Stripped Holes in Cylinder Head for Intake Manifold Bolts

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Jimbo_74_Duster

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Hey All,

I was putting my intake manifold back on to my Small Block 360 when two of the bolts just spun upon becoming flush with the surface. After looking closely I realized the threads were definitely shot.

They are cast iron heads and I figured I could carefully attempt to heli coil them, but I realized the holes are on a slight angle from the surface of the heads. Does anyone have info on the angle of these holes? I thought I could measure the angles with a gauge of some sort and then use an aluminum block with the same angle drilled holes to steady the drill for the pre heli coil drilling.


Anyone have thoughts on heli coiling into a cast iron cylinder head at an angle? Any tricks or am I going about this the wrong way.

Thanks
 
Jimbo_74_Duster said:
Hey All,

I was putting my intake manifold back on to my Small Block 360 when two of the bolts just spun upon becoming flush with the surface. After looking closely I realized the threads were definitely shot.

They are cast iron heads and I figured I could carefully attempt to heli coil them, but I realized the holes are on a slight angle from the surface of the heads. Does anyone have info on the angle of these holes? I thought I could measure the angles with a gauge of some sort and then use an aluminum block with the same angle drilled holes to steady the drill for the pre heli coil drilling.


Anyone have thoughts on heli coiling into a cast iron cylinder head at an angle? Any tricks or am I going about this the wrong way.

Thanks
Click to expand...

Sounds like you are going about it the right way.
As far as I have ever seen the intake threaded holes are at a right angle to the head on cast iron heads.
Maybe set your intake on with a couple of bolts in it to help you see the angle.
 
Unless you have "64" or "65" 273 or magnum heads, they are Not at a right angle to the surface. Thanks Volaredon and Badlittlered. I measured them about 8 degrees so probably between 7 and 9 degrees is correct, but I do not know the theoretical correct angle. 3/8-16 thread. Or use Timeserts. Use a torque wrench, a beam type.

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I'm wondering if the heads or deck has been shaved, and the bolts might have been crossthreaded
 
Problem with intake manifolds is your four center bolts being so close to the manifold runners. If you don’t used the exact needed length they either don’t give full engagement or that go in at a bad angle. I try to open the holes a little bit.
 
Heli coil is the preferred repair, however I have seen nuts used on the center hole bolts to give the bolt something to bite on when stripped .
 
This reminds me, Years back we had a 67 GT 500 here for repairs. The owner bought a 2 four barrel intake and tried putting it on a 428 by himself. After not being able to thread the bolts in due to the block being decked. He hammered every one in flush. He called us after there was an intake leak. Not only did he destroy the threads he cracked the heads.

There are times you need to get someone experienced to help for damage control. Use a 1 inch tall hardened fixture with the proper hole for the drill bit being used. Also make sure the tab from the hela-coil doesn't end up in the engine. Had a Harley here with one caught in the oil pump. Trials can get Costly
 
I repaired a head once with a Time-sert, because it's an open hole on both ends I didn't expect a Helicoil to lock in like it would need to.
 
Being a tool and die maker during my working years, I would suggest you take it to your automotive machine shop.
 
Once there is a hole, a larger drill with proper grind will have to follow that hole. There is nothing to push it one direction or the other. It could be done with a handheld drill and be very close to the same center. I would consider larger bolts (even a metric size) before Heli coils and locktite. Of course you would need to enlarge the holes in intake a bit also.
The highest temp locktitie available might fail in a head, especially near the crossover passage. They get mighty dang hot.
 
Using a hand drill in my opinion is a bad idea, you can get an oversized hole real quick cause you are drilling with the outside edges of the drill and you can’t hold the hand drill steady enough. Better to do it on a drill press and best of all on a milling machine with head clamped down.

Helicoils are hardened and are a stronger thread than than the holes in the head now. Plus the hole and helicoil tap will produce a smaller hole than the next size up.

And **** metric anything.
 
67Dart273 said:
I'm wondering if the heads or deck has been shaved, and the bolts might have been crossthreaded
Click to expand...
I once was chasing the threads on a small block prior to hot tanking, it was the wrong tap.!!
It wasnt cheap to heli coil all of them
 
Most people don't realize that the major diameter of a thread is very close to the minor diameter of the next size. So where 3/8" threads are totally stripped the hole is now very close to the drill diameter req'd for a 7/16" tap.
 
RedFish said:
Most people don't realize that the major diameter of a thread is very close to the minor diameter of the next size. So where 3/8" threads are totally stripped the hole is now very close to the drill diameter req'd for a 7/16" tap.
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I would hate to try getting a 7/16 bolt in some of these holes that are close to runners. Heck I have to get the correct length bolts with 12 point heads on
Many of mine.
 
ch1ll said:
And **** metric anything.
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Boy you can say THAT again!!!!! On the bolt thread angle of a LA intake: it's NOT 90*to the intake flange. They are 7* off of that.i found that out the hard way. .I took a set of magnum heads in to a regular (non automotive) machine shop with a set of LA intake gaskets and told them to drill them out, they did so exactly perpendicular to the intake surface and when I went to assemble it the bolts only touched on the outer(valve cover side) surface of the intake, there was lots of daylight under the bolt heads towards the inside of the intake. I ended up using those heads with their original threads as manufactured on another magnum engine.
 
volaredon said:
Boy you can say THAT again!!!!! On the bolt thread angle of a LA intake: it's NOT 90*to the intake flange. They are 7* off of that.i found that out the hard way. .I took a set of magnum heads in to a regular (non automotive) machine shop with a set of LA intake gaskets and told them to drill them out, they did so exactly perpendicular to the intake surface and when I went to assemble it the bolts only touched on the outer(valve cover side) surface of the intake, there was lots of daylight under the bolt heads towards the inside of the intake. I ended up using those heads with their original threads as manufactured on another magnum engine.
Click to expand...
And this is a metric bolt's fault?
 
No not at all but metric hardware sucks all the while.
I have many thousands of dollars worth of SAE tools and these days all but useless unless I'm working on my own older stuff.
 
These days, lol. Metric cars have been around for 40 years now. Get with the game brother. My fractional tools gather dust.
 
pittsburghracer said:
I would hate to try getting a 7/16 bolt in some of these holes that are close to runners. Heck I have to get the correct length bolts with 12 point heads on
Many of mine.
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The other aggravating thing is when (not saying you particularly) people judge bolt size by the wrench size. I've seen 1/4-20 bolts that take a 5/16, a 3/8, a 7/16 and sometimes even a 1/2" wrench to work them, and some are even Phillips or straight slot or even Allen head ... all are a 1/4" threaded shank.
So many people think a 1/4" fastener is really a "7/16 bolt"
 
volaredon said:
The other aggravating thing is when (not saying you particularly) people judge bolt size by the wrench size. I've seen 1/4-20 bolts that take a 5/16, a 3/8, a 7/16 and sometimes even a 1/2" wrench to work them, and some are even Phillips or straight slot or even Allen head ... all are a 1/4" threaded shank.
So many people think a 1/4" fastener is really a "7/16 bolt"
Click to expand...
Or is that 6mm is 10mm. Lol. Just busting some balls bro. That's how we roll.
 
Bodyperson said:
These days, lol. Metric cars have been around for 40 years now. Get with the game brother. My fractional tools gather dust.
Click to expand...
Yeah the worst were the "1/2 and 1/2" (half SAE and half metric). Or when people assume that everything is metric.
The last trans my son sent in for a bench build (last one to that place as well, never again) a 4wd 727 no less, we sent it in with just enough bolts to hold the pan in place as we removed it upon removal to drain it..... It came back with a mix of 5/16 (which they are supposed to be) and M8 bolts holding the pan on... I ended up having to helicoil all but a few of them to stop it from leaking once it was reinstalled in his truck.
 
volaredon said:
Yeah the worst were the "1/2 and 1/2" (half SAE and half metric). Or when people assume that everything is metric.
The last trans my son sent in for a bench build (last one to that place as well, never again) a 4wd 727 no less, we sent it in with just enough bolts to hold the pan in place as we removed it upon removal to drain it..... It came back with a mix of 5/16 (which they are supposed to be) and M8 bolts holding the pan on... I ended up having to helicoil all but a few of them to stop it from leaking once it was reinstalled in his truck.
Click to expand...
If you wrench enough, you get used to it. It was bad during the transition. I assume they were using up old stock.
 
volaredon said:
The other aggravating thing is when (not saying you particularly) people judge bolt size by the wrench size. I've seen 1/4-20 bolts that take a 5/16, a 3/8, a 7/16 and sometimes even a 1/2" wrench to work them, and some are even Phillips or straight slot or even Allen head ... all are a 1/4" threaded shank.
So many people think a 1/4" fastener is really a "7/16 bolt"
Click to expand...


The millwright book of bolt sizing was drummed into my head. Lol. Sure saved me a lot of running.
 
if you have room why not carefully place a washer and nut on the backside of the bolt through the head with the valve cover off? You are only trying to achieve a seal on the manifold. If you get torque spec the manifold doesn't know it has a nut versus threaded?
 
Broke Farmer said:
if you have room why not carefully place a washer and nut on the backside of the bolt through the head with the valve cover off? You are only trying to achieve a seal on the manifold. If you get torque spec the manifold doesn't know it has a nut versus threaded?
Click to expand...


Please Dont make this harder than it has to be. Let’s drop a nut down inside the engine. Give me a break. Lmao.
 
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