• Facebook
  • Twitter
  • LinkedIn
  • Instagram
  • Youtube
Helicopter Flight Training Sponsors


All Entries


Helicopter Maintenance Tips July 2015

Posted 7 years 20 days ago ago by Scott Skola

Only one tip this month. But when I learned this trick, it was one of those magic moments.

ATA 63
Bell 407:  Another item that used to perplex me was reinstalling the K-FLEX driveshaft. It wasn’t too bad on the earlier models, but once the aft T/R driveshaft flywheel was “incorporated” to form the new thicker rotorbrake (R/B) disc up front, it became a little tighter getting the shaft to drop in. And when Bell increased the size of the transmission drive flange it became down right impossible without a little persuasion. That was until a friend showed me the light. And I use his initials as the submitter.

It’s hard to explain this tip, let alone try and draw it out. But it works. Just need to hold your mouth right.  

First, be sure to use the correct K-FLEX compression tools. The SKSP part number tool is used on the latest shaft assembly. Install the forward and aft compression tools per the M&O and compress shaft flex-beams till the hardware bottoms out.

Second, do not install the R/B disc on the free wheel unit (FWU) flange.

Using the diagram below as a basic guide we’re ready to give it a try. This can be done from either side of the aircraft, but I prefer the right side. Slide the R/B disc in front of the FWU flange and place the compressed K-FLEX shaft engine side up on transmission deck.

Cradle the R/B disc in one hand lifting it up toward the engine compressor housing. The important thing is the get the top portion of the R/B disc opening (B) above the top of the FWU flange (A). Slightly tilt the top of the disc back a bit.

The idea is to get the R/B disc up at an angle so it sits a smidgen aft allowing the shaft to clear the transmission drive flange.

Now grab the K-FLEX shaft in the other hand and place the top of the K-FLEX engine flange (C) into its mounting area (green portion) on the R/B disc. Position the shaft at about a 20 to 40 degree angle.  Sometimes when the planets align the shaft will miraculously drop in when you lower the transmission side of the shaft. But normally it does not, so don’t give up.

Jiggle the disc around while repeatedly stabbing the engine side of the shaft and lowering the transmission side. Sometimes the engine oil lines, especially the #1 bearing scavenge line, will limit the vertical height you can lift the disc. Sometimes the flex-beams on the K-FLEX hit the firewall. When you hit the sweet spot you’ll know. The shaft will settle to the deck and the disc will drop in front of the FWU. F’n magic. When that happens take a break, you’ve made it.

It took me several different attempts to get the hang of it. After that it became such a sure thing I started to win a few bets. Bottom line it works. Good luck! [Submitted by KH]


Send an email to [email protected] Enter tip type (general, aircraft, component, ground support, etc.) in subject line. Describe the tip in as much detail as needed and be sure to include any basic info for those readers who lack experience on specific model. Ensure the aircraft/component model and your credit preference (anonymous, nickname, real name) are included in the email. No email addresses will be shared or permanently stored and will be deleted once tip is posted in the blog.  

About the author: After a 32 year career in maintaining helicopters, Scott provides limited maintenance consulting services through his company, TEK Aviation LLC. He can be contacted at [email protected].

*And to keep the hounds at bay, the information contained in this blog is for discussion purposes only.*