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Loose head bolt geo metro

Geo Metro loose head bolts… I have a 96 Metro, and for some reason the head bolts loosen by themselves, leading to over heating and planing head … well you know.
I had a farm for 20 years and took care of all equipment myself, have rebuilt numerous motors, but this geo is the first I have seen where the bolts loosen. This is the third time. I know they are tightened right , because I have the tools and experience, but not with this. Other than jb weld in the bolt holes,any ideas?
thanks
pues

Are you sure they are tightened correctly? One first torques them in a very specific sequence to a number and on more than a few cars you have to tighten them according to some preset angle. In other words, you have to crank them another, say, 50 degrees (not sure if that’s required on a Geo but you may want to check the service manual. It is not an unusual thing, from what I’ve seen).
Also, usually these bolts are one time use because they are meant to stretch a bit. Could it be someone redid the head gasket and used the original bolts?
Could it be that the procedure calls for locktite blue or red, perhaps?

Like RemcoW said, I’m wondering if you’re not reusing head bolts that can’t be reused. A lot of the critical fasteners on cars (e.g. many axle nuts), including many head bolts are one time use.

When engines overheat the heads can warp and result in head bolts being too tight or too loose.

Have you tried realacing the bolts with new ones?

is the car a 3 cly. or a 4 cly. Fel Pro recomends new bolts on the 3 cly. but not on the 4 cly.

This is a good question. If this car uses TTY (Torque-To-Yield) bolts, they cannot be reused. They will never again achieve the proper clamping force once they are removed after being installed. The way you can tell TTY bolts is by the torque instructions. If the last torque spec requires a turn to an angle instead of a torque setting, the bolts are TTY and must be replaced anytime they are removed after being installed.

Here’s a quick tech guide to TTY bolts:freeasestudyguides.com/a1_4.html

The torque to yield scenario seemed to be a “drama queen” effort to appear superior, and requiring much greater care. Whenever reasonably possible I have replaced tty bolts but on occasions when doing so was outrageously expensive or impossible I have measured the old bolts and if all were uniform in length re-installed them with no problems. On a few occasions I have bought bolts salvaged from junked engines and used them to replace individual bolts that were apparently stretched. Engine design engineers have sometimes gone to great lengths to make themselves seem important. Did MoPar build an engine with non standard main bearing cap bolts and head bolts? I recall some outrageous problems with one of the Dodge 4 cylinder engines when the dealer’s only solution to broken bolts was a factory short block.