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How to clean rusted thread bores?

Discussion in 'Motors' started by jsmoke, 24 Dec 2020.

  1. jsmoke

    Capodecina

    Joined: 17 Jun 2012

    Posts: 10,896

    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?
     
  2. sovietspybob

    Mobster

    Joined: 25 May 2008

    Posts: 3,214

    Location: North Wales

    I'd personally use a tap and go nice and gently
     
  3. Maccapacca

    Don

    Joined: 13 Apr 2010

    Posts: 18,107

    Location: Sunny Sussex

    Wind a tap in and out is the only way really.
     
  4. Finners

    Mobster

    Joined: 27 Mar 2009

    Posts: 2,868

    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
     
  5. kaiowas

    Capodecina

    Joined: 18 Oct 2002

    Posts: 10,441

    Location: Castle Anthrax

  6. Mercenary Keyboard Warrior

    Capodecina

    Joined: 4 Aug 2007

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    Location: Wilds of suffolk

    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
     
  7. jsmoke

    Capodecina

    Joined: 17 Jun 2012

    Posts: 10,896

    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?
     
  8. tom_e

    Man of Honour

    Joined: 26 Dec 2003

    Posts: 28,385

    Location: Shropshire

    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
     
  9. drakulton

    Wise Guy

    Joined: 20 Apr 2015

    Posts: 1,795

    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.
     
  10. bainbridge

    Mobster

    Joined: 9 Dec 2009

    Posts: 4,491

    Location: Bristol

    That's an excellent idea I'll try and remember that.
     
  11. jsmoke

    Capodecina

    Joined: 17 Jun 2012

    Posts: 10,896

    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
     
  12. rodenal

    Capodecina

    Joined: 7 Dec 2011

    Posts: 10,291

    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
     
  13. Finners

    Mobster

    Joined: 27 Mar 2009

    Posts: 2,868

    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.
     
  14. jsmoke

    Capodecina

    Joined: 17 Jun 2012

    Posts: 10,896

    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
     
  15. rodenal

    Capodecina

    Joined: 7 Dec 2011

    Posts: 10,291

    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?
     
  16. kaiowas

    Capodecina

    Joined: 18 Oct 2002

    Posts: 10,441

    Location: Castle Anthrax

    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
     
  17. jsmoke

    Capodecina

    Joined: 17 Jun 2012

    Posts: 10,896

    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.
     
    Last edited: 24 Dec 2020
  18. rodenal

    Capodecina

    Joined: 7 Dec 2011

    Posts: 10,291

    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.
     
  19. tl45

    Hitman

    Joined: 26 May 2014

    Posts: 636

    Location: Warrington

    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.