Home > VansAirForceForums

- Donate yearly (please).
- Advertise in here!

- Today's Posts | Insert Pics

Old 06-26-2018, 03:29 PM
Raymo's Avatar
Raymo Raymo is offline
Join Date: Nov 2014
Location: Richmond Hill, GA (KLHW)
Posts: 1,875

This happened to me during my last condition inspection. I tried the thread-chasing tool that comes with the spark plug cleaning kit from ACS and it just made it worse.

Grab the heli-coil with a pair of needle nose or duck-bill pliers and slowly twist/pull it out. Have someone with experience guide you through the installation of a new one.
RV-7A - Slider - N495KL - First flt 27 Jan 17
O-360-A4M w/ AFP FM-150 FI, 1 PMag, Vetterman Trombone Exh, SkyTech starter, PlanePower Alt
Catto 3 blade NLE, FlightLines Interior, James cowl, plenum & intake, Anti-Splat -14 seat mod and nose gear support
All lines by TSFlightLines

"The object of the game, gentlemen, is not to cheat death: the object is not to let him play."
Patrick Poteen, Sgt. U.S. Army
Reply With Quote
Old 06-26-2018, 05:08 PM
deek deek is online now
Join Date: Mar 2013
Location: Flathead Lake Montana - 8S1
Posts: 311

Originally Posted by lr172 View Post
Cross threading in native metal is different than cross threading a threaded insert. The insert is more bendable due to the way it is manufactured. It is more like spring steel. It is the spring tension that holds the insert in place. If you look closely, you will likely see that the threaded insert is bent and not deformed. A thread chaser can only remove damaged threads on native metal, by breaking it off or shaving it. It can't un-bend the threaded insert back into it's original shape and it likely to start unthreading it out of the cyl head. I would examine closely with a 10X glass. As mentioned, if the threaded insert is removed incorrectly, it can damage the outer threads in the cyl head. Also, if it is bent, it will likely grip the chase once you go through the bent area and you may not be able to get the chaser out without pulling the insert and damaging the outer thread. Damage here, will required welding up the hole and re-tapping, if that is even possible and guaranteed to be expensive.

They make tools to properly remove helicoils and this would be the best path for you. It would only take a few minutes for a mechanic with the right tools to do this job safely.

In respect for the previous poster, I agree that a chase can be attempted if the operator is very careful about not letting it get tight or bind. I only fear that someone inexperienced may go too far and get in trouble. I feel it would be easy to get past the point of no return. A good examination of the damage should provide guidance on the likelihood of a chase addressing the issue.

^^^^ Really good advice here OP; the safe course of action is a simple helicoil R&R. I've chased helicoils, but I've also practiced first on scrap cylinders I have laying around in the hangar. I recant my advice about chasing, and suggest you have someone come over and simply replace the helicoil insert. If you were in Montana I'd do it for you

'83 LongEZ - N888EZ 3,508 hours
'89 LimoEZ - N26EZ 686 hours (sold)
A couple of Glasairs and a Lancair 320...
Next: a RV14 need something to build
Reply With Quote
Old 07-11-2018, 04:56 PM
AtomicDog's Avatar
AtomicDog AtomicDog is offline
Join Date: Nov 2016
Location: phoenix, az
Posts: 15
Talking It worked

Thanks every one for my education. I had no idea they were helicoils. However I had already ordered the back-tap tool, so I tried it. I carefully started with the smallest diameter that would engage the threads. After several passes I had worked up to the full diameter and the tape went smoothly thru the threads. However when installing the plug it was still possible to **** the spark plug and start it wrong. But after several attempts I was able to get the plug in correctly and torq it down. Eventually I will have to replace the helicoil, but not today.

Larry Mcc
RV-8, sold
RV-9A, flying 6/18/2018
Reply With Quote
Old 07-11-2018, 05:15 PM
lr172 lr172 is offline
Join Date: Oct 2013
Location: Schaumburg, IL
Posts: 3,568

Glad to hear it worked out well and without any problems.

RV-6A / IO-320, Flying as of 8/2015
RV-10 in progress
Reply With Quote

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

All times are GMT -6. The time now is 05:15 AM.

The VAFForums come to you courtesy Delta Romeo, LLC. By viewing and participating in them you agree to build your plane using standardized methods and practices and to fly it safely and in accordance with the laws governing the country you are located in.