Snapped 2 head bolts

[2ndwind]

Just FYI. I was helping a friend put his engine together. He swears by antisieze. We put some on each bolt, torqued all to 29 ft-lb then up to 61ft-lb as my manual called for. We snapped the first two and didn't continue. Luckily, because of the antisieze one unscrewed even though it was 90% twisted apart. The other broke of completely just a hair above the block. It backed out easily with a small vice grip.

The next day my friend put all bolts in (from another engine) with antisieze torquing to 56 ft-lb. None broke.

I decided to do some research and found that putting antisieze on a bolt can INCREASE the TENSION on the bolt by up to 71%! Holy cow! No wonder they snapped. Using oil only increases the tension negligibly. Also re torquing was found to be most stable with previously oil-lubricated bolts vs. dry vs. the high tension variability with antisieze. I also read from 30-40 yr. mechanics, including some on this forum, that they have only used light oil when putting head bolts and such in.

My friend then said that may explain why he has periodically stripped the threads out of some Chevy and Ford blocks over the years. He even had to junk one block.

Lesson learned: NO ANTISIEZE ON ANYTHING THAT HAS TO BE TORQUED WITH A TORQUE WRENCH.

[aj81spider]

Thanks for that. I anti-seize everything and had no idea.

I did a quick Google on anti-seize and torque and there are tons of links saying the same thing.

Learn something new every day.

[So Cal Mark]

really important to use a tap to chase all of the threads before installing bolts along with lubricating the threads

[majicwrench]

I'm a huge fan of following directions. Most manuals with state what, if anything, to lube head bolts with.
Just to add, since we are talking head bolts, Any engine with blind head bolts holes, like our fiats, very important to blow out holes w compressed air. Coolant, oil, debris fills bolt holes and you will hydrolock as you tighten bolt.

[RoyBatty]

Also do yourself a favor and find a torque meter that will work to the appropriate values.
As opposed to the click style torque wrench. The torque meter will let you observe the actual torque reading as you pull it up.
Even if the manual does not call for it, on something like the head torque, I prefer to make several passes in the torque sequence starting at about half the final torque and stepping it up a little at a time to the final value.
On the final torque hold the torque meter indicator to keep the final value for a 5 count or so. If the bolt turns more, then start over on the 5 count after you have regained the final desired value. It's a method I learned for torquing aircraft engine cylinders and it has always worked.