Rotorway Forums

Over the past 40 years of maintaining and instructing in Rotorway helicopters one issue has reared its ugly head countless times. You are flying along when suddenly you notice a new noise coming from the engine bay. You make a precautionary landing and discover that one or more exhaust manifold bolts have backed out either all the way and are now missing or enough to allow the exhaust gadget to be torn leaking red hot combustion gasses out toward your fuel tank.

What do you do now? You could elect to continue flying home with the very real possibility that the hot exhaust could burn through your plastic fuel tank.. not a good choice. You need to fix it before flying but where are you going to buy that exhaust gasket and the needed bolts before some cow in the pasture you landed in rubs your helicopter into the dirt.

Here is the simple solution that I came up with and it has worked out very well with no blown exhaust gaskets or lost bolts encountered since we started installing this simple modification. I ordered new drilled head exhaust bolts from the company listed on the package and replaced the old style bolts with the drilled head bolts. After the new bolts are torqued to spec, run a piece of safety wire through the drilled head of each of the 3 bolts on each manifold. Run the wire in such a manner that the bolt cannot back out, the wire keeps it from unscrewing at all.

The two bolts that this may not work on are on the inside corner under the top manifold bend where sometimes there is not enough room to get that new bolt started. If that is the case you can loop the safety wire over that one torx head bolt on each side to keep it from backing out and the same wire runs through the heads of the other two bolts on that manifold. You may wish to try this mod, you will be happy that you did. The bolts shown are a tad bit longer that the original bolts so I added two or three washers under the head of each bolt to prevent them from bottoming out in the threaded hole.

After seeing this post i just went out and picked some up from my local fastenal ~2 minutes from my house... its been on my to-do list... i did not get the drilled ones however because the original bolts are 5/8" in length and these are easier had, undrilled. i am thinking of using a lock washer as opposed to drilling them. im not against safety wire! all for it actually, i also figure Lycoming and continental engines exhaust manifolds are held on with lockwashers and nuts so that should work here aswell. 

the most important thing is to torque to spec and re-torque after a few heatcycles... the socket cap screws allow easy access while the 12-point was a nightmare with the exhaust wrap.... actually now that i think of it safety wire could hinder an allen wrench from seating to torque check. either way. good job, and excellent recommendation! should have been this way from the start.

The lock washers may work just fine but I was concerned that the intense heat from the exhaust may relax the spring tension of the lock washers allowing the bolts to loosen. Let us know how the lock washers work for you over time.

the heat does affect them, so they are for sure only one time use, but these lock washers in particular work by "biting" into the material in the loosening direction aswell so its not just the spring tension holding them.

It’s very important retorque these after a few runs , they will definitely be loose and need tightening. Another important thing to look for is, the flange on the pipe needs to be flat. I always grind or file the flanges perfectly flat. They typically spot weld the flange in 3 places then weld all the way around. Many times this can result in three lower areas of the flange where they spot welded it. This where it will blow out the gasket.
I’ve always used just a flat washer and made sure to retorque. Never had a bolt back out , and I never safety wire . Makes it impossible to check and retorque.

My experience over the years that I have been using the safety wire has been that the wire holds the bolts in place and when I check to torque it holds where I set it. Different strokes Homer.

Keep the tips and tricks and pictures coming Orv.   These are invaluable for us builders and new owners.