AlfredHitchcock Posted July 30, 2013 Report Share Posted July 30, 2013 One step forward, two steps back........ Ive pulled the head stud retorqueing the head on my 4. I didnt pull the stud out, but because it was only in about 3-4 threads I could feel the stretch so removed it. It couldnt have ever been in deep enough. Couple of questions please. 1) Ive bought a 1/2" unc tap which has 13 tpi and it seems the stud is 12 tpi. Which is correct? 2) I notice that the correct length of stud is 9". The one Ive removed looks different to the others (poor quality) and is only 7" long!!! Are they screwed into the head 2"? And is the different tpi why it wouldnt go deeper in the block? 3) Ive obviously damaged the block top few threads. Is it possible to recut the thread with the correct tap or have I got to drill the thread out and helicoil it? Quote Link to post Share on other sites
RogerH Posted July 30, 2013 Report Share Posted July 30, 2013 (edited) Couple of questions please. 1) Ive bought a 1/2" unc tap which has 13 tpi and it seems the stud is 12 tpi. Which is correct? Are you sure the stud is 1/2". The stud should be 1/2" and the thread 1/2" UNC 13TPI It would appear you have a 1/2" BSW 12 TPI 2) I notice that the correct length of stud is 9". The one Ive removed looks different to the others (poor quality) and is only 7" long!!! Are they screwed into the head 2"? And is the different tpi why it wouldnt go deeper in the block? Have a look at the Moss catalogue to see which stud you need. There are no 7" studs If there is a TPI mis-match then it will not go in far - but will cause damage. 3) Ive obviously damaged the block top few threads. Is it possible to recut the thread with the correct tap or have I got to drill the thread out and helicoil it? Even if you re-tap the dodgy threads they will be weaker than ideal so a helicoil may be your best option Somebody has put a Micky Mouse stud in your engine. Roger Edited July 30, 2013 by RogerH Quote Link to post Share on other sites
Motorsport Mickey Posted July 30, 2013 Report Share Posted July 30, 2013 I'm with Roger, with this size stud you should have no problem with a Helicoil/Recoil (trade name equivalent)repair. You can do it with confidence, the repaired thread will be stronger than the original ! Mick Richards Quote Link to post Share on other sites
AlfredHitchcock Posted July 30, 2013 Author Report Share Posted July 30, 2013 Roger you really are becoming my saviour in these troubled times . I think you are totally correct in saying I have a 1/2" bsw stud as Ive found a very old tap that matches the crappy stud and its got 1/2" 12 WTH (12 tpi whitworth?) stamped on it. OK next question is helicoils - where? how? Quote Link to post Share on other sites
AlfredHitchcock Posted July 30, 2013 Author Report Share Posted July 30, 2013 Dont know whats happened to my avatar! Quote Link to post Share on other sites
RogerH Posted July 30, 2013 Report Share Posted July 30, 2013 Get a kit off ebay. It shouild include the special tap, coils and insertion tool. Roger Quote Link to post Share on other sites
AlfredHitchcock Posted July 30, 2013 Author Report Share Posted July 30, 2013 Will this one do the job? http://www.ebay.co.uk/itm/THREAD-REPAIR-KIT-1-2-UNC-CAN-BE-USED-WITH-HELICOIL-INSERTS-/300918023150?pt=UK_BOI_Metalworking_Milling_Welding_Metalworking_Supplies_ET&hash=item46101ca3ee Quote Link to post Share on other sites
RogerH Posted July 30, 2013 Report Share Posted July 30, 2013 (edited) In essence yes but the coils need to be inserted for the full depth of the hole or as near as damn it. I don't know if you can get coils the full length that you need - I'm sure somebody will help out here - otherwise see if it is possible to insert a number of the shorter ones to make up the full length. Roger These people do 1" coils http://www.ebay.co.uk/itm/Genuine-Helicoil-thread-inserts-UNC-/151089503847?pt=LH_DefaultDomain_3&var=&hash=item232da2de67 These do 1.5" long coils. http://www.engineering-supplies.com/sub/427/unc-wire-inserts-/ Don't know if there are longer ones Edited July 30, 2013 by RogerH Quote Link to post Share on other sites
AlanT Posted July 30, 2013 Report Share Posted July 30, 2013 How many turns of thread are there on the end on a good stud and how many thread turns have you damaged? A 12 TPI wont screw into 13 TPI more than about 2-3 turns I would expect. So maybe you still have 90% of the thread turns in place. This would do for me. If they pull out and you have to Helicoil then you have lost nothing. maybe would work OK for many years. I dont much like Helicoils. You cant get a Helicoil right to the bottom of a hole. They always have to stop short. You may wind up Helicoiling this and not get any more actual thread turns. Quote Link to post Share on other sites
RogerH Posted July 30, 2013 Report Share Posted July 30, 2013 Hi Al, yes I agree with your comments - it all depends on the damage to the top couple of threads. If they can be cleaned then it may be worth giving it a go without the helicoil repair. TRy running the 1/2"UNC tap into the hole to see if the threads can be cleaned. Roger Quote Link to post Share on other sites
AlfredHitchcock Posted July 30, 2013 Author Report Share Posted July 30, 2013 How many turns of thread are there on the end on a good stud and how many thread turns have you damaged? A 12 TPI wont screw into 13 TPI more than about 2-3 turns I would expect. So maybe you still have 90% of the thread turns in place. This would do for me. If they pull out and you have to Helicoil then you have lost nothing. maybe would work OK for many years. I dont much like Helicoils. You cant get a Helicoil right to the bottom of a hole. They always have to stop short. You may wind up Helicoiling this and not get any more actual thread turns. Alan Going on how far I could get the bad stud back in the hole I would say 3 1/2 turns which is only about 10mm max. So at least that much will have been stretched/damaged. This explains why the stud has had to be shortened by 2" to get it to be anywhere near. Ive ordered a new 9" stud and will be able to see how much UNC threaded portion there is. I'm thinking I could I drill out the first 10mm damaged thread, carefully clean out the rest with my tap and still get 40 - 50 mm deep with the new stud. What do you think? Quote Link to post Share on other sites
ChrisR-4A Posted July 30, 2013 Report Share Posted July 30, 2013 (edited) Is it one of the long studs which go right down near the main bearing? If so check there is not the remains of a broken stud still in the hole. Use a thin rod to see how deep the hole is first. If clear try tapping the hole out first instead of drilling. As long as you have 1.5x to 2x the thickness of a head nut then should be ok as the nut would strip first. same logic if helicoiling i would say 1.5 ins helicoil would be ok. When fitting new stud don't over tighten, stud torque is always a lot less than torque on nut, not sure exact figure, anyone else know? instead use some stud lock and leave overnight before fitting head. Edited July 30, 2013 by potts4a Quote Link to post Share on other sites
AlfredHitchcock Posted July 30, 2013 Author Report Share Posted July 30, 2013 Ive tried a thin screwdriver down the hole and I'm 99% sure there is no broken stud in there. Looking from the front its the 2nd one back on the righthand row of studs. Not sure if thats the one by the main bearing? I identified it as a 9" stud from the moss parts drawing. Quote Link to post Share on other sites
AlanT Posted July 31, 2013 Report Share Posted July 31, 2013 You may not be able to use a tap on this unless you have an extra long one. The usual fix is to use a srcap stud and grind a sloping face at about 20 deg on it. The "flat" then reconstitutes the thread without getting jammed. You will need a long cotton bud to catch up all the swarf in the bottom of the hole. You will be surprised what you fish out of there! Somebody on here will know by how much you can drill deeper into the block just here. Long before I used a Helicoil, I would have won a few extra turns by doing this, if I really needed them. Quote Link to post Share on other sites
AlfredHitchcock Posted July 31, 2013 Author Report Share Posted July 31, 2013 The tap Ive bought is 7" long so is long enough but its a second, so hasnt got much taper to start me off. The hole is definately blind then? I had visions of a broken stud in the bottom. Quote Link to post Share on other sites
AlanT Posted July 31, 2013 Report Share Posted July 31, 2013 (edited) There was a topic on here that discussed drilling deeper into the block. Production threads deep in castings rarely have full thread profile right to the bottom. You can probably win an extra turn by carefully tapping. Often I grind a new flat bottom on taps so as to get a bit further down. Make sure hole is EMPTY at the bottom before doing this. This is big enough for the risk of breakage to be small unless you get stupidly rough. Carbon-steel OR HSS tap? Be careful with cheap carbon taps, the teeth can chip off and jam. I'd get a good make used off eBay rather than an Indian import. Edited July 31, 2013 by AlanT Quote Link to post Share on other sites
RogerH Posted July 31, 2013 Report Share Posted July 31, 2013 Lets gather our thoughts together. There has been a lot of good info here but perhaps there is an easy way and a hard way. The top 3 1/2 threads may be damaged There is no broken stud in the hole Most of the thread should be in good order. Try to see if the new tap will run down and pick up the old thread. However if the damaged thread is too icky then the tap may start to cut out of sync with the old thread. Do not tap too far; 3 or 4 turns just to see if its aligned. (if it was possible to back tap the hole -coming up from below - then it would be easy) If it can't be aligned then using a drill smaller than the helicoil tapping drill clear the smallest amount of damage thread out of the hole. The 1/2UNC tap should then be able to pick up on that. Insert new stud and nip up ( I do not think these are torqued in as the nut torque will hold in place). Place head on top,add nut/washers and torque. I think 100ft/lbs rings a bell. If all is well then remove head and carrying on with the build. If the thread strips or feels as if it is going (the deeper thread could be corroded) then you are back to helicoils etc but you are no worse off. Comments! Why did they fit a 1/2 BSW stud these are not common - it was no accident. Roger Quote Link to post Share on other sites
ChrisR-4A Posted July 31, 2013 Report Share Posted July 31, 2013 The stud you are replacing is one of the 4 long ones which surround the central main bearing. I would leave the hole as it is don't try and depen it. Your biggest problem is getting the tap started and keeping it square to the block. It may be necessary to buy or borrow a first taper tap, a short one will do just to get it started square. In a workshop the block would be mounted on the table of a big drill stand ( a pollard or similar) and the tap in a chuck would be turned by hand to get it central and square. Same process for Helicoils. Hopefully the stud you took out had followed the original thread and when you retap the new threads at the top will lign up with the old ones lower down. I would try to retap the top bit first and then try the stud because if you run the long tap right down you may remove some of the original thread as the two threaded parts align themselves. When starting the first tap get someone to help you look in the plane you cannot see to make sure it's square as possible.best of luck. Quote Link to post Share on other sites
AlanT Posted July 31, 2013 Report Share Posted July 31, 2013 A taper tap would easily pick up in the right place. This one may not. I'd spin it up and bring up a rotating grinder and "taperise" it a bit. Could probably do this in a pillar drill. Quote Link to post Share on other sites
AlfredHitchcock Posted July 31, 2013 Author Report Share Posted July 31, 2013 OK Ive just tried to get my tap down the hole and soon realised that what was left in there was the remnants of an old helicoil. That explains the 1/2" BSW stud. In hindsight I can see what must be the OD of the previous helicoil tapped into the block to a slightly wider diameter and have found at least 1 other done this way. I have drilled out the remains and assume I will need to get a helicoil kit containing the reamer and retap it. Worse case will be if the helicoil tap is different and my hole is getting oversized. I assume there is a standard OD for a 1/2UNC helicoil isnt there? Sorry guys but this is all new to me and I'm floundering at bit. Quote Link to post Share on other sites
RogerH Posted July 31, 2013 Report Share Posted July 31, 2013 OMG!! If the original stud hole has had a helicoil inserted for the 1/2BSW stud then this may cause a problem. Both 1/2 UNC and 1/2 BSW share the same apprx diameter for tapping. This means that the UNC helicoil thread will not match up with the thread in the block as it is cut for BSW. How deep dies this helicoiul go down the hole ( please say 1/2") Are you sure it is a helicoil and not a curl of broken thread!! Can you take a photo to show anything important. If the top 1/2" has not got this BSW helicoil thread in it then by removing the coil itself you should have clearance to insert the 1/2" UNC stud into the UNC thread below (I hope it is there). Roger Quote Link to post Share on other sites
AlfredHitchcock Posted July 31, 2013 Author Report Share Posted July 31, 2013 Right.........deep breath........the hole has been drilled/tapped the whole way down. I assume its the same size! The broken helicoil was quite deep in the hole - 2" ish and was definately a helicoil and not broken thread. My 1/2 UNC tap goes all the way to the bottom without even touching the sides now! Can I get oversized OD 1/2UNC helicoils and drill and tap a slightly bigger hole? Quote Link to post Share on other sites
AlfredHitchcock Posted July 31, 2013 Author Report Share Posted July 31, 2013 Do these shed any light Roger? Quote Link to post Share on other sites
Motorsport Mickey Posted July 31, 2013 Report Share Posted July 31, 2013 (edited) OK...deep breaths now. I'm sure Roger hasn't keeled over having seen the photos and will shortly be answering your query but here's a couple of observations. If you examine the thread (BSW ?) cut into the block it hasn't got a complete thread form finished in it, ie the tops of the thread are missing and it shows a "blunt" thread profile. I guess this was the finished thread cut by the BSW helicoil tap, and on the good side if it goes to the bottom of the hole there will be lots of it. Presumably because the hole dia at the top is originally clearance on the 1/2inch UNC this may have not had enough base material left to cut a complete thread form in, hence the blunt topped theads. I don't know if you can view down the thread to the bottom area (mini inspection camera ?)of the block, but it may be that in the bottom area the thread form is more complete, if so I think that a one off special stud with this block thread form in it may be the way forward. If you examine the amount of material left around the stud hole I wouldn't like to try and drill another hole to accept another Helicoil thread form, I feel it could make the narrow area into the waterjacket susceptible to cracking in the future. Whereas a long stud with a thread form up the shank such as to allow the stud to be screwed in from the top would give a comprehensive increase in thread area (even if some of it is not fully formed). More inspection required but I think that a one off stud with this thread form maybe the best solution, if so research would be needed to locate a manufactured one, it would not be a good idea to consider cutting a thread on a stud, you need a "rolled" thread form to avoid a cut thread causing a stress riser which would fail on the thread. Mick Richards Edited July 31, 2013 by Motorsport Mickey Quote Link to post Share on other sites
RogerH Posted July 31, 2013 Report Share Posted July 31, 2013 (edited) Oh Dear. Firstly don;t panic (there will be plenty of time for that later). If the hole has been helicoiled and the 1/2"BSW stud didn't fit then perhaps the hole has been tapped for a 1/2" UNC helicoil. Clearly a 1/2UNC tap will fall through as the helicoil size is bigger. Can you look and measure down the hole to see what TPI it is - if it conicides with the 1/2UNC thread form then you may be in luck. A piece of wire with a hooked end can count the thread as you drag it across. If it is 1/2UNC then you now need to obtain a deep 1/2"UNC helicoil. The links I provided went up to apprx 1 1/2" deep Roger oooops spelling mistakes Edited July 31, 2013 by RogerH Quote Link to post Share on other sites
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