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The mkiv Supra Owners Club

Plugs


mrboomberang
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If the bolt has sheared off flush with the head, the best advice I can give you, is to use a cobalt drill bit, and drill very slowly into the remainder of the bolt centre. Then use an 'easy out' to remove it. Soak it in a penetrating oil a few hours before you try, and keep any swarf out of the spark plug wells

 

 

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I had to extract quite a few bolts in my recent sub frame swap where the bolt heads were so corroded they rounded or turned off altogether. I used a couple of techniques to tackle them successfully with drilling and tapping or using a stud extractor.

 

Drilling out is going to be difficult on a stranded stud from a small size bolt in the centre of the engine bay as the chances you'll be reaching over and drilling straight and true is not that great. If you end up drilling at an angle you could end up with an oval hole with part of the seating thread drilled away and no way to cut a new one. If you do go drilling use the left hand reverse drill carbide bits on a hammer setting which will have a chance of catching and unscrewing the stud. Bad news is the Supra bolts seem to use tough steel and they don't drill easily even with new quality drill bits. I've never been that lucky to have a left hand bit bite though and had to completely drill out. If the worse comes to the worse and you do damage the seating then you can recover the situation by drilling a larger hole and use a helicoil insert to restore the thread. I'd probably want the head on a bench though to ensure a perfectly vertical hole is drilled.

 

If you have lost the bolt head then presumably you can remove the coil packs and cradle to clear access to the damaged bolt stud and if there is any protruding you have options available.

 

If you can grind flats into the bolt stud then you can use a small adjustable or standard spanner.

If you can weld globs of metal onto the top of the bolt stud then you use a stud extractor. I prefer doing this to drilling.

If you do end up drilling then put some cotton wool down into the plug area to catch any swarf as you won't be able to vac it out afterwards.

 

So you'll need a hammer drill, 6mm left carbide drill bit, mig welder, 6-12mm stud extractor and a steady hand to have all options.

Edited by rider (see edit history)
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All the above with a couple of tips.

 

The bolt is only a normal grade M6 bolt so should not need any specialist drills (HSS or Cobalt).

 

Centre pop the centre of the broken bolt and start using a small bit 2.5-3mm. Then step up maybe to 4mm and drill again.

 

Two options after this/ Either use an easy out to pull out the remaining metal OR drill out to 5mm and re tap.

 

The only difficulty is a steel bolt into an aluminium casting so be accurate with the first drill and hence centre pop.

 

Tap should be M6x1.

 

These cars will have plenty of issues like this now so these skills are good to have.

 

Use lubricant when drilling and maybe penetrating oil before you start.

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Has anyone broke the bolt that holds number two coil pack in place any help appreciated tried drilling it out but no good ? Missfires when hot

 

/QUOTE]

 

You say you've had a go at drilling it so what state is the bolt in now ? can you take a photo

 

You're talking about the bolt that holds the coilpack bracket to the cylinder head ?

 

If its the bolt into the cylinder head you could make a plate to bridge the gap to the next bracket

and use that to clamp the other in place

 

You could also use this method and use the bracket as a drill guide but you'd need to be careful

and use as light a drill as possible, using the bracket would help you keep the drill square to

the head and in the centre of the broken bolt

Edited by Dnk (see edit history)
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  • 2 weeks later...
Has anyone broke the bolt that holds number two coil pack in place any help appreciated tried drilling it out but no good ? Missfires when hot

 

/QUOTE]

 

You say you've had a go at drilling it so what state is the bolt in now ? can you take a photo

 

You're talking about the bolt that holds the coilpack bracket to the cylinder head ?

 

If its the bolt into the cylinder head you could make a plate to bridge the gap to the next bracket

and use that to clamp the other in place

 

You could also use this method and use the bracket as a drill guide but you'd need to be careful

and use as light a drill as possible, using the bracket would help you keep the drill square to

the head and in the centre of the broken bolt

That's what I'm planning on doing mate cheers

 

 

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