Drilling undertray bolts out

[KarlBristol]

Well the car will be going off for its engine conversion soon

When it comes back my regular updates/ car improvement sessions will start again

One of the first jobs I'm looking at doing is drilling out the old undertray bolts as they have pretty much all snapped.

Two questions in relation to this:

1) What size and thread stainless steel bolts should I use? Does anyone have a link to the appropriate ones?

2) Should I drill them out and re-tap the threads with my tap and die set or...
Should I order something like this

http://www.Rivetnut.co.uk/Rubber.htm

Anyone used these? Any good?


Any help would be appreciated

[Steve Horrocks]

M6x1 iirc. Tapping drill size will be 5mm and a standard M6 tap will suffice.

[Peter Gidden]

M6x1 iirc. Tapping drill size will be 5mm and a standard M6 tap will suffice.

What he says.

[KarlBristol]

Thanks for the replies

Are the rivetnuts worth using or should I retap the threads?
Im just worried the new bolts will snap in there and have to be redrilled again in the future...

[Steve Horrocks]

Stainless screws will suffice & a touch of copper slip if you feel the need.

[Kinsy]

You could also invest in some left handed drill bits, the broken ends may come out then

[KarlBristol]

Right ... Quick question then

Is it worth using one of these (ie do they work)

http://www.ebay.co.uk/itm/5-PIECE-PCE-D ... _600wt_689

Or would this be best to buy and use (left handed 5mm drill bit...)

http://www.ebay.co.uk/itm/New-Dormer-HS ... _500wt_922

Thanks

[KarlBristol]

Also in relation to the bolts - what would be the best depth?

Eg 20mm, 30mm, 40mm
I don't want them sitting proud, and equally I need them to take to the thread...

[Steve Horrocks]

Screw extractors aren't great on the small dia screws really. Honestly, there's no biggy to regular drilling out, the left hand drill bit is a lovely option but it's money you don't need to spend IMHO.

[jack-p]

You read my mind on this one karl, or maybe i got you thinking along the same lines when i was talking about it before.
I think you'll be fine just drilling and tapping. Im hoping most of mine unbolt and can be replaced but i dont think theres anything left to unbolt on yours
I smell another car day in the air

[jack-p]

You read my mind on this one karl, or maybe i got you thinking along the same lines when i was talking about it before.
I think you'll be fine just drilling and tapping. Im hoping most of mine unbolt and can be replaced but i dont think theres anything left to unbolt on yours
I smell another car day in the air

[LimeyMk1]

Easy Outs become very f'in Hard to get Outs when they snap. The thinner ones are easy to snap and impossible to drill out (hardened steel).

I'd go with a left handed drill bit as well, the heat and action of the bit will probably start removing half of the broken bolts.

I'd get a mixture of stainless bolts but I reckon most will be 10-15mm.

[Peter Gidden]

Drill, tap and use 20mm stainless bolts and penny washers.

[Slarty]

it's money you don't need to spend IMHO.

Fully agree.

The key to removing a broken bolt is to make sure you centre punch as close to (read, exactly) the middle of the bolt as you can.

If you have a full drill bit set, run a smaller diameter one through first, maybe a 3mm. Then step up to a 4mm, then finally a 5mm and tap the thread.

Personally I wouldn't bother using stainless bolts either. Good grade cap heads (10.9 ton) and some copper slip and you shouldn't ever have a problem again.

[Peter Gidden]

But steel bolts rust (regardless of strength). Stainless bolts cost pennies and won't rust.

Seems a no brainer if you're going to the effort of drilling and tapping.

[KarlBristol]

But steel bolts rust (regardless of strength). Stainless bolts cost pennies and won't rust.

Seems a no brainer if you're going to the effort of drilling and tapping.

I agree - if I'm doing it I'm doing it right

Copper slip, stainless bolts and washers
Drill out and tap new threads

I will probably attack it once the engine is done, maybe early next year...

[KarlBristol]

Ps thanks all for advice and help in this thread - it is appreciated

[wenguin]

Sorry to dredge up an old thread, but I'm going through a similar undertray fix.

I'm dropping my car in for a garage to drill out the snapped bolts and replace all the fixings with s/s bolts and washers. However, I have to source the bolts and washers myself!

I had a look at screwfix but they seem to mostly do screws/odd heads on the bolts. I've found these on Amazon, will they be suitable?

http://www.amazon.co.uk/Stainless-Steel ... uctDetails (2 packs, 20 bolts in all)

http://www.amazon.co.uk/Repair-Washers- ... RZ21W6YWYA (20 penny washers)



I need to make sure they use an M6 tap in the bu88ered bolt holes, then these new bolts will fit in.

However, will these new bolts also fit in the old bolt holes that didn't snap? I'm wanting to replace ALL of them with s/s.

Thanks!

[Draven]

If they drill them out they'll have to rethread them which will mean they will most probably be one size bigger. Unless they use a helicoil which would be rather expensive for the entire under of the car i think.

[wenguin]

If they drill them out they'll have to rethread them which will mean they will most probably be one size bigger. Unless they use a helicoil which would be rather expensive for the entire under of the car i think.

Ah. So the standard bolts are M6, so if they drill it out it will likely be M7?

If so, with the stuff I linked above, I should get about 20 of each M6 and M7? 20 is enough to do all the trays right? I like wide margins for error