: Intake Manifold Cracked at Bolt Heads

05-01-09, 12:15 AM
Click pictures below for full size high resolution photos of intake manifold bolts.

For my 99 STS, i tightened up the Intake manifold bolts and studs to 8lbs. All but one of them cracked the plastic on the intake just around the bolt heads. a The thing is, the bolts kept moving and either my brand new torque wrench is a piece of junk or these bolts just keep drilling themselves into the intake manifold as if it was a knife cutting through butter, without ever hitting the 8lbs mark.

Could this be causing a vacuum leak in the engine or are the holes where the cracks are too far away from any air passages?

Because they cracked, maybe the intake manifold isn't seated properly? I think I might need to buy a new one. Repairs on this 99 STS are NEVER ENDING!

http://img7.imageshack.us/img7/7251/cracked1.th.jpg (http://img7.imageshack.us/img7/7251/cracked1.jpg)http://img13.imageshack.us/img13/2127/cracked2.th.jpg (http://img13.imageshack.us/img13/2127/cracked2.jpg)http://img12.imageshack.us/img12/119/cracked3.th.jpg (http://img12.imageshack.us/img12/119/cracked3.jpg)

05-01-09, 11:09 AM
It is taking too long to download those pics on dialup. I'll have to look at them at work, but if they are not holding the manifold down, then yes, it could be a vacuum leak. I'd pull them and check the threads before going any farther. If the bolts are turning THAT easy the threads may be stripped and you'll have to Helicoil them if the base metal is still OK.

05-01-09, 01:29 PM
The 10mm bolt torque on your manifold is 89 in/lb which comes out to 5.5 ft/lb. To accurately get to this (light) torque, you need an in/lb wrench.

A lot of torque values changed over the Northstar model run, so you really need a good Factory Service Manual for your particular car for this type of surgery.

05-01-09, 01:31 PM
I don't think those cracks are a leak point. I too used a torque wrench on those bolts during my HG project and I was amazed how many turns it took.