That sickening feeling we've all had....

[PHILIP2908]

DK/DS special progress: had the head skimmed to try and solve the massive oil leak I had.
Head now back on and just bolting down the cam carriers...........when........we all know it...........the resistance suddenly disappears. One stripped thread; well 3 actually.
I think this is due to some abuse its had in a previous life.
I was using the figure of 8ft lbs as given in the Haynes manual for 6mm threads.
Q: has anyone got any experience of Helecoils in an alloy head? The screw holes look to be blind and as long as I cover up the oil holes and valve springs I should be OK....
Whaddya think?
All advice welcome.
Thanks in advance.

[Trigger]

These de-thread all the time and I helicoil these every day.

[UK Pete]

Yes well known for there weakness,  helicoil is cheap and simple, just make sure you cover up well and hoover the swarf up
chin up fella this can be very disheartening especially after all the other shite you have had, you will get there in the end
pete

[ginger_jim]

Yup....had to do a couple in mine too.  Then the camchain adjuster bolt threaded too.  I bought a cheap kit although ive lost the special drill bit somewhere along the line :-(  For a 5mm tap is the drill bit something like 4.8mm?

[matthewmosse]

Some heads they all let go, seems to depend on the previous life of the engine, Helicoils are ok as a fix but can wind back out again sometimes - I have been told timesert is a better alternative that adds serations to the insert so it is less likely to wind back out with the bolt. I have yet to try a timesert as I have a fair number of helicoils to use up.

[AshimotoK0]

Some heads they all let go, seems to depend on the previous life of the engine, Helicoils are ok as a fix but can wind back out again sometimes - I have been told timesert is a better alternative that adds serations to the insert so it is less likely to wind back out with the bolt. I have yet to try a timesert as I have a fair number of helicoils to use up.

I have heard that 'Timeserts' are better too Matt.. Helicoils used to be made near me in Beverley by Armstrong's..my mate Roger used to run the production line there in the late '60's . They also had an in-house  hard chroming line, as they made shock absorbers too.

[royhall]

Don't know its technically correct but I usually loctite the helicoil when I'm inserting them. Not had a single one ever come out again since I started doing that. Had a few before though. Never had to actually remove one, so that may be where my loctiting policy will go wrong.

[Bryanj]

Timeserts or keenserts but you may have to order the tap for the outside as they used to be 10mm but the odd pitch

[PHILIP2908]

Hello again, Happy to report job done. Got a 6mm helecoil kit off ebay and set to drilling holes in my cylinder head. Blimey, that alloy is like butter; swarf flying everywhere....
Had to fix 3 of the 4 threads, wound the helecoils in with a bit of Loctite (as suggested here - thanks) and another nervous moment when torqueing up the cam carrier bolts. But all went fine, so happy days!!
Thanks for all the confidence inspiring advice as this was a job I wasn't looking forward to.
Regards,
Phil d'A

[Trigger]

Butter, more like margarine  I don't even drill them, just straight in with the tap. Should of done all of them as I have known these original threads to strip under engine vibration 

[UK Pete]

Well done phil
pete

[Jontyp]

Just a bit of info if anyone wants it. When producing threads in soft material (the alloy used in these engines is a perfect example  ) it's often best to use a roll-tap (as opposed to one that "cuts" the thread). I would suggest that is true even for the wire-thread insert tapped hole. A roll tap does what it says really in that it has no cutting edges but compresses the material structure to form the thread resulting in a stronger thread. I haven't checked to see if roll taps are available for helicoil inserts but it might be worth it (I'll certainly be checking when I come to strip/rebuild my motor.

[Trigger]

Never heard of or seen a roll tap for coils. I always run a M6x1 tap down all the threads, and if it pulls any threads then a coil is required

[Bryanj]

Seen a roll form for spokes but never a tap

[Jontyp]

Well, there you go, you can indeed get roll taps for helicoil insert threads.

http://www.engineering-supplies.com/sub/332/metric-helicoil-sti-hss-taps-/