Exhaust manifold bolts

[billsz]

Hi,I'm on my 4th 280zx and have looked over dozens more. I have come to the conclusion that somewhere around 140K miles the last exhaust bolt by the firewall breaks off. Rencently I found a '83 280zx with only 71K miles and it is also missing that last bolt. Maybe its not a mileage thing and more of a year thing. I think it has to be a heat problem and that mileage has something to do with it. But this Z with 71K seems to early, and yes I beleive the mileage is correct, many things point to its accuracy. Does anyone have the true reason why all these bolts are missing. Thanks, Bill

[First Gen Z]

It's a real common dilemma with aluminum pieces that are held together with steel fasteners. Corrosion in the threaded aluminum bores locks the fasteners in place. Add to that the soft Japanese fasteners and you have broken bolts and studs. There are several methods of removal. Most are time consuming and tedious.

[hls30.com]

I think it has more to do with thermal dynamics and the stresses the heating and cooling cycles in that area create within a fastener. I think the corrosion issue is a problem that contributes to difficulty in removal, not in breaking before removal.

I have seen more cars in this situation than I can count, some with very low miles-but lots of driving cycles.

Will