heli coil

[Rick-bond]

Has anyone had their spark plug heli coil pop out when removing a plug.   i bought a $100kit with a blue handle/ its junk/ dont buy it.  there is another kit out there for 3 times the price  5523-18  has anyone used it. ( or both of these. )    

[EricJ]

There's a Lycoming SI that talks about it, SI 1043A, and lists PNs for a couple tools.   I can't find a stand-alone copy, but this link has it at the end of the pdf.   Probably not that helpful, but it's all I got. 

https://support.cessna.com/custsupt/contacts/pubs/ourpdf.pdf?as_id=50867

If you figure something out, let us know!

Edit:   The tools are shown on P2 here, items 33 and 34:

https://www.lycoming.com/sites/default/files/SSP-384 2nd Edition.pdf

 

Edited March 21, 2021 by EricJ

[A64Pilot]

I would suggest having an A&P pull the cylinder and I’d take it to an engine shop and let people that do it all the time do it. Have them inspect the cylinder and maybe go back with new rings unless the old ones show no wear, the engine shop will know exactly how much to hone the cylinder if needed.

I know you just want to screw in a new Heli-coil, but that may not be the best course of action. it can be replaced on the engine but requires tooling that your not likely to be able to get, and as easy as it is to pull a cylinder I’d just do that, it’s the safest way, safest as in least likely to cause further damage.

[N201MKTurbo]

You don’t need the whole kit to just replace the helicoil. You can probably do it with needle nose if you are careful.

This assumes the threads are not buggered up. Helicoils are springs and as you twist the tang in, the spring will get smaller making it easy to turn in. It isn’t possible to screw it back out using the tang. The helicoil will expand and jamb into the hole. If it isn’t all the way in you can grab the exposed coils with a needle nose pliers and unscrew it.

Use a needle nose pliers to break off the tang so it doesn’t drop into the cylinder.
 

If you haven’t done it before, it would be best to have someone who has assist you.

[N201MKTurbo]

There are plenty of You Tube videos about helical thread inserts. Watch a few.

I was proposing on a machine to automatically insert thread inserts in military avionics assemblies. I learned way too much about thread inserts.

[RJBrown]

In spite of the fact that Lycoming has approved the use of Helicoils to repair damaged spark plug hole it is not the best product to use.
It is obvious that the Helicoil brand coil inserts are approved and legal.

Are the solid inserts also legal to use in certified engines? Picture 4 shows a Helicoil brand solid inset. They work.

I my extensive experience in auto repair taught me that each type of insert has its place but spark plug repairs are better done with a solid insert.

A helicoil is both an item and a brand name. Helicoil the company also makes solid inserts. Solid inserts work much better than the coil inserts for spark plug repair.

The attached picture #1 is from the brand Timesert. I use it to show the difference between coil and solid inserts. There are many brands of these products.

Coil type tend to come out often, are not permanent and can cause additional thread damage. They should only be used in permanent installations. They should not be used where removal is expected, like a spark plug. Solid inserts used in conjunction with high strength Loctite are more permanent and much less trouble.

Picture#2 is the thread repair stuff left in my toolbox from 40 years auto experience. I’ve done many over the years.

picture 3 shows 3 different tools used. 
bottom one is used to clean up threads. If threads can be cleaned up and can accept the proper torque clean up is the best first option.

the top tool has two sizes of threads the smaller thread matches the original spark plug size. The larger part is the thread size for the insert.

The use of this tool helps keep the new threads centered and straight.

the center tool is harder to center and rarely used.

If a coil type insert was used you probably need to re install the same type.

 

Edited March 21, 2021 by RJBrown

[carusoam]

If I remember correctly...

Our cylinders start out with a coil in there from the beginning... right?

 

Just a memory check... thanks. 

Best regards,

-a-

[N201MKTurbo]

17 minutes ago, RJBrown said:

In spite of the fact that Lycoming has approved the use of Helicoils to repair damaged spark plug hole it is not the best product to use.
It is obvious that the Helicoil brand coil inserts are approved and legal.

Are the solid inserts also legal to use in certified engines? Picture 4 shows a Helicoil brand solid inset. They work.

I my extensive experience in auto repair taught me that each type of insert has its place but spark plug repairs are better done with a solid insert.

A helicoil is both an item and a brand name. Helicoil the company also makes solid inserts. Solid inserts work much better than the coil inserts for spark plug repair.

The attached picture #1 is from the brand Timesert. I use it to show the difference between coil and solid inserts. There are many brands of these products.

Coil type tend to come out often, are not permanent and can cause additional thread damage. They should only be used in permanent installations. They should not be used where removal is expected, like a spark plug. Solid inserts used in conjunction with high strength Loctite are more permanent and much less trouble.

Picture#2 is the thread repair stuff left in my toolbox from 40 years auto experience. I’ve done many over the years. The big box is the helicoil kit Lycoming approved.

picture 3 shows 3 different tools used. 
bottom one is used to clean up threads. If threads can be cleaned up and can accept the proper torque clean up is the best first option.

the top tool has two sizes of threads the smaller thread matches the original spark plug size. The larger part is the thread size for the insert.

The use of this tool helps keep the new threads centered and straight.

the center tool is harder to center and rarely used.

If a coil type insert was used you probably need to re install the same type.

 

Lycoming and continental engines come from the factory with helicoils in the spark plug holes. 
 

They are special helicoils with serrated coils. Although you could probably insert them with a pair of needle nose pliers it takes a special tool to stake the helicoil in place.

If it was me, I would see if I could borrow it from the engine shop.

[A64Pilot]

I believe the issue is that as the old insert is removed, it’s going to mess up the threads some as it was staked in there, so it may not be possible to simply thread a new one back in.

‘ Then you still have the staking issue.

[RJBrown]

It appears I gave an automotive lesson only. The picture contains the aviation lesson from the above link.

 

[carusoam]

Great pics RJ!

Are you working in the shop today?

Or just have these on your phone already?

 

MS is can be extra amazing on some days...

Best regards,

-a-

[EricJ]

2 hours ago, carusoam said:

If I remember correctly...

Our cylinders start out with a coil in there from the beginning... right?

 

Just a memory check... thanks. 

Best regards,

-a-

Yes.   The heads are aluminum so the helicoil helps keep the plugs from seizing in the head or blowing out.

[Guest]

From the IPC.

[PT20J]

@M20Doc, curious how often these come out with a spark plug.

Had a bear of a time removing a plug from an R-1830 on the museum DC-3. Turned out someone didn't put the copper washer on it and the threads protruding into the combustion chamber carboned up. Still it didn't do any damage when we finally got it out. But, I'm not sure P&W used helicoils.

Skip

[laytonl]

Don’t mean to hijack this thread (no pun) but has anyone used threaded inserts for wheel hubcap screws?  I’ve got two loose screws in one wheel and was thinking of using an insert or taping out to a larger size.  Lee

[OR75]

it is easy to mess the helicoil when you try to put back it a spark plug or when you use an extension for compression measurement 

aligning the plug/tool is not easy ... just take your time and don't force it 

there is a Lycoming SB on how to replace the helicoil 

you do NOT need to pull the cylinder 

[N201MKTurbo]

While I was researching Helicoils today, I found out Lycoming has 0.003 and 0.010 oversized Helicoils just in case you screw up the process. 

[Guest]

1 hour ago, PT20J said:

@M20Doc, curious how often these come out with a spark plug.

Had a bear of a time removing a plug from an R-1830 on the museum DC-3. Turned out someone didn't put the copper washer on it and the threads protruding into the combustion chamber carboned up. Still it didn't do any damage when we finally got it out. But, I'm not sure P&W used helicoils.

Skip

I have an 18mm Helicoil set and have used it to replace one Helicoil in a Lycoming cylinder.

Clarence

[Guest]

1 hour ago, laytonl said:

Don’t mean to hijack this thread (no pun) but has anyone used threaded inserts for wheel hubcap screws?  I’ve got two loose screws in one wheel and was thinking of using an insert or taping out to a larger size.  Lee

I’ve installed numerous 8-32 Helicoils in wheels, it’s quite common.  

Clarence

[laytonl]

Thanks Clarence.  Lee

[BDPetersen]

As an old Franklin guy (which have 14mm plugs and are famous for having a helicoil back out), I know enough to suggest there is the proper tool for the job. Staking was mentioned already and I believe is the key to a successful installation with the right tool. Then caution must be used not to over torque the spark plug. I’m thinking the little 14mm plugs were torqued to 20 in/lbs.  In other words, don’t over tighten.

[larrynimmo]

10 hours ago, laytonl said:

Don’t mean to hijack this thread (no pun) but has anyone used threaded inserts for wheel hubcap screws?  I’ve got two loose screws in one wheel and was thinking of using an insert or taping out to a larger size.  Lee

“Threaded inserts” or nut  setters are a different product used for sheet metal attachments...need heli-coil for wheel casting (hubcaps)

[Rick-bond]

RJ. These are the tools i mentioned. They are $5000. Canadian on aircraft spruce. It would be way cheaper to buy two new cylinders on the port side 

[RLCarter]

Heli-Coils (spring type) do not back out unless something is damaged. Thread inserts can be installed without the corresponding installation tool but I don’t recommend it unless you’ve done a bunch of them. The “tang” at the start of the insert compresses the helix for installation as is designed to be broke off in one direction, breaking the tang off incorrectly will damage the bottom thread. I’ve installed hundreds of both Heli-Coil and Timeserts over the years and a few Sav-A-Thread insert which I’m not a big fan of (the DO back out)

side note or more of a question....... Why are all spark plugs metric threads?

[A64Pilot]

16 hours ago, laytonl said:

Don’t mean to hijack this thread (no pun) but has anyone used threaded inserts for wheel hubcap screws?  I’ve got two loose screws in one wheel and was thinking of using an insert or taping out to a larger size.  Lee

That’s an excellent use of a helicoil. I would put blue loctite on them when I installed them. Don’t use red. Loctite is to keep them from backing out with the screw, and blue isn’t nearly as permeant as red is.

When I was building drag bikes back in the day when we got over about 200 HP, the transmission gears would have so much torque going through them that they would pull the bolts out of the case and split the case, bolts stripped the aluminum case of course.

‘The fix was to drill out and helicoil the case, the larger diameter of the helicoil made it hold into the case much stronger and we never had any more split case problems.

‘Plus for items that are often removed, you have steel on steel threads as opposed to steel on aluminum, I believe that’s why our cylinders heads are helicoiled from the factory, but a lot of cars and motorcycles screw plugs into aluminum heads and it works just fine, so maybe not?

‘However I’ll agree with the other poster, a Timesert is likely superior in most cases, but I would not put one in a head, it could possibly interfere with the plug dissipating heat to the head, probably not, but I wouldn’t do it.

Edited March 22, 2021 by A64Pilot