Recently, one of my customers was baffled when I suggested a new $200 ARP High Performance Series Cylinder Head Bolt Kit to go along with his new cylinder head.
"...but nothings wrong with the the old ones."
Although that could be potentially true, spending $1,200+ on a prime new quality machine finished head and having your mechanic put in 15+ hours of labor to swap these, you might as well. Here's a few things to take into consideration as to why:
1. Bolts stretch. Like a spring, if you were to pull it apart then try to squeeze it back together to its original form, its pretty much impossible. As the bolts are tightened the first time, the amount of tension these bolts have to go through to keep the gasket connected is immense, and with that being said, its normal for a bolt to stretch as it tightens.
2. You wont get the same tension with already used bolts. We can use them again its not impossible, but its already gone through some wear.
3. Don't pay for double the work. You're mechanic doesn't mind, its our job. But if this happens, I gerantee you'll buy the new bolts the second time around (because the first ones will be obliterated) ;) .
Get it right the first time.
SO. If your curious and want to learn how to blow a new head gasket?
Don' buy new bolts.