head bolt torque

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green67cuda

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ok....question....i understand torqueing in 3 stages to get even and uniform clamping...however....
when you do that according to the torque order. when you get the last one torqued, the first one has a bit to go to get back to that torque value again....

so do you torque in the proper order up to the torque spec and leave it, or should i torque them to spec twice?

also....they need to be retorqued after x-long because of new bolts, correct?
 
when you are done at the final torque ...your done after 500 miles or what ever they recommend re torque them unless the head gasket manufacturer says not to i NORMALLY USE ABOUT 500 MILES FOR RETORQUE MILEAGE (ITS NOT THE ACTUAL MILEAGE IT IS THE REPEATED HEATING AND COOLING OF THE ENGINE AND THE NORMAL FOR 500 MILES IS ABOUT RIGHT
the way I DO IT IS FOLLOW THE SAME TORQUE PATTERN AND ONE AT A TIME LOOSEN 1/4 TO 1/2 TURN THEN PULL BACK DOWN TO THE FINAL TORQUE SETTING THEN GO TO THE NEXT ONE IN THE PATTERN REPEAT UNTIL DONE
 
when they stop moving, they are torqued..If it takes 4 times, then it takes what it takes. As far as retorquing, I've never had to. With steel of Felpro, or Victor, or Mr Gasket.
 
ok...one vote for one round of final torque value, and one for going through the sequence multiple times at final torque value...

i got to thinking....you are supposed to torque in at least 3 stages up to final torque...well, the closer you get to it, the more the steel shim will be compressed, and by the time yo get to final torque, it should be compressed well, so it shouldn't need multiple passes through the sequence....

i'm using 4 rounds to get there....20, 40, 60, 70....don't guess i'll have a problem
 
My first job out of college was developing bolt torquing procedures for jet engines at Pratt & Whitney Aircraft. What I learned from that 6 months of my life is using a torque wrench to tighten bolts is a very in accruate activity.

So regardless of what is in an FSM manual for steps this is what I do;

1. run a tap down all the head bolt holes and use some brake cleaner to clean out any debry and crud.
2. make sure the underside of the bolt heads, both sides of the washers and the surface of the head are smooth and free of burrs.
3. If you have a die run them of the threads on the bolts, if not examine the threads carefully and fill off any dings or burrs. Use the solvent to clean the threads of any crud. The bolts should sping down into the bolt with no resistance.
4. Regardless of what the FSM states always use at least some clean motor oil on the threads, bottom side of the head and on the washers. Definately use the lube provided with bolts like ARP.
5. Regardless of the the FSM. Run all the bolts down finger tight plus a 1/4 turn to seat the head and gasket.
6. Following the FSM recomended toquing pattern the first step should be no more than 25 ft-lbs. Then no more than 10 ft-lb increments to you reach the specified torque.
7. Always go around a couple of times at the specified torque to make sure they are all even.

The most important thing for long life of the head and gasket is even clamping force, this has become critical with aluminum heads on iron blocks to the point that torque to yeild bolts are specified almost universally on new cars now. But for us iron on iron guys removing all sources of friction is appropriate. A simple burr can reduce the clamping force by as much as 40% even though the bolt was torqued to the specified value
 
I agree with dgc333 ...he has nailed it as for the proper procedure. The reason they went to "stretch" bolts and degree of torque is because the old fashion method left a wide variation between bolts when torqued. With stretch bolts you take in a wider range of variables to create a more even torque. Import cars with their aluminum to aluminum and aluminum to cast surfaces have been using stretch bolts for 15 + years.
but for all practical purposes, 3 rounds of torque to the manufacturers spec is sufficient for cast iron engines and by the 3rd round there isnt any appreciable loosening of the prior bolts
 
dgc333 Thank you for that info I never knew that. I have always done it like green 67 cuda explained. I will have to rember that way when I change my heads.
 
Outlaw, the reason for more smaller steps is to even out the clamping forces. The testing I did was with bolts at P&W were all strain gaged to actually measure the clamping force being provided by the bolt. There was definately an improvement in the distribution of clamping force from bolt to bolt when they were torqued in smaller increments. You are likely correct that 3 steps will get the job done but I see it as a no cost way of doing a better job.

F
 
your 100% right , but after working as a mechanic for 30 years you come to realize that you cant take that kind of time with every car (I realize at home this is different)
when your under the gun and you soon realize that three steps is sufficient for the factory then it becomes sufficient for you. I also figure the factory is going to cover their butts so if 4 times was really better then they would say 4 times. One hole in your theory on clamping force, in solid plates you would be right but in a cast design with differing thickness' and holes for water and oil and cylinders the equal force therory gets killed . to be equal each would have to be a different clamping force to compensate for the illregular thickness and and the above mentioned holes. but in theory and a perfect world you are right . You have to excuse me on working smarter (less torqueing) and working harder (torqueing more to get the same results) or else 1 pound increments would be even better.
just my 2 cents worth and 30 years experience
 
Even though I worked my way through college teaching automotive engine basics at a night school and working part time in a garage plus several years working for my father inlaw part time when he first opened his own garage I am coming from a home hobbiest standpoint and not from the pressures of flat rate. So I would agree 100% that to the professional mechanic an extra 15 minutes spent doing multiple steps will cost money.

In regards to to clamping force I am refering to the the force the bolts are applying to hold the head to the block. The water jackets and shape and configuration of the head and block will certainly have a varying impact on the strain in the metal but if the thickenss of the block and head decks are sufficient then there will be very little variation in the clamping force.

The key is the total force applied by the bolts holding the head to the block being greater than the force due to temperature variations and cylinder pressure trying to force them apart.
 
Actually we are both right and both splitting hairs ....LOL
so on a total different note , since you obviously have a technical background you might find this interesting as its along the same idea. I used to own a cryogenic tempering service.This is/was cutting edge science of using liquid nitrogen to temper metal and non metalic items without the damage of heat(plus it goes to the core of the item). I had to set up a comparison to show the effectiveness of the process.Though its not scientifically correct and accuracy is suspect, it showed in a laymans fashion the effectiveness of the process.I had a 1 inch thick steel bar and a 5/16 steel bar matched and drilled for 1/4 bolts. We used plasti-gage to show the clamping force by laying it lengthwise down the 1 inch thick bar and clamping it down with the 5/16 plat. Using grade 8 bolts we torqued it to 40# then measured the plastigae to determine the clamping force off the grade 8 bolts(as a control group) then we did the same thing with some grade 5 bolts that had been cryogenic tempered. the grad 5 bolts actually transfered more clamping pressure to the plastigage than the grade 8 bolts did because of bolt stretch. Not that a grd 5 is a replacement for grd 8 (sheer and torsional couldnt be tested by us at that time ) but it was only to show the metaurogical (sic) change by the cryoprocess without becoming brittle. Thats it in a nut shell as i dont want to write a report on it as I say it was a laymans demo but i thot interesting . Also worked on golf balls too by gaining approx 35 yards longer drives ...LOL
 
I would venture a guess that the cryo treated grade 5 bolts had the surface of the threads hardened enough that it overall reduced the friction between the bolt threads and the threads in the plate enough that the 40 ft-lbs resulted in more actual rotation of the bolt resulting in the increased clamping force. It is easy to vary the tensile loading in a torqued bolt by as much as 30-50% by varying the friction with a lubricant.

I had a similar situation that one day I was walking through the factory where I worked and saw a worker with a breaker bar and pipe trying to tighten bolts on the cover of a 6000psi pressure transmitter. When I asked why he wasn't using the automatic torquing cow he said that they always leaked when pressure tested when using 174-PH bolts (these bolts were used in place of a B8 bolt when the transmitter was to be installed on an off shore drilling rig to resist corrosion). The standard bolts when torqued to 75 ft-lbs with the cow didn't leak when pressure tested.

I was off on a mission to figure out what was going on. I took some the B8 bolts and nuts and made up a fixture so I could torque them in the tensile tester in the lab. A B8 when torqued to 75 ft-lbs would generate 7500 lbs of force. Took the 17-4PH and did the same thing, I only got 3000 lbs of force. Friction in the threads was reducing the actual rotation of the nut at 75 ft-lbs reducing the clamping force. Now what the factory worker unknowingly was doing was increasing the torque to get back to the same clamping force.

My options were to purchase additional equipment and create a separate work station so the 17-4PH could be torqued at 150 ft-lbs. This was not the best choice since we had limited space at that point in time and the gang torquing cows for all the different configurations was quite capital investment.

Back to the lab. I tried a B8 nut on the 17-4PH bolt and bingo we were back to 7000 lbs of force at 75 ft-lbs. Now the B8 nut was not an acceptable solution because of he corrosion issues. So I tried some plating on the 17-4PH nut and found a zinc plating did the trick. So we revised the spec on the 17-4PH nut to include a zinc plate and green chromate wash (green to make them visibly different that the yellow chromate on the B8's). Problem solved an no more works using a breaker bar and potentially hurting themselves.
 
Yep! :) Been an engineer for 30 years now and I am always learning something new. Worked in research, new product development, manufacturing, regulatory affairs and I am currently do reliability and system safety work for a telecom integrator. It's been a great career.
 
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