Re-Torquing head bolts

I'm curious what others do when re-torquing head bolts.

I've always just thrown the torque wrench on and hit it, but recently I saw somebody loosening each bolt a little bit first.

I can understand the logic behind that, but I have mixed feelings on trying it. I've never had any trouble from doing it my way, so why change now, but I'd still like to hear other's opinions.

Have I been doing it wrong all these years?

Ive always did the same as you, put a torque wrench on it and check them. We weren't told at Vo-tech to ever loosen them and then re-torque. I think mainly the re-torque is for bringing them back up to spec after the warm up changes the original cold setting so that it isn't under torqued.

I do that to break the sticktion (static friction) of the bolt head/threads. My reasoning is that a 2 or 3 degree loosening is irrelevant to the current seal on the gasket, and prevents the wrench from "seeing" the set the bolt has taken. The reasoning follows from experience. Pulling the wrench tighter only often finds the bolt meeting torque spec as is. If I break it loose a tiny bit that same bolt might make 10 degrees further in the tight direction that it would not have had, but still to the torque specified. Turn of nut and bolt stretch methods (turn to yield) are common now because twisting force is inconsistent with clamping force. Jim

Never did hear about loosing up a nut then retorque where is the logic behind that. This sitensuregets out some weird stuff old wives tales and away too many "i think" when they have never done the task.

Be assured I break the sticktion only a very tiny fraction of a turn, and only one bolt at a time. No failure has ever chased me on this. Jim

I wounderd about this as I just had to do one on a JD diesel. The manual said to break them loose 20deg then re torque. Just for my info I torqued them first and they didnt move. I then marked them loosened them and re torqued they Tightend about 10 deg more, every one of them.

Janicholson is correct. Proper technique is to loosen them a few degrees then take them back up to the proper torque. Breaks the sticktion,
lol.

well that's why I ask - seems to make more sense to "come up" on a torque spec than just kind of hit it, have it click, and feel that it's good.

For the same reason you don't want to minimize stopping and starting the torque wrench in the first place when you're setting any torque.

In the grand scheme of things, I can't imagine it matters all that much. As I said, I've never had any leaks/had warpage from the way I've always done it, so it can't be all that innacurate.

Thanks for the input guys

I've never done it, but from what I'm seeing on here, sounds like a good idea. Especially if the factory is recommending it, and the results prove it gains a few degrees. I can't see it really hurting anything as long as the bolt is only loosened just enough to break the friction and not relieve the force. I would be sure the cooling system is not under pressure though.

can't edit - I meant you DO want to minimize starting and stopping - not NOT minimize it!

Case recomends loosening and then retorquing them. That's what I've done and it works. And yes, I always get a bit more this way over just hitting them again.

International Harvester manuals say not to loosen any of them but to just tighten any that are below the torque specifications.

I have only seen the loosen then retorque method recommended for bolts that tread into cast iron. On a steel nut on a steel bolt it would not be necessary. The loosen than retorque method is specified in the factory IHC and Deere engine manuals I have. I have also seen it in factory GM small and big block manuals.

I was taught to torque to spec,let them set about an hour,back off one flat and re-torque .

A lot of newer engines do not give a final torque spec. Even some of the older engines have revised their specs. John Deere is one that comes to mind. They use TTT -Torque Turn Tightening. Torque to a certain spec, and turn another 90 Degrees is common.It is not recommended to reuse these bolts or to retorque them.

The only time I loosen them first is if they don't gain any by just torquing them. Mark the starting point, back them off, then re-torque and you can see what was gained. Only do one bolt at a time. Deere's updated procedure for 4020 era engines uses a 3 step procedure with the third step being done after the engine has been run enough to warm up. The additional torque on the third step will gain without backing off first.

If the block threads were properly chased and cleaned. Then new fasteners used instead of the old stretched bolts. Re-torquing would be a mute point.

I should have added that case's specs call for retorquing after the engine is warmed to opperating temp. I would imagine that a warm bolt will stretch more than a cold one.

Hello JRSutton,

I always do the same thing.....read the manual. They know what works best,

Guido.

a warm bolt will not stretch more than a cold bolt but a warm bolt will lengthen with a rise in temp so thats why many specs call for torquing when warm

you mean moot
moot point

Problem is all manuals do not say the same thing! If the bolt was properly lubed before the first torque and your retorquing after the first warm up it would not gain anything to loosen it first. I doubt it would hurt anything to loosen them one at a time as you retorqued either.

Just to add another point, some torqueing specs have changed through the years with the addition of using aluminum heads and on other parts which may make some difference. A lot of good info here.

Maybe a "mute" point means just don't mention it to anyone I will admit, Ive used that before too lol...

In EVERY case, the manual takes priority. What is told by the people that made the engine should be regarded as the LAW. So, having said that, I will add just a few points of information.....
Unless instructed to do so, re-torqueing a warm engine is not advised. The main reason is how to tell just HOW warm it "should" be. While the bolts DO expand and lengthen when warm, so also does the surrounding material like the block and head. Overall, it should be a net zero result.
NEVER, NEVER, EVER re-torque stretch bolts. These are torque to yield bolts, and once yielded, are meant to remain as they are until the next time a head is removed. And then they are meant to be replaced.
When re-torqueing, I would personally recommend loosening a few degrees first, then re-torque. The initial force required to start the bolt turning can exceed the torque that has been applied to the bolt. This results in an inaccurate torque reading.
In EVERY case, the procedure given in your manual for that machine is the gospel truth for that machine. Whether it be an engine, a transmission casting, a bearing housing, or whatever.
Also, know that the accuracy of the torque to the inch-pound is not nearly as important as the UNIFORMITY of the torque. Uneven torque causes metal castings to warp. Evenly tightened castings will generally live longer as a rule.

Alan, that is true. Another thing that has changed is gasket technology. Back in the flat head days, gaskets were really thick and compressible. That's where the retorque really comes into play. Not so much bolts stretching when hot, but the gasket compressing. Going back with anything other than the factory gasket will make a difference.

(quoted from post at 16:39:50 02/22/16) you mean moot
moot point

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Oops yes

Hello Dick L,

Every manual that is OEM works every time. Torque values are just that. Follow the instructions and move on,

Guido.

Well for what i ususally work on i have never loosened any of them as when the engine is at operating temp of 165-200 degrees there is no need to back off because the head bolts are loose . Now i get a little fussy here as before we even start to stuff the pieces and parts into and engine EVERY hole in that block is chased with a bottoming tap , all holes are cleaned out and degreased nad blowen out with air . All bolt threads are chased and wire brushed cleaned and dry . Main bolts are lightly lubed same as the rod bolts and head bolts . Now one thing here on any blind hole do not get carried away with the LUBE thing as you can cause a blind hole to crack due to Hyd compression . That is easily done on a bigger Cummins engine as to others why take a chance . Over the years i have also found that ok ya retorqued the head when it was up to operating temp it may surprise you that when you think your done go back over the center ones again as oh they are loose . Many times i have pulled the heads on stuff due to a blowen head gakt and found the bolts in the center were loose . Also helps to have your torque wrwnch sent in every so often and have it checked and serviced , i do mine once a year. Yep Snap off hammers me 105 buck for this on my 1/2 drive as it gets the most use , the other three just collect dust. Only tractor engine i have worked on that the BOOK said NO retorque was on a A/C 5040 that i did last year. It said nothing about installing new head bolts and they did not look like a torque to yield style . But i do believe that getting the engine up to operating temp is the key and at times this takes a good while to do so . Ten to twenty min. does not get the job done . The block being WARM to the touch is not operating temp. . On the I H tractors you can cover the rad and run them for twenty min. and the temp gauge has NOT made it to operating temp . It may have started to move but it ain't there yet . Heck Running my 806 on a New Holland 355 grinder mixer grinding a full load will hardly get it up to operating temp. But once you get them warmed up work fast as they start to cool .

(quoted from post at 13:04:26 02/22/16) I should have added that case's specs call for retorquing after the engine is warmed to opperating temp. I would imagine that a warm bolt will stretch more than a cold one.

Click to expand...

No need to imagine: The effect of temperature is small however, the Modulus of Elasticity, denoted as "E", does decrease with temperature increases. For steel the effect would be an approximate 1.6% reduction, going from 100 degrees F to 300 degrees F. That means to maintain the same clamping load at 300 degrees the bolt would need to be stretched an additional 1.6%. At 1000 degrees you would need to stretch the bolt an additional 18%.

I agree 100% on cleaning the threads just as you described, that's exactly how I do it. You'll never get an accurate torque reading with rusty/dirty/rough threads.

In fact tractor vet - you may remember the reason I have this particular head off was due to a blown gasket - on an engine that was recently rebuilt by the previous owner. (new to me farmall 560)

What I cleared out all of those bolt holes in the block answered the question for me of why this newly installed gasket probably blew. I don't think they've been cleaned in 60 years. Thick,dry, black gritty nastiness. I had to chase them and flush them several times.

Same with what I wire brushed off the bolt threads. Nasty.

had the head been on there for 20 years that'd be one thing, but as I said, this thing was just rebuilt. Somebody clearly rushed the job.

Just a question. Do all manufacturers of vehicles run new engines until hot then re-torque the head bolts before installing the engines?