Time to re- torque head bolts...

[worzella]

.....or have I waited too long ?

 

Rebuilt motor about 3000 miles ago and had a todo to re-torque the head bolts. I have conflicting notes. One says after 600 miles and other said 5000.

 

Opinions? Should I do it ASAP or wait that extra 2000?

 

Regardless my notes say 1/4 turn to loosen in proper pattern and re-torque with proper pattern

 

Thanks - Randy

[Preyupy]

Every engine rebuilder has their own system of engine break in.  It depends a lot on the engine and more importantly the type of head gasket and head bolts.  You didn’t say what engine you are dealing with but given this site primarily deals with M10 based engines let’s start there.  If this is a close to stock engine (compression ratio and gasket materials) the need to retorque the head is based more on the compressibility of the head gasket and number of heat cycles than mileage.  

 

Long story made short, retorque as soon as convenient and I never back the bolts off first, just retorque to the stock specification. Ifthe bolt moves fine, if not even better.   

[Schnellvintage]

Agreed, +1 for above. Preyupy said it perfectly.
Retorque means exactly that. Torque bolt again to standard or last torqued value, without backing off first.


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[roadhog0]

+2. That's what I do.

[2002Scoob]

Back to the HG... if it’s final torque procedure is not an overall value, but an angle measurement, do you still need to retorque? I thought not?


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[Buckeye]

Service Information Bulletin See section 4

 

[AustrianVespaGuy]

Also plan things so that you do the post-break in valve adjustment at the same time while you have the valve cover off!

[TobyB]

I am conflicted, personally-

the angle method was something that was supposed

to eliminate retorques.  But it DOES loosen.  Far less than 63 ft- lbs

used to, but it loosens.  Is that what it's supposed to do?  I dunno.

 

Then there's the 63 ft- lbs, and retorque later.  Like Preyupy, I thought, 

"if it doesn't turn, better".  But then I read all of Carroll Smith's books, and

discovered that if the bolt didn't turn, I could 'click' it loose just a 1/32nd of a turn-

and then it WOULD retorque, quite a bit MORE than the 1/32nd I'd use to break it

loose.  So the threads were bound, and there wasn't the full tension on the fastener.

 

So now I follow the sheet that comes with the gasket, and hope for the best*

 

t

*except on racing engines, where I can't resist a retorque after the first weekend on the engine.

[landon]

From a structural engineering viewpoint, the angle method should give you a more accurate measure of tension in the bolt. We never recommend torque wrenches because they must be calibrated and the bolts must have some lubrication to avoid binding and false readings. This is a big variable. The trick to the angle method is determining a "snug tight" condition from which to start measuring the angle. The BMW procedure uses a torque wrench to get this point and again the wrench should be calibrated. Start too soon and you don't achieve adequate tension. I'm not sure how that relates to a compressible gasket so maybe someone has a mechanical engineering viewpoint?     

[Preyupy]

If you read all of the information that is available on threaded fasteners this all becomes a moot point because you will not have any extra time to actually work on your car or drive it.  The M10 engine was not designed with a torque to yield head bolt.  Many of the later BMW engines did starting with the M20 engine. 

 

The original specification for head bolt torque was to get there in 3 stages 35-45Nm (25-33ft.lb) 60-65Nm (43-47ft.lb) 68-72 (49-52ft.lb)

 

We found that on our early race engines using stock non cutter ring gaskets 70 ft.lbs did the best job of keeping the headgasket intact without distorting the top of the cylinder bores or crushing the cylinder head around the rocker shafts. 

 

If you get a set of ARP head studs the top end of the stud is a fine thread and they specify a torque of 90ft.lbs!!!!!!  not a torque angle! 

This is based on the tensile strength of their fastener and obviously gives little or no consideration to either the block or cylinder head as far as structural damage.  The 1st problem you will have is that fact that you have crushed the aluminum cylinder head around the rocker arm shafts and you will have a hell of a time removing them.  Unless you bored the block using a suitable torque plate (using the ARP studs torqued to 90ft.lb) you will have a problem with the top of your cylinder bores being out of round because of the increased load put through the top of the block.  Each one of these studs has a clamping force of at least 11,000 lbs when installed (that is a total of 110,000 lbs for all 10 studs!)

 

You need to hold the head in place,  no one has proven to me that the stock Head bolts are incapable of doing that job.  at roughly 80 ft.lbs of torque the stock head bolts start to deform the top of the bores enough you really need to use a Torque plate (I use them for all engines anyway).   I have built a number of engines using the ARP studs but I sure don't use their torque spec, usually because someone has supplied me with the stud kit,  it makes taking the head off in the car a lot harder

[dang]

I guess I'm confused (again).  I thought you used the angle method with stretch bolts to ensure the bolts go past the elastic point.  Aren't the bolts on a 2002 head torque bolts (name?) and just get torqued at multiple values up to the set point?  If you start out with a torque wrench and end with angle pulls, doesn't that defeat the purpose if the bolts are not stretching?

[worzella]

Thanks all!! 

 

I will review my receipts to see what parts I used. 

[TobyB]

18 hours ago, dang said:

I guess I'm confused (again).  I thought you used the angle method with stretch bolts to ensure the bolts go past the elastic point.  Aren't the bolts on a 2002 head torque bolts (name?) and just get torqued at multiple values up to the set point?  If you start out with a torque wrench and end with angle pulls, doesn't that defeat the purpose if the bolts are not stretching?

Nope, not past the elastic point.  They stay in the elastic range.  

 

the M10 is designed for the bolts to be within their elastic range- and under the deformation

point of the head, which seems start to happen north of 80 ft- lbs on a stock fastener.  Oiled, as per instructions.

 

Which I have used on every engine I've opened.  I don't even change them if I don't see any visible damage, and they all measure

the same length.  

 

t

only has head gasket problems when overheating, detonating, or both.

[dang]

7 hours ago, TobyB said:

Nope, not past the elastic point.  They stay in the elastic range.  

 

the M10 is designed for the bolts to be within their elastic range- and under the deformation

point of the head, which seems start to happen north of 80 ft- lbs on a stock fastener.  Oiled, as per instructions.

 

Which I have used on every engine I've opened.  I don't even change them if I don't see any visible damage, and they all measure

the same length.  

 

t

only has head gasket problems when overheating, detonating, or both.

 

Okay, let me ask it another way then.  Standard M10 engine head bolts are larger diameter and were typically torqued down with a torque setting on a wrench, but now they are also torqued down with an angle wrench to specific degrees?  My understand is that angle wrenches are only used with stretch bolts, smaller diameter that "lose their molecular alignment" and then self harden, so to speak.

[TobyB]

Yeah, one can only speculate that the head gaskets that come with that specification

are designed for it, as the elastic limit of an M10 head bolt is WAAAYYYY beyond what

70 ft- lbs can achieve.

 

The M10 angle method is VERY different than the VW/later BMW way- it's fractions of a turn,

rather than whole turns after a 'start' torque. (THAT makes my stomach turn.)

When I had race engine heads off regularly, I compared the torque to the angle method, 

and found that they were pretty similar in result.  The then- current gasket would be within

1/4 turn of 'bottoming'* when the angle method was used, and the 66 ft/lbs was

within a 1/2 turn, but maybe not as consistently.

* when the gasket 'bottomed', the fastener pretty much stopped turning and torque went up very rapidly with any rotation.

 

Anyway, in short, I think the angle science is in the crush of the head gasket, nothing to do with the fastener.

 

t