Assitance in Parts

[WebMaster]

This was on the other list server thread. I suggested that it be posted here
Please respond to: TeamNMA@afnet.net

Dear 337 flying colleagues.

I've been a part of the group since 2000 and have posted a couple questions
here before with tremendous success, and have greatly appreciated your
assistance. I'm operating the following Skymaster in West Africa, Aircraft:
1978 T337-H S/N 33701865. As I'm solo out here pilot/mechanic, I appreciate
any and all input. Parts are hard to come by, and returns are next to
impossible. I have to be accurate the first time. I'm coming to the states
for a meeting the 8th through 18th, and hope to get some parts purchased to
take back with me.

I've got a few technical questions.

1) - Engine mounts. I've got some cracking and want to get them replaced.
My parts manual shows the same number for both the front and rear engines.
C299501-0301. (4 assemblies for each engine). Someone who has changed these
out before on this year aircraft, can you confirm that these are indeed
accurate numbers and if you are aware of any additional considerations, i.e.
should the associated AN7-47A and -50A bolts be automatically changed?

2) - Turbo Charger check valves. I've been advised that the turbo charger
check valves need to be changed each five years. There are two valves on each
turbo charger, a lower one and an upper one - 3142-00-5 (lower) HE646-2
(upper). Should both of these valves be changed on each turbo charger every 5
years?

3) - Charging system. I would like to get a stock of spare parts in my fly
away kit, as well as I need to replace a failed relay. The charging circuit
board (on the front firewall) has two small relays on the bottom of the board
(left and right) which trigger the "Alt Failed" light on the console from the
respective (front / rear) alternator. One of the relays has corroded and is
not repairable. I would like to find two of those relays, as well as purchase
replacement diodes for all of the diodes on that board. Does anyone have the
part numbers for these relays, as well as the part numbers for the diodes?
Then,,,,do you know where I might order them?

4) - Chargine system again. I have a pulsing in the electrical system. The
dash lights, cabin lights, have the rapid pulsing - very annoying and I'm sure
not good on equipment. I can remember it being discussed once, but don't see
that I kept the email in my files.

Thanks for any assistance.


Todd Aebischer
NMA - Africa West
Abidjan, Côte d'Ivoire
West Africa

[Richard]

Boy, I wish someone could answer this one too. I've been wondering about the check valves on my airplane. They are original from 1967. I've rebuilt them a couple of times, but the bodies are starting to show their age.

Rebuilding them is very easy. Most of the internals are stainless steel and don't ready show any appreciable wear, however the rubber components take a beating from the heat. The lower drain flapper takes most of the abuse.

Does anyone know where to find these? I've tried several places and no luck.

Richard

[Mark Hislop]

Todd:

As far as the diodes are concerned, I replaced mine a few years ago with identical parts from Newark Electronics. Actually, the new parts had better voltage ratings. If I recall correctly, Cessna wanted several hundred dollars each for the two big power diodes. I got them at Newark for about $30 each. I will try to dig up my records and get the part numbers for you.

In regards to the pulsing lights, that is a common problem with the Skymaster. It is caused by your system voltage fluctuating up and down. This fluctuation is usually caused by resistance in the alternator field circuitry. First, try running on one aleternator at a time, in case the problem is in only one circuit. (Most likely it will be in both.) Check each connection point in the field circuit...The field circuit breakers, the alternator field switches, the connections to the voltage regulator, the master switch, etc. Clean them and make sure they are tight. If that does not cure the problem, then you may have to replace some of the components, particularly the alternator field switches, the master switch, or the circuit breakers. Even a very small amount of resistance in the field circuit causes the voltage regulator to call for higher voltage, and when it sees the higher voltage, it calls for less voltage. This cuases the system to "hunt" with the voltage spiking up and down. I had to replace the master switch and alternator siwtches in my aircraft to make the problem go away, even though they ohmed out OK. The good news is that the switches are cheap and easy to replace.

Mark

[Guy Paris]

Mark,
I misplaced the info I had on the diodes that I changed several years ago. I hope you can find the info on the ones that you got. Think they need to changed again. Guy (the old 72 driver)

[WebMaster]

Please note that this post was originally done on May 3, 2003. Please also send your replies to the email address
TeamNMA@afnet.net