Insert for spark plug

[Womblejohn]

Hi , mx5 mk 1
Got a retap and insert to do but tap won't enter hole , insert is 14 mm and fits plug , so do I need to ream stripped hole out first , many thanks

[Catnip64]

Helicoil?
These instructions suggest drilling the original threads out first before tapping the hole: http://www.repairengineering.com/helicoil.html

[Womblejohn]

Catnip64 said:

Helicoil?
These instructions suggest drilling the original threads out first before tapping the hole: http://www.repairengineering.com/helicoil.html

Not a helocoil its a solid aluminum solid insert , bought off ebay with no drill bit and supplier doesn't know
https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2...

[Womblejohn]

The original plug came out intact so shouldn't be any steel thread left in ,

[paintman]

Looks like you've bought a very cheap Chinese imitation of a timesert.
Doesn't even seem to be anyone using the Neilsen labelled one on youtube & that's a worry - as is the fact that the seller hasn't a clue either.

Timesert isn't cheap, but Sealey do their VS301 which is slightly cheaper.
www.youtube.com/watch?v=g3oLj2AOzXw

Looking at ebay offers for M14 plug repair you have both the insert type & the wire Helicoil type. The latter comes with a drill bit which will be specific for the coil & they don't usually publish the drill size!
If you look at the Sealey it has an unusual two diameter tap. The first portion follows the original threading & the second portion then cuts the right diameter & thread for the insert. Ensures the job is true to the original. Yours looks like you just have to press down hard & hope it cuts straight!
Another here which is much the same with the two diameter tap:
www.youtube.com/watch?v=moVQf3PQLmo

I wouldn't want to risk using the one you've got.

Edited by paintman on Monday 6th May 22:11

[227bhp]

You need a pair of sliding verniers to measure the OD of the insert and some thread gauges to tell you what the thread is, when you've done that you can research what drill size to use and buy one.

Otherwise the usual applies - just take it to someone who knows what they are doing and already has the necessary tools to do it.