cylinder head bolt question

[nismo300zx1990]

I have a 1990 n/a and i have to take the right side head off to replace the head gasket qnd possibly the head it self. My question is do i need new head bolts when doing this? I know some cars have a one time use head bolts do to them stretching. Is the 300zx like that?

[t.mcginley.jr]

Yes, you will need new head bolts. The stock head bolts on all 300zx are one time use, torque-to-yield bolts. So after they are torqued down, they stretch and once you take them out they are no good. I think a new full set is $75-80 from Z1. Only ARP head studs are reusable.

[nismo300zx1990]

What would happen if i used the bolts again? Just curious because head gasket kits dont come with bolts kinda odd

[t.mcginley.jr]

A handful of people have reused old head bolts without issue supposedly. The problem is that when the bolt is torqued to 90 ft-lbs it stretches. So when you try and use them again and torque them down the torque won't be accurate. Again, a few people have reused them, some of which added 5 or 10 ft-lbs to make up for the stretching but that's just guesswork. If you torque the used head bolts to 90 ft-lbs, it's possible that they won't seal the head correctly because it really isn't at 90 lbs.

[nismo300zx1990]

That could have been my problem in the first place other then overheating my car. I used my old bolts because when i bought my rebuild kit it never came with head bolts so i thought i could use them again. Of course overheating my car didnt help either. I am just hoping i didnt warp a head. I have knocking noise when i accelerate sounds like exhaust leaking throught the head gasket.

I guess when i do the right side head i will do the put new bolts in the left side too. Now im pretty sure i dont have to pull the motor because i have had the heads off before when i removed the motor the first time. Any tips that will help me would be appropriated. I would like some tips on the timing belt to do this by myself if thats possible lol.

[Ziggy1621]

A handful of people have reused old head bolts without issue supposedly. The problem is that when the bolt is torqued to 90 ft-lbs it stretches. So when you try and use them again and torque them down the torque won't be accurate. Again, a few people have reused them, some of which added 5 or 10 ft-lbs to make up for the stretching but that's just guesswork. If you torque the used head bolts to 90 ft-lbs, it's possible that they won't seal the head correctly because it really isn't at 90 lbs.

Please explain... cause as you know I'm doing a build and haven't purchased new ones. The FSM calls for torquing them down, then pulling them back and re-torquing again. I'm confused as to how that is different than reusing them.. Just curious

[nismo300zx1990]

Ziggy i dont know if this will help but when i did my rebuild i didn't buy new head bolts and ended up blowing a head gasket. I also overheater my car so im not sure on what one was the coporate but when i redo my head gakets im replacing the bolts. If your in there dont take the chance but it's your choice.

[Ziggy1621]

Yeah, I had not heard of torque to yield before, so after some research I understand the why now. Good thing I saw this cause I should be coming back from the machine shop next week.

[nismo300zx1990]

Yeah i didnt use new ones because when i bought my rebuild kit it didnt come with bolts so i figured i didnt need them. But now i know

[t.mcginley.jr]

I honestly don't know why the torque procedure for the head bolts is like that, but I'm guessing Nissan engineers had their reasons. Must be something with how the steel needs to stretch. Only ARP head studs are reusable like that, but I think they're like $400-450. New OEM head bolts are $80 I think from Z1 or CZP