Topic: M6 thread repair tips?

[Don R]

 I have a head or two that are pretty nice except the M6 threads are pulled. What are the best repair options for helicoil, timesert, big sert? How deep do the threads need to go? 
 

[Pbeattie89]

I've used helicoils with good results. I would get a 1.5d  kit(the length of the insert is 1.5 times the width of fastener). I am no expert by any means, but cycleX advertises using helicoils in their cylinder blocks. They should be plenty strong enough to use in the head.

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[willbird]

The non branded terminology for heli-coil is "STI".....using that term to search might give you more results.

I would think 2x diameter would be plenty but I might get some 1x coils to have on hand too.

Bill

[CycleRanger]

For a low-torque M6 a helicoil should be sufficient.
I had to helicoil one of the studs on one of my XS650 tappet covers a while back.
Because it was very stripped I chose to drill it out to M7 and used a M7 helicoil then installed a M7-M6 step-stud. It worked very well.

[bryanj]

Keenserts or timeserts are better but need more metal arround the hole

[calj737]

You could probably jump up to an M7 bolt actually. A thread forming tap should have no problem enlarging the hole enough to simply use an M7x1.0 bolt. Sure, these bolts will be different, but you could use intentionally different headed bolts to help distinguish them.

[Don R]

 I have a standard M6 helicoil set but no deep ones, I now know the terminology a little better and to look for 1.5x or 2x. and STI.
  M7 might be OK on the ones that haven't already been fixed by a ham-handed sasquatch. L0L! When I saw 5/16" in my early diecast (pre-23,000)? head I didn't want to believe it. Even under the nickel washers, although the Allen heads did work out there. 

[Kelly E]

M7 might be OK on the ones that haven't already been fixed by a ham-handed sasquatch. L0L! I did 1/4" x 28 once and still regret it.
  When I saw 5/16" in my early diecast (pre-23,000)? head I didn't want to believe it. Even under the nickel washers, although the Allen heads did work out there.

Our 80' GS 1100E four 5/16"x18 helicoils on cylinders 2 and 3 exhaust. We tried to find 5/16" to 8mm conversion studs but no luck. It was barely okay work so we chose to not mess with them.

[Don R]

 I ordered a set of stainless M6 in several lengths.

[HondaMan]

I use the SS threaded inserts, matching the lengths as closely as possible with the standard lengths of the inserts.
In the case of those 4 long bolts that hold the cam bearing towers in place: before the K3, most of the heads had as few as 3 threads (max 5) in those holes. I use full 1/2" (12mm) length versions in those holes - which Honda threaded to full depth starting in the K3 for sure, and some of the K2.

[madsundaysurvivor]

If you don't want to go crazy in the future, I would use Helicoil M6 where there is space.
 If you finally tap to a larger size and use stainless steel screws on cases aluminium, be sure to use copper gauze, otherwise, over the years, galvanic corrosion due to the difference in materials may cause you to lose the thread when removing them.

[PeWe]

I prefer Time-serts, especially for cam towers. The 4 studs + corresponding bolts + the 4 center for longer bolts.
The longer bolts sit where there are more meat in head so the thicker self threading inserts can be used.

**** Note! ****
Be aware of not drilling too deep in the 4 center thread holes for cam holders. Easy to drill thru  and get oil leak. My K2 head I link to below had  holes thru by its earlier owner(s).
I created new bottoms with JB Weld just before thread inserts went in.
Checked depths OK with cam tower tightened with its longer bolts without hitting the new bottoms. Not fun to find out too late when head is finally tightened on engine.
*********

I have had several helicoils that went bad. The bottom part that should be broken when the coil is driven where to sit did not go off completely. Made life for bolt very bad. That with the original heli coils. The cheap copies worked better.

For covers, time serts, the softer black ones. Easy to grind off flush if it has a stick out.

Time sert kits cost some.
I have for M6. Even a big sert M6 kit for next size when even the std Time sert has gone.

I replaced some bad helicoils with time-serts. Drag out the coils and could mount the time-sert direct. Same thread. I glued the inserts with Loctite 272.

I got a sudden bad M8 for exhaust stud. Did not bother with an expensive Time-sert kit. Bought a cheap helicoil type of kit.


A head thread repairs.http://forums.sohc4.net/index.php/topic,180088.msg2088008.html

I later used that head on my K6 for a while. It is now on the shelf as a spare.

It had been ported by an amateur many years ago. Probably for +900cc.
I got it cheap. My local shop updated the port jobs and opened it up for 34mm in valves.

It got the chambers fixed too + decking it to shrink chamber diameters and volumes.

http://forums.sohc4.net/index.php/topic,184356.msg2134543.html#msg2134543

One thing leads to another!

[MRieck]

Helicoils work well if you do a couple of things. As Per said measure depth prior to drill....I use the depth gauge on the Vernier calipers. Invest in a 6mm STI bottom tap. Use the tapered tap first then follow it up with the bottom tap....it prevents the insert binding in the hole. Use threadlocker on the insert and put a small chamfer on the drilled out hole....the insert screws in much easier with the chamfer. Also....use the longest Helicoil you can get in there....in general I use a 12mm length.

[HondaMan]

Helicoils work well if you do a couple of things. As Per said measure depth prior to drill....I use the depth gauge on the Vernier calipers. Invest in a 6mm STI bottom tap. Use the tapered tap first then follow it up with the bottom tap....it prevents the insert binding in the hole. Use threadlocker on the insert and put a small chamfer on the drilled out hole....the insert screws in much easier with the chamfer. Also....use the longest Helicoil you can get in there....in general I use a 12mm length.

+1
On all of these!
I've been using the clone versions of the M6 insert lately because their tang (on the bottom) breaks off easier than Helicoil's own. That's good and bad: good if you follow Mike's tips, bad if you don't bottom-tap the hole. Having a small, flat-bladed screwdriver with magnet on the shank will help to fish out the leftover piece. When they are 'stainless steel' inserts (which I favor) it is almost always type 18-8, so it will come to a magnet.

[Don R]

  I got a set of 100 with 5 lengths from 1xDia to 3xDia so I assume that's 20 of the 18mm deep ones. They are the stainless-steel ones.
   On the early head and cylinder, I'm going to leave the 4 holes under the nickel washers 5/16" and just use the Allen head bolts that were there. The oversize holes under the cam towers get bushings that I bought already. The cam towers will get epoxy and tube sleeves.
  The tips here will come in handy, I'll check to see if the PO drilled through the head and if so, I'll epoxy the bottoms.
  I have a couple otherwise unmolested heads that the threads felt soft when torquing so I stopped there, they get the m6 coils.
 
  Thanks for your expert input, should save me learning a couple things the hard way.

[rotortiller]

I use SS heli-coils or variant and I try to employ the longer ones to take the bolts full thread length as much as possible in high stress applications like cam towers with high lift cams/strong valve springs. That will give the strongest attachment, and much stronger than timeserts etc. ,  that has been structurally tested and proven.  A couple of interesting videos, but as they say with the horse and water lol.                                 

           

[69cb750]

Another video ...

8mm bolt
---------
EZ LOK $60 712ip
HHIP $20 528ip
Time Sert $100 508ip
Heli coil $25 473ip
Aluminum threads 326ip

[PeWe]

Helicoils work well if you do a couple of things. As Per said measure depth prior to drill....I use the depth gauge on the Vernier calipers. Invest in a 6mm STI bottom tap. Use the tapered tap first then follow it up with the bottom tap....it prevents the insert binding in the hole. Use threadlocker on the insert and put a small chamfer on the drilled out hole....the insert screws in much easier with the chamfer. Also....use the longest Helicoil you can get in there....in general I use a 12mm length.

Glue the coil will definitely help.
Let it cure well before the bolt goes in.

I like the Time-sert where the bolts will be removed and fastened many times.

Or thin goods. I believe a glued insert will  work better then.
M6 is max 9Nm maybe 10Nm with a long thread .

Time sert kits are very expensive. A cheap helicoil type set is a must have anyway. I have both M6 and M8.

[MRieck]

Helicoils work well if you do a couple of things. As Per said measure depth prior to drill....I use the depth gauge on the Vernier calipers. Invest in a 6mm STI bottom tap. Use the tapered tap first then follow it up with the bottom tap....it prevents the insert binding in the hole. Use threadlocker on the insert and put a small chamfer on the drilled out hole....the insert screws in much easier with the chamfer. Also....use the longest Helicoil you can get in there....in general I use a 12mm length.

Glue the coil will definitely help.
Let it cure well before the bolt goes in.

I like the Time-sert where the bolts will be removed and fastened many times.

Or thin goods. I believe a glued insert will  work better then.
M6 is max 9Nm maybe 10Nm with a long thread .

Time sert kits are very expensive. A cheap helicoil type set is a must have anyway. I have both M6 and M8.

Yes...watch the torque and don't discount your mechanical feel. Honda torque valves are too high. A 12mm helical will yield max torque. As Don said.... 12mm Helicoils etc have maximum thread grab...that's what you want....you will break a bolt before pulling that insert out.