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Block threads stripped torquing head

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M

Murray

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We were finishing up my engine rebuild today when, while torquing the ARP head studs, the threads in the block on one of the long studs stripped. Has anyone had any success using a heli-coil to fix this problem? Any other possible solutions?

Thanks,

Murray
 
Might help if we knew what car you are talking about; since your profile says you don't own a Triumph ...
 
I can't speak to the heli-coil, but I was reading up on the arp studs and their web site states that the head studs are to be hand-tightened only and that bthe torque applied to the nut will serve to seat the stud, just a heads up in case that may have contributed to your trouble.
Mike
 
Sort of a coincidence.

I've just finished putting ARP studs in my TR4A block. I could not "hand tighten" four of the ten studs, including both 9.5 inch studs, so I called ARP and Moss Tech Support.

The consensus was that there must have been grit or debris on the bottom of the seats. I swabbed them with a homemade engine Q-Tip dipped in oil, used a gun barrel rod and wire brush attachment to ream them, and then dried them out. Then blew out the holes with compressed air.

My fear was stipping the threads. In the end, on three of the four I had to apply a little force with the allen wrench fitting on the top of the bolts, and all seemed to seat well enough.

Are you sure you didn't just strip the last few threads; because there's plenty of thread below those. On my car the final adjustment had each stud sitting about 13/16 above the head face.

If you did badly stip the threads, I'm told a heli-coil will do fine, though if it were me I'd need a shop to handle that.

I'd like to hear how it all works out. Good luck.
 
Heli coil should work. However I recommend researching your local machinists to see if you can get Keensert inserts... In my opinion they are a better design for durability..
 
Does a Keensert or HeliCoil mean that a new kind of head bolt is needed? Tell me the head won't need to be drilled out, too?
 
Kentvillehound said:
Tell me the head won't need to be drilled out, too?
Click to expand...

I could tell you, but I'd be lying.

Where exactly did the stud snap, and did you extract all of it?
 
No, the beauty of the Helicoil and probably the other brand also, is that you will drill out the hole in the block and use the same bolts that you were going to use. You have to drill out the hole, re-tap it and insert the helicoil. The tap, inserts and insertion tool comes with the kit. you have to have the drill bit and the drill. I just bought a 5/16 X 18 kit today to redo some transmision bolt holes. Local auto store $20.00.

I would make sure that the stud hole you're working on is clean and at the right depth. I had to clean all of mine out. I used a tap with an extension to clean all of mine out, as I recall it was tedious and time consuming job. Also remember that the left rear (manifold side) is a different length because of the lifting hook that goes there.

Good luck with the fix.

Tinkerman
 
The big problem with putting in a heli-coil in one of those deep holes is access. As Tinkerman mentioned, chasing the threads required an extension. The same would go for a drill, and you'd have to get the right type insert tool...the one that looks like a tap, not a prewinder type. The other problem you might encounter is the diameter of the hole leading down to the threads. IIRC, that hole is not much wider then the stud diameter which means a heli-coil tap and the insert itself might not fit down in there.
 
Kentvillehound said:
Tell me the head won't need to be drilled out, too?
Click to expand...
IF the original threads are stripped all the way to the bottom of the hole, you may not need to drill. The stripped threads will be just slightly smaller than the drill size, and the special tap will act as a reamer to some extent. I've done this, tho not way down inside a TR block like that.

My approach to drilling would be to grind a square on the drill shank (same size as the tap) and use a tap extension on it. You're likely going to have to find or fabricate a special extension anyway, since no ordinary collet is going to fit down that hole; so use it for the drill as well. Then you get to drill the old fashioned way, with no power assist
grin.gif


It does work, oddly enough ... I've even drilled a hole for a Helicoil by just holding a large chuck in my hands since there was no drill motor available to me that would take such a large bit/chuck (15mm as I recall).

Long drill bits in a suitable size do exist, but the example I found at Rutland was over $40.
 
martx-5 said:
IIRC, that hole is not much wider then the stud diameter which means a heli-coil tap and the insert itself might not fit down in there.
Click to expand...
The tap & insert are only one thread depth larger (on each side) than the original thread (about .550" for a 1/2-13 according to the catalog I have), so I think they will fit. At worst, you'll wind up cutting light threads all the way down and having to screw the insert down them.
 
In my TR3A (with a TR4 engine), one of the shallow head bolts had already been helicoiled. The block was also a little bit cracked around that area (on the water jacket side), but not enough to cause me any real concern. It was actually drilled out incorrectly, and the helicoil was installed about 5 degrees off vertical, which made getting the head off interesting, but getting it back on impossible with the stud inserted. I ended up installing all the studs except that one, then threading that last one once the head was on. It worked fine.

I used the ARP studs. Step one is to clean out the holes. I ran the stud down in the hole and ended hitting debris on most of the deep ones. I used a pick with some paper towel on it and a lot of carb cleaner to loosen up the gunk.
 
On the last tr3 engine I rebuilt, I pulled out all the head studs to inspect them for straightness and whatever. I had to use a pipe wrench on a couple and I found that unsettling. The long ones were really stuck. After I got them out, I notice a lot of sludge build up. I was able to get a tap in there with some spray oil and clean out the threads. I think I used a ÂĽ socket on the back of the larger tap and perhaps a magnet. Anyways a lot crap came out of there and I was quite nervous about breaking the tap off down in there because that would be a big problem. Anyways would it be possible to clean yours out good and gain some ground and see if you can get a new stud to hold. The actual factory taped hole was deeper than I thought it would be after I got the junk out by maybe 3/4.
 
I'll ditto the part about being sure the hole is clean (seems kind of obvious?). I soldered a length of small copper tubing to an air gun, so I could stick the tip of the tubing into the hole and blast stuff out.
 
I had a head bolt that refused to come loose. It was one of the deep ones and it required a couple of heat cycles to finally break free. All the others came out fairly easily.

00018.jpg


It was the one in the top right, to the left of the red prybar... Looking now, I see some rust from the head gasket leaking. That's probably why it was difficult to remove.
 
When it happened to me, I was able to access a mag drill. You find center, activate the magnet, make sure the drill is vertical, and start boring. If you can find one, do it. They work wonderfully.
For a heli coil, the recommended drill size for 1/2" is 17/32".
A thin wall keensert requires a 37/64" drill and a 5/8-11 tap, while a heavy duty insert requires 45/64" and a 3/4-16 tap.
 
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