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1275 Cooper 's' Head Stud Fitting

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#1 dunejunkie

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Posted 02 September 2019 - 07:29 PM

Hello all,

I'm in the process of rebuilding my 1275 for my innocenti. I bought the competition head stud kit from minispares for the 11 stud head. In the instructions, it says to drill an tap the water pump side stud hole (where the one head bolt previously was) from the existing 5/16" upc to 3/8" upc. However the hole has been helicoiled, not sure if thats from factory or as a result of a pulled stud. I removed the helicoil, and tried to thread the stud into the "un-helicoiled" hole. It began to thread smoothly at first and then about half way down it stopped. I tryed to run a chaser by hand and same issue. I understand that helicoil uses a special tap (sti tap i believe), but would it be possible to run a 3/8" upc tap through? Or am i better of redoing the helicoil and running an ARP head bolt? Thanks!



#2 carbon

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Posted 02 September 2019 - 07:49 PM

If you ever come across another block drilled for 11 studs, and with a helicoil fitted for a 5/16 UNC at the water pump end just leave it and use the orginal style bolt.

 

Your 5/16 UNC helicoil was almost certainly factory fitted. All of the S blocks and original 11-stud 1275 (Innocenti & 1300GT) blocks I have seen have had this 5/16 helicoil.

 

If you do refit this 5/16 bolt please remember the torque is only 25 ftlb. They shear if you try to get 45 ftlb.



#3 DeadSquare

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Posted 02 September 2019 - 08:05 PM

Hello all,

I'm in the process of rebuilding my 1275 for my innocenti. I bought the competition head stud kit from minispares for the 11 stud head. In the instructions, it says to drill an tap the water pump side stud hole (where the one head bolt previously was) from the existing 5/16" upc to 3/8" upc. However the hole has been helicoiled, not sure if thats from factory or as a result of a pulled stud. I removed the helicoil, and tried to thread the stud into the "un-helicoiled" hole. It began to thread smoothly at first and then about half way down it stopped. I tryed to run a chaser by hand and same issue. I understand that helicoil uses a special tap (sti tap i believe), but would it be possible to run a 3/8" upc tap through? Or am i better of redoing the helicoil and running an ARP head bolt? Thanks!

 

You are going to have to helicoil your block to take the 3/8" stud, which shouldn't be there.

 

The 5/16" bolt was to make people stop and think "Oh yes, that one is different"



#4 nicklouse

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Posted 02 September 2019 - 08:14 PM

just fit the bolt and tighten correctly. you do not need anything "comp" there.



#5 InnoCooperExport

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Posted 02 September 2019 - 08:25 PM

This all reads very familiar! My Innocenti 1275 block was helicoiled as well at the waterpump stud. I ended up using a the bolt from a 1275 S (10 stud 1 bolt) which was a perfect fit. Same as Carbon suggested. 



#6 dunejunkie

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Posted 02 September 2019 - 08:29 PM

Yeah 

 

You are going to have to helicoil your block to take the 3/8" stud, which shouldn't be there.

 

The 5/16" bolt was to make people stop and think "Oh yes, that one is different"

 

 

 

Yeah thats what i figured, however there doesnt seem to be enough meat in the block to drill for a 3/8 helicoil, so I will probably stick with the 5/16" bolt

 


 

just fit the bolt and tighten correctly. you do not need anything "comp" there.

 

 

Thanks for the quick reply, fitting an original sized bolt seems to be the most hassle free option, the head bolt i pulled out was in somewhat rough shape, and the ARP bolt is cheaper than the original part so i figured I would go with that. Had anyone ever used sealant on the threads of that bolt since the hole goes straight through into the water jackets? not sure its necessary, just a thought I had. Thanks



#7 nicklouse

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Posted 02 September 2019 - 08:31 PM

how do you mean rough shape? as long as the threads are sound it is good.



#8 Moke Spider

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Posted 02 September 2019 - 08:32 PM

Even if a 3/8" Stud is fitted here, you shouldn't torque it over 25 ft/lb as the deck there is fairly thin.



#9 dunejunkie

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Posted 02 September 2019 - 08:34 PM

If you ever come across another block drilled for 11 studs, and with a helicoil fitted for a 5/16 UNC at the water pump end just leave it and use the orginal style bolt.

 

Your 5/16 UNC helicoil was almost certainly factory fitted. All of the S blocks and original 11-stud 1275 (Innocenti & 1300GT) blocks I have seen have had this 5/16 helicoil.

 

If you do refit this 5/16 bolt please remember the torque is only 25 ftlb. They shear if you try to get 45 ftlb.

Oops missed this post. Thank you for the info. I do recall the torque being less for the bolt than the rest of the studs, but thanks for the reminder (its been 5 years since I did the head gasket on this motor. I will put a fresh 5/16 helicoil in and run the original size bolt. Thank you everyone for the quick replies!



#10 dunejunkie

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Posted 02 September 2019 - 08:37 PM

how do you mean rough shape? as long as the threads are sound it is good.

The bottom of the bolt has some corrosion/pitting on it. If that doesnt matter, then i suppose i could save a few bucks and reuse the bolt. However, i just figured if i am doing new studs all around, it wouldnt hurt to replace the bolt as well. Im putting an order in to minispares today for some cooling system parts.



#11 DeadSquare

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Posted 02 September 2019 - 08:43 PM

 "Yeah that's what i figured, however there doesn't seem to be enough meat in the block to drill for a 3/8 helicoil, so I will probably stick with the 5/16" bolt."

 

If you have removed the 5/16" helicoil and tried a bolt in the hole, will the replaced 5/16" helicoil now hold structurally ?



#12 Retroman

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Posted 02 September 2019 - 09:21 PM

If you have a tame engineer you can stitch it back to the original thread

 

It is better if the bottom does not go into the water jacket too

lxDtrH4.jpg



#13 dunejunkie

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Posted 02 September 2019 - 09:32 PM

 "Yeah that's what i figured, however there doesn't seem to be enough meat in the block to drill for a 3/8 helicoil, so I will probably stick with the 5/16" bolt."

 

If you have removed the 5/16" helicoil and tried a bolt in the hole, will the replaced 5/16" helicoil now hold structurally ?

I only threaded the bolt in by hand, i didnt use a wrench or try to force it in. I should be able to just install a new helicoil insert. I used an easy out to remove the old insert, and it came out quite easy.



#14 DeadSquare

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Posted 02 September 2019 - 09:37 PM

 

 "Yeah that's what i figured, however there doesn't seem to be enough meat in the block to drill for a 3/8 helicoil, so I will probably stick with the 5/16" bolt."

 

If you have removed the 5/16" helicoil and tried a bolt in the hole, will the replaced 5/16" helicoil now hold structurally ?

I only threaded the bolt in by hand, i didnt use a wrench or try to force it in. I should be able to just install a new helicoil insert. I used an easy out to remove the old insert, and it came out quite easy.

 

 

Fair enough.  Clean it well and use Locktite to help hold the helicoil in the block.







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