Head bolt Torque Specs

[rb6667]

Getting ready to adjust the valves. (68 280 SL)  Any tips on head bolt torque procedures appreciated.

Thanks in advance





rb6667

67SS Chevelle
67SS Nova
67 Malibu
68 280SL

[ja17]

Hello rb,

You'll need a 10mm allen stud to begin. I like to use a good quality 1/2" drive allen stud.

You will need to disconnect the linkage cross-over rod (it pops out of the socket on the intake easily). Two special 10mm nuts hold it to the bracket above the spark plugs. Be sure  that these special nuts are installed with their curved surface inward so they center up the likage exactly during re-assembly. The brake booster hose will also need to be dis-connected and moved out of the way. Sometimes a floor jack is placed under the transmission and lifted slightly to allow the valve cover to clear the hood latch on the firewall. Normally if the rear tranmission mount is good and spaced upward correctly, this step is not needed. Be prepared to replace the valve cover gasket. This is re-usable and will last for years, however if it has gotten brittle and stiff ovwer the years it will need to be replaced. When the valve cover is off you may wish to check the slack on the timing chain and the play in the vertical timing gear (under the tach cable connection see previous posts "vertical timing gear").

Warm engine to operating temperature. Remove radiator cap to relieve pressure in the cooling system (important) before beginning re-toque. Follow the factory torque sequence (working from the middle outward), loosen only one head bolt at a time about one full turn, then re tighten it to 80 ft. lbs. (for a 280SL engine hot), then move on to the next bolt.

Be sure to loosen and tighten only one head bolt at a time before moving on to the next. You will be amazed how loose some of the bolts may have gotten over the years. Also watch that the steel valve cover hold down straps do not twist and contact the cam shaft during re-torque or you will get a mysterious tapping noise.

Let the engine cool completely before adjusting the valves.

Joe Alexander
Blacklick, Ohio

[jameshoward]

Joe,

I tried this on my car using your direction in a similar post, but I did not loosen the bolts first, I just put the torque wrench on them at the correct setting to see if the bolts were loose. The torque wrench cracked on all of the bolts and I therefore assumed that they were all at the correct setting. Having read what you've put here, am I to assume that my bolts may not be correct as I did not loosen them first then tighten?

James

[rb6667]

Joe, Very good information.  I am interested in why the bolts are to be loosened, and then re-torgued?  I've been a hands on car guy since the 60's, and have worked on German, and USA models all my life.  This is the first time I have heard of this procedure.  Please educate me.

Thanks for the response.


rb6667

67SS Chevelle
67SS Nova
67 Malibu
68 280SL

[ja17]

Hello,

Yes, this is a bit un-nerving. The head bolts can become stuck and to break them loose most often will require much more than the specified torque. So just trying to tighten them may not move the bolt at all until the crud is broke loose. Loosening the bolt first will do this and then you will get a true re-tightening. The important information is to be sure to release the pressure in the cooling system by unfastening the radiator cap and also loosen and tighten only one bolt at a time.

These are not "stretch style"  bolts which never need re-torqued, as used in latter Mercedes-engines.

I have used this method on these engines for over forty years and have never had any problems. Often subjecting these engines to the rigors and abuse of competition. The 280 series engines have only about 3 or 4mm of surface between cooling passages and the combustion chamber between each cylinder. These head gaskets must be kept torqued.

Yes James, you may not have gotten to full torque, it depends how stuck your head bolts have become over the years and how long since your last re-toque. I normally re-torque and adjust the valves at 12,000 mile intervals.

Joe Alexander
Blacklick, Ohio

[jameshoward]

Joe,

Thanks, as ever. I'm going to give this a go at the weekend, and at the same time check the tach bushing using your other post with photos on that subject.

James

 

[rb6667]

Joe, With that little "Meat" between the cooling passages and the chamber, no wonder this needs to be re-torqued.  Not a lot of Margin there.  Now it makes sense!

Thanks for the heads up.



rb6667

67SS Chevelle
67SS Nova
67 Malibu
68 280SL

[merrill]

Joe,
Hi,
So, long story short, I re torqued the head on my 66 230 sl using the procedure you posted on oct 07.
I did this because I noticed I was low on coolant and saw coolant trails on the block. I thought the coolant trails were from the numerous times I had to remove the IP and spilled coolant in the process.

Anyway, I used the 65 ft lbs for the head bolts which is the spec for the 230.
I used my torque wrench to loosen the bolts to see which were still tight. 
Only 5 of the 12 caused the torque wrench to click when loosening.  Yikes!
Tightened all up per the procedure.

Anyway, so about 250km later, today, I saw 3 trails of coolant on the side of the motor.
2 on the drivers side and one on the passenger.

The motor only has about 1800 miles on it from the rebuild at metric motors.
I did re torque the head after about 300Km when I go the car back up and running.

My first thought is to go ahead and re torque again.
Thoughts?

Thanks
Matt

[ja17]

Hello Matt,

Yes, at this point you have nothing to loose by trying it again. If it were me I  would even go 5 lbs over specs at this point.  Make sure the engine is still warm and the radiator cap has been released.

[thelews]

Others may disagree, but I don't loosen when retightening.  The force to loosen is different than to tighten.  I just check or tighten as needed using the prescribed pattern.  Tight is tight, and as long as it's to minimum spec and the head is not leaking, I leave well enough alone.  I've heard of others loosening all the bolts before retightening.  Talk about looking for problems...just asking to break the seal at the head gasket.  And, don't forget to check the valve clearances AFTER retightening.

[Benz Dr.]

Joe has the right procedure. It's the way I do it and the only way it should be done. One at a time not all at once.

 The amount of force to loosten the bolt is of no importance. Some will turn a lot more when tightened from the original position and some won't move at all. Keeping them all the same is what you should be looking for. Brief periods of overheating or hot running will make the head move around quite a bit so you need to take up any slack and keep it all tight.

The 280SL engine has a very fine slot milled into the block between each cylinder where coolant can run. So in fact the distance between the cylinders is less than 3 or 4 mmm when you take that into account.

[ja17]

Hello,

Alfred was present when I did the procedure on a 280SL. We noted that it took much more than the  80 ft. lbs of torque to break a head bolt loose. During the re-torque, we noticed the head bolt actually tightened down further than its original position. My interpretation of this is that some of the head bolts get "set" or stuck. It was no longer holding the head down tight but was just stuck. Loosening then re-tightening allows a accurate re-torque.

John is correct, you do not want to break the seal, that is why it is important to relieve the pressure in the cooling system before beginning and never loosen more than one bolt at a time during re-torque.

If you read some of the early Mercedes Factory Manuals, they actually describe the loosening and re-toquing procedure. These early engines used the same type and size head bolts, gaskets etc.

Now if you want to get scared, try changing a camshaft on your engine. You'll need to have at least eight head bolts loose at the same time!

Anyway I respect other opinions on the subject since there is no clear documentation on these specific engines.

I have been using this procedure since these cars were new. Never had any problems except on the cars that had never had  re-torque. These engines have problems with loose or stuck head bolts.

Some moden Mercedes engines require no re-torque at all. They use improved head gasket material and special "stretch style" head bolts which keep pulling down even after years of heat cylcles.

[merrill]

Hi All,
well, re torqued the head yesterday following the procedure Joe posted.

Drove the car and did not notice any leaks. 

Thanks again

[Naj ✝︎]

The procedure of first loosening and then retightening bolts has also to do with dynamic vs static coeffieients of friction.
Hence the torque wrench should click while the bolt is being tightened, not when static.
I believe all older engines, even new built ones used this procedure until the stretch bolts came into use.

naj

[rogerh113]

Didn't see any mention in the write-up of the smaller bolts up by the timing chain.  Do those need to be adjusted/retightened as part of the re-torquing process, and if so is there a spec (or is it just by feel and not toooo much)??  I also assume that they are done at the end of the process (if at all).

Regards -- Roger

[ja17]

Hello Roger,

These bolts do not hold back any engine compression pressure. Just carefully checking them by hand is more than adequate!  Be gentile.

[merrill]

Joe,
well, when you mentioned going 5 lbs over spec got me to thinking about my torque wrench.

Were I work we have a calibration station for the torque tools our technicians use. I realized It had been 2 years since I had my wrench checked.

Took it in and I was 9 lbs light on each setting (10 lb increments) up to 60 lbs.
Then at 60 it was way off.

I ended up purchasing a new torque wrench, had it checked and it was dead on.
I just re torqued the head yesterday, did the valves today and I will now keep an eye out for
any leaks.  I am doubtful any will show up now.

This lesson reminded me to make sure my torque tools are cared for and properly stored and used.    From now on I wlll get them checked at least once a year and I will follow the proper break in procedure each time I use them.

Snap on and precision instruments make an item called a "torque comparator" which is simply a dial gauge tool that verifies the torque setting on the wrench.  I may purchase one to keep an eye on my torque tools health.    The snap on tool is 2x the precision instruments version. they start at $200.

The torque comparator is much cheaper than the calibration equipment I have seen online for well over $1,000.    I guess if one had the need a torque comparator would be cheap insurance if precision work is called for.

any way, thanks again

[ja17]

Hello,

These small 6mm diameter allen bolts can be tightened by hand. These bolts hold down the chain gallery area of the head. This area is not under pressure like the compression chamber areas of the head. I suspect, that most of the time, these bolts are passed on a re-torque with no bad consequence.

[merrill]

well, there is one faint trail of coolant still leaking on the drivers side of the block just forward of the #4 spark plug

Any thoughts on where to go from here?  Should I re torque the head again?

[wwheeler]

I just torqued my 280 head bolts tonight and noticed one puzzling thing. My engine was rebuilt by the PO 15,000 miles or 12 years ago.

I warmed the engined up with the radiator cap off, so no pressure was built up. I removed throttle linkage and valve cover quickly so that the engine was still quite warm (with it being almost 100 F outside, it won't cool off quickly anyway). The #1 bolt was incredibly tight and I almost could not get it loose. Once it did release with a loud, unnerving crack, some small air bubbles were released around the oily bolt head but wasn't for more than a second. The other bolts got much easier to loosen as I went along and the air bubbles only released on the first 6 bolts or so. After that, no more air bubbles. Was this air from the cylinders that may have still been under pressure? Maybe I should have waited a little longer to loosen the bolts after stopping the engine. It definitely was not coolant coming out from the bolts.

I did find some bolts were pretty easy to loosen and those tended to be the outer bolts. Any thoughts on the escaping air?   

[mulrik]

Just a word of advice from the oracle.
I just retorqued my cylinder head bolts to 80 ft-lbs. But just recently discovered that the right setting for a 250 is actually 65 ft-lbs. Now what to do? Do I leave it as it is or re-torque one bolt a time to the correct specification.
The engine is totally restored this summer. Should also note that the reason why I retorqued was that I had a small leakage of coolant from between the head and the block just above spark plug # 6. The retorqueking slowed the leakage, and now it has sealed itself completely somehow.
Fear that the bolt or the block will take damage from my 20% overtorque, but on the other hand I also fear that my gasket will start to leak again or other bad things will show up if I loosen and retorque correctly. I have no idea why it leaked in the first place.
Retorque or leave it?
Thanks as always!!
BR,
Ulrik

[ja17]

Hello Mulrik,

Your leak is fixed and you did not break anything. I would leave it alone. Your next retorque in the future you may just set it a little lower (75 lbs.)

The bolts are actually the same on the 280 and the 250 engine, so there not much chance of one breaking.

[glenn]

Just removed the head on a '67 250SL.  The 10mm Allen rounded out 2 head bolts in the process.  Had to drill out and off the head bolts.  After lifting the head off, the 2 headless bolts(now 2" studs) screwed out by hand.

[Ron]

Hey Joe, thanks for this.  I agree with you and others, it seems clear that you need to loosen one turn, tighten to spec.  Radiator at atmospheric pressure. 

I have a 230SL with this head: 127 010 5020

I have done 4 retorques up to 65 ft-lbs.  The amount of water at top of dip stick (condensed) is almost 0 now, and the car no longer exhausts white smoke.  But it still has blue smoke after warming up for 20 minutes or more.  Could I go to 70 ft-lbs without cracking the head, or just do more 65's?

And, it has the tap in the cam shaft.  How do I get that to stop, loosen all bolts on that?  I'm worried that's going to break!  The rockers are adjusted, many checks.  It sounds like the middle of the cam is tapping.

Ron