heli coil drill size for a 3/8 bolts (power steering pump bracket to head.

[sujitroy]

The 3/8 x 16 bolt holding the power steering pump bracket to cylinder head is shot. I plan to heli coil it. The drill to use is listed as a 25/64. Can I use a 10 mm drill instead? A 25/62 drill comes up as 9.92 mm. Amazon has a $7 deal for 12 sizes including a 10 mm. A single 25/64 drill costs about $6. I'm not too worried about drill quality as I'm going into Ali.

Sujit

[joel h]

hi, do you already have the inserts? because if you buy the kits they come with the correct drill bit, inserts, tap and tang breaker.

[KOY 23]

Why bodge it by tapping metric threads in an imperial car? Get the proper kit.

[mallardstag]

Why bodge it by tapping metric threads in an imperial car? Get the proper kit.

I don't think he's proposing to insert a metric helicoil, just drill to 10.00mm instead of 9.92mm for tapping for 3/8" bolt.

Personally I would buy the correct drill as they're only a couple of $$

[jakesmig]

Why bodge it by tapping metric threads in an imperial car? Get the proper kit.

If I were a purist, which I most certainly am not, I would take the opinion that any helicoil, correct thread or not, is a bodge.

Most of our cars are still on the road because PO's and ourselves have utilized 'bodges', some of which may have been corrected, others that have been accepted, and others welcomed and taken as desirable. After all EWP systems, header tanks, lumenition kits, silicone hoses, silicone HT leads, 2 pack paint, 15" wheels etc. etc.are all bodges. You cannot purchase original spec tyres, they aren't produced anymore, then the replacements are bodges. Millers oil is a bodge because it wasn't original spec, the list goes on and on.....

Probably very few Stags exist that don't have 'patern' parts on them, so technically, most cars will be bodged.

Nothing wrong with bodges which are technically and structurally competent, if you see them and don't like them don't buy the car, if your cars got them, change them or accept them, simple.

micro rant over.

John.

[KOY 23]

Personally I would buy the correct drill as they're only a couple of $$

Agreed, I also believe using the wrong size drill is a bodge.

[new to this]

I would use the right size drill that comes with the kit,using a 10mm drill may mean the helicoil is a loose fit

[Goldstar]

I’ve never actually needed to drill into the head just used the supplied tap that came with the kit. Worked fine for me.

[marshman]

The difference in size between 10mm and 25/64ths is 3 thou or 0.08mm. Whilst it is always best to use the correct size drill, in the case I can't see it making one bit of difference, it will knock 1.5 thou off of the thread peak that the helicoil goes into. So if you don't have a 25/64" drill a 10mm drill will be just fine - which I think was the question! I also suspect you would get away with a 9.5mm drill as it is only a tapping drill into aluminium.

BUT as others have said helicoil kits include the drill, tap, tang breaker, insert tool and of course the helicoils. I can only assume the original poster has "lost" the correct drill.

Roger

[DJT]

If I were a purist, which I most certainly am not, I would take the opinion that any helicoil, correct thread or not, is a bodge.

Best stop flying then, as they are approved for use in the aircraft industry............

[v8ken]

Kit I had when I did mine,said you don't need the drill for aluminium,,just tap into the hole,remember to keep backing off to remove the swarf.Ken.

[sujitroy]

The heli-coil kits, State side, without the drill are around $20. The kits with the drill are about double. I do plan to use the correct size imperial 3/8 coil. Based on Goldstar and v8ken's input I'll just get the basic kit.


Sujit

[jakesmig]

Best stop flying then, as they are approved for use in the aircraft industry............

Said I wasn't a purist, look back.it's there for all to see.

I've used them when needed, not that that was my point....

[dasadrew]

Best stop flying then, as they are approved for use in the aircraft industry............

.... and Ferrari use helicoils in the alloy engine parts as factory standard on new engines.....

[DJT]

Said I wasn't a purist, look back.it's there for all to see.

I've used them when needed, not that that was my point....

My point was that using Helicoils should not be considered a bodge. It is a perfectly legitimate method of repairing a thread in aluminium parts. Considered by many to be stronger than the original alloy thread. Hence Drews point about Ferrari.