Forum

[Steve T]

Hi everyone has anyone used this insert kit
XXR TOOLS 14MM SPARK PLUG CYLINDER HEAD RETHREAD TAP REAMER HELICOIL REPAIR KIT

[Steve T]

Let's try again here's the link
http://www.ebay.co.uk/ulk/itm/291373376616

[jefrs]

I have had a TR7 alloy head spark plug thread repaired because a plug exploded out of it.

A special insert was used not a Helicoil, apparently Helicoil springs are a bit olde school and leaky.

A special tool was used by the garage that followed the remains of the spark plug thread in so it all stays square, and then the new insert thread is driven and bonded (Loctite?) in. Without disassembly.

What they used was far more precise than that Ebay offering

My point is that it is an expensive professional tool but a quick routine job for a garage workshop, pretty cheap too. Don't use Helicoil.

[Adrian]

I used a very similar kit with a solid insert when I drilled and tapped an Electra-X head for a conventional Bullet decompressor valve, and found that using a hand-held drill for the final bore before tapping the thread wasn't a very good idea at all (I bought a small bench pillar drill soon after that). Fortunately it all cleaned up nicely with the special reamer tap supplied and gave a good continuous thread, which has both held and not leaked past the insert. I used a good smear of thread locking compound during assembly, though not too much as you don't want any on the internal thread.



A.

[Steve T]

Thanks for the replies guys, I was thinking of using one for the oil drain plug. Steve

[PeteF]

Trouble is, the oil drain plug only holds on a few threads. Not enough to make any sort of helicoil work. A solid insert is the way to go.

[jefrs]

Engineering - a screw thread uses just four turns of thread to achieve maximum mechanical strength, any more are redundant/backup; it's also the minimum number of threads needed to hold a screw tight. E.g. the oil drain plug must have at least four turns of thread.

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Take it along to a car garage with a proper old school workshop (it'll be one the local dealerships outsource jobs to when they haven't a clue what to do) and ask them to do an insert on it with the right tools. Probably as cheap as buying the kit. A car workshop because they get more and varied work and hence have more toys in the toolbox.

[jefrs]

Also do be aware that metric threads are not all alike. Commonest is 1mm pitch but we also get 0.7mm pitch and there are a few others.

Screws into aluminium alloy should not use the finest pitches because they have shallow thread depth. The material and mating area also determine torque. It can be worked out from the breaking strain. The only one I can remember is mild steel breaks around 10 tons per square inch; we want it tight not broken, and it's the area of the four turns of thread. That's why the torque on a small bolt is not a lot - "as tight as is tight and no tighter".