How to never snap a bolt?

[ChocolateFrog]

Some bolts will just snap.

Trying removing an undertray or wheel arch liner from a 20 year old car.

Use penetrating oil, ideally well before the job starts.

Wire brush bolt down to remove loose rust, dirt and debris.

If it starts to move and goes tight, then tighten it back up a few times to work loose.

Lastly, it can't snap if it's liquid, get the oxyacetaline out.

[Nads02]

Thanks everyone, read everyone's replies and now I'm thinking is it a waste of my time and money to wd40 my car? About once a week I check my fluids, tyres, replace wiper wash, and wd40 my cars door hinges and bolts which I can see. My car does drive very smoothly and I haven't snapped any bolts on my yaris.

But if I was to use the penetrating oil recommend would that be too much? Would I end up damaging threads over time etc?

[InitialDave]

You don't need to spray things with WD40 all the time as any kind of preventative maintenance. If you want to do something like that for corrosion prevention, I'd say maybe something like ACF50 or Bilt Hamber Dynax is a better choice, though either way, it's more beneficial around winter.

Some greasing of the door hinges at servicing time is worth it, but other than that, shouldn't be needed regularly.

[LimSlip]

Nads02 said:

Any ideas on how to never snap a bolt?

The only guaranteed way to achieve this is to never attempt to undo a bolt. Fasteners corrode and seize and even the best and most careful people will shear them off occasionally.

[Mave]

Nads02 said:

Thanks everyone, read everyone's replies and now I'm thinking is it a waste of my time and money to wd40 my car? About once a week I check my fluids, tyres, replace wiper wash, and wd40 my cars door hinges and bolts which I can see. My car does drive very smoothly and I haven't snapped any bolts on my yaris.

But if I was to use the penetrating oil recommend would that be too much? Would I end up damaging threads over time etc?

You're not going to damage threads by squirting penetrating oil on them, but you might damage hinges by washing the grease away with penetrating oil. I'd suggest that the majority of the fasteners on your car won't be touched in their lifetime, so don't over think it. Spend half hour on the one that's tricky when you need to remove it, rather than hours worrying about the ones that never need to come out and will probably come out easily anyway.
If you must do something then stick a blob of heavy grease on them to get moisture getting to them in the first place.

[tapkaJohnD]

I'm glad so many agree that WD40 isn't a penetrating oil, and useless to loosen a rusted bolt!
I use Innotec Deblock.

Tightening before trying to loosen was mentioned by the PO, and is really worth while.
My tip is to listen to the bolt as you undo it! If it starts to 'squeal', stop! Unwind, re-oil, wait and try again. That squeal menas extreme friction and stress in the bolt, so that it is likely about to break.

[GreenV8S]

Nads02 said:

Any ideas on how to never snap a bolt?

With experience (or a torque wrench) you will know when the applied torque is approaching the strength of the bolt, and avoid simply twisting it off. Repeated heat cycles and torque applied in both directions will gradually work it free. There will still be times where even with all the care in the world, it'll snap.

[105.4]

GAjon said:

Always I do the last bolt first, it’s always the last bolt that snaps, so if you do that one first it will be taken by suprise and not snap.
Sometimes do the middle bolt first or some other random order just to confuse the fkers.

Always keep them guessing.

This also applies to rounded off heads and Alan key head stripping.

bravo GAjon, bravo.

I’ll try that and report back with my findings.

[105.4]

Eric ‘O’ from South Main Autos spending 27 minutes, trying every trick under the sun, to remove a snapped stud.

https://youtu.be/regeJNeDyrE

[Demelitia]

Pupbelly said:

Krikkit said:

Easiest way is never to touch them!

There's a few ways, but sometimes the shank just under the head is too corroded and can't get the remaining portion of bolt loose.

Imho the best starting point loosening a bolt is to wire brush any crust, then soak it in penetrating oil (which WD40 isn't), and if possible then apply some heat before slightly tightening before loosening, preferably loosening with an impact wrench.

Always thought WD40 was the 'go to' for rusty bolt removal - what is a preferred juice?

I've heard of diesel and something mixed being used.

Brake fluid with acetone (nail varnish remover is an easy source of it) is about the best stuff I’ve used.
The acetone thins it down and allows it to creep. It’s also a good way of making use of old brake fluid that’s been exposed to air and moisture for too long.
Wire brushing any areas where the internal and external threads meet will help if you have access. Failing that, Do the head of the fastener and use a piece of tool steel or a pick to scrape the join between fastener head and surrounding metal.

[HustleRussell]

A cup of tea is very often the difference between stubbornly persisting with brute force, and chilling out and trying a different tack.

[Rueh]

HustleRussell said:

A cup of tea is very often the difference between stubbornly persisting with brute force, and chilling out and trying a different tack.

I second this, a decent cup of tea is sometimes all that’s needed. Obviously doesn’t work for the seriously seized, sometimes taking the head of the bolt off with a grinder, releasing the stress on the thread, will allow the remaining part of the bolt to be wound out with vice grips. Or leave you with a little stump that twists off...

[eltax91]

Rueh said:

I second this, a decent cup of tea is sometimes all that’s needed. Obviously doesn’t work for the seriously seized, sometimes taking the head of the bolt off with a grinder, releasing the stress on the thread, will allow the remaining part of the bolt to be wound out with vice grips. Or leave you with a little stump that twists off...

Quite, I think it’s probably a heat and vibration thing. You cut the head off, you’ve just put heat and vibration down the whole thread to break the rust.

Similarly last week on my defender I started drilling the top of a bolt because there was no access for the grinder or dremmel. Was just backing the drill off to put some more cutting oil on and it bound up and wound the bolt out.

[Chimune]

The heat option has always confused me and seems more like an 'all else has failed' action.
If you heat the top of the bolt, Shirley:
1.you are making the bolt expand into an already very tight hole. Does that actually squeeze the head away from the surrounding metal by a mm?
2. Weakening / fatiguing the bolt metal. A glowing bolt will be softer and more likely to fail.

I can see how heating the surrounding metal might help, but i don't understand the physics of heating. What's the theory here?

[Mave]

Chimune said:

The heat option has always confused me and seems more like an 'all else has failed' action.
If you heat the top of the bolt, Shirley:
1.you are making the bolt expand into an already very tight hole. Does that actually squeeze the head away from the surrounding metal by a mm?
2. Weakening / fatiguing the bolt metal. A glowing bolt will be softer and more likely to fail.

I can see how heating the surrounding metal might help, but i don't understand the physics of heating. What's the theory here?

I think you're basically making the parts move around a bit compared to each other, but without applying any torque. If you expand the bolt into the tight hole, the corrosion gets crushed and you get more clearance when it cools again

[Nampahc Niloc]

Chimune said:

The heat option has always confused me and seems more like an 'all else has failed' action.
If you heat the top of the bolt, Shirley:
1.you are making the bolt expand into an already very tight hole. Does that actually squeeze the head away from the surrounding metal by a mm?
2. Weakening / fatiguing the bolt metal. A glowing bolt will be softer and more likely to fail.

I can see how heating the surrounding metal might help, but i don't understand the physics of heating. What's the theory here?

You’re also heating the surrounding material, so the hole expands too.

[sliks]

Chimune said:

The heat option has always confused me and seems more like an 'all else has failed' action.
If you heat the top of the bolt, Shirley:
1.you are making the bolt expand into an already very tight hole. Does that actually squeeze the head away from the surrounding metal by a mm?
2. Weakening / fatiguing the bolt metal. A glowing bolt will be softer and more likely to fail.

I can see how heating the surrounding metal might help, but i don't understand the physics of heating. What's the theory here?

The differing rates of expansion and contraction break the bond created by corrosion. Freezing actually does a similar job, and there is instant freezing products available for this purpose. Heat works better in my opinion

[Chimune]

Freezing seems much more logical as the bolt shaft will shrink in the hole, but heating - everything just getting bigger together which doesn't seem a good use of resources (in my mind).

[thebraketester]

Chimune said:

Freezing seems much more logical as the bolt shaft will shrink in the hole, but heating - everything just getting bigger together which doesn't seem a good use of resources (in my mind).

The idea is you heat the surrounding material and the differential of expansion between that and the bolt is what gives you a few tenths extra 'slack' which can be the difference between and stuck and moveable bolt.

[Nads02]

Thanks for the replies everyone, I've ordered plusgas for future working on cars. Ideally I want something to spray so it'll do the job. Got a bit of a bargain yaris recently but needs exhaust work, brakes doing up and front shocks have seen better days. Luckily my dad's yaris has a dying clutch, but has a nearly brand new exhaust. Most likely going to scrap my dad's yaris, fix up the new yaris and then charge my dad for the loss (probably £100 as a guesstimate). But will be using plusgas everywhere, snapped 2 bolts before and it wasn't fun!