Helicoil fitting procedure - help needed!

[Swell]

I'm just about to fit a helicoil thread insert to a hole where a sheared cylinder head bolt has been removed.

The hole has been filled so I need drill the hole and I'm trying to work out what the depth of the hole needs to be, and am not sure how far into a hole you can wind a helicoil. I've depicted it here:



The last 5mm of the tap is tapered, so I'm assuming that I won't be able to wind in the helicoil this last 5mm. Is this right? Assuming the head gasket is about 1mm thick, the bolt will extend 16mm into the hole. But if I can't use that last 5mm, the threaded part of the hole can only really be 14mm. I'm assuming I'll need to use a shorter bolt and 2 helicoils.

Is this right or can I wind the helicoil in that last 5mm?

 

[Bifflefan]

Re: Helicoil fitting procedure - help needed!

The last 5mm of the tap is tapered, so I'm assuming that I won't be able to wind in the helicoil this last 5mm. Is this right? Assuming the head gasket is about 1mm thick, the bolt will extend 16mm into the hole. But if I can't use that last 5mm, the threaded part of the hole can only really be 14mm. I'm assuming I'll need to use a shorter bolt and 2 helicoils.

Is this right or can I wind the helicoil in that last 5mm?

Taps are tappered, Bottoming taps are not, or atleast just the first thread is.
The heli-coil will need to be one thread below the surface when installed. More is ok less is not.
I really dont think you need to stack 2 in the hole, I dont know the torque your going to put on it either tho.

I would measure the depth of the other holes and go that deep again.

After rereading your post, I dont think mine is going to help you.
I dont think I'm understanding your question, sorry.

 

[F_R]

Re: Helicoil fitting procedure - help needed!

Swell, I think you pretty much have the situation figured out. Heli-Coils come in different lengths. Generally, it only needs to be one diameter in length. That is, a 5/16" diameter needs to be at least 5/16" long. More is ok though. In fact, the inserts are sold with the length specified as a factor of the diameter.

As already said, a bit below the surface, and of course it can't extend down into the tapered area. If absolutely necessary, two coils can be used, but don't run the second one down tight against the first one or you won't be able to break the tang off. But I have found very few cases where it was necessary to use two.

 

[Swell]

Re: Helicoil fitting procedure - help needed!

One thing I'm not sure of is which end of the helicoil the tang should be when inserted? Your post suggests it should be inner-most. Also is it necessary or a good idea to use some sort of adhesive to hold the helicoil in place or do they tend to stay in the location they are inserted to?

 

[Frank Acampora]

Re: Helicoil fitting procedure - help needed!

Heli-coils go in tang first. They are generally stronger than the original tapped hole. IF you stack two, there is a slight chance that you will mismatch the threads and not be able to screw in the bolt fully--just use one.

But my question is: If the stripped hole has been filled, with what, and if filled with weld, why not just drill and tap to original size?

 

[Swell]

Re: Helicoil fitting procedure - help needed!

The original hole was ragged after a fairly torturous removal of the sheared bolt - I made a bit of a pigs ear of it to be truthful. The hole was fine further in but the first 5-10 mm was ragged. So I filled the whole thing with chemical metal - equivalent of JB weld - fitted the cylinder head, spotted through the cylinder head hole to get the correct centre, removed it and drilled it from there. I filled it as I couldn't see how I could drill it accurately with a ragged entrance to the hole.

Just successfully drilled and tapped it actually, so now I've just got to fit the helicoil. I'm going for 2 and will take the risk, as I need to make the most of the metal there in order for it to take the torque.

Do the helicoils hold themselves in place?

Also, can a helicoil be removed if needs be?

 

[F_R]

Re: Helicoil fitting procedure - help needed!

The coil goes in tang end first as already mentioned. You do have the insertion tool, right? Spring tension holds it in place. Hopefully you don't have to take it out again. But if you do, Heli-Coil makes a removal tool. OR...you can use a sharp tool like an ice-pick to bend the outer end of the coil inward toward the center, making a tang on the outer end. Then grab that with a suitable tool and unscrew it out.

 

[rodbolt]

Re: Helicoil fitting procedure - help needed!

be aware.
doubling the ss helicoils in Aluminimum usually leads to a destroyed hole when you attempt to remove the bolt next time.
a single standard helicoil will handle any torque your gonna use on a 5/16ths head bolt.
done way to many here in the salt pond,especially the inner row on crossflow jonnyrudes and head bolt holes on saltwater cooled chevys and fords.

 

[kenmyfam]

Re: Helicoil fitting procedure - help needed!

Agree ^^^^^ 100%

 

[Swell]

Re: Helicoil fitting procedure - help needed!

Oh well - too late unfortunately. Just fitted 2 helicoils. Worked well enough and the screw goes in just fine.

I hadn't heard of that issue before - only issue I've read about previously is the risk of the 2 helicoils not lining up, something I couldn't really imagine happening as they both occupy the same outer thread.

How does it destroy the hole? Is it due to the bolt seizing on one of the helicoils? Is there anything I can do now to reduce the chance of that happening? Maybe use some anti-seize grease?