Stripped Thread Aluminum Head
Thread Starter
Instructor
Joined: Feb 2005
Posts: 207
Likes: 13
From: Belmont California
Stripped Thread Aluminum Head
I stripped a thread for the intake manifold on an aluminum head.
How do I fix it- helicoil? Can I do it with out removing the head? Of course I'll have to remove the intake manifold.
Thanks in advance.
TT
How do I fix it- helicoil? Can I do it with out removing the head? Of course I'll have to remove the intake manifold.Thanks in advance.
TT
Drifting
Joined: Nov 2004
Posts: 1,628
Likes: 293
2020 C3 of the Year Finalist - Modified
go to your local auto store and buy a Helicoil set for that thread pattern......there should be directions on the package......
or you could use a tap and get a larger bolt ....which I wouldn't recommend though.
this happened to my cousins 98 mustang corbra on an exhaust bolt hole.....put the heli coil it and it's fixed! I've heard some say it's actually stronger than it was before.....atleast you're not having to fight an exhaust side bolt hole.....
hope this helps you
or you could use a tap and get a larger bolt ....which I wouldn't recommend though.
this happened to my cousins 98 mustang corbra on an exhaust bolt hole.....put the heli coil it and it's fixed! I've heard some say it's actually stronger than it was before.....atleast you're not having to fight an exhaust side bolt hole.....
hope this helps you
Drifting
Joined: Oct 2007
Posts: 1,458
Likes: 1
From: Collinsville MS
St. Jude Donor '08
You may also want to check with your Cadillac dealer. This is a common problem with the Northstar engines, they have a special tool and insert (not a helicoil) that supposedly fixes it forever. My dad just had to have his heads fixed on his.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,116
From: Crossville TN
There are several brands of threaded inserts: Helicoil, Keensert, etc. The one you want depends on the type of hole (thru hole, bottoming hole) and how secure you want it to be. You must have enough "meat" in the head to drill out the old threads and get a tap deep enough for the insert to fully engage. If you have a short bottoming hole, you may need to buy a bottoming tap (full threads all the way to the end). Just don't drill thru to a water passage, etc.
Thread Starter
Instructor
Joined: Feb 2005
Posts: 207
Likes: 13
From: Belmont California
I think it is a blind hole so I may need a bottoming tap. I'll do a search. I want a repair with simple tools and I don't want to take off the head.
Thanks for the responses so far.
TT
Thanks for the responses so far.
TT
Racer
Joined: Aug 1999
Posts: 414
Likes: 3
From: Mineral Ridge Ohio
Whichever thread repair insert you choose to use will require you to drill the hole to a diameter needed for a tap size that the insert is made for. Since you are dealing with a blind hole, you may want to try using a stop collar on the drill, as the drill will most likely "grab" and basically thread itself into the hole. It is probably a good idea to increase the drill sizes in very small steps until you are at the size the tap calls for. I am guessing the drilling will be done freehand, and by stepping up slowly with the drill sizes, they will be more likely to follow the centerline of the hole. Pack the flutes of the drills and tap with grease to keep the chips under control and there should not be any metal getting where it will do harm.
Thread Starter
Instructor
Joined: Feb 2005
Posts: 207
Likes: 13
From: Belmont California
Thanks blu73- my main concern is following the correct angle into the head with a hand drill. Following a hole that is already threaded, soft aluminum (compared to steel) and not being sure the hole is square with the intake face can all contribute to a hole at the wrong angle.
TT
TT
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,116
From: Crossville TN
With aluminum, blu73 is right. It's best to start with a drill size that will just clean out the threads first, then drill to the finished pre-tap size. Not drilling out much metal will lessen the chance of the drill "biting in" and overdrilling or wandering. When you set the drill in place at the start of the hole, eyeball how perpendicular the drill is in TWO directions [90 deg. apart], then try to maintain that position while drilling. Remember, the weight of the drill can cause it to go off line in aluminum.
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Burning Brakes
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Drifting
Joined: Apr 2002
Posts: 1,716
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From: New Baden Illinois
I just discovered the other day that one of my intake bolt holes was stripped. It would not clean up with a tap. It was the rear most hole on the driver's side. The engine is on the stand, so I did not have to manuever around the other parts in the car. I drilled it, tapped it, and inserted the helicoil all with the heads AND INTAKE still on the block. The hole on the intake is larger than the hole on the head.
I really did not want to use a helicoil, but it had to be done.
I really did not want to use a helicoil, but it had to be done.
Team Owner
Joined: Jul 2004
Posts: 40,368
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From: Redondo Beach, California
I've often wondered if it'd be a good idea to just go ahead and helicoil threaded holes, in aluminum heads and manifolds before installing them. Seems like good preventative maintenance. Particularly the exhaust manifold threaded holes in heads.
Drifting
Joined: Sep 2001
Posts: 1,427
Likes: 1
From: Boxford Mass
Aluminum threads are weak. I've used helicoils a few times and they work great. Before you start cleaning the threads out, get your helicoil. I think most helicoils even tell you what to use for your problem. They work great.
I would worry too much about keeping it straight. You aren't going to take much more than the threads off anyway. Just mark the depth with a piece of tape on the bit so you dont go too deep.
Team Owner
Joined: Jan 2006
Posts: 37,637
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From: Crossville TN
One of the "problems" with aluminum parts is that folks using them don't realize they should change the bolt torque values used for different sized bolts. The thread [in aluminum] is much weaker than a steel thread; but a steel bolt in aluminum "grabs" better than in steel. So the torque values are necessarily different. If you use the same torques as in steel, many times it is too much force for the thread.
