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Re-coiled the cylinder head - lots of pics

12K views 31 replies 17 participants last post by  zed.inc 
#1 ·
Follow up to the below thread..........

http://www.m5board.com/vbulletin/e3...valve-covers-removed-lots-pics-long-text.html

Here's how I Re-Coiled the stripped cylinder head holes..........

Tools required for the job........
The custom tap for the re-coil states a 6.2mm drill is required, I went with a 6mm drill as the cylinder head is made from cheese figured it would be OK.



I chose the longer of the 2 coils, pictures show coils and located on collar bolt.......





The 6mm drill would nearly fit in the existing stripped hole so figured it would not be removing much material. I measured the depth of the hole at about 20mm and put a marker on the drill at 18mm so I would know when near the bottom of the hole.







Prepared the paitent for surgery, don't forget to cover your alternator as well.........





Put a bit of WD on the drill and in the hole, lined the drill up, critical part this, and gently operated the drill, as the alloy is soft the drill will want to snatch at it so you got to be careful here, small incremental rotations, plenty of lube!! As figured not much material left in the hole....





Cleaned the hole out with cotton buds and vacuum........



Aligned the tap, took some time over the this, setting it correctly on the first few threads is important. Took that long to set it up the sun had come out.......



I then started to cut the new thread, really took my time here, half turn forward, quarter turn back, removed the tap after 4 or so threads to clean up tap and hole and re-apply lube.........continued to do this until tap was fully inserted into hole.........





Removed tap, rinsed and repeated for other 2 holes, new threads looked good nice shine on them, no snags anywhere, tried to capture new thread.....



Coil on the insertion tool..........



Although I started the coil by hand to ensure it was seating correctly in the new thread.......



Drove coil until the top most thread was below seal surface on the cylinder head......









Snapped off the drive tag on the coil and vacuumed it out of the hole......



Cleaned up the new coiled holes..........



Inserted the collar bolt, threads felt great, nice and tight but no resistance whilst tightening down.............




Thats it, took me 2hours to sort all 3 holes out, it went that well I was tempted to do the other head but after inspecting the threads they seem OK so left them alone. I was ultra careful on every operation, after all its the cylinder head, not like if I mess this up just order another one.........Drei Bond 1209, new collar bolts and sealing washers turned up yesterday, plan to put the covers back on next week.....


Mike
 
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#3 ·
Gotcha........even so, presusre was on.........
 
#8 ·
yeah I had heard that Ger and was arguing with some fella in work who was stating that its just the same, I will now show him your reply..........nice one........
 
#9 ·
You've effectively turned an M6 thread into something resembling a M7 (or even M8) thread.
A larger thread will have a larger contact surface area, so the resultant force per unit area experienced by the aluminium is reduced, leaving more 'headroom' for applied force.

You've certainly got stronger threads!
 
#10 ·
Helicoils to the rescue again! Nice work.
 
#11 ·
Nicely done! Great pictures and write-up, thanks!
 
#16 ·
Thanks for the write up. That is almost exactly how I did it, but I did not use a drill, I Just used a drill bit with the tap tool to turn it. I was to scared to screw up with a drill.
 
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#17 ·
yeah I know what you mean about the drill, fortunately the drill speed is realted to trigger squeeze, still was scared of screwing it up........

and yes thats my garage 'M' PC with the F10 as desktop background.............
 
#21 ·
Looking at a similar repair. How did you ensure the new thread was cut straight and down?
 
#22 ·
The tap will ensure it will cut down as long as it picks up correctly, not sure if you could mess up on the 'down' bit of the cut, as for straight I started it off really slowly until I felt it bite into the aluminium, then spent a while ensuring it was square to the head using eyesight, once I was a thread or so in I stepped back and re-checked for alignment, best advice here is just take your time, slowly slowly, you'll be OK.
 
#24 ·
I know this is an old thread, but for those of you who have completed this repair, what size helicoil did you use. I mean I know M6x1.0 but how long were the coils themselves? I found a helicoil kit at PepBoys locally, but the coils inside are only about have the length of the threads on the original bolt. I've been down to AutoZone, O'Reilys, Home Depot, Lowes, Ace Hardware....with no luck. I'd appreciate any help. Thanks
 
#25 ·
I'll check the kit I used and let you know the length of the coil, I'm not back in work until Saturday so it'll be after then.
 
#27 ·
M6 x 1 - coil length is 4.4mm, M6 x 1.5 - coil length is 6.8mm, hope this helps
 
#29 ·
I left it flush with the top of the hole. Once the coil is in it will be solid, the bolts should be torqued down, I think it's 10Nm, the info is in TIS so I'd check to be sure, do you have TIS?
 
#32 · (Edited)
Gents,

I'm in the process of fixing a stripped thread that's causing a horrendous leak on my DD. I don't have access to a helicoil kit, just a standard tap-and-die set. I sourced the M6x1.0 helicoils separately.

To cut the new thread, the closest tap size I can find is a M8x1.0. However, when I measure the helicoil's outer thread pitch I find it fits 0.9 much better than 1.0. To confirm this, I tried to thread the helicoil through a M8x1.0 die. The helicoil wanted to stretch out to accommodate the larger thread pitch. My concern is that the M6x1.0 bolts will not fit if I try to force the helicoil to stretch in this manner. In fact, I used the valve cover bolt as a helicoil driver for the die test and it refused to go in more than a quarter of a turn.

A quick Google search seems to suggest that M8x0.9 is not a standard size. I'm chumped by this one. What can I do?

EDIT: Looks like M8x1.0 will work. I tried mounting the non-driver end on the M8x1.0 die and it twisted in beautifully.
 
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