My son is replacing the head gasket on his Rodeo, He bought a new set of head bolts and i believe he torqued them to spec. There were some issues with his installation (my words) so he had to tear the engine back down and start over. I know TTY bolts are supposed to stretch or yield upon reaching the correct torque, but I can't tell if they have stretched because I can't find the bolt specs on the googles. Since the bolts have only been through one torque cycle, can they be reused?
I wouldn't recommend it. You can't always see the stretch and it's possible that some stretched more than others. I would use new bolts to be 100% sure.
Without specs to check them (and assurance they're identical to the factory bolts) they're single use.
Just as a side note, steel can stretch and return to shape several times. Think of a car spring or a paperclip. Now, you can stretch it so much that it doesn't return to its original length. The thing is, I don't know which cylinder head bolts specifically are on that teetering edge of being too small for the job, or whatever other engineering reason there might be for TTY (you want to be in the middle of the 'spring' part before you stretch too much to preload for head gasket compression I think). So it's cheap insurance not to take a chance on that. I think there are some very rough rules, like if the threads still go in smoothly then the thread pitch is the same and the bolt is ok to use although that's nowhere near as thorough as what you might read in a repair manual. Likewise, if the bolt holds its torque value, how can you tell if it has been weakened or not? I feel like that can be explained without pages of physics terms. If you wanted to check yourself, I suppose you could get one new head bolt and measure them.
Just happened to find a length spec from a random supplier. They are nominally 100 mm. Using my trusty HF calipers (only slightly more accurate than a wooden ruler) i measured out one of the original head bolts at 100.35 mm, and one of the replacements at 100.78. So, TLDR, just told the kid he's gotta buy new head bolts. Thanks for the input everyone!
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