According to the old guru, the bolts are torque to stretch not torque to yield. The reason they cannot be reused is that they come new with a proprietary sealing compound already applied that is not multi-use."better head bolts" is not the answer. Northstar head bolts are torque-to-yield pieces - the action of torque plus degrees of additional tightening stretches the bolts and loads the cylinder head with clamping pressure. You cannot reuse Northstar head bolts - you install new ones any time the head is removed. Even in the newer engines, you have head gasket failure, you install either cylinder block bolt hole inserts (for new head bolts) or you stud the block. The main Northstar problem is failure of the (aluminum) cylinder block head bolt hole threads - one or more holes have threads fail, you insert all 20 holes.
Head bolts have changed, yes. Bolt total thread length was changed several times. Bolt/hole thread size and pitch were changed several times. You need to know which engine series you're repairing because the head bolts (among many other specs) were changed several times over the engine production run.
Get into www.rockauto.com. Compare the cylinder head bolt pictures for 2007, 2004, and 2002. (Click the little thumbnails for a zoom, simply close the zoom in your browser.) You should be able to see the thread length and pitch differences. 2004 saw the length/pitch change and that's easy to spot. The earlier ones are more subtle but part number comparisons show the differences.
According to the old guru, the bolts are torque to stretch not torque to yield. The reason they cannot be reused is that they come new with a proprietary sealing compound already applied that is not multi-use.
My source is a Cadillac engineer that was an original designer of the Northstar that used to frequent this site but got himself in trouble by truthfully answering sensitive questions. He said the head bolts are not torqued beyond the yield point but are torqued to a stretch length and are safe to reuse except for the proprietary locking/sealing compound that is applied during manufacture.Caution: Ensure the cylinder head bolts that are being used are the proper pitch or engine damage will occur. The thread pitch on the M11 cylinder head bolts and the engine block cylinder head bolt holes have been revised. In order to prevent engine damage it is important to identify which thread pitch is being used. Cylinder head bolts with a pitch of 1.5 mm have a thread length of about 48 mm (1.890 in) long. Cylinder head bolts with a pitch of 2.0 mm have a thread length of about 67 mm (2.638 in) long
Every fastener has an elastic limit, commonly referred to as its yield point, or more properly, "the threshold of yield." Up to this point, if the load on a fastener is released, the fastener will spring back to its original length. When a fastener is stretched into the yield zone, some of the elasticity is permanently lost. Once the bolt is stretched it cannot be used again. Sealing compound has nothing to do with it.
The problem was never the bolts, it was the threads in the block. GM never installed any inserts from the factory. Timeserts were an authorized dealer repair, and Norms inserts and probably others by now came along later. The jury is still out as to whether the lastest northstars are actually fixed or not. I feel that they may be improved.The next time you do a head gasket job on a northstar measure the old bolts to the new ones. The locking/ sealant is available in 8 oz. bottles. It took GM from 1993 to around 2004 to fix the head bolt problem. There first fix was to increase the length of the insert and kept the thread pitch the same. Most of the time the insert would pull out. I think in 96 some independent company’s came out with course thread inserts with new bolts or studs and they would hold. It took GM about 11 to fix the problem when it was solved years earlier. GM has spent a lot of money fixing the Northstar, Head bolts, oil leaks, oil consumption, chain tensioners , half case bolts and ect.
Your right the bolts are not the problem. It was the fine threads in the block. When we used the factory inserts there was an 8 to 10 comeback ratio. Then there great idea was to make the inserts longer and fine thread. Same ratio. Then they tried again with fine thread same problem. Then Norms came out with coarse inserts and bolts and if done right it never came back for head gaskets. I can’t tell how many times we had to do inserts on motor that we were replacing piston and rings for oil consumption, the threads would just pull out.The problem was never the bolts, it was the threads in the block. GM never installed any inserts from the factory. Timeserts were an authorized dealer repair, and Norms inserts and probably others by now came along later. The jury is still out as to whether the lastest northstars are actually fixed or not. I feel that they may be improved.