To torque or not to torque?

[FGN59]

I was talking to the mechanic who takes care of all my (relatively modern) cars the other day. This guy started out in a specialist shop for older cars restoration, before opening his own shop (for contemporary cars), and still dabbles into old cars and engines on the side as a hobby (he is not an MB specialist).

He told me that, as far as he knows, most if not all the head gaskets sold nowadays do not require retorquing after their initial installation, ever. To the contrary (he says), retorquing will probably degrade the quality of the bond between engine block, gasket and cylinder head, resulting in problems and possible damage further down the road, and should be avoided. Unless the new gaskets (installed in an older engine) were manufactured 'the old way', in which case it would need regular retorquing, but he never sees any 'old type' gaskets sold nowadays.

Speaking from my own experience:

The engine on my Dec 68 US specs 280SL has been completely rebuilt a little over two years and about 1700 miles ago. After some initial poor performance, I got the distributor/coil correctly set up, and it has been working really well since, even though I believe some FIP fine tuning is still necessary (which I am slowly developing the guts and understanding to maybe deal with, after reading hundreds of posts on this wonderful forum).

I had the cylinder head retorqued and valves adjusted by an 'oldies' specialist after the first 800 miles (that was before I spoke to the other mechanic...), and frankly didn't notice much difference before and after (but then, not being very experienced with this engine, I may not be a good judge of that).

What to think? Should the head be re-torqued regularly with modern gaskets? Are the gaskets now sold for our cars of the 'modern' type?

[Cees Klumper]

The idea behind re-torquing would be that a new gasket shrinks slightly in the beginning, so in order to make sure the head is torqued down to spec, after some time the bolts need to be torqued again to the specified value. If your mechanic is correct, that modern gaskets don't shrink anymore -the value of which is obvious- the re-torquing is not necessary anymore. But, it is also not harmful. Because when you try and re torque that new gasket, you will find that it is still/already at the specified value. So you will not introduce any additional force. That's my thinking, anyway. Should be easy to verify with the supplier/manufacturer of your new gasket.

[FGN59]

Well, his theory is that in order to torque, you first have to detorque, and that’s where problems may develop...

[Vander]

According to the technical manual the service interval for re-torquing the head/adjusting the valves is every 12,000 miles. Remember to re-torque the head hot, and adjust the valves cold. More information can be found in the manual.

[ja17]

Over the years, I have noticed, that the engines which have never been re-torqued, seemed to be the ones that end up with stuck rusted head bolt problems, and head gaskets that seep coolant. Modern engines use "stretch bolts" on the cylinder heads. The M130 head bolts are not "stretch bolts". The reason for using stretch bolts in modern engines is that they are designed to keep the torque constant even if the head gasket shrinks a bit. Stretch bolts are actually designed to be elastic. With a M130 engine, if the head gasket shrinks a bit from time or heat cycles, the bolt torque actually becomes less. It is true head gaskets are improved with better materials and construction these days, but our engines do not use stretch bolts and I am not convinced that complete shrinkage has been totally eliminated from the modern head gaskets. I guess time will tell, for me, I will, continue to re-torque.

[Iconic]

I was thinking about the whole bolt stretch component to this. I'm glad Joe brought it up.
Joe, as a point of clarification on the re-torque process, I simply put the socket on the head and torque to the appropriate value.
I do not, loosen first, then torque.
Which do you do, just apply the torque, or loosen, then re-torque?
I can't see any harm at all in simply applying the correct torque to the bolts.
Thanks for your help !!
Mark

[mrfatboy]

I would interested in hearing JA17’s method. Here is the instructions that came from Metric Motors.

[ja17]

Yes, I follow those instructions. The break loose torque is almost always quite a bit more than the tightening torque, especially if the bolts were not oiled correctly during the last assembly whenever that was? So it is critically important to always loosen the radiator cap to relieve pressure in the cooling system first. I then loosen each bolt one at a time and re-torque. I loosen it about one turn before re-tightening to spec. I then move to the next bolt, in proper sequence. Do not ever loosen all the head bolts at one time.  If a little oil seeps down the bolt shaft and onto the threads of the bolt when it is loosened, that is probably a good thing. I also do the first re-torque procedure after the first warm-up when a new head gasket is installed. This is also a good time to re-adjust the valves as everything is settling-in after being dis-assembled.
Of coarse you hear of rare accounts of head gasket failure or head bolts breaking when attempting to loosen them. The fact is that most likely, the head gasket was already failing from lack of re-torqueing. In such cases the coolant had previously migrated past the failing head gasket and into the head bolt holes in the block and caused the head bolt to rust and seize.

[Iconic]

Thanks Joe !
This is very clear.
Mark

[Rolf-Dieter ✝︎]

Thanks Joe !

To torque or not to torque?

Well, all I can say to this question is do it when ask for it, in fact do it for all fasteners if you like to use them again and again.

Last year while taking a spin in my Pagoda with 2 of our local Pagoda owners here in London, Ontario I encountered a Fan and Water Pump failure. The cause was later quite evident. My Mechanic stated that one of the bolts was over torqued. Repair bill for this failure was over $4,000-

See attached photos below. One of the remnants of the fan blades punctured the hood from below.

Hood repainting = 2,000- Canadian plus tax
Parts Fan, belts, water pump = 700- US
Labour for repair = 1,175- Canadian

Re-Tourque .... oh yes you bet (on my daily driver I have my wheels re-checked after changing wheels from summer to winter and visa versa.

From now on I ask my Mechanic "What tourque value will you be using for thos fasteners when it comes to changing gaskets etc.

Engineers developed torque values for safety also that fasteners are not overstreached etc. So use tourque values? Oh ja I say !!!

[ja17]

Hi Dieter,

That's scary!  Those blades are magnesium, strong but very brittle. I know of one that had a damaged blade which broke off and went completely through the steel hood of a Mercedes sedan!

[Rolf-Dieter ✝︎]

Hi Joe,

yes, it was very scary, my two companions were already parked in the gravel parking spot (I was last in our small caravan of 3 having not seen the left turn flasshing light from the 250SL in front of me). I made my u-turn to get to the gravel parking ara when the failure happend it sounded like my motor fell off the car. I shifted like crazy to come to a stop and not hitting one of the other Pagodas (the Park being opposite on the Pagoda to my SL 63 did not help in the moment of crisis). Anyway it was very scary and noisy.

Stay safe !

Dieter

BTW. I am not repairing (the hood "the little dimple does not bother me at all and will dean as a conversation topic at car shows LOL). The paint shop cannot garantee a perfect colour match to the rest of the car so I shall leave it as is.

[mercakungen]

Hello,

According to the Elring instructions the first re-torque should be done after the first warm up.
The symbol is confusing... we all know that these bolts are not for single use.

[ja17]

Thanks "mercakungen",  Also I see in the photo that this is a modern head gasket with a red sealing strip.

[FGN59]

Alright, thank you all for the collective wisdom. Retorque it shall be henceforth!

[Benz Dr.]

Thanks Joe !

To torque or not to torque?

Well, all I can say to this question is do it when ask for it, in fact do it for all fasteners if you like to use them again and again.

Last year while taking a spin in my Pagoda with 2 of our local Pagoda owners here in London, Ontario I encountered a Fan and Water Pump failure. The cause was later quite evident. My Mechanic stated that one of the bolts was over torqued. Repair bill for this failure was over $4,000-

See attached photos below. One of the remnants of the fan blades punctured the hood from below.

Hood repainting = 2,000- Canadian plus tax
Parts Fan, belts, water pump = 700- US
Labour for repair = 1,175- Canadian

Re-Tourque .... oh yes you bet (on my daily driver I have my wheels re-checked after changing wheels from summer to winter and visa versa.

From now on I ask my Mechanic "What tourque value will you be using for thos fasteners when it comes to changing gaskets etc.

Engineers developed torque values for safety also that fasteners are not overstreached etc. So use tourque values? Oh ja I say !!!

I looked at your picture and I'm not seeing that failure.  It's only a 8mm screw with a10 mm head that holds the visco clutch onto the hub on the water pump. It's not possible to over-torque those screws because the small 10 mm head will round off first. Limited acess means an open ended wrench which limits torque anyway.