Are new main, rod and head bolts necessary?
When it comes to performance engines? Absolutely! Just remember this; the ONLY thing holding your engine together, (the rod caps in place, the heads onto the block, and the crank in the main caps, and so on), are the bolts. If you use old, worn, rusted or cheapie bolts, then they are sure to stretch or let-go. When bolts stretch, things get loose and start to move, or “walk”. When things get loose or walk, failure is eminent, and that eminent failure can be REALLY costly!
Look at the image and see what happens when a perfectly good looking bolt loses its temper or hardness. It stretches. Yes, those are the same two bolts from the same type of connecting rods. The one on the right was ran hard for a few seasons. It "looked" just fine to the naked eye before it went back into the rod after a freshen-up. I mean, look at it. It looks all nice and clean... it's shiny, and the threads look perfect, just like the bolt on the left, except it was fatigued. That would have for sure led to the rod cap not staying in place, which is a catastrophic failure, all over a bolt that costs less than a cafe latte' at your favorite coffee joint. So is it worth it to run old bolts that might "look" okay? No!
When it came time to torque it back to spec in the rod, it just wouldn't get to its final torque value because it began to stretch, and stretch, and stretch... until it elongated and got super thin in the middle. Again, your eyes can't see metal fatigue, loss of temper, or small amounts of stretch that weaken it. Luckily this one gave indication by not letting me get to the final torque value before I knew something was way off.
I can’t begin to tell you how many home rebuilt or “bargain priced” engines I've seen in my day that had old, re-used bolts in them, or "bargain priced" inferior quality aftermarket bolts. A bolt might “look” good, but what do you have... X-ray vision or something? You can't see fatigue or minor stretching by simply looking at a bolt. The only way to see if a bolt is strong or not is to test it in a Rockwell tester, and the only way to test one in a Rockwell tester is to stress it until it breaks, and then say; “Gee, that bolt was strong”, or “Gee, that bolt sure was weak”. So testing a bolt isn’t exactly an option, therefore new, strong, high quality bolts are an absolute must in any performance engine if you want it to survive and last. And as you can see, even the best quality bolts fatigue, or over-stretch sooner or later under use and abuse, so it's always a good idea to change-out all of the old bolts and put some new, stronger ones in. This goes for rod bolts, main bolts, and head bolts. It's what I call "cheap life insurance".
Almost all high-end, aftermarket connecting rod manufacturers use ARP bolts their rods. Most of them have their brand name stamped into them along with ARP's name as well. The reason I always chose to use ARP bolts in all of the engines I built, and why almost all high-end connecting rod manufacturers choose ARP too, is because of their quality and strength. Again, the only thing holding your motor together are the bolts, so they had better be strong and the best quality possible. They definitely have my stamp of approval!
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