Quinten Posted October 16, 2014 Author Share Posted October 16, 2014 Had ordered a couple of 5/16 UNC nuts which arrived today and I cut the unthreaded part from the bolt. Screwed 2 nuts on and then using a spanner tried to undo the nut closest to the head. Bolt snapped off straight away, leaving me with an even bigger problem. The only thing I noticed is that the screw thread on the head is through the casting, so hopefully with a carefully selected drill bit I should be able to remove it... he says hopefully Quote Link to comment Share on other sites More sharing options...
tisme Posted October 16, 2014 Share Posted October 16, 2014 What a er ! Cheapest fix is to drill a small hole then use the appropriate drill and tap - Namrick have a good range http://www.namrick.co.uk/acatalog/Home_U_N_F__and_U_N_C__Taps__Dies_and_Tapping_Drills_154.html I assume the studs are UNC in the head and UNF for the nut (looking at the picture from Burtons) http://www.burtonpower.com/stud-exhaust-to-cylinder-head-fl840.html Helicoil kits are quite expensive (£30?) but as you shouldn't need to remove the studs in the future I'd have thought just a drill and tap should suffice - use brass nuts and they shouldn't seize up in future http://www.burtonpower.com/exhaust-brass-nut-5-16unf-extra-wide-nb516f.html Quote Link to comment Share on other sites More sharing options...
s2rrr Posted October 18, 2014 Share Posted October 18, 2014 If you first drill a small hole central to the stud then increase it slowly to no greater than the internal thread diameter of the stud the remaining metal in the head will be the threads only. The nearer you get to the root diameter the flimsier the remnants are and sometimes and I repeat sometimes the threads will peel out due to the head you are putting in drilling and the release of pressure by removing the metal. If you are very fortunate you may just need to clean up the thread that's left. If you go for a straight retap you will be lucky to follow the original threads and you may end up with a mess of threads which will only leave you a few options. Drill and tap a larger size or helicoil not ideal but an option. If you have access to a Zeus Engineers tables booklet it will give you stuff like tapping sizes and various dimensions. Its easier explained on an internet accessible picture. Hope that helps rather than confuses. Bob Quote Link to comment Share on other sites More sharing options...
Quinten Posted October 18, 2014 Author Share Posted October 18, 2014 After failing miserably with my HSS drill bits I've just picked up some Cobalt drill bits from Toolstation. Hopefully these will at least drill into the bolt. What an incredible grief is this car giving me Quote Link to comment Share on other sites More sharing options...
peet Posted October 18, 2014 Share Posted October 18, 2014 Cobalt drills from toolstation work well Quinten - I,ve had the same lovely jobs as you over the years! At least it's sorned and off road at the moment... and think how well sorted it'll be next summer! Quote Link to comment Share on other sites More sharing options...
Quinten Posted October 18, 2014 Author Share Posted October 18, 2014 Cheers peet. Half the difficulty is finding the right tools at the right price Quote Link to comment Share on other sites More sharing options...
Quinten Posted October 19, 2014 Author Share Posted October 19, 2014 Cobalt drills FTW! Went from 3 to 4 to 5 to 5.5 to 6mm and although a lot of the old bolt is gone now, it has left enough behind to warrant a re-thread.How do you use a tap? There seems to be 2 or 3 pieces involved? On the Namrick website they refer to "1 Taper and 1 Bottoming Tap per Set", but what does that mean? Also, if I rethread the 5/16 UNC thread, I need to use the 6.6mm drill they also supply? What about their comment on "Carbon Steel unsuitable for stainless steel, cast iron and high carbon steel" ? Looking at Wikipedia, the Crossflow cylinder head is cast iron?Would this be more suitable? http://www.chronos.ltd.uk/acatalog/info%5fHEL51618%2ehtml Quote Link to comment Share on other sites More sharing options...
peet Posted October 19, 2014 Share Posted October 19, 2014 You use the coarsest one first, the one which looks like it's a stripped thread.. It's 2 turns forwards and one back, take your time. If it binds up just undo a bit and take another bit - don't force it at all at risk of snapping it off!! - of course I have already done this so telling you now so you don't have to!! Quote Link to comment Share on other sites More sharing options...
darve Posted October 19, 2014 Share Posted October 19, 2014 Use a cutting lube as well 1 Quote Link to comment Share on other sites More sharing options...
peet Posted October 19, 2014 Share Posted October 19, 2014 Oh yes!! Sorry forgot that! Quote Link to comment Share on other sites More sharing options...
alexander72 Posted October 19, 2014 Share Posted October 19, 2014 Q, If you nee d any help let me know. Cheers mate Quote Link to comment Share on other sites More sharing options...
Quinten Posted October 20, 2014 Author Share Posted October 20, 2014 I'm still none-the-wiser what tap I need. There's such a bewildering amount of 'steel' that I'm hesitant to buy anything. I would normally prefer a tool set (like this or this) but am dubious about their usefulness at the price point they are when I've seen individual taps at the same price! Then there are the thread repair kits (like this or this) but they seem to be more useful when you are beyond repairing the existing thread?Of course I could just buy an individual tap set (like this or this or this or this), but then I would still need to buy the appropriate drill bit (6.6mm apparently). Quote Link to comment Share on other sites More sharing options...
peet Posted October 20, 2014 Share Posted October 20, 2014 If the size you need is in the £15 set buy that. Remember I said don't force it - def don't with these! You should be able to do a good few holes with them if used carefully! IF they break replace them with a better quality one - the really expensive ones would last a long time - you only have a dozen or so holes so I'd just get tool station or screwfix ones. I'd re-tap all the others too just because I can for piece of mind.. And if you should break one of - tap it out with a an old screwdriver anticlockwise - erm yes done that myself a few times...! Quote Link to comment Share on other sites More sharing options...
Quinten Posted October 21, 2014 Author Share Posted October 21, 2014 The set contains the 5/16 UNC tap that I need, but I'm just worried it is going to be off the same chocolate quality as the screw extractors I once bought. It only needs to last the once (as I'm not planning to ruin any more threads ), but it does need to work in one go... Am currently favouring the thread repair kit, as it is a complete set and allows me to completely remove the remains of the screw (which is of unknown strong material, possibly 12.9 high tensile steel) before I put the delicate thread tool on it. The disadvantage is... well, is there any? Quote Link to comment Share on other sites More sharing options...
s2rrr Posted October 21, 2014 Share Posted October 21, 2014 Quinten, I would try and pick out if its possible any removable pieces of the old bolt thread this could however create problems later in that a tap may jam. If you can attempt to give the tap a start by picking out any old thread it may be possible to rethread purely by cutting out the old bolt threads. It may also be possible to do it with the plug tap but its a big if. The taps are 1st or taper tap this has the smallest end dimension and basically is tapered the most to allow for minimal removal of metal starting the thread. The 2nd tap is between the two, less tapered and not a full thread. The plug tap is a full thread tap with a stubby end and should be used to cut the last remnants and will give what it says on the tin. The usual format is to gently get the taper tap to start by screwing it in until you feel it engaging slightly buy cutting material, this may be half a turn only and it will tighten up, at that point undo 1/4 turn to break the cutting off and clear the tap. Try to keep the tap in line and not wobbling about but it can be tricky. Re-tighten the tap and you will feel the cutting action but don't be tempted to go too fast too soon it may end in disaster. Slowly progress 1/2 to 1 turn and 1/4 back until you are happy. Have a look inside the hole and see what the thread looks like if you are lucky it may be cutting the same original thread. Take the taper tap in by the process above until you are through the casting by which time you should be able to use the 2nd or plug tap to complete the process. It may be necessary to have a trial run on a spare piece of metal to get the feel of things. Be aware if you become too enthusiastic and wind in the tap too far it may jam and if its a cheaper material tap it could snap, then you have a bigger problem. Give it a bash and consider if it all goes wrong could you fit a bolt with a nut on the back, you are close to the plug but you may have room, all is not lost. I would not use stainless bolts by the way. Carbon steel Studs and brass nuts makes life easier in some respects but if you have space issues. Drilling out a snapped stainless bolt is another factor of difficulty. Hope that helps, just take your time, try the practise hole to get some confidence. Bob Quote Link to comment Share on other sites More sharing options...
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