Bull Bar Cowboy Posted September 6, 2006 Share Posted September 6, 2006 Following on from the excellent example shown by Les ............... this was this afternoons job ....... something we talk about but rarely see ........... Having just been plagued by this on the V8 ……. I am fairly sure it was caused by the threads in the Ali block beginning to let go, and leading to this, All three inner row log bolts exhibit the same problem …… the fix is to helicoil ….. and anybody that runs an ali blocked engine should be familiar with the process. This is the 7/16 x 14 UNC kit….. The size of the inserts are a function of the thread diameter ……… so you get lengths of 1.5D, 2D, 2.5D, 3D etc. The kits are supplied with 1.5D and these are not suitable for this application as we need the whole of the bolt thread engaged to cope with th 70ft/lbs torque. This shows 1.5D, 2.5D and 3D inserts. Ideally the 3D would be the answer, but these are blind holes and using a blind tap will not FULLY thread to the bottom of the hole. Experience tells mew a 2.5D will do the job fine. To safeguard from Ali swarf ….. of which there will be a lot ……….. use duck tape to cover the bores and ‘rag up’ the valley. Check the depth of the holes using a depth gauge ……….. use this setting to mark the drill and count how many threads need to be engaged on the tap. Using the kit supplied drill ……. Carefully drill out the existing theads ………. A very steady hand and low speed is the secret …… you want round holes and not oval ……. So two hands and NO drill wobble whatever …………. A variable speed air drill is best as they are small……….. but Mr Bosch is OK too. Once the holes are drilled ……… clear them with an airline. Next…………. Tap the hole to take the insert. The best cutting compound for Ali is Rocol …….. but if you have not got any to hand, then use PARAFIN as this is an excellent cutting medium for Ali. Fill each hole with Parafin and then start tapping, The hole on the left has been tapped and the one on the right is filled with paraffin and ready to tap Make sure the tap enters the hole at right angle to the material ……… Tap slowly and methodically applying equal pressure to both side of the tap holder. Every now and again reverse to tap by half a turn to break the swarf from the cutting edge. If you don’t do this then there is a chance that the tap can bind and wreck the new thread. The tap will bottom before reaching the bottom of the hole due to swarf build-up. Remove the tap and clear the hole with an airline ……… you may need to do this a couple of times until you reach the required thead depth. When the tap is reinserted ….. fill the hole with paraffin again and find the cut thread by hand …… its all to easy to cross thread a tap. Eventually the required depth is reached ………. As found from the depth gauge. mount the insert on the insertion tool by fitting the ‘tang’ into the drive slot and adjusting the collar to suit the insert. Note the ‘Tang’ break off marks on the insert ……. Gently screw the insert in the new oversize thread ………. Make sure that they are screwed in until the insert is ¼ to ½ a turn below the surface. This shows all three fitted ……… difficult to see the inserts Use the Tang tool to break off the tangs ………. Place onto tang and a smart tap with the hammer does the trick. All the tangs are now broken off and in the bottom of the hole ……….. they must be removed as they could get caught up on the thread and cause damage. Blow each tang out with the airline ……… like so Check each hole by hand screwing the bolt in to the full depth of thread…. Carefully blow off the swarf and remove the tape and rag …….. just like brand new….. That’s all………………. Ian Quote Link to comment Share on other sites More sharing options...
Andy Posted September 6, 2006 Share Posted September 6, 2006 excellent, i've always wondered how you do that. Quote Link to comment Share on other sites More sharing options...
dollythelw Posted September 6, 2006 Share Posted September 6, 2006 you sure thats not a recoil kit Ian?? tin hat time... Quote Link to comment Share on other sites More sharing options...
Bull Bar Cowboy Posted September 6, 2006 Author Share Posted September 6, 2006 Jez, Nah ………. Its actually a unicoil kit …….. cos the main agent is only 10 minutes drive from here …….. bl00dy useful folk…… However, people understand the generic name better ............. well maybe .......... Ian Quote Link to comment Share on other sites More sharing options...
dollythelw Posted September 6, 2006 Share Posted September 6, 2006 Quote Link to comment Share on other sites More sharing options...
02GF74 Posted September 6, 2006 Share Posted September 6, 2006 some q.s 1. what stops the helicol from moving once it is in the hole? 2. what would happen if the tang broke off before the cool was fully inserted - would you be able to get it out? put a blob of paint on the tap to mark the depth so no need for guage oh, you realise that the helicoil wil be much stronger than the original ali thread? Quote Link to comment Share on other sites More sharing options...
Turbocharger Posted September 6, 2006 Share Posted September 6, 2006 Cheers Ian - more bargain-basement tech stuff. I've heard a lot about helicoils but never seen one in action. I mean, I only studied mechanical engineering at a top university for five years - why tell us about techniques like this when we could be learning more maths, eh? Quote Link to comment Share on other sites More sharing options...
nas90 Posted September 6, 2006 Share Posted September 6, 2006 Excellent, long time since I used a helicoil, so can we put this in the techy section please mods? We have had some top tips this last few days. Quote Link to comment Share on other sites More sharing options...
Orgasmic Farmer Posted September 6, 2006 Share Posted September 6, 2006 Excellent post Ian. My only experience of a helicoil was when I blew a spark plug out of a Talbot Horizon doing 80 on the M4. Made a hell of a dent in the bonnet! Managed to wedge it in enough to drive home at 30 but then used a Helicoil as a permenant fix. Worked really well. Quote Link to comment Share on other sites More sharing options...
Les Henson Posted September 6, 2006 Share Posted September 6, 2006 Excellent thread Ian. looks very professional. I've never had to do this job, and didn't realise how it was done. Tech archive material for sure. Les. Quote Link to comment Share on other sites More sharing options...
western Posted September 6, 2006 Share Posted September 6, 2006 Superb Ian, a worthy thread for the Tech Archive to answer the 2 questions from 02 some q.s1. what stops the helicol from moving once it is in the hole? 2. what would happen if the tang broke off before the cool was fully inserted - would you be able to get it out? 1. the action of the helicoil gripping the surrounding structure prevents it from coming out & the design of the coils, if you look closey they're a diamond shape so will bite into the material it's fitted into 2. there's a special removal tool in the insertion kit, some helicoils have a break off tang if they're for through holes others have a fixed tang for blind [dead end] holes as per the ones shown above. hope that explains OK. Quote Link to comment Share on other sites More sharing options...
BogMonster Posted September 6, 2006 Share Posted September 6, 2006 Excellent thread Ian another one for the tech archive Quote Link to comment Share on other sites More sharing options...
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