mercedes engineer - a Godsend, Haynes manual -the devil incarnate
 

Working on my engine swap project into the SD, I refer to the Haynes manual for engine mount bolt to body torque because it's handy - the FSM cd is in the computer upstairs and I'm covered in grease in the garage.
96ft lbs.
That seems high I thought to myself - the bolts are smaller than wheel studs and look to be "brass," but surely the manual must be right. I mean there it is in black and white - someone took the time to write, edit, and publish these figures, I'm sure they have a proof reader, so I continue on with my trusty clicker torque wrench. Crank, crank, crank, SNAP!
Uh oh.
Jack up the engine, remove the mount, ragged break inside the mount. CRAP!
Hey....What's this bolt for?
<remove bolt> Hey look! The hole is threaded all the way through. I pull the other mount bolt, hit the hole with PB Blaster and thread it through the back side. It works - It pushed the broken stud out enough to get the vice grips on it and pull it out.
Now some engineer toiling away in a dank, dark Stuttgart dungeon in the early '80s must have thought to himself - Hey, for 3 pfennig ?sp?, we can make this better, let's do it! And it actually got by the bean counters.
It's a really sad day when a simple thing like this - that made my day - is cut to save a few cents.
The Haynes manual, however will no longer be a reference for anything other than an alternate photo angle.

Now the lowly TD must have been cheaped out on - no access hole in the mount!

I think that Haynes divided when the should have multiplied when converting Nm to ft/lbs. The 617.95 manual specifies 70 Nm for that bolt, which converts to approx. 52 ft/lbs. If you do the conversion backwards, what do you get? 96 ft/lbs!!!

The bolts are not brass. The corrosion-preventing cadmium plating just makes them look like they are.

As a rough guideline, the screws on a M/B should be restricted to these values..........if no additional data is available:

6mm: 12 ft.-lbs.
8mm: 24 ft.-lbs.
10mm: 50 ft.-lbs.
12mm: 100 ft.-lbs.


.........see a pattern there?

I have found errors casually flipping through the Haynes 123 diesel manual. The most recent one I found last night. In the section showing pictures of the headlamps. The caption under the US headlight, Haynes calls it a UK version while the UK version photo they call it a US version. Not as serious as an erroniously high torque figure but confusing nonetheless.

The MB manuals are not without inconsistencies, either.

But I do suspect that the Haynes manual is directly responsible for many of the stripped engine mount threads reported on the forum. (It seems that the aluminum threads strip before the 12mm bolt breaks in most cases.)

Not so much inconsistencies, just plain no info, like for example, no torque specs for the manifolds or turbo to manifold, to name a couple.

Fortunately, early ths year I was able to score a 4-book set of W123 factory repair manuals off Craigslist for $75. I have some Haynes manuals for other makes, only because my local Fairfax County library system decided it would be a great shelf-space saving idea to discard all their Mitchell auto repair manuals.
I find the Haynes manuals to be pretty crappy, with much info on changing parts, but limited diagnostics, and lots of frustrating lawsuit-inspired references to the 'home mechanic', as in "Because the complexity of this repair is beyond the scope of the home mechanic, we recommend taking the vehicle to a professional repair shop."

Happy Motoring, Mark

Providing torque specs for some items but not others? Sounds pretty inconsistent to me!!!

I think that could be part of the definition of an inconsistency.

The MB service manual does not have any torque specs for the manifold.

I have used the haynes manuals for years and never broken a bolt, that I remember. There is no substitute for judgement. If you feel that the torque specified is too high you have to back off.

Myself, I find the nm and foot pound values listed side by side very confusing and often mark out the nm so that I don't use the wrong value when using tools calibrated in foot lb.

Sorry you had the trouble and glad it worked out without too much pain.

Tom W

The Haynes is a reference book. Rather than blaming the "book" why not accept responsibility. Common sense states that the size of that bolt will never support that amount of torque! None the less, I empathize with your dilemma and hope in the future when you whack your finger with a hammer, you don't blame the hammer.

Whoa, easy there captain ahab, put the cat back in the bag. 'Common sense' can be a slippery thing, I have certainly made a questionable choice (or 2) during my greasy wrenching adventures. TG learned something, and now so have I. Thanks for sharing.

That does not change the fact that the torque value in question in incorrect in the Haynes publication. There have been a number of reports on this forum of stripped threads in the engine support as a result of overtorquing the mount bolt.

Have you heard the saying "Good judgement comes from experience. Experience comes from bad judgement?"