question: to retorque or not retorque the head bolts

[deQuincey]

question: to retorque or not retorque the head bolts, SOLVED !!!

hi,

this is a little question, but it can become important

i did redo my engine one month ago, so it was closed and prepared and reinstalled in the car, and i have droven the equivalent to 600miles, (1000km) with it

the manual says that i have to retorque the head bolts after that driving distance, but i am not sure to do or not to do so

opinions, please ?

the procedure seems to be: undo each bolt 1/4 of turn in the prescribed sequence, and then retorque it at the value of the third stage of the torquing sequence (72 N.m)

do you agree on the procedure ? any tips ?

 

[HB Chris]

When I rebuilt the head I torqued the bolts to the spec but did NOT loosen them first after 600 miles. I did not replace the bolts either. I got maybe one more click from the torque wrench on each bolt.

Chris

 

[dang]

If it were me I'd probably just check the torque without loosening them first. The only drawback I see is not knowing if any of them are over torqued. Non-stretch bolts, like the ones on our coupes, don't need to be replaced when reusing.

 

[deQuincey]

If it were me I'd probably just check the torque without loosening them first. The only drawback I see is not knowing if any of them are over torqued. Non-stretch bolts, like the ones on our coupes, don't need to be replaced when reusing.

i doubt that would be correct !

when you have those bolts for two months inside the engine, they get stuck (glued to the washer and head), so there is no chance of checking the torque, apparently when you check the torque you can read even higher values than the initially given

i think that is the reason for undoing the bolts first

 

[HB Chris]

I followed the instructions that came with the Head Gasket which was confirmed by Mesa Performance here in Costa Mesa where I bought it.

Chris

 

[HB Chris]

When I retorqued the bolts and it "clicked" it doesn't mean the bolt ever moved, if it was at the proper torque already. Some may have moved very slightly. My head gasket specified torque, not degrees, so that is what I did.

 

[MMercury]

The easiest answer is to follow the instructions that came with your head gasket, or find the manufacturer's web site and see what it/they recommend.

It is likely that the 30+ year old shop manual you are using was last updated in 1976. As noted in an earlier post, BMW superseded its prior head bolt torquing recommendations with a "tighten, rest and angle" method - in or around 1986. This later method presumptively permits more accurate and uniform torquing results than the previous method. http://www.e9coupe.com/forum/showthread.php?t=9556

Fel-Pro is a popular head gasket brand in North America, selling gaskets for the M30 engine. (It is possible that they sell some of the same gaskets as Elring or Goetz, but I cannot confirm this.) Fel-Pro's website offers a head bolt gasket installation guide that appears to be current. http://olybrake.com/pdf/fel_pro_torque_specs_guide.pdf(See page 18 ) They recommend a multistage torquing process with a final "re-torque" at 600 miles. The guide is ambiguous as to whether re-torquing involves loosening each bolt before applying the final torque value as is a common practice in other reference works, such as the BMW shop manual (http://www.e9-driven.com/Public/Library/BMW-E9-Manual/pages/en/11121010.html#refertoc)

"Caution! Tighten cylinder head bolts after 1000 km (600 miles). This is done by loosening the bolts slightly and then tightening them to the specified torque¹."
​

Haynes also suggests checking the torque wrench settings of the head bolts after the first 600 miles, advising to check the bolts when cold.

"This time slacken each bolt one quarter of a turn before tightening it to the specified torque. Always tighten the bolts in the sequence given in the diagram."
​

Checking to ensure that the torque values are accurate by listening for the click of the wrench - without loosening the bolt - may prove problematic. If one accepts the view that static resistance or friction is generally greater than dynamic friction, using the same click-type torque wrench for a pre-torqued fastener may affect the accuracy of the wrench and possibly lead to over-torquing. At least the two references (BMW and Haynes) imply as much, otherwise, why would they both suggest this approach?

For a more scientific, albeit general, discussion of fastener installation, including "preload scatter,"see: http://arp-bolts.com/pages/technical_installation.shtml
http://issuu.com/arpbolts/docs/catalog2.pdf?mode=embed&layout=http%3A%2F%2Fskin.issuu.com%2Fv%2Flight%2Flayout.xml&showFlipBtn=true
http://www.boltscience.com/pages/faq.htm#4

Another consideration is that the method for re-torquing probably is probably not that critical inasmuch as most torque wrenches (other than beam type) are notoriously inaccurate, especially if they haven't been recently re-calibrated.

Videos for re-torquing BMW Motorcycles engines may be instructive: https://www.bmwmc.net/uploads/tm11/R4V EngSvc115_medium.wmv and http://www.youtube.com/watch?v=x69Tn7Gsk5c and http://www.youtube.com/watch?v=P6Cb6lmFMME&feature=related

Under the circumstances, if you did not receive instructions from your gasket manufacturer specifying that your gasket did not require re-torquing, or you did not install the gasket using BMW's newer angle torque recommendations, it would seem that slightly loosening the bolts before re-torquing is consistent with the advice given by at least one gasket retailer and the (older) shop manual. To reiterate an earlier post: "There is probably nothing inherently wrong with the factory's 40-year-old torquing prescription as found in the shop manual. Many engines with cylinder heads that were attached using the 'old method,' somehow manage to remain on the road today."

More food for thought: http://forums.corvetteforum.com/c5-t...procedure.html

 

[HB Chris]

Hmmm, how do I move and modify my posts at the same time? I think we've beat this one to death.

 

[deQuincey]

thanks to all, specially to the extended answer of mmercury

i made a check in the web page of victor reinz, that is the make of the gasket that bmw provides you with

bad news on one hand, the specs of victorreinz gaskets are of the type of torque+angle, and do not require retorquing...., the problem is that i didnt knew that when closing my engine (no specification was endorsed to the gasket) so i decided to follow bmw manual instructions, the famous three stage torquing procedure

it must be said that the engine was built and closed outside the car, so the intermediate warming up step cannot be done

as mr.mercury says there is nothing wrong with it, the newest torque+angle procedure was developped to avoid the antieconomic retorquing procedure, but this later procedure involves the using of special bolts that are aimed to be done passing the yield strength so entering in the plastic side of the material diagram, this is done by means of the last step ( angle ), of the later procedure

so, as a summary, considering that i have used the gasket and more important, the bolts (new bolts in my case), in a conventional way using a three stage procedure, i consider that in order to be coherent with the procedure used until now, i MUST retorque my bolts

and what it is also clear is that i must retorque them by prior loosening them a quarter of a turn to retorque in the dynamic range of the friction so avoiding false values of torque as mrmercury clearly stated

agree ?

regards

 

[MMercury]

i made a check in the web page of victor reinz, that is the make of the gasket that bmw provides you with

bad news on one hand, the specs of victorreinz gaskets are of the type of torque+angle, and do not require retorquing...., the problem is that i didnt knew that when closing my engine (no specification was endorsed to the gasket) so i decided to follow bmw manual instructions, the famous three stage torquing procedure

so, as a summary, considering that i have used the gasket and more important, the bolts (new bolts in my case), in a conventional way using a three stage procedure, i consider that in order to be coherent with the procedure used until now, i MUST retorque my bolts

agree ?

Yes, for what it's worth.

The purpose for the final “re-torque,” after several hundred miles, was to ensure even and consistent clamping loads exerted by each head bolt - after repeated thermal cycles. Head gasket and head bolt technology has evidently progressed so that a more accurate result can be achieved by the torque+angle method**. According to VReinz's site, the “old school” graduated torquing procedure can result in +or- 30% deviation in clamping force for each fastener, whereas the torque-angle method results in a +or- 10% deviation. http://www.reinz.de/pictures/39-00129-10_PI_2_Bolts-low-e.pdf

I do not think the method for a final re-torque of the head bolts is extremely significant, since you are attempting to fit within a permissible range of fastener tension. Thus, merely checking that the bolts are significantly “torqued” (as described by Chris, without loosening each bolt), is probably adequate for your purposes.*** However, the fact that BMW and Haynes both advise slightly loosening each bolt before a final tightening seems equally compelling. To borrow from another blogger's explanation: "When retorquing, you have to loosen them a bit, you don't have any other choice. This is because the dynamic friction coef[ficient] is lower than the static friction. This means it takes MORE torque to move a static object than it takes to keep it in movement. When torquing bolts, you have to make sure the bolt is actually moving when you reach the desired torque." http://www.3geez.com/forum/showthread.php?t=70225

I suppose it bears mentioning that others recommend loosening each bolt slightly before re-tightening them (even with the torque-angle method).

____________________
​

"CAUTION: Undo only one cylinder head bolt at a time, then tighten it to the correct torque and angle. Only then move on to the next bolt." http://www.fordscorpio.co.uk/manual/engines/tdi/TDICHBolts.pdf

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​

"To address an external oil or coolant leak from the cylinder head gasket when no engine overheating or other running complaints have occurred, it is only necessary to retorque the cylinder head bolts. Cylinder head removal and gasket replacement is not necessary in most cases. This procedure should be done when cold and this procedure should be followed completely on each headbolt. If any bolt does not tighten completely, that bolt must be replaced with a new bolt.

"STEP 1 Unplug the connector and remove the ignition discharge module and spark plugs
Undo the crankcase breather pipe on the valve cover
Remove the nipple for crankcase ventilation and vacuum fitting from the valve cover
Remove the valve cover
STEP 2 Loosen one bolt at a time and do the procedure for each bolt
STEP 3 Tighten to 44 ft lb
STEP 4 Tighten a further 90 degrees
STEP 5 Repeat for all bolts in sequence from the link below:" http://www.thesaabsite.com/Saab_head-gasket-retorque.htm

____________________

​

Despite all of the above, if you are seeking additional peace of mind, you might still consider substantially complying with the gasket manufacturer’s instructions - at least with respect to the final torque-angle procedure. In other words, why not skip to the final recommended step for torquing each bolt along with the directed final angle? If this requires loosening each bolt before torquing and “angling,” several authorities indicate this is permissible. Of course, even though the "old fashion" method can result in being 30% above or below the recommended clamping values, who is to say, you still could not obtain 0% deviation?

http://www.tracystruesoaps.com/tutorials/850hg/p8.html

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**http://www.hexagon.de/tasignat.htm

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***BMW's shop manual's Deutsche to English translation is unnecessarily confusing. For example it describes the 600 mile "re-torque" as the bolts being "tightened again" and not merely "checked" or "remeasured." It also seems to contemplate even more tightening "at normal service intervals."

"Run engine to operating temperature. After the test run let engine cool off to 35° C (95° F). Give final torque to cylinder head bolts. The cylinder head bolts are tightened again after a distance of 1000 km (600 miles) and then at the normal intervals." http://www.e9-driven.com/Public/Library/BMW-E9-Manual/pages/en/11121000.html

​

The "3.75" manual continues by describing the tightening process:

"Note: Tighten cylinder head studs again after 1000km (600 miles). To do this, first loosen studs slightly and then tighten to specified torque1."
​

This description differs from an earlier version "6.72" which advises:

"first loosen studs somewhat and then tighten to specified torque." ​

 

[sfdon]

A couple of comments....

First of all- MMercury is owed a least a good bottle of wine for all his well thought reasoning.

I would caution anyone for attempting to re-torque if they do so by loosening the head bolt too much or for too long of a time. A huge risk of residual oil in the bolt bore filling the area below the bolt and then fracturing the block as the bolt is re-torqued.
I also wonder where the 72 Nm for the 3rd torque number is coming from? My reading of the BMW torque specs show 100 Nm for 3rd torque where 100 Nm =73 lbs
When I re-torque e30 heads to stop oil leaks, I always loosen slightly with a breaker bar and then re-torque with the torque wrench that is stored at 2-5 lbs of torque.

 

[Luis A.]

...then re-torque with the torque wrench that is stored at 2-5 lbs of torque.

Don, can you explain that statement.

 

[sfdon]

From the Team Torque Website...

Torque Tips
Caring for your Torque Instruments



• Storage: All torque instruments should be stored in their original case. Avoid any storage locations that are subject to high or low temperatures and high humidity. "Clicker" style torque wrenches should always be turned down and stored at the torque wrenches lowest possible setting.



Reasons for Torque Wrench Failure


• Improper Storage - Storing the tool in conditions that will lead to the corrosion in the tool. High humidity areas for instance. Storing "clicker" style torque wrenches in any setting besides the lowest one will cause main spring wear and failure.

 

[IS3FIFTY]

so, as a summary, considering that i have used the gasket and more important, the bolts (new bolts in my case), in a conventional way using a three stage procedure, i consider that in order to be coherent with the procedure used until now, i MUST retorque my bolts

Your reasoning makes some sense but you have to keep in mind that today's Reinz gasket is designed to work with stretch bolts (which I assume is what your new bolts are) whereas the original equipment head gasket used non-stretch bolts. So, the steps as described in the original BMW manual don't apply to the modern head gasket/bolts combination (including the re-tightening after 1000 km).

Furthermore, there is no such thing as re-torquing stretch bolts. By design, these bolts are not elastic, and once stretched they do not come back to their initial shape and elasticity. That's why we don't re-use stretch bolts when installing a new HG.

At this point, other than buying a new set of bolts, you can try to evaluate what the delta between the torque that you applied following the steps from the manual and the torque/angle required for the new bolts is and apply this delta (if delta there is) to the bolts. In any event, do not remove the bolts to start over again because, now that they have already stretched some, if you remove them and re-torque them 1) you will not get the required clamping force, and 2) they may break when you go through the torque + angle procedure again (because now you're stretching them in their plastic state).

This is my recommendation as former product director for Goetze and Payen but I'm sure that the Reinz guys would tell you the same thing.

 

[deQuincey]

thank you all very much for your comments

ok, it is difficult to summarise all the information, tips, and so on, but i will try somehow to complete the puzzle

one of the key doubts i have now is to know if my bolts have gone to the plastic side of their behaviour, it is clear for me that if they already are in that plastic side i can not loosen or retorque them, but how can i possibly know that ?

who knows if the assembly procedure of the head gasket done by the old three stage method is leading the bolts into the plastic side ?

i can not be sure, but i dont think so, mi assumption is that the bolts are already before the yield strength point, that means, beingin the elastic side i can loosen them and retorque in a conventional way even being strech bolts...., and what are the reasons for this ?, ok i assume that the three stage old way is not intended to movethe bolts until the plastic side of their behaviour, yeah, the only doubt is that probably the diameter of the new bolts is slightly smaller that the original ones so their yield streghth is lower.... ? ? ?

what i would not attemp is to retorque them in the angle way

in any case i am considering the one by one loosenign plus retorquing sequence

are you confortable with my thoughts, or you see any failure ?

and thanks again

 

[deQuincey]

First of all- MMercury is owed a least a good bottle of wine for all his well thought reasoning.

I would caution anyone for attempting to re-torque if they do so by loosening the head bolt too much or for too long of a time. A huge risk of residual oil in the bolt bore filling the area below the bolt and then fracturing the block as the bolt is re-torqued.
I also wonder where the 72 Nm for the 3rd torque number is coming from? My reading of the BMW torque specs show 100 Nm for 3rd torque where 100 Nm =73 lbs
When I re-torque e30 heads to stop oil leaks, I always loosen slightly with a breaker bar and then re-torque with the torque wrench that is stored at 2-5 lbs of torque.

hi, sfdon, i have just rechecked the third stage values in my books and it says: 68 to 72 N.m, and it coincide in the HAYNES, and in the BMW BLUE BOOKS !

so the question is where does that 100N.m come from ? my engine is a 3.0CS

regards

 

[dang]

I've never heard of replacing non-stretch bolts with stretch bolts. How do they compensate for the larger sized bolts and fewer number of bolts? Not disagreeing, just never dealt with it before. I suppose its all done with the make up of the metal, but them's some big bolts!

 

[MMercury]

Your reasoning makes some sense but you have to keep in mind that today's Reinz gasket is designed to work with stretch bolts (which I assume is what your new bolts are) whereas the original equipment head gasket used non-stretch bolts. So, the steps as described in the original BMW manual don't apply to the modern head gasket/bolts combination (including the re-tightening after 1000 km).

Maybe, maybe not. :wink:

I suppose the point of the exposition gets lost in its length. The target “final“ torque can be measured in a number of ways, some of which tend to be more accurate than others. Loosening “slightly” or “somewhat” or “one quarter turn” before final tightening is far from exacting directions, but as DonSF suggested, the biggest concern in leaving the fastener under tension. This, of course, presumes that each head bolt was lightly oiled as described by the Reinz pictorial.

Respecting deQuincey’s concern about going plastic, if he stayed within the “range” of recommended torque settings with the old style (non-stretch) bolts, it is probably not a concern. When a bolt becomes stretched, the stretching makes it plastic. The stock OEM bolts used in the E9 were designed differently than the torque to yield bolts used in newer applications. Absent abuse, the older style bolts do not (usually) become permanently deformed after final torque is applied. The torque-to yield bolts do become permanently deformed, so if deQuincey used new torque-to-yield or stretch bolts, backing off and re-tightening them by any method would seem unwise.

IS3FIFTY raises an interesting point regarding the newer instructions and whether they should be followed only with use of the newer style gasket and the newer style bolts, or for use with a newer gasket and older style bolts. I would submit that the amended torque-angle instructions can be used with the newer gasket and the older style bolts. Again, the older torque-in-stages method is tried and true, and probably could be used without issue. But conventional wisdom is that the torque-angle method is presumptively more accurate. If you look at the BMW 1986 bulletin, it specifically states “Revised tightening procedure for cylinder head bolts, valid for old and new version bolts.” It continues by stating that the [new] procedure “should” be followed on all BMW engines and that the procedure/s “eliminate the requirement for cylinder head retorquing at pre-delivery inspection and 1200 mile inspection.” I would not be surprised if some of the other manufacturers or retailers did not offer similar advice, although it is probably to their economic benefit to always encourage the use of brand new fasteners and gaskets, whether or not they are absolutely necessary.

 

[MMercury]

I've never heard of replacing non-stretch bolts with stretch bolts. How do they compensate for the larger sized bolts and fewer number of bolts? Not disagreeing, just never dealt with it before. I suppose its all done with the make up of the metal, but them's some big bolts!

Dang, please take a look at the '86 bulletin. You will note that there are at least two variations of head bolts [long and short shouldered] and (for all I know) possibly more. I think the point being, not to mix them up. :wink:

 

[Luis A.]

MMErcury,

Good info. Are these bulletins online somewhere? My binders date from 1/76 and I'd love to have all updates such as this one. TIA!