head bolt issue

godavid

SCCoA Member
I stripped out a head bolt. I had torqued it down to 42 and had started to torque it down to 52 when it stripped. I had tapped out the holes with a 7/16 #20 tap to clean out the holes. Where did I go wrong and how can I fix this?
thanks
 
Well first off the bolts are metric. You can figure out your error from there.
 
Most likely you are going to have to have a heli coil installed to repair the damage.
 
If you used that tap on every hole, I'm afraid that the answer most likely will be yes.

Could you not tell that you were removing threads as you ran it down? Always check the thread pitch of a fastener prior to chasing threads bud.
 
You are going to have to drill out the old threads and helicoil every single hole. They will require more than one helicoil per hole due to the depth of thead engagement. The thread that you shold have chased with is M11x1.5. Good luck your gonna need it. Thats a lot of work you got ahead of you, you will be better of pulling the block so you can drill the holes straight.
 
Aaaaaaaaghhhhhh!!!

I don't think that's a hand drill job. I'd want the block out of the car and taken to a machine shop for HeliCoil installation. You want those holes EXACTLY perpendicular to the deck surface. All kinds of bad things can happen if the head bolts are not right on the money. And, whoever you have put them in better know what they're doing. You don't want a bolt pulling out.

FYI: Virtually all fasteners on these cars (and most all cars since the 80's) are METRIC. Man, that's a tough lesson to learn the hard way...

JD
 
I have not seen a M11x1.50. The only thread sizes I've seen are M10 and M12. Taken the motor out is not an option. An M12x1.50 is too loose but M12x1.75 seems to be good. Can someone tell me if the M12 1.75 is the right thread size? thanks
 
M12 1.75 is the size and pitch on the mains and the heads I believe. I can check for you.
 
Thanks, I was just at O'Reilly's to order a heli coil. When I checked the thread size 12mmx1.75 the the bolt would only go in about five or six turns and stop. The 7/16x20 tap did the same thing. The guy that milled my heads told me this thread size but I don't think he knew that the bolts were metric. So, trying to find the right thread size seems to be a trial. Thanks for your help. By the way can I still use these head gasket they are the Mls? I'm looking into taking the engine out of the car. thanks again.
 
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The correct thread for the head bolts is M11x1.5, I have that tap. I just did my headgaskets last month, it cost me about $18 for it. You can get them about any where www.mcmaster.com . To use a helicoil you must redrill the hole STRAIGHT, then retap the hole with the special tap that comes in the kit and then install the helicoils. You will have to install mulitple helicoils per hole since the thread in the block is about 2 inches deep.
 
Also keep in mind that some of the head bolts may go into a water jacket hence the reason to have to use thread sealant. As you drill etc those bits may be going into the block....
 
While I hate to overstate the obvious, everyone else seems to be missing it!!

Since your already dealing with 7/16" holes, why not find the appropriate 7/16" head bolts or studs and fix it that way????
 
Can someone, please get me the correct head bolt size? Sorry but, I went to mcmaster.com and could not find 11mmx1.50 tap size. thanks
 
As stated by others, the correct head bolt thread size is M11 x 1.50. You'll have to look a bit harder for the correct tap.


cheers
Ed N.
 
thats what i thought ,was use the next size up on the bolt.

the M11 x 1.50 bolt isnt easy to find ,and your past that ,at this point and the tap might be hard to get as well

if you stick with metric bolts and or studs you'll want to be using 10.9 grade bolts or studs ,if american bolts or studs ,a grade 8

use the studs if possible...but try and up-size it

but that seems easier than the heli-coil and will work a lot better

http://www.engineeringtoolbox.com/inches-mm-conversion-d_751.html

maybe this might help ,it's a conversion table for threads (chart)

7/16 ,so this table says is 11.1125 the the next one down the list 11.5000 this depends on the tap used

anyway it might help to convert the size's
 
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Let's see if I have it right. If I tap with a 12mx1.75 that will be better than if I heli coil the holes? thanks
 
i would think that bolts or studs ( use studs ) ,would be the ticket ,skip the heli-coil idea if at all possible..
if metric - use grade 10.9 - if american bolts grade 8
check the chart might help
 
It has been suggested that since I screwed up on all the holes that I might want to get another block. My question is: are all the 3.8 fords the same? thanks
 
No all Ford 3.8 blocks are not the same. An SC block is completely different then all of them. There is an SC cast into all SC blocks, you need to use and SC block due to many different reasons.

M11x1.5 bottom tap
www.mcmaster.com

Part number 26015A216 $18.23

To use the M12 tap you will have to redrill all the holes with the correct drill size for the larger tap. I suggest at this point that you take the block to a professional and let them do it.
 
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