How to clean rusted thread bores?

Soldato
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Need a bit of a crash course. I have a couple of 13mm thread bores that have rusted inside the bore and hence new bolts will not go in, at least not without massive force which I dont want to do, wd40 or brake cleaner doesn't seem to be enough. So far I've briefly read up on thread chasers and taps but unsure which way to go.

I'm going to look for plastic or wire brush that will fit see if that works I need to get this sorted asap. Also I'm dubious about using a wire brush incase I flatten the threads.

How would you deal with this?
 
Soldato
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Yeah running a tap down the hole is the easiest solution.

What is it on? 13mm is an unusual size are you sure it's not Imperial?

Thought I'd ask as if you are just measuring with a ruler or similar it could be 1/2inch
 
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a nice hack for cleaning old threads is to create a sort of bolt tap hybrid

Get a bolt of the correct size and file a single or a couple of grooves down the thread, just the top few will usually be enough, as you wind it in it helps clear out the corrosion
You may need to go in and out a few times but you in effect do re tap the thread, and the cost is peanuts with little opportunity to mess it up
 
Soldato
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Yeah running a tap down the hole is the easiest solution.

What is it on? 13mm is an unusual size are you sure it's not Imperial?

Thought I'd ask as if you are just measuring with a ruler or similar it could be 1/2inch
Yeah running a tap down the hole is the easiest solution.

What is it on? 13mm is an unusual size are you sure it's not Imperial?

Thought I'd ask as if you are just measuring with a ruler or similar it could be 1/2inch

Not 100% sure it's 13mm.

So do you just buy a tap the same size as your bore i.e in this case you'd buy a 13mm tap, and how are the taps able to move the rust/crud whereas the bolt can't?
 
Man of Honour
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Not 100% sure it's 13mm.

So do you just buy a tap the same size as your bore i.e in this case you'd buy a 13mm tap, and how are the taps able to move the rust/crud whereas the bolt can't?
Yep same size/pitch as the current thread and because they're designed to cut into metal so they're more than hard enough to cut through the rust
 
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Depending on what type of tap you use they can be tapered to work their way in and also have longitudinal grooves for waste material to collect.
 
Soldato
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a nice hack for cleaning old threads is to create a sort of bolt tap hybrid

Get a bolt of the correct size and file a single or a couple of grooves down the thread, just the top few will usually be enough, as you wind it in it helps clear out the corrosion
You may need to go in and out a few times but you in effect do re tap the thread, and the cost is peanuts with little opportunity to mess it up

That's an excellent idea I'll try and remember that.
 
Soldato
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Yep same size/pitch as the current thread and because they're designed to cut into metal so they're more than hard enough to cut through the rust

So there are chaser taps and regular taps, I don't really want to risk cutting incase I mess it up, so I guess I'm looking for a chaser tap?

Also what about rust remover?

And what is this it's always on Google and seems to be able to handle multi thread pitches, why is one tool able to do that?

https://www.eurocarparts.com/search...Orhi1aabZYUYOgBihrYFVD6TPwhZHt84aAj5kEALw_wcB
 
Soldato
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Never used one of those but it looks like it's just got multi pitched sides a d as it's not cutting a whole new thread you just need to start it on the right pitch for it to clean things up.

I personally use the bolt method mentioned above, takes a few seconds and pretty much always works so long as you take your time backing it in and out a few times. I don't like using taps on the car if I can avoid is as inevitably I snap the thing in an area with impossible access
 
Soldato
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So there are chaser taps and regular taps, I don't really want to risk cutting incase I mess it up, so I guess I'm looking for a chaser tap?

Also what about rust remover?

And what is this it's always on Google and seems to be able to handle multi thread pitches, why is one tool able to do that?

https://www.eurocarparts.com/search...Orhi1aabZYUYOgBihrYFVD6TPwhZHt84aAj5kEALw_wcB

That is for external threads so for repairing/cleaning up bolts. It's a thread file with multiple thread pitches.

You really need to narrow down the thread size and pitch and you can then buy a tap. If the hole is blind you will want a plug/3rd tap to run down it.

Traditional taps are either sold is sets or individually

Sets include 1st/2nd/3rd(Plug) taps and if tapping a new hole you use them in order to achieve a full thread in a hole. If like you, you just need to clean it up a 3rd(plug) tap will be fine or a 2nd at a push. Hopefully that hasn't made things even more confusing.
 
Soldato
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That is for external threads so for repairing/cleaning up bolts. It's a thread file with multiple thread pitches.

You really need to narrow down the thread size and pitch and you can then buy a tap. If the hole is blind you will want a plug/3rd tap to run down it.

Traditional taps are either sold is sets or individually

Sets include 1st/2nd/3rd(Plug) taps and if tapping a new hole you use them in order to achieve a full thread in a hole. If like you, you just need to clean it up a 3rd(plug) tap will be fine or a 2nd at a push. Hopefully that hasn't made things even more confusing.

Yeah it has a bit, not sure what 'pluging a third tap' means. It looks like you have to buy a set as the individual costs are quite high and just as well buying set.

I really grudge having to do this and a lot of Toolstation products are crap.

What do you think of this, all I can find and I need the car tomorrow.?

https://www.toolstation.com/hilka-tap-die-set/p75650
 
Soldato
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Thought it was a 13mm you needed though(as mentioned before pretty unusual)? That set only goes to M12, unless you meant a 13mm head?
 
Soldato
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First thing is to measure the bolt properly to establish what thread you need. You’ve mentioned 13mm, is that the diameter of the threaded section (unlikely) or the size of the spanner you used on the head (more likely). 13mm is the standard head size for an M8 bolt (Bolt sizes are measured across the widest part of the threaded section). Next you need to measure the thread pitch (this is the distance between threads). Standard M8 is 1.25mm thread pitch although M8 fine (1mm thread pitch) is also fairly common on cars. Easiest way to measure this is to measure at least 10-20 threads and then divide the measurement by the number of threads. (With experience you can just eyeball it and tell the difference) Once you’ve got both measurements you’ll know what thread you are trying to repair (M8x1.25 or M8x1 for example). If the diameter of the threaded part is nearer 13mm then we will need to establish whether you have M12, M14 or some 1/2” imperial thread (Imperial threads are a whole new level of complexity I’m not getting into unless we need to)

Good quality taps are not cheap. Buying a single tap in the right size is likely to result in getting a decent quality product whereas a cheap ‘set’ will just be junk
 
Soldato
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Thought it was a 13mm you needed though(as mentioned before pretty unusual)? That set only goes to M12, unless you meant a 13mm head?

It's M12 which is 12mm I believe, can you confirm that?

Edit: yeah just measured bolt with calipers it's 12mm so M12, so that set above has right size, also it's 1.5mm pitch.

Now the concern is getting the tap broken in the hole, which could happen with cheap tools.
 
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Soldato
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Ok so if it's a 12 X 1.5 I'd buy a specific tap for that, I assume you're planning on running it over the existing threads rather than redrilling / helicoil etc?

Just take your time, use oil or some sort of lubricant, make sure it's straight, use only hand force and don't be scared of backing it out a bit and it will work out fine.
 
Associate
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Typically going in with a tap it helps to do small turns followed by backing it out then going in again. So maybe do half a turn, back it out 1/4 turn to help draw up any debris, go back that 1/4 turn then do another half turn and so on.

A trick to double check the tread pitch of bolt and tap match, lay them next to each other and check the thread peaks interlock together.
 
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