what causes a hairline crack?

[66nathen]

66, 289, 302 heads and rods......had a blown head gasket....got it fixed...still have coolant getting into my oil. Shop thinks its a hairline crack...they said they're high pressure overnight tests showed no signs of moisture left from the blown head gasket. a week later i get milky oil again. now they want it for 3 days or so for more testing. So my question is, what causes a hairline crack?

 

[hotrodredneck]

a lot of things could cause it, detonation, overheating, poor handling of the head before it got to you...bad casting, bad machine work...the list goes on

 

[66nathen]

when i had my head gasket fixed, they sent the heads to another shop for checks, cleaning and other work. could they have cracked it possibly?

 

[hotrodredneck]

hard to say....no way you would be able to pin it on them, since so many things could have done it...heck even torquing it down wrong could have done it

 

[ratio411]

How are you using 302 rods in a 289?
They are too short for a 289 crank...

 

[ForceFed70]

Are you sure it's not the head gasket again? Always take what a shop tells you with a grain of salt. Especially when it comes to a failed fix, or reoccuring problem.

Last time this sort of thing happened to me it was because of a warped cylinder head causing poor head gasket seal.