Threads in head for cam carriers stripped

[Zaphod]

I now have my cam clearances set. However while doing so noticed 2 damaged threads in the head for the carrier bolts. These appear to be M8 threads and I have some M8 helicoils and the tap for them but the drill but has gone walkaboit but it seems to be an 8.3mm drill? But are there any issues with helicoils for this purpose? (I’m not sure if they are too long)

[AndyC]

Helicoils are the go-to solution to this 9all too common) problem.

[Zaphod]

I guessed it was common, the manual does not help. My feeling it that each time you take the carriers the tension in the valve spring pulls the last section of the threads out, I have a feeling that’s why the studs are there at each end to try and avoid this

[Pete Boole]

Yep - 8.3mm for M8 Helicoil. 1.5D insert is the longest you can get in - 2D leaves a thread hanging out.

Pete

[bash]

Its very common, I did all mine with helicoils because they are stronger than the standard thread.
Bash

[rbgosling]

A little secret - quite a few components in the Mercedes F1 engine are helicoiled from new, as standard, because it's better than cutting a thread in the Aluminium. Especially for the smaller threads. Once I learned that I never needed to feel again like a helicoil was a bodge, it can now be considered an enhancement!

[MetBlue]

Interesting.
Makes slot of sense when you think about it, as you say, especially on smaller threads.
Tony

[Lotus-e-Clan]

A little secret - quite a few components in the Mercedes F1 engine are helicoiled from new, as standard, because it's better than cutting a thread in the Aluminium. Especially for the smaller threads. Once I learned that I never needed to feel again like a helicoil was a bodge, it can now be considered an enhancement!

I seem to recall Honda did this too as std ? Maybe some bike engine /grearbox threads?

Done this on the imp race engine since 1970s. My 1965 Imp WSM refers to the use of Helicoiled threads. The SMART Roadster sump threads are all heli-coiled too (SMART engine alloy is made from cheese!). No way a bodge!

[barker_001]

A little secret - quite a few components in the Mercedes F1 engine are helicoiled from new, as standard, because it's better than cutting a thread in the Aluminium. Especially for the smaller threads. Once I learned that I never needed to feel again like a helicoil was a bodge, it can now be considered an enhancement!

This is common practice in the aviation industry too, for aluminium castings.

[Marten]

A little secret - quite a few components in the Mercedes F1 engine are helicoiled from new, as standard, because it's better than cutting a thread in the Aluminium. Especially for the smaller threads. Once I learned that I never needed to feel again like a helicoil was a bodge, it can now be considered an enhancement!

This is common practice in the aviation industry too, for aluminium castings.

Aluminium galls easily so it is a poor thread material. Steel (as in a Helicoil ) is much better and more durable so you see them in parts which see a lot of wrenching. Also the Helicoil has a larger surface area (larger OD) so you engage more aluminium, so that makes it stronger

[rbgosling]

One thing to watch for (don't ask how I know ) - if you use pre-applied threadlock, if you then try to unscrew it you can end up unscrewing the helicoil from the aluminium, rather the screw from the helicoil. Something that is not fixable if someone doesn't have a helicoil kit at the track with them...