FP-5, & MUX-8A datalogger
Garmin Aera 660
TruTrak autopilot (GPS coupled)
uAvionix Tailbeacon ADSB-Out
Infinity grip w/Matronics trim speed control
Reiff engine preheater
TCW oil cooler air damper w/servo drive
AntiSplat oil mist separator
MH O2 system

Location: Santa Fe, NM (KSAF)

Last edited by Tom @ N269CP : 08-09-2019 at 03:41 PM.
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  #2  
Old 08-08-2019, 08:54 PM
Steve Melton's Avatar
Steve Melton Steve Melton is offline
 
Join Date: Apr 2011
Location: Cincinnati, OH
Posts: 2,141
Default

if you are using AVgas vs Mogas I think you are fine. I had a shift like that from premature mag wear. it was even across the cylinders but I needed to reduce power to avoid exceeding 390F. the mag timing had advanced to 31 deg. I borescoped the cylinders and all was fine. no further issues in 300 hrs. borescope it to ease you mind.
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Cincinnati, OH
RV-9A, Tip-up, Superior O-320, roller lifters, 160HP, WW 200RV, dual impulse slick mags, oil pressure = 65 psi, EGT = 1300F, flight hours = 700+ for all

Simplicity is the art in design.

see Amanda Melton for www.rvplasticparts.com
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  #3  
Old 08-08-2019, 09:03 PM
Tom @ N269CP Tom @ N269CP is offline
 
Join Date: Oct 2017
Location: Green Cove Springs, FL
Posts: 78
Default

Quote:
Originally Posted by Steve Melton View Post
if you are using AVgas vs Mogas I think you are fine. I had a shift like that from premature mag wear. it was even across the cylinders but I needed to reduce power to avoid exceeding 390F. the mag timing had advanced to 31 deg. I borescoped the cylinders and all was fine. no further issues in 300 hrs. borescope it to ease you mind.
Steve,

I use 100LL...I didn't want to reduce power because of the shallow climb rate and being lower than usual to the ground. I normally reduce rpm to 2400 rpm for climbout at around 400 ft AGL and leave the throttle WOT due to the higher altitudes here. All temperatures returned to historical norms at cruise ~20"Hg/2280rpm/7.2 gph/182 mph TAS.

I will borescope the cylinders.

Thank you for sharing your experience.
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Kind regards,

Tom
Machinery Engineer
==================================
RV-8 N269CP
O-360-A1A w/Hartzell CS prop on 100LL
Slick-IC+PMag ignitions
Steam gauges
EI UBG-16, FP-5, & MUX-8A datalogger
Garmin Aera 660
TruTrak autopilot (GPS coupled)
uAvionix Tailbeacon ADSB-Out
Infinity grip w/Matronics trim speed control
Reiff engine preheater
TCW oil cooler air damper w/servo drive
AntiSplat oil mist separator
MH O2 system

Location: Santa Fe, NM (KSAF)

Last edited by Tom @ N269CP : 08-08-2019 at 09:14 PM.
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  #4  
Old 08-08-2019, 10:59 PM
rvbuilder2002 rvbuilder2002 is offline
 
Join Date: Jul 2005
Location: Hubbard Oregon
Posts: 8,276
Default

Internal timing (e-gap adjustment) will have no effect on the actual timing of the mag to the engine. Who ever installed the mag just didn't follow normal procedures or didn't do them correctly.
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RV-6A (aka "Junkyard Special ")
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  #5  
Old 08-09-2019, 02:12 AM
Tom @ N269CP Tom @ N269CP is offline
 
Join Date: Oct 2017
Location: Green Cove Springs, FL
Posts: 78
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Quote:
Originally Posted by rvbuilder2002 View Post
Internal timing (e-gap adjustment) will have no effect on the actual timing of the mag to the engine. Who ever installed the mag just didn't follow normal procedures or didn't do them correctly.

I'm going to have another shop review this in the morning. I'm getting conflicting advice.
__________________
Kind regards,

Tom
Machinery Engineer
==================================
RV-8 N269CP
O-360-A1A w/Hartzell CS prop on 100LL
Slick-IC+PMag ignitions
Steam gauges
EI UBG-16, FP-5, & MUX-8A datalogger
Garmin Aera 660
TruTrak autopilot (GPS coupled)
uAvionix Tailbeacon ADSB-Out
Infinity grip w/Matronics trim speed control
Reiff engine preheater
TCW oil cooler air damper w/servo drive
AntiSplat oil mist separator
MH O2 system

Location: Santa Fe, NM (KSAF)
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  #6  
Old 08-09-2019, 04:49 AM
Red Mtn flyer Red Mtn flyer is offline
 
Join Date: Jul 2017
Location: Carson City, NV
Posts: 73
Default not conflicting, just confusing

FIRST, you set the e-gap [which is what Slick calls 'internal timing']. A lot easier to define if I could show you one...
SECOND, after inserting a lock pin to keep the armature from rotating [maintaining that 'e-gap'], the magneto is installed on the engine , and timed to give you the spark at specified BTDC. [Aaand remove the lock pin, please]
So: if the timing checks to 25 BTDC after installed, and your engine requires 25 degrees, you are set to go --- both "settings" will be correct.

To your original query: by all means, scope, particularly the 'hot' cylinder. I infer you'll be having an A&P do that; tell her you're looking for det/ pre-ignition damage, they'll know what that would look like.

A suggestion: The more you learn about how to fix them [correctly], the more confidence you'll have in the work you pay for. And yes, a lot of shops are understaffed - and under-experienced; it is not going to get better for the foreseeable.
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  #7  
Old 08-09-2019, 07:38 AM
n82rb's Avatar
n82rb n82rb is offline
 
Join Date: Jan 2007
Location: fort myers fl
Posts: 812
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get it checked out, but don't get to torqued up right now. if you are running 100LL the odds of detonation damage are low unless you have built it with higher compressions than normal. the detonation margins that lycoming designed in are pretty wide. ask some of the guys at RENO what they are running there engines at, its actually scary.

bob burns
RV-4 N82RB
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  #8  
Old 08-09-2019, 08:33 AM
rvbuilder2002 rvbuilder2002 is offline
 
Join Date: Jul 2005
Location: Hubbard Oregon
Posts: 8,276
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Quote:
Originally Posted by Tom @ N269CP View Post
I'm going to have another shop review this in the morning. I'm getting conflicting advice.
The E-gap adjustment (internal timing), is setting the contact points opening point so that it occurs at the moment that the highest voltage is being induced by the magnet into the coil.
The timing of the mag to the engine is a totally different process and is done with an indexing pin locking the position of the distributor rotor so that the mag can be properly timed to the rotation of the engine.
So, even if the internal timing of the mag. was incorrect, if the proper timing adjustment process were used when the mag was installed on the engine, the spark would still occur at the proper time. The only issue would be that the spark output of the mag would be less than it is capable of (this will often cause poor starting performance).

I agree with others that it is unlikely that timing at 30 degrees has caused any type of damage to the engine.
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Any opinions expressed in this message are my own and not necessarily those of my employer.

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Hubbard, Oregon
RV-6A (aka "Junkyard Special ")
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  #9  
Old 08-09-2019, 08:40 AM
rocketman1988 rocketman1988 is offline
 
Join Date: Jun 2010
Location: Sunman, IN
Posts: 1,668
Default And

..:And yes, a lot of shops are understaffed - and under-experienced;...

That is no excuse. Years ago, we had a C421 in for an annual. Long story short, the shop either did not replace or used a wrong sized cotter pin in the elevator trim tab linkage. This led to the linkage disconnecting while climbing through FL190. The tab then was free to move on its own causing the right elevator to enter a divergent flutter mode. This snapped the three bolts that joined the left and right elevators (thankfully). My dad landed the aircraft safely and the investigation began...

My point is, if you go to a shop and the aircraft is signed off, you should have a reasonable expectation that the aircraft maintenance was done correctly and the aircraft is safe to fly. Understaffing or lack of experience is no excuse for not doing something correctly...

The funny part is the shop that did the work on the 421 still expected the $10,000 annual to be paid...
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Aerospace Engineer '88

RV-10
Structure - 90% Done
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  #10  
Old 08-09-2019, 09:15 AM
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rocketbob rocketbob is offline
 
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Location: 8I3
Posts: 3,306
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Couple of comments:

1. Scott is spot on in his description. E-gap can be off, but final timing will be correct. Less spark energy if its off. I normally set e-gap by feel.
2. 30 degrees of advance wont hurt anything short-term.
3. Sounds like the mechanic didn't have a buzz box.
4. Pin on a slick is only used when inserting the mag into the accessory case. You immediately pull the pin after the nuts are snugged. DON'T rotate the engine with the pin in place!
5. A trait of an excellent mechanic is the ability to disassemble, reassemble, and time a magneto without any difficulty. A really excellent mechanic will be set up to re-magnetize rotors. Ones that can't or have to send mags off to have someone else do it...meh. Just my educated observation.
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