Jump to content

Fitting Helicoils

Bull Bar Cowboy

Recommended Posts

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……………….


Link to comment
Share on other sites

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?

Link to comment
Share on other sites

Superb Ian, a worthy thread :hysterical: for the Tech Archive

to answer the 2 questions from 02

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?

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.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...

Important Information

We use cookies to ensure you get the best experience. By using our website you agree to our Cookie Policy