Reusing cylinder head bolts.
 

I'm replacing a timing chain on my daughters 04 sunfire with a 2.2 ecotec. I'm doing it on a budget for her.

Because I'm half way there I was thinking its would be a good idea to change the head gasket and clean things up. The car has 200.000 miles on it but it is unknown if it's the original engine.

The manual states the head bolts should not be reused. In the past I have reused head bolts if they were not stretched.

Has anyone reused head bolts on the ecotec engines without an issues. Or should I just get replacement for her.

Get a new set. You should never re-use headbolts. They are cheap.

When I asked for a quote to replace the head gasket on my 2008 2.2L, the guy told me he saw nothing about stretch bolts. However, the GM manual says to replace almost every nut and bolt. It's hard to tell when they really mean it!

I just checked eBay; they are cheap! You can get a gasket set including bolts for around $120. Some do indeed say "stretch bolts". Bolt sets around $25-$80.

http://www.ebay.com/itm/2002-06-GM-2-2L-DOHC-Ecotec-Head-Gasket-Set-with-Bolts-Kit-Z22SE-L61-L42-Engine-/160795252341?fits=Year%3A2004%7CModel%3ASunfire&hash=item257024d675&vxp=mtr

They're "Torque to Yield" bolts Lucky, new ones will be required to maintain proper torque and prevent future head warping and gasket issues.

Ok majority rules. New head bolts it is.

Better to do it now, then have to do everything all over again with possible more damage from a blown head gasket!

This got me thinking.

Aluminum alloy block steel bolts.

How does 22 lb-ft + 155 degrees stretch the bolt? How could you manage to stretch the steel/iron bolt before stripping the threads?

Just a tech question.

Think it's a matter of areas between the cross section of the bolt and the area that the threads engage in the block. (i.e. thread depth X how many turns around circumference of bolt). A very simplified example - bolt is 1 inch square cross section. thread surface contact is 5 square inches. Torquing bolt produces 20 pounds of clamping force. bolt sees 20#/1sq" = 20 psi . block sees 20#/5sq" = 4 psi. Again a very simplified, exaggerated example, but agreed, seems a steel bolt would win over aluminium block. But physics is weird, can't "screw" around with it ! (ow,ow,ow,ow ... :D )

Very good question donbrew.

My thinking is the industry's tech guru's came up with this "stretch" idea many, many years ago. The iron block and heads era.
I think the present day guru's just use some of the old terminology for present day engines specs.

In reality, I doubt stretch has much to do with it. But, new bolts should be used because the new bolt's threads will be clean and undamaged and will yield more accurate torque readings. The old bolts may have small trace aluminum deposits imbedded in the threads.

Well, that's my theory anyhow.

I get the torque plus degrees part, but don't see how that tiny bit of torque plus that small bit of degrees would have any effect on "torque to fail" fail being the operative word.

Thanks, now I can get some sleep!