[Oscar The Grouch]

Focus man, Focus.,Oct 23 2009, 12:12 PM Wrote:Also remember that the head bolt that you have removed from the engine should not be re-used.  Most all of todays engines use a torque to yield head bolt that streches slightly when initally installed.  Get a new set of bolts.

Quote:Torque-to-yield bolts are exactly what they sound like. They stretch to the yield point as they are tightened. These bolts are commonly used where exact clamping loads are required on parts. You may find them used to hold cylinder heads, connecting rods, crankshaft main bearing caps, flywheels and front engine dampers. When a shop manual indicates that a bolt is to be discarded and new ones used, they are almost always torque-to yield bolts.

Buying new bolts every time one is removed seems expensive and a waste of time. After all, the old bolts still look good, but looks can be deceiving. Reusing the old bolts can cause expensive engine failure. During the tightening process, the bolts have been pulled to their elastic limit. The bolts actually stretch. Only new bolts can provide the even clamping force needed on today’s engines.

[right][snapback]296350[/snapback][/right]

That sounds like some marketing mumbo jumbo to sell more bolts. I've never ever heard of this.

edit: NVM. I see now. Here's the link to Car and Driver on the info.

http://www.canadiandriver.com/2004/03/03/a...-tightening.htm