Vauxhall Big Block helicoil guideThis guide was taken for an XE/LET block but should equally apply to C20NE blocks, and probably even the newer ecotec family of 2ltr big blocks.
A common problem occurs with these blocks when torquing the cylinder head. If the bolts supplied are too short then they can tear the thread straight out of the block. This typically happens on the head bolt hole nearest the dipstick tube.
Helicoilling is the process of repairing a damaged thread by drilling the hole oversize, tapping it to a larger thread then using a threaded insert to bring it back to original dimensions. This is typically a stainless steel insert, which if installed correctly is stronger than the original thread.
The kit you need for a Vauxhall big-block is
M11 x 1.25 which is not the most common M11 thread, so be careful when ordering to ensure the pitch is correct. It is also a good idea to make the switch to headstuds at this point, which are re-usable and put less strain on the threads.
Begin with the cylinder head removed
If the block is in-situ, take your time in preparing it so that swarf cannot enter the oilways, waterways or bores. I found the best way was to degrease the block then use a couple of layers of newspaper and duck tape to seal it all off except the hole being worked
Next up, use the supplied drill bit (11.4mm for this instance) to drill out the damaged hole. This makes it slightly oversized
Then use the supplied tap. This is the same thread as the
outside of the helicoil insert.
You'll then be left with a hole full of swarf
I used firstly a magnetic screwdriver to pick up as much of it as possible. The block (and therefore swarf) is iron so this works well.
Next I used a screwdriver covered in moly grease to pick up any leftover debris and also give the threads a light smear of grease
The result...
With a flash...
Next up take your helicoil insert and the supplied driver. Note the helicoil has a tang at one end (the bent bit!). This end goes into the block first. Adjust the driver so the insert sits snug inside it
Wind it into the block using the driver with a little downward pressure.
Be careful - winding it in too far may be irreversible! Check regularly to see the progress of the insert into the block and stop at the recommended depth (in this case - 1/2 turn from the top of the thread).
Go too far in and your stud won't bite!Here's the fitted helicoil
Finally get a hammer and the supplied tang-break
Use the break as a punch, and give it a short, sharp blow from the hammer to break it off, then recover the tang with your magnetic device.
Job done!
