Broken Intake Tab

[SlopeStyleDJ]

So I just had my Dauntless Buick 225 V6 rebuilt at the machine shop, and I was reinstalling the intake when it all went terribly wrong. When I was giving the tenth and last bolt its final torque, the casting cracked. My Haynes book said 45-55 ft-lb, but I think it must be wrong. The tab that broke is the one on the front driver side, the tab that has been thinned to allow clearance for the distributor, and it also uses a Torx bolt for the shallower head.

What is the right torque setting?

How critical is the bolt in that location? Is it certain that my coolant will leak and wipe out the engine if not repaired?

Is it possible to fix the tab?

My old heads were shot and the machine shop rebuilt some newer ones, which meant I had to go with the newer intake that they boiled clean for me, and then i painted it. I'm hoping I don't need to source a new intake...

Any help or advise would be greatly appreciated!

 

[SlopeStyleDJ]

Picture of the damage.

 

[Hedgehog]

It could be welded. I'd try that first, talk to your rebuilder.

 

[Torxhead]

I would suggest installing a large thick flat washer under that torxhead to apply pressure on whatever is left. If you have to grind away those radiused corners to make to fit. It is quite a weak point. Maybe a hex head bolt would work better also.

 

[Lumpy Grits]

If that is a 3/8"x 18thd, dia bolt. Haynes(as usual)is dead WRONG on the torgue spec.
The torque should be in the 25-30 ft/lb range and all bolts tightened in a criss-cross pattern from the middle out, like you do head-bolts.
I'm think'n you have a warp'd manifold--
LG

 

[hdgapeach]

I'm with LG. You're at about double the necessary torque you should have.

As far as the busted intake, take it off and have a welder with plenty of cast experience weld the broken piece back on, or, have him build up the missing area so the hole can be re-drilled. You'll still have to "machine" the mating surface flat and make sure the top of the bolt hole is flat and square with the top of the head.

Check with the shop and ask if they machined the head surfaces. If not, straight edge the tops to see if they're warped (what LG said).

I'd also be on the lookout for another intake, just in case!

Haynes should be liable for stupid info they print (JMHO).

 

[Hedgehog]

I was also thinking that something is warped. If that tab were seated nicely against something solid it wouldn't have been able to move enough to crack like that.

Put a washer under that bolt, no matter what you use.

 

[SlopeStyleDJ]

Awesome advice. Thanks. I'll take it to the welding shop and check for flatness.

 

[Lumpy Grits]

Awesome advice. Thanks. I'll take it to the welding shop and check for flatness.

Keep us updated-

LG

 

[TeamRush]

You hit the head on the nail,
LG his the nail on the head.

The MAXIMUM torque is about 35 ft.lb. on a 3/8" bolt.
In cast iron, you are right on the edge of stripping the bolt hole out at 35 ft.lb. if nothing else goes wrong first.

The guys are CORRECT about the washer.
There are two things I see here, (Failure Analysis),

1. This isn't a clean 'Snap' of the cast/overpressure of the head of the bolt would have created.
This looks like the bolt head to shank was tapered and EXPANDED the hole to the point of breaking the cast in two places.

2. A washer will usually be STAMPED out of sheet metal.
It till have a TAPER on one side,
And a square edge on the other.
Make sure the TAPER meets the BOLT.
The two ROUNDED shoulders will mate.

Before install,
Check to see the washer will drop all the way to the bolt head.
That means the tapers MATE well.

If there is even a crack of light between the two,
Enlarge the hole slightly so the head hits the washer.

You can also use an OVERSIZE washer and grind away areas for clearance on the intake.
This will make a custom fit that will spread that load out to ALL AVAILABLE surface area on the intake,
Preventing another failure.

If the surfaces are painted, like yours, then torque the bolt to specification,
Come back in a week or so,
Loosen the bolt slightly and retorque.

The paint will migrate a little, since it's not a solid,
And that might allow the bolt to loosen.
Heavy paint will for sure migrate/be compressed out, so a retorque as you check things out after running the engine is a pretty good idea on 4 or 5 different inspections, a week to month apart.

 

[Lumpy Grits]

I wondered if that hole was undersized and or a bit 'off-location'.
One should always test-fit all fasteners for fit/clearance before install. If possible.
Not uncommon to 'adjust' a mounting hole with a larger drill bit.
LG

 

[Hedgehog]

Excellent point on the hole. I also noticed that the pieces looked a little twisted in place. Turning the bolt creates not just a downward pressure vector, but also a turning vector. Many forces at work. I believe a relatively soft washer will deform and take up some of the twisting vector on the tab.