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Old 06-01-2016, 10:45 AM   #1
42 1/2ton
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Default Retorque Heads

Has anyone ever NOT had to retighten the Head Nuts or Bolts on a flathead after several heating/cooling cycles?
The reason I ask is I have 200 miles on a 1942 239. The trip lengths were from 5 miles to 35 miles. I have tried to retorque several times after cool down and the nuts seem to be at spec. The engine is new overhaul.

Ed
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Old 06-01-2016, 10:52 AM   #2
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Default Re: Retorque Heads

There should have been around three retighten after cool down cycles when the engine was first assembled. After that it should remain stable. The head bolts/nuts do not have to move, they just have to be checked.
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Old 06-01-2016, 11:21 AM   #3
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Default Re: Retorque Heads

It seems to depend mostly on the quality of the fasteners. I tend to use ARP studs/washers/nuts in my performance builds - and they don't tend to stretch much, so they hold the initial torque reading quite well. The readings can definitely be influenced by the usage of a good stud assembly lube (or not) - which really helps with accurate readings and consistent clamping forces.

Also, the head gaskets can influence this as well - as there are quite a few different types of construction. So - it is certainly possible that your torque readings have held up.

I've found with some of the "new studs and hardware" suppliers (non ARP), that the grades of the materials are such that multiple re-torques are usually necessary. This is just an observation of mine . . . nothing scientific about it.
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Old 06-01-2016, 12:44 PM   #4
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Default Re: Retorque Heads

Thanks JSeery and Bored and Stroked for the reply. I was concerned because I have never been able to move the head nuts on this engine after overhaul during a retorque check.
Thanks very much.

Ed
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Old 06-01-2016, 06:07 PM   #5
J Witt
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Default Re: Retorque Heads

I always retorque after a few (3-5) hot to cold cycles and do it with the engine cold.

I do the retorque in the same pattern, working from center to outer edges of the cylinder head or whatever the assembly is.

Set the torque wrench to the specified torque and then break the nut loose, ie opposite of tighten, then tighten the nut to torque in one smooth motion, with the nut always turning until it reaches the spec torque. A reversible ratchet torque wrench is good for this operation.

The reason for breaking the nut loose, then tightening it is that the static level of friction in the threads and surface under the nut is higher than the sliding friction present while the nut is turning.

Often if you just torque the nut at the prescribed level, it will not move at all, but if you follow the above procedure, you will find that the nut has rotated a bit further past the initial position when it comes up to the prescribed torque.

The object of this exercise to put a certain amount of stretch on the stud that equates to compression (clamping) of the gasket. My own opinion is that the thermal cycling allows some equalization of loads and stresses in the block-gasket-head-studs-nuts assembly and some of the fasteners will relax to a lower level of stretch than others.

By the way, most torque specs I've seen are for clean and dry fasteners. If the threads are lubricated most specs recommend reducing the torque by about 10%.

Hope this is of interest,

John
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Old 06-02-2016, 02:57 AM   #6
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Default Re: Retorque Heads

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Through ignorance I never torqued my 81A motor and never had any issues. However, after rebuilding an 8BA I kept blowing head gaskets; this stopped with retorquing until there was no more movement in the bolts. This took more than three heat cycles. I used old bolts on the 81A and new bolts on the 8BA, with quality gaskets on both.
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Old 06-02-2016, 04:49 AM   #7
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Default Re: Retorque Heads

No matter which studs or nuts you are using there is always the need to re-torque unless you have purchased the, very expensive, MLS(Multiple Layer Steel) gaskets. The instruction regarding loosening before re-tightening is spot on. The condition often referred to as "stick-slip" can require much higher force to break the bolt or nut loose than the torque spec calls for. I suggest selecting one of the nuts which seems not to move and mark the position then loosen and re-torque and take a look at the new position.
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Old 06-02-2016, 06:49 PM   #8
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Default Re: Retorque Heads

Thanks to all that responded to my question. JWL I will give it another try by marking a few nuts and see if they tighten.

Thanks to all
Ed
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Old 06-02-2016, 07:16 PM   #9
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Default Re: Retorque Heads

Just curious, when these engines were first built, was there a re-torque procedure performed either before or after installation in the vehicle?
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Old 06-02-2016, 07:31 PM   #10
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Default Re: Retorque Heads

Yes. "Ford recommended to its dealers that these nuts be retightened after the first 300 miles, which was/is good advice." ~ David G. Rehor, The 1932 Ford Book
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Old 06-03-2016, 05:00 AM   #11
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Default Re: Retorque Heads

Quote:
Originally Posted by Steve Staysko View Post
Yes. "Ford recommended to its dealers that these nuts be retightened after the first 300 miles, which was/is good advice." ~ David G. Rehor, The 1932 Ford Book
Interesting, wonder if in as much as '32 was the first year for the V8, it was a precautionary measure and if the same procedure continued to '53.
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Old 06-03-2016, 05:13 AM   #12
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Default Re: Retorque Heads

Yes, this re-torque was required at the Ford dealership I was most familiar with in the 1950's. It was done at the pre-delivery and again at the first check-up.
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Old 06-03-2016, 05:44 AM   #13
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Default Re: Retorque Heads

Quote:
Originally Posted by JWL View Post
Yes, this re-torque was required at the Ford dealership I was most familiar with in the 1950's. It was done at the pre-delivery and again at the first check-up.
So it was basically a dealership procedure and was not included information in an owners manual like some maintenance information is today.
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Old 06-10-2016, 03:19 PM   #14
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Default Re: Retorque Heads

Thanks to all for input. I finally had a chance to get back in the shop and try to retorque the heads. Marked the first 3 nuts in the tourque sequence and found that they did move (tighten) after I loosened slightly. Have retorqued all left hand head nuts except the 3 that attach the oil filter canister which I cannot get the torque wrench on. These I did tighten but by placing a combination wrench on them and tapping the wrench with a rubber hammer until I moved the nut approximately as much as the other nuts moved with torque wrench.
Does anyone have a better way of doing the nuts under the oil filter?
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Old 06-10-2016, 05:05 PM   #15
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Default Re: Retorque Heads

What you did is actually called "turn of the wrench", which is a valid method of getting the proper stretch on the stud or bolt. The method involves turning the nut down to a firm pull on a wrench to seat the nut and then turning the nut a specified number of degrees further.

Your method is probably OK since this whole torque thing is a little bit variable anyway, assuming you can't get a torque wrench on the nuts.

John
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Old 06-11-2016, 05:18 AM   #16
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Default Re: Retorque Heads

Yes, there is a tool which will reach around and over the oil canister, in most cases, and accept the torque wrench. It sort of looks like a box end wrench shaped with a "U" handle and has the 1/2" female square drive at the upper end. But, MANY Flatheads have been done using your described method.
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Old 06-11-2016, 07:19 AM   #17
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Default Re: Retorque Heads

When I did the top end on my Harley last year the book called for an initial torque of like 20 lb-ft and then tighten 90 degrees or a quarter turn. Given so many variables I'm surprised this method has not been cross referenced to older cars. I know some newer cars have studs or bolts that once stretched are considered unusable. I have a hard time wrapping my head around this as so many bolts and studs have been reused so many times for so many years without incident. It seems the goal is to maintain a given pressure uniformly across the gasket surface.
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Old 06-11-2016, 04:14 PM   #18
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Default Re: Retorque Heads

Frank,you may know all this, but for those that don't, there a two different systems:
The old way was to put tension on the assembly without stretching things beyond their elastic tension / length (what ever its called)
This allowed components to be re used time and time again, but a re torque is required.
The newer system is called"Torque to yield" This is where an assembly is torqued to a certain value, and then is pulled down so many more degrees.(there are many variations on this)
This is a one shot method in that it does not require a retorque. The studs /bolts are usually only good for one use, because they are stretched past their ability to shrink back. (if you were to use them again, they may break, or worse break in service) Think of the advantage for the modern motor vehicle manufacturer and how much work there would be to re torque a head.
Note for us old guys. When putting a head on that is "torque to yield" it is critically important to mark each bolt, as you go, because you cant go back and check it (If you try to go down another 180 degrees its probably going to break!) All make sense?
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Old 10-28-2016, 07:16 PM   #19
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Default Re: Retorque Heads

very old but informative thread dealing with torqueing head bolts. This is actually what I needed to read
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Old 10-29-2016, 12:54 AM   #20
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Default Re: Retorque Heads

Bluebell,we reco quite a lot of the small Japanese diesel engines in our shop. It's very scary after, say, a spec of 40NM+90deg+90deg doing the 2nd 90deg. Even with the correct lube on the threads and under washers,if fitted,some bolts come down ok BUT others creak and grown and you would swear that they will break. Touch wood it hasn't happened yet. As a side note to the retorque procedure we put a small paint pen mark on the bolt head and on the head next to it. That way we we can see if the head gasket is still coming down.
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