Spark plug thread repair kits

[DamirGTI 362]

Seems like the preferred method for fixing spark plug threads nowadays is using time serts .

However, browsing some older posts (when time serts weren't yet available, I guess), I found a few cases of heli coils being used and apparently without issues for years afterwards .

Any experiences with this, and why would a heli coil be bad or should it be considered a less desirable way for such a repair ?

I can find loads of heli coil kits from various brands, and pretty much only Chinese copies of the time sert which, from what I can see, rely on Loctite only to secure the insert from unscrewing .

Pro kits of time serts are over $200 + import and tax, which is not something I'd really justify paying for occasional odd cases . 

Is Loctite alone enough to secure those time serts from unscrewing, or is some kind of knurl locking system on the insert needed to go along with the Loctite ?

[SRDT 246]

Time-serts are not like regular inserts with standard external threads one size bigger. Just like Helicoils you need a dedicated tap to install them and the upside is that you remove as little material as possible. In fact the corresponding drill sizes are the same as Helicoils so they are just as good when you only have a few mm of alloy between the spark plug and the valve seats.

 

The last few internal threads on a Time-sert are not fully machined and will be cold rolled during installation to keep it in place by pushing on the external threads. That's why you need to counterbore the hole, the Time-sert flange will stop it there and the install tool will have to roll the threads to go further down. If you really need to you can skip the counterbore and grind the top of the Time-sert flush once it's in place.

 

On a XU10 8v head maybe you could also simply go with a more classic insert with a metric thread on the outside.

[DamirGTI 362]

Yes that is for the "proper" time-sert system , i've seen some demo videos for those , neat solution ! but quite a bit expensive kit . 

 

Other variations seem to be just the insert , with certain brands having knurled top side to lock them into place by taping with the tool provided in the kit , and last ones which are commonly sold all over the place now are just the inserts without any means of securing them into the head apart from the loctite seems like ?! 

 

Like so : 

 

1 "The real" time-sert tooling kit

2  Some kind of USA insert system with knurled inserts 

3 Chinesium variant 

[SRDT 246]

The external thread has more surface so using Loctite 266 should be enough to keep it in place unless the spark plug is seized.

[DamirGTI 362]

Loctite 278 is +350C !

But still, I think the Helicoil would do the trick as well , and will leave one more repair option for going bigger if ever needed .

 

Staking the alu. around the Helicoil insert at say 4 corners ,each 90°, should prevent it from unscrewing out along with the spark plug, which seems to be the main reason people dislike them over other repair solutions .

Not sure if thread lock works on spiral inserts like Helicoil, never tried yet .

Anyhow, I've seen those inserts unscrewing out with the plugs too, likely not properly installed, at least the ones with the knurls .

On that 2.0 T head , I've one spark plug hole fixed with the Helicoil, and another with the inserts kinda like those Chinese knock-offs .

Done by previous owners , no idea for how long it was like that and how many miles/km's, but they were for sure driving !