720inOlyWa Posted January 19, 2015 Report Share Posted January 19, 2015 I hear two trains of thought, referring to head bolt replacement. Many respected voices say.... “Nah”. Others insist it is a must. Where do you stand on this important question? The official 720 service manual doesn’t reference replacing the head bolts in any place that I could find. And Z24 head bolts are not available from the regular retail auto parts store, it seems. When I did my 1,000 mile check, I noticed that the head bolts were no longer at 58 ft. lbs., but loosened at closer to 48, instead. Now that the truck has been decommissioned to re-do the head issues thoroughly and correctly, I noticed that most of the head bolts loosened at about 40- to 42ft. lbs.. I have no firm idea whether this experience is pertinent data related to re-using old head bolts, or any one of a number of other factors. But it did set me to wondering about whether or not it was wise to re-use them. What do you think? And if you are ardent about replacement, where do you get yours? Thanks! Quote Link to comment
MicroMachinery Posted January 19, 2015 Report Share Posted January 19, 2015 I think I bought new head bolts the first time I rebuilt an L series. After that, I reused the old ones. Just examine to make sure they're not compromised in some way (cracked or stretched). These aren't stretch bolt style like on VWs, but if they clean up and look OK, I say go for it. In a perfect world, you would replace them... but I wouldn't fear them failing you if you had to reuse them. Just be sure to clean them up, chase the holes in the block, and lube them before installing. 1 Quote Link to comment
john510 Posted January 19, 2015 Report Share Posted January 19, 2015 Well i put new ones in just for peace of mind.I got them through one of the wholesale Nissan parts suppliers on the internet.After spending a lot of time and money for a nicely rebuilt engine i was not going to take a chance on 30+ year old bolts. Quote Link to comment
DanielC Posted January 20, 2015 Report Share Posted January 20, 2015 More important than replacing the head bolts is retorquing them. Even the new ones. Different head gasket materials, and construction, as well as different metallurgy in the head bolts themselves, and the design of the engine, determine if the head bolts are replaced when rebuilding an engine. Consider the L-engine in a 521. Six easy to remove cam cover bolts, and the head bolts are there, and easy to retorque. Retorque them until they no longer loosen, usually when you adjust the valves. Datsun knew this, so no need to engineer head bolts that do not require retorquing. Now consider a Ford Aerostar. (my other car) The 4.0 V-6 engine is crammed into a space it barely fits. Because of air conditioning, emissions stuff, fuel injection stuff, and other issues, when replacing the head gaskets, you have about 35 to 40 steps before you get down to where you can see valve covers. This engine uses "torque to yield" headbolts, and using them once uses up the "stretch" in the bolt. You replace the headbolts every time you remove the cylinder heads. In short, you do what the factory service manual says to do. 1 Quote Link to comment
datzenmike Posted January 20, 2015 Report Share Posted January 20, 2015 40 year old bolts are as good as the day they were made. They are totally reusable. I see nothing wrong with a re-torque although not required. 1 Quote Link to comment
Z-train Posted January 20, 2015 Report Share Posted January 20, 2015 Just be sure to clean them up, chase the holes in the block, and lube them before installing.Yes,yes,No. No lube is used. If you use lube it changes the torque value. Quote Link to comment
MicroMachinery Posted January 20, 2015 Report Share Posted January 20, 2015 Lubing them makes the reading more accurate, actually. Excess friction is what throws a torque spec off.. this is why ARP gives you special lube that they require you to use with their hardware. 1 Quote Link to comment
wayno Posted January 20, 2015 Report Share Posted January 20, 2015 I have always wondered about the ARP headbolt/stud kit, mind you I am not saying anything bad about them, they fixed my headbolt issue I was having on my LZ23. The thing that makes me wonder is the thread slope for the nut on the top, one is supposed to use the lube, and torque them to a final 61lbs, but with a final 61lb torque on that fine thread, it would seem like that would actually be more force than a stock bolt at 60lbs with a course thread. I am not bitching, I have not had to make another headgasket since using the ARP kit, but I just cannot wrap my mind around 60lbs on a course thread, being the same on a fine thread, to me that's like saying that 60lbs on a 3 foot breaker bar will be the same as 60lbs on a 2 foot breaker bar, it's not the same because of leverage, same as different thread slopes. Quote Link to comment
Greased monkey Posted January 20, 2015 Report Share Posted January 20, 2015 I have always wondered about the ARP headbolt/stud kit, mind you I am not saying anything bad about them, they fixed my headbolt issue I was having on my LZ23. The thing that makes me wonder is the thread slope for the nut on the top, one is supposed to use the lube, and torque them to a final 61lbs, but with a final 61lb torque on that fine thread, it would seem like that would actually be more force than a stock bolt at 60lbs with a course thread. I am not bitching, I have not had to make another headgasket since using the ARP kit, but I just cannot wrap my mind around 60lbs on a course thread, being the same on a fine thread, to me that's like saying that 60lbs on a 3 foot breaker bar will be the same as 60lbs on a 2 foot breaker bar, it's not the same because of leverage, same as different thread slopes. What's heavier a ton of bricks or a ton of feathers? 0.o Quote Link to comment
wayno Posted January 20, 2015 Report Share Posted January 20, 2015 It's not the same, two different thread slopes, it's about leverage, in this instance, a twisting leverage. As far as I know, house jacks all have fine threads, as we need the leverage to lift the house, and we are strong enough to turn it, but using the same jack with course threads, we might not be able to turn it, we might not be strong enough, in other words, one turn on a fine thread house jack would move it one inch up, while on a course thread, one turn would move it two inches, and it would be much harder to turn, same thing with a chain hoist. What's heavier a ton of bricks or a ton of feathers? 0.o Quote Link to comment
datzenmike Posted January 20, 2015 Report Share Posted January 20, 2015 Most of the 60 ft lbs of torque on a head bolt is wasted on overcoming the friction between the bolt and the block threads and maybe only 10% are actually clamping force. Fine threads have more contact area than coarse threads and will create more friction. A fine thread can be safely torqued slightly higher than a course thread but 60 ft.lbs is close to 60 ft. lbs coarse or fine. Quote Link to comment
HRH Posted January 20, 2015 Report Share Posted January 20, 2015 All of you are wrong! There are lubed bolt torques and un-lubed bolt torques. ARPs torque specs are meant to be reached with the lube they provide. ABSOLUTELY REPLACE ORIGINAL L HEAD BOLTS IF GIVEN THE OPTION!!!! You know why? They're 40 years old and they break the shit off! I ignored the first broken bolt the last time I put an L motor together and had the entire head torqued down when the second one broke. As a rule, I only install factory Nissan NEW L bolts or ARP stud kits. I'm done reusing old head bolts. Don't cheap out on fasteners that could result in a leaking head gasket. Since I used the ARP head stud kit, I have had ZERO problems with headgaskets even without re-torquing. Food for thought. 2 Quote Link to comment
MicroMachinery Posted January 20, 2015 Report Share Posted January 20, 2015 All of you are wrong! There are lubed bolt torques and un-lubed bolt torques. . :lol: show me in the FSM the "lubed bolt torque" vs "un-lubed bolt torque" specs. Show me. Quote Link to comment
Draker Posted January 20, 2015 Report Share Posted January 20, 2015 Depends on application ^^ Some manufactures say lube.. some say dry dog it. That's a technical term. 2 Quote Link to comment
HRH Posted January 20, 2015 Report Share Posted January 20, 2015 Exactly. Ask ARP. Datsun specs are dry bolt torques, not wet. Quote Link to comment
MicroMachinery Posted January 20, 2015 Report Share Posted January 20, 2015 Depends on application ^^ Some manufactures say lube.. some say dry dog it. That's a technical term. Are we still talking about fasteners? Quote Link to comment
Draker Posted January 20, 2015 Report Share Posted January 20, 2015 What is a fastener? Quote Link to comment
wayno Posted January 20, 2015 Report Share Posted January 20, 2015 I was not wrong, I was right to use an ARP head stud kit, all my issues went away, I was really tired of making headgaskets. :lol: All of you are wrong! There are lubed bolt torques and un-lubed bolt torques. ARPs torque specs are meant to be reached with the lube they provide. ABSOLUTELY REPLACE ORIGINAL L HEAD BOLTS IF GIVEN THE OPTION!!!! You know why? They're 40 years old and they break the shit off! I ignored the first broken bolt the last time I put an L motor together and had the entire head torqued down when the second one broke. As a rule, I only install factory Nissan NEW L bolts or ARP stud kits. I'm done reusing old head bolts. Don't cheap out on fasteners that could result in a leaking head gasket. Since I used the ARP head stud kit, I have had ZERO problems with headgaskets even without re-torquing. Food for thought. 1 Quote Link to comment
RTB Posted January 20, 2015 Report Share Posted January 20, 2015 Gotta use the zx bolts with the ring in the top if you have them. Quote Link to comment
MicroMachinery Posted January 20, 2015 Report Share Posted January 20, 2015 "So in conclusion, you can either reuse the old ones, or buy new ones; the choice is yours. Both methods have worked countless times and been tried and proven over the years. Follow the directions for cleaning and torquing in the Factory Service Manual, and may your rubber ever meet the road. Let us bow our heads.." 3 Quote Link to comment
720inOlyWa Posted January 20, 2015 Author Report Share Posted January 20, 2015 Note to self: “Think before you start a thread. What could possibly happen?” Thanks, everyone in Ratsun land! Quote Link to comment
dr.feltersnatch Posted January 20, 2015 Report Share Posted January 20, 2015 I have always wondered about the ARP headbolt/stud kit, mind you I am not saying anything bad about them, they fixed my headbolt issue I was having on my LZ23. The thing that makes me wonder is the thread slope for the nut on the top, one is supposed to use the lube, and torque them to a final 61lbs, but with a final 61lb torque on that fine thread, it would seem like that would actually be more force than a stock bolt at 60lbs with a course thread. I am not bitching, I have not had to make another headgasket since using the ARP kit, but I just cannot wrap my mind around 60lbs on a course thread, being the same on a fine thread, to me that's like saying that 60lbs on a 3 foot breaker bar will be the same as 60lbs on a 2 foot breaker bar, it's not the same because of leverage, same as different thread slopes. Actually my underdtanding is it would be the same. 60ft lbs is 60 ft lbs. Thebsize of the bar just makes it easier to turn. The way I understand it is 1 ft lb is a 1 lb weight hanging 1 foot from the center. Now 2 ft lbs could be either 2 lbs at 1 foot or 1 lb at 2 feet. The clamping force would be the same. Quote Link to comment
wayno Posted January 21, 2015 Report Share Posted January 21, 2015 If I had a way of testing this I would, but all I have is a bathroom scale, and I don't think that will work. Quote Link to comment
dr.feltersnatch Posted January 21, 2015 Report Share Posted January 21, 2015 here ya go this explains it. i hate the website layout though... https://www.wisc-online.com/learn/career-clusters/stem/cad407/what-is-torque Quote Link to comment
wayno Posted January 21, 2015 Report Share Posted January 21, 2015 OK, this is how I see that it works, you have bolt TENSION, which is how hard a bolt is clamping down an object, then you have TORQUE, which is how hard one twists a bolt to reach a certain tension, and then there is THREAD SLOPE, which is how many turns it takes to move the nut a certain amount of distance. I submit that when one torques a course threaded bolt to 60 pounds of torque, it will get to X amount of tension(clamping force), I also submit that when one torques a fine threaded bolt it will take less pounds of torque to reach X amount of tension(clamping force), and I suggest that if one torques the fine thread bolt to 60 pounds of torque, it will equal Y amount of tension(clamping force) which will be more tension(clamping force). Now there is also another factor here that is called FRICTION, from what I read I am guessing it has a factor in this, I just am not sure how much it is. I received an "A" in algebra, but I never really took the course, I was transferred into that algebra class the last two weeks, and all they did was crossword puzzles, I believe that the school screwed up, and covered their ass by transferring me into that class at the last minute, so I received an "A" in that class, and they in theory did their job in the eyes of the public. Can someone on here figure out what "X" and "Y" tensions would be with the torque value being the same on the different thread slopes? Quote Link to comment
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