Lotus Elan

Helicoil. advice on an issue please

PostPost by: wotsisname » Mon Jun 15, 2020 9:31 pm

20200615_220949.jpg and
helicoil fail
Hi all,
Ive hit a snag putting in a helicoil. This is the second Ive put in, so not much experience.

These are 3/8th UNC for the thermostat housing. I had a bad day and used the wrong torque setting (spanner vs bolt size error in reading the WSM), stripping the thread.
I drilled and taped using the items supplied in the helicoil kit.
The first one went in nicely.
The second was stiffer and it looks like it has gone in on every other thread.. if this is possible. The tang has hit the bottom (it should have only gone about 1/2 way and part of the thread sits above the hole. The tang is still attached.
Any thoughts on how to deal with this.. anyone manage to wind one back out..
I thought it wise to stop and ask at this point.
regards
Adrian
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PostPost by: nmauduit » Mon Jun 15, 2020 9:47 pm

It may be that too much down pressure was applied initially and not starting into the beginning of the thread then instead of engaging into the thread it slided insid of it for a few threads untill it eventually fell into the thread further down.

What I would try first is to undo at least the top threads that are out of whack with a plier by coiling the wire towards the inside to relieve the spring tension, hole filled with oil to lube it. Depending on how brittle the coil is (which brand etc.) you may be lucky and able to take it out. You may try first on a junk piece with a spare coil to get a feel for the manouver. Then an other approach would be to use a thread extractor of the proper diameter (problm this loads the alloy, and the coil out of thread will likely damage the top threads to some extent).

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PostPost by: Elanman99 » Mon Jun 15, 2020 10:21 pm

The fact that there is some of the insert exposed will make removing it fairly easy. I suggest separating the top turn of the insert and gripping tightly with mole grips (mole grips vertical) you should then be able to rotate the mole grips and by rotating them clockwise whilst pulling them upwards. The insert will reduce in diameter slightly whilst you do this and be wrecked, the female thread in the ali will also suffer a bit but after cleaning up with the tap should be good enough to take a new insert.

Why did you opt for 3/8"UNC? The standard size is 5/16" and going larger leaves less room round the bolt head for spanner. Also unless the holes are blind the gasket around the fixing holes will be very narrow.

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PostPost by: h20hamelan » Mon Jun 15, 2020 10:57 pm

i trust time sert, after a few issues with helicoil

https://www.timesert.com/

wonder if a modified screw extractor would help, thinking if it were shorter. maybe you could get a groove/channel lock to add the pressure from top and bottom while turning

good luck
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PostPost by: mikealdren » Tue Jun 16, 2020 7:29 am

TIme-serts look excellent but they are also very expensive. Are Wurth the only UK supplier? If so, I guess you need a trade discount?
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PostPost by: nmauduit » Tue Jun 16, 2020 7:50 am

Elanman99 wrote: I suggest separating the top turn of the insert and gripping tightly with mole grips (mole grips vertical) you should then be able to rotate the mole grips and by rotating them clockwise whilst pulling them upwards. The insert will reduce in diameter slightly whilst you do this and be wrecked, the female thread in the ali will also suffer a bit but after cleaning up with the tap should be good enough to take a new insert.


I would rather try counter-clockwise to reduce the coil diameter while undoing it upward (regular hand thread)
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PostPost by: Elanman99 » Tue Jun 16, 2020 8:03 am

nmauduit wrote:
Elanman99 wrote: I suggest separating the top turn of the insert and gripping tightly with mole grips (mole grips vertical) you should then be able to rotate the mole grips and by rotating them clockwise whilst pulling them upwards. The insert will reduce in diameter slightly whilst you do this and be wrecked, the female thread in the ali will also suffer a bit but after cleaning up with the tap should be good enough to take a new insert.


I would rather try counter-clockwise to reduce the coil diameter while undoing it upward (regular hand thread)


That was a rather stupid error I made. I did mean to say anti-clockwise.

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PostPost by: 2cams70 » Tue Jun 16, 2020 9:43 am

There's a special tool available for removal of Helicoil (or Recoil) inserts. It digs into the insert thereby gripping it so you can wind it out anticlockwise. There's no problem with Helicoil inserts in the right application. The advantage of them is that you only have to remove the very minimum amount of material in order to create a new thread. Remember to never use Loctite threadlock in combination with a Helicoil and don't use them in applications like spark plug thread restoration. It's also best to drill out the hole for the insert using a fixture. A hand held drill is not really accurate enough.

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PostPost by: alan.barker » Tue Jun 16, 2020 10:20 am

To remove a Helicoil all you need is hard steel pin. We used to use a Cable Harness pin that are used to set out Wiring Harness on a board.
You tap the pin down between the Insert and the Alloy pushing the end of the Insert into the middle. Grab it with some Pliers pull it out and throw in the Trash Bin.
Now take the special Helicoil Tap which is not a standard thread in you fingers. Screw it gently into the Tapped hole to clean up any burrs.
Measure the depth of the tapped hole. The Helicoils come in different lengths Dia x 1, Dia x 11/2 or Dia x 2.
In the Helicoil Kit choose the correct length (maybe a little less but no longer). You can shorten the length of an Insert with a pair of good Side Cutter Pliers.
The Helicoil needs to be screwed in so it is a 1/4 turn below top surface.
Put some grease on the Helicol and put on Insert Tool (some have a fork or some have a step) to screw/drive the Insert into hole. Only use your fingers and no forcing and it will screw in nicely.
When a 1/4 turn below surface remove insert tool and take the Tang breaking tool.
Slide Tang Breaking tool down the centre of Helicoil and give the end a smart tap with small hammer.
Take a piece of wire with a little blob of grease on the end to remove the Broken Tang.
Job done.
Alan
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PostPost by: 2cams70 » Tue Jun 16, 2020 10:43 am

The tool winds the insert out without any damage done to the threads in soft aluminium. If you pull the insert out with pliers you'll round off the tips of the threads in the casting (been there done that). Much better to just wind them out backward with the correct tool for the job. It's not an expensive tool.
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PostPost by: el-saturn » Tue Jun 16, 2020 10:48 am

if you cant extract it (almost impossible), then you can "take" the extra length off (angle grinder) if there´s at least 3/8" (length) +! of thread in there! sandy with a new cometic gasket (foamy), even less!
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PostPost by: rgh0 » Tue Jun 16, 2020 10:49 am

2cams70 wrote:There's a special tool available for removal of Helicoil (or Recoil) inserts. It digs into the insert thereby gripping it so you can wind it out anticlockwise. There's no problem with Helicoil inserts in the right application. The advantage of them is that you only have to remove the very minimum amount of material in order to create a new thread. Remember to never use Loctite threadlock in combination with a Helicoil and don't use them in applications like spark plug thread restoration. It's also best to drill out the hole for the insert using a fixture. A hand held drill is not really accurate enough.

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Sorry to contribute to a bit of thread drift but helicoils in twin cam spark plugs are really the only practical option IMHO due to the proximity of the valve seats unless you want to weld up and redrill and tap the plug. hole. Inserts will generally hit the valves seat OD especially on racing heads with big inlet valves.

Long term to recover a head I would weld and retap but I have used heads for many years with a helicoil in the spark plug. Just make sure when you insert the helicoil that it is trimmed and not inserted to deep so as to not project beyond the full enclosure area in the head as the thread extends down one side more than the other due to the combustion chamber shape and if the helicoil gets into this area it can break off and give your head and piston some grief before it exits ( been their done that :roll: )

Having stripped a couple of spark plug threads over the years I always use nickel antisieze of the plugs threads now.

attached photo of a standard big valve head that shows the issue of plug and valve seat proximity
IMG_8615.jpg and


cheers
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PostPost by: alan.barker » Tue Jun 16, 2020 11:35 am

It's good to exchange different ideas about
Inserts Helicoil, Armstrong or others.
I worked as a QC Engineer in the Aerospace Industry chez Marconi Space Portsmouth UK for 20 years. Most parts were Alloy Anodised and all had Wire Thread Inserts.
+1 Rohan for using Wire Thread Inserts for Spark Plugs spot on.
Alan
Ps. The tips/thread crest are already not there if to spec
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PostPost by: 2cams70 » Tue Jun 16, 2020 11:46 am

Helicoils aren't ideal for spark plug hole repairs because they aren't positive lock and can wind out in frequent use high temperature applications like spark plugs. They also aren't the best for transferring heat from the plug to the head. There's better options for spark plug hole repair if you can fit them - maybe that isn't an option on a LTC.
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PostPost by: rgh0 » Tue Jun 16, 2020 1:19 pm

2cams70 wrote:Helicoils aren't ideal for spark plug hole repairs because they aren't positive lock and can wind out in frequent use high temperature applications like spark plugs. They also aren't the best for transferring heat from the plug to the head. There's better options for spark plug hole repair if you can fit them - maybe that isn't an option on a LTC.



Yes agree helicoil not ideal in a spark plug given the more frequent insertion and removal and implications if it moves but it will work if your careful and until you can do / afford a more permanent repair by welding and re-tapping. Other better inserts for this service struggle to fit unfortunately as they require a larger drill and tapping than helicoils and there is just not that much room until you hit the hardened steel valve seat inserts and the dramas that will cause

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