12 replies to this topic

[patricksouth]

Right so one of the heater takeoff studs snapped off in the head so i drilled it out and tapped it and for whatever reason the thread did not take so went up a size and had the same result now what are my options as obviously i cannot go too large as the bolt will not fit throught the base of the takeoff,help in desperate as i need to get the car running this weekend

[stealth05]

fit a helicoil these are like a tight wound spring that you screw into the hole so you can use the smaller bolt to fit the helicoil .

 

dav

[Cooperman]

You need a Heli-Coil kit at 1/4" UNC size. With the kit you will get a special size drill, two taps and around 10 Heli-Coil wire thread inserts.

That is the professional way of doing the job.

[patricksouth]

Thanks chaps im guessing this will be an internet order as im sure my local halfrauds will not stock this.....will machinemart stock them

Edited by patricksouth, 03 July 2014 - 08:40 PM.

[RedRuby]

Machine mart doe stock helicoil kits but they only seem to do metric sets

[patricksouth]

I did notice that ahh well will have a look local tomorrow and of not i will order one of tinter web

[KernowCooper]

I hope your second drilling though is not gone outside the scope of the correct sized heli coil

[Cooperman]

If it is vital that you have the car this weekend, you could try bonding a stud into the head using 'JB-Weld' or similar metal adhesive (Araldite 'Steel' for example). 

Allow it to set and don't tighten the nut too far. it could be a temporary fix until the Heli-Coil kit arrives.

[Stiggytoo]

Or whack a metric bolt in there for the time being - that's how I found one of my heads.

[nz_seamless]

Also you might want to look into what you are doing when you tap things if two attempts "haven't taken"

[dklawson]

Also you might want to look into what you are doing when you tap things if two attempts "haven't taken"

 

+1

 

I am sure neither of us wants to sound rude or insulting but before using a HeliCoil tap (or any other tap) review what you did before that made the tapped hole you produced not acceptable.  Something must have been done wrong.  It could be something trivial like your selection of the tap drill size.  

 

For 75% thread (typical in industry) the rule of thumb is to subtract the pitch from the major diameter of the fastener and that is the tap drill size.  For example, 1/4-UNC (the original heater stud size) is 1/4 x 20.  1/20" = 0.050".  Therefore your tap drill for 1/4 UNC is 0.250" - 0.050" = 0.200"... so you can use a 5mm drill or a 13/64" fractional drill as the pilot drill for a 1/4 UNC tap

 

The HeliCoil kit may or may not come with the correct drill bit depending on the type of kit you buy AND if you buy a real HeliCoil brand kit.  Regardless, somewhere on the instructions that come with the kit it will identify the size bit to use.

[patricksouth]

Thanks for all ur help will get a heli coil kit and sort it.to be honest i was stumped my self as i have successfully tapped alot of components in the past without a single problem but this cylinder head has played me right up,i understand it was probable my mistake but cant for the life of me put my finger on it,oh well i will take this as a life lesson and move on...cheers all

[nz_seamless]

Yeah certainly did not want that to sound snide. I for one have wasted an awful lot of my own time but not having my mind fully on the job and choosing a drill size which is the full diameter of my intended fastener.

 

"Right, 6mm bolt, where's my 6mm drill bit. Drill drill drill. Tap tap. Hmmm. This feels a little too easy..."

"*******!"

Weld, grind, redrill, retap. Swear to pay more attention next time.