A certain amount the leeway is constructed into virtually every manufacturing facility part. Take project Rust Bucket"s turbocharger for example, i beg your pardon is now creating 37 pounds of rise instead of much less than 20. Or the transmission, which as well as a brand-new torque converter, is taking care of twice the strength it to be designed to. As we acquire into the 400-500 speech range, we"re walk to start worrying around our stock head gasket blowing, i m sorry could very well happen, especially because we"re going come be using nitrous oxide.

You are watching: 12 valve cummins head bolt torque specs


From the factory, Cummins uses a torque-angle an approach of tightening head bolts, which generally will result in a torque spec of a little much more than 115 lb-ft. We"d heard racers were having success at wrenching down the share bolts past factory torque specs, and were running 600, 700, or even more horsepower on stock head bolts without blowing a head gasket. Everyone seemed to have a different idea of exactly how things must be done, or how tight you must torque down the manufacturing facility hardware, but a usual consensus seemed to be the 125 lb-ft the torque was a pretty great number.


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See all 12 photosTo gain accessibility to all the bolts, ours intake pipe and also fuel lines had actually to come off.

Now, prior to you operation out and also tighten all your 12-valve"s head bolts come 125, recognize a few things. An initial off, bolts will actually stretch. When you tighten lock down past specs, 2 things have the right to happen-one, the bolt will stretch only slightly, and its clamping force will be higher than stock, or two, the bolt will stretch also much, and also weaken. If the bolt weakens, that may have actually less clamping force than stock, or in a worst case scenario, break.


So how do you know if one of your head bolts is in the risk zone? because that one, the bolt will certainly feel "buttery." it will store turning, yet won"t tighten up any much more than a particular amount. To keep empirical track of any butter bolts, we an initial torqued them every to 100 lb-ft, and also found the some had to it is in turned 1/8 to 1/4 the a turn to also reach the 100 lb-ft mark, describe that 20 years of running may have actually stretched ours bolts already. Once we obtained to 100 lb-ft, we marked all the bolts to keep an eye on any type of that were transforming excessively. The engine to be still hot as we tried the first bolt, which us took up to 110 lb-ft, then tried because that 115 lb-ft. In trying for that following step, the bolt kept turning an ext and an ext without reaching the 115 lb-ft "click" the the torque wrench. We made decision to leaving it be, and let the engine cool off. Us loosened it increase a little, then placed it earlier to 100 lb-ft.


After a three-hour break to allow the engine cool off, us tried the again. This time us went from 110 lb-ft to 115 lb-ft in just around 1/8 that a turn (45 degrees), so us felt the bolt to be holding this time. Us then tightened them every to 115 lb-ft, then finally to 120 lb-ft, whereby we stopped. In our wrenching native 100 lb-ft come 120 lb-ft, all the bolts had turned at least 30 degrees, while part hit a quarter turn (90 degrees) indigenous stock. Every the head bolts only needed about 1/8 the a revolve to jump 5 lb-ft, so us were fairly certain the they had all clamped down properly.


So what now? Well, currently we feel better about advertise our truck towards the 500-horsepower mark, particularly considering few of our head bolts were listed below the factory torque specs. Once we gain there, however, we"ll it is in doing it right and upgrading come a set of ARP head studs, which provide much more clamping pressure than bolts. However for now, we"re willing to see how much we deserve to push the share parts. Hey, better us break stuff than you, right?


Disclaimer:Just since we walk this doesn"t median you have actually to. We"re advertise 200,000-mile factory contents to their limit, and if you"re to plan on re-torquing your very own Cummins head bolts, be an extremely careful and do so in ~ your own risk.


Method #2In talking through a few other high speech head bolt guys, we uncovered that few of the an ext serious racers use a different torquing procedure. After ~ letting the van sit overnight to whereby it is fully cold, they"ll take out one bolt at a time, coat that in oil, then torque that in 5-10 lb increments come 125 lb-ft. Oiling the bolts provides them a friction benefit over share bolts that might have shed off all their oil, and also it likewise makes certain all the fasteners are clamped down evenly. Us took a couple bolts out of Rust Bucket to check to see if any were oiled, and also some of the center bolts were, however the exhaust side bolts had actually long due to the fact that gone dry, which describes why they didn"t turn as much. It takes much much more torque to turn an un-oiled bolt 보다 an oil one, therefore if girlfriend really desire to do it "right", we"d suggest this method.

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Proof Load and Yield StrengthGive yourself 2 points if you know what this terms mean. We were kinda hazy ~ above the subject until we began researching our head bolt dilemma. We"d heard horror stories of people breaking bolts, so us double-checked on the proof fill of our grade 12.9, 12mm head bolts. Together it turns out, the bolts were rated at 123 lb-ft the torque in ~ 90% proof pack when gift torqued through SAE 10-weight oil. What is evidence load? it is a measure up of once a bolt will begin to deform and stretch, and is commonly a 90% value of the bolt"s yield strength-the value when it finally gives way and loser its clamping force. We uncovered the actual minimum number as soon as a grade 12.9, 12mm bolt must start to give method to be around 151 lb-ft that torque. Due to the fact that non-oiled bolts can see a torque analysis of around 20% greater than oiled versions, we felt pretty for sure that we weren"t damaging anything by torquing ours down to a "mere" 120 lb-ft un-oiled.


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See all 12 photosNext we torqued every the bolts to 100 lb-ft and significant them. Make sure to use smooth, also pulls with the speak wrench. It likewise sometimes would certainly take more than 100 lb-ft to break the bolt loose, so the wrench would click when when the bolt started turning, then once it clicked again we would stop. The men at large Power Diesel have tightened plenty of a head bolt, therefore they are acquainted with exactly how they are supposed to "feel."
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