I need some help reinstalling a head on a d16y5, I changed the head from one to another but head bolt #8 won't fully seat, it will get almost tight then get loose again. Does this specific bolt need to be longer than the rest? The other hear bolts all seat fine. Please help, I have to finish this by tomorrow so my parents can go to boise, its their only car.

 

That bolt is stretched or the threads are stripped you can try a brand new bolt or another used one and see if its able to be properly torqued,

 

Does the Y5 have the raised bump like the Y8 that needs the longer bolt?

Also OP didn't mention if it's the same head going on.

If it is and the Y5 is like the Y8, one of the bolts will be longer and could be in the wrong hole.