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Mar
16
2020

Maintenance Checks - Bell 407

Posted 71 days ago ago by jhadmin


The 407 intake cowl assembly is notorious for corroding in salt-laden environments, especially on the intake shelf and intake screen supports. One proactive measure is to remove the shelf and screen support associated steel nut plates, strip the factory paint, and apply a new coat of epoxy primer and a quality polyurethane paint. Then reinstall the nut plates with dissimilar metal tape between the nut plates and aluminum metal. The result won’t be 100% corrosion proof, but will make it much easier to manage. 


For a second intake cowl tip, on a regular basis mist/wipe a coat of Corrosion X over the interior cowl areas to include the shelf and screen support. Just remember a little goes a long way.


And to make it easier to remove and install the intake cowling, replace the stainless steel MS mounting screws with AN3 stainless bolts. It’s usually considered a minor alteration, and the bolts provide a better method of removal and installation than the Phillips screws.


Moving forward to the forward cowling (or servo cowling to some people)... be sure to keep an eye on the cowl L/H and R/H latch hook deck areas. Over time the cowl seal will flatten, allowing the hooks to chafe the deck. Bad news. One preventative tip is to bond a wear pad to the deck under the hook area to protect the deck from damage.


Another transmission deck area that is susceptible to damage is at the junction with the forward engine firewall. Stainless steel and aluminum don’t get along well, so this combination can lead to corrosion issues. Keeping this joint area clean and applying Corrosion X on a regular schedule will go far to keep this area corrosion free.


Same goes for the deck area under the transmission pylon mount flanges where stainless steel shims usually reside in three locations. These pylon mounts are a life-limited component and require replacement. One tip is during the pylon replacement process, carefully remove the existing shim pack and coat both sides with a corrosion-preventative grease like Braycote prior to reinstalling the pylon mount. 


A separate tip on the pylon mount replacement: substitute the original Proseal 890 that seals the pylon mount pad to the transmission deck with Proseal 870, which is a lower adhesion type sealant. Removing PS 890 can be a bear and has led to unintentional deck damage, whereas the PS 870 reduces that risk yet still seals the mount. In most cases this will also be a minor alteration.


To kick off the new year, I’ll leave you with a DIY special tool that comes in handy when working around the transmission deck with all of the cowlings on. At times the transmission oil pressure transducer will give up the ghost at the most inopportune times, like offshore on a toadstool when the wind’s blowing 25 and pulling a cowl is out of the question.


Enter the T.M. Mark II transducer ROTORwrench...It’s nothing fancy, but considering you can’t get any normal wrench/crowfoot on the transducer due to its narrow wrench-flats and close proximity to the intake cowl shelf and K-Flex shaft, it’s the little wrench that could.


Take any 5/8” open-end wrench and cut it to 3” in length as shown in Figure 1 below. Next, grind the wrench head to a thickness of approximately 1/8”. Be sure to test fit on an actual installed transmitter. And there you have it: a game changer. It beats locking a pair of vise grips on the transducer to remove and install. 


About the author: After 32 years maintaining helicopters in various capacities, Scott concluded a full-time career with a major operator in 2014. When not pursuing future writing projects, he can still be seen around the flight line tinkering on aircraft for beer money.






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