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Stripped Threads-Best Fix?

Kaw-Liga

Sr. Member
Joined
Aug 30, 2006
Messages
533
Loc.
Palm Coast, FL
Hey all, this might sound kind of "newbie-ish" of me, but one of the bolts connecting my thermostat housing to my AL intake manifold is stripped out causing a slow leak of coolant. It is slow enough that I can drive it to work and back home(about 7 miles round trip) I just check the fluid before I leave. I will be taking the manifold off this weekend to fix it. I got my new intake gaskets, and new thermostat housing gasket, but what I know that best way to fix the hole. The way I see it is I could drill and tap to the next largest hole or have a heli-coil installed. I know nothing about heli-coils, just that it is an option. So what are your thoughts? Drill and tap or have a heli-coil installed for me? Thanks for the info!

Rob
 

maws75

New Member
Joined
Nov 13, 2006
Messages
37
I`ve used a heli-coil to fix stripped out threads on my manifold before held up good , just have to be careful drilling the hole so you don`t go to far.
 
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OP
Kaw-Liga

Kaw-Liga

Sr. Member
Joined
Aug 30, 2006
Messages
533
Loc.
Palm Coast, FL
I think I'd let the local machine shop do the heli-coil if I go that route. I was told that the kit was about 30 bucks and that they'd do it for me for the same price. It doesn't matter that the manifold is Aluminum does it? I wasn't sure if that changes anything. If I do the heli-coil do I only have the one hole(stripped one) to worry about or would I/they do the second hole too. I want the bolts on the housing to be the same size, so I guess I'm asking if the heli-coil changes the size of the hole like drilling and tapping would do? Does that make sense?

Rob
 

70_Steve

Old Guy
Joined
Dec 13, 2002
Messages
8,317
If the 5/16 bolt stripped out, it would be repaired with a helicoil that would leave you with a 5/16 bolt hole. Helicoils are the best way to go. If I remember, outboard motor manufacturers were installing helicoils (or equivalent) as stock. If I had a machine shop install one, I'd have both done. But then, I'd buy the helicoil kit and do it myself, just so I'd have the kit for future repairs.
 

BwoncoHowie

C-4 Wizard
Joined
Nov 11, 2002
Messages
3,571
Heli-Coil. If its the upper hole you can install a Heli-Coil without removing the intake manifold. If its the lower hole then do both, only because there is the potential for a lot of corrosion to form in the area. If you can tap a hole you can install a Heli-Coil. Heli-Coils are stainless steel thread inserts that are actually stronger than the original aluminum threads cut into your manifold. If you can drill a straight hole, and if you can hold a tap straight while cutting threads, then you can make a beautiful repair using a Heli-Coil.
 
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Kaw-Liga

Kaw-Liga

Sr. Member
Joined
Aug 30, 2006
Messages
533
Loc.
Palm Coast, FL
Thanks guys, I actually just got home from work and was reading about them. It is the bottom hole so I will take off the manifold and yeh, I think I'll do both and yeh, i think I'll do them myself! Then I cam hold my head up high when that leak stops cause I'll know I fixed it myself!

Rob
 

RRRAAAYYY2

Bronco Guru
Joined
Nov 10, 2004
Messages
1,684
Loc.
Brantford, Ontario
Dont fix what aint broke. Unless the top hole looks like it is ready to be stripped, I wouldnt mess with it. Wait until it is stripped and then do it.

Helicoils are no better than the original thread, as they are installed just like a bolt. They are more a thread reducer bringing the thread down to one size lower themselves. My point is only: 1) You can strip a helicoil just as easily as a regular threaded hole, 2) And they dont increase the foot lb force you can use to tighten bolts, in other words you cant use a Johnson Bar on them.
 

70_Steve

Old Guy
Joined
Dec 13, 2002
Messages
8,317
Helicoils are no better than the original thread, as they are installed just like a bolt. They are more a thread reducer bringing the thread down to one size lower themselves. My point is only: 1) You can strip a helicoil just as easily as a regular threaded hole, 2) And they dont increase the foot lb force you can use to tighten bolts, in other words you cant use a Johnson Bar on them.
I don't mean to start a helicoil debate, but... :p

To me, helicoils are better that the original thread in aluminum. First, you don't get the galling that you would with aluminum when you forget to use a thread lubricant. It's the galling, not over-torquing, that usually causes the thread failure. Yes, the stainless will gall, if that's your intention, but much less so than the aluminum with a mild steel bolt. Second, you have to tap a larger threaded hole to insert the insert (;D ), so if you accept that the stainless is stronger that the aluminum and if there's a failure, it will be the aluminum, you now have more thread contact area and should be able to apply more torque before a thread failure occurs. In theory, of course...

There really is a reason why a lot of manufacturers are installing helicoils as stock in aluminum casting. I mentioned outboard motor manufacturers in my previous post.

Sorry, RRRAAAYYY2. Just giving you a hard time!!;)
 

357Bronco

Sr. Member
Joined
Oct 13, 2006
Messages
999
Loc.
New Hampsha
Dont fix what aint broke. Unless the top hole looks like it is ready to be stripped, I wouldnt mess with it. Wait until it is stripped and then do it.

Helicoils are no better than the original thread, as they are installed just like a bolt. They are more a thread reducer bringing the thread down to one size lower themselves. My point is only: 1) You can strip a helicoil just as easily as a regular threaded hole, 2) And they dont increase the foot lb force you can use to tighten bolts, in other words you cant use a Johnson Bar on them.

I disagree, properly installed, with loctite, I believe the heli coil is stronger and is less prone to future problems. I'd do both. But we all do things different, what do I know?.....I enjoy removing, gasket cleaning, re-sealing, and installing the same manifold for second or third time as much as everyone else.
 

bax

Contributor
Old Member
Joined
Aug 22, 2005
Messages
14,491
Ok I just want to add, go with a fine thread / coarse thread stud and after you install the Helicoil epoxy or locktite the stud into the manifold and use a nut and washer with some anti seize on it and you will never have a problem again with that bolt.
Bax
 

TwoHorses

Jr. Member
Joined
Feb 14, 2006
Messages
114
Loc.
Milwaukee
My .02

We only use heli-coils here at work when the design calls for repeated removal of the bolt (or whatever your threading into the tap). If the thread is only being utilized as a one time install... then the heli-coil isn't needed. It when you frequently need to remove something that the heli-coil comes in handy... for the obvious reason it is steel and has a better wear quality. The heli-coils use a tap anyhow into the aluminum to gain grip. The only difference is some heli-coils utilize pins to knock in to prevent them from slipping... kind of like adding a key on to a shaft.

I read fast thru this thread.. so sorry if I repeated anyone. The one thing I didn't see that I would be concerned with is the frag/shavings from the drilling and tapping. I'd hate to load that stuff up inside my manifold!!! Take care in blowing that stuff clear.

Good luck!!

:)
 

BwoncoHowie

C-4 Wizard
Joined
Nov 11, 2002
Messages
3,571
Thanks 70_Steve you explained it very well and I agree. I have been installing Heli-Coils in aluminum Transmissions for decades with no issues with strength whatsoever, and sometimes you have to get that T-stat housing TIGHT to make it stop leaking. They really help when there is repeated tightening Like a T-stat that is recommended by many manufacturers to change it every 2 years. Or say an alternator adjustment bolt for belt tension. Sorry, RRRAAAYYY2, you are a super sharp electrical guy but this is one area I disagree. :p

I don't mean to start a helicoil debate, but... :p

To me, helicoils are better that the original thread in aluminum. First, you don't get the galling that you would with aluminum when you forget to use a thread lubricant. It's the galling, not over-torquing, that usually causes the thread failure. Yes, the stainless will gall, if that's your intention, but much less so than the aluminum with a mild steel bolt. Second, you have to tap a larger threaded hole to insert the insert (;D ), so if you accept that the stainless is stronger that the aluminum and if there's a failure, it will be the aluminum, you now have more thread contact area and should be able to apply more torque before a thread failure occurs. In theory, of course...

There really is a reason why a lot of manufacturers are installing helicoils as stock in aluminum casting. I mentioned outboard motor manufacturers in my previous post.

Sorry, RRRAAAYYY2. Just giving you a hard time!!;)
 

RRRAAAYYY2

Bronco Guru
Joined
Nov 10, 2004
Messages
1,684
Loc.
Brantford, Ontario
No, it is all good. My experience with them is on smaller bolts, so maybe that is why I see them the way I do. Do notice in their own video that they dont claim you can increase the ftlb force of the bolt, just wear and even clamping force (good things fore sure).

Dont get me wrong, I am not against helicoils at all, and I am not disagreeing with what you guys are saying. My main points where "Dont fix what aint broke" and helicoils are good but they are not a magical product with no possible downside, you can mess up the install. And if you do then you are into welding and retapping, which is $$$. Which I only pointed out because of my first point.

The last time we bought any helicoils we bought them in bags of 100. But as I said all small sizes, 1/4" and under 99 percent of the time.
 

El Jefe

Bronco Guru
Joined
Oct 20, 2002
Messages
1,166
Do notice in their own video that they dont claim you can increase the ftlb force of the bolt, just wear and even clamping force (good things fore sure).

and to beat a dead horse from a LONG time ago: the clamp force comes from bolt stretch; higher torque on the bolt = higher bolt stretch* = higher clamp force.

(*if done within a specific range, dictated by the bolt's and nut's size and material)...;D
 

blubuckaroo

Grease Monkey
Joined
Jun 11, 2007
Messages
11,795
Loc.
Ridgefield WA
Why was it stripped?

I've had the same thing happen putting a thermostat housing on an aluminum manifold. It's usually on the lower bolt on a small block ford since the bolt is partially covered by the timing cover and the bolt sometimes gets started cross threaded. It is important to chase the threads before reassembly. Since a tap is too long to fit the lower hole, I use a grade 8 bolt with a groove cut in the threads that works as a tap to chase the threads. If you need to overtighten it to get a good seal then something is wrong with your sealing surfaces. Run a draw file accross both to make shure they are real clean. I've seen lots of housings with warped faces that couldn't seal.
 

fordguy

Contributor
Bronco Guru
Joined
Jan 23, 2005
Messages
5,497
what kind of thermostat housing do you have. those fancy chrome steel ones are notorious for not sealing.
 
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