It comes from decades of experience as a Journeyman mechanic ~ I don't just change parts, I try to learn new things on every job .

Wasp Waisted fasteners go back a long time, to the early 1940's that know of and being an air cooled mechanic (VW's & Motocycles mostly) I learned long ago that preventing broken or stripped out bolts & studs in high clamping situations coupled with large scale and frequent thermal cycles are the most important places to use them .

I know the DieselHeads here are a vast collective of knowledge and spare parts, I bet someone here has the correct original bolt lying 'round......

If I did I'd ship it to you post haste .

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

In the Factory Service Manual both on the CD and in the printed manual there is only a torque on the rocker arm bracket bolts.

Concerning the click type Torque wrenches. I saw a vid on one of the racing teams. He had the Engine on the stand and used a Click Type Torque wrench and went through the tuque sequence clicked on each bolt 3 time. When he was done he re-did all the bolts again clicking 3 times on each bolt and when he was finished he did the same thing one more time.

__________________
84 300D, 82 Volvo 244Gl Diesel

One of the good things about a torque wrench with a dial gauge is that you can use a cheater bar on them because the length of the handle dose not change the toque.
However, the longer handle often puts you too far away to read the dial. You, usually need 2 persons.

__________________
84 300D, 82 Volvo 244Gl Diesel

I too use a click typ, American made torque wrench and click it at least twice .

When I worked in L.A.P.D. Air Support we had a torque wrench testing & adjusting rig, I found it very handy, my old wrench from 1972 or so was almost 1/2 pound off after decades of Commercial Service .

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

Over approximately 25 years of routinely using Mercedes-Benz FSMs on W123-617s, I have discovered an abundance of instances where said FSMs leave out plenty of relevant information (in my view). Why? I have no idea.

As a matter of personal judgment and choice, I routinely replace relevant bolts on said W123-617s with replacements from M-B. A small price to pay to sleep better at night and stay calmer by day. Your mileage, as the phrase goes, may vary.

1) [See highlight] If the bolt had already been tightened to a torque that was greater than the setting on the wrench, then the wrench would immediately click without any further rotation of the bolt.

That is the sentence I was referring. I see that you did not use the word bottom. I meant no negativity toward you at all in either post and I am truly sorry for any negativity I may have caused by my perhaps loose use of terminology.

My original comment was stimulated by me observing guys at the tire shop going to the click then rotating the bolt another 1/8 of a turn. I am sure they think they are going a doubly good job but in my mind that extra turn after the initial click is all over torqueing.

For the record I have the highest respect for your comments on the forum. They are always filled with excellent information spoken in the context of a truly conscious professional.

My comments are based on the perspective of a formerly advanced hobby mechanic but now more of an interested observer and internet groupie. My mission is to offer general advice here and there, possibly make someone smile....not to make anyone frown, especially you Frank.

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Way back when as I was getting my GM training I noticed the lack of pertinent info and asked why were so many common service procedures not being mentioned in what I thought would be the 'bible' of tech/repair info ? .

'Because you're expected tp have taken previous factory training and know these basics' I was told .

Humph, not a good reply IMO .

I'm retired from spinning wenches now yet I'm still learning and sharing my limited knowledge .

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

This morning I wrote an MB parts vendor for guidance on what the correct replacement part # is. He sent me exactly the catalog listing I posted in post 10, except in English (attached). And to reiterate an earlier point, the grey bolt in the pictures many are so sceptical of is part number N304014010009, obtained from MB by Pelican.

Moreover, I have a trusted Mercedes-only indy mechanic nearby who has been in business since 1970, so diesel W123s were his bread and butter for the middle years of his career. He liberally dispenses technical advice to customers learning to DIY, but I don't like to ask too frequently, lest I strain the relationship. But I finally broke down and called him this morning as well. He gave me only the N304 part as the correct part, and said that these bolts were not supposed to be torque-to-yield bolts, and that some prior mechanic likely installed those in error. This didn't seem quite right to me, as I feel sure I have seen photos of these bolts in tutorials, and they looked like ones I pulled out. He did say there was a relevant VIN-split, but I didn't want to take too much of his time, so I didn't want to ask him what the part # was for the split.

I'm guessing the part # for the split is the A112 number listed in the catalog. I'm tempted to order it for science, but it goes for between 60 and 80 bucks. If I knew it was the correct part, I'd gladly pay for it, but I have no idea what to think now.

Ironically, I just completed a valve adjustment on my other 83 240, which is my daily driver, last weekend, and I should have looked at the head of the bolts on that engine while the valve cover was off. But that was before the N304 bolts had come in the mail, so this issue wasn't on my mind. I'll probably pull the cover this weekend just to see what's there.

Attached Thumbnails

 

The necked-down capscrews as used in these applications are not torque to yield, rather, they are tightened to a specific pre-load within the elastic range of the material. A torque to yield fastener is tightened past the elastic range and into the plastic (yield) range.

A decided waste of money; the necked-down version has been superseded.

Interesting info. My 2 om617 turbos both have the same necked down capscrews that ya broke.

If this kinda thing really bothers ya, drop me a PM. I have a spare head that’s cracked...

I think I'm convinced now that the bolts I bought are the intended replacement part, so I think I'm just going to put those in and see how it goes. But thanks for the offer, and I'll keep it in mind if something goes wrong.

My mechanic is surely not remembering some things correctly, as so many 616 and 617 engines seem to have the capscrews, it seems. In his defense, his son does most of the work anymore, so he probably hasn't taken the rocker arms off a W123 diesel personally in a number of years.

Thank you, I'm happy to be learning things like this. Also thank you for the information about torque vs. shear limits earlier. This was all new to me.

I agree, this doesn't seem like a good reply. It is indeed reasonable to expect people reading the FSM to know "basics", but I don't think some of the omissions we've been considering here fall under the head of basics.

The purpose of necked-down bolts is so the shaft is more elastic, to act more like a spring to maintain a more constant clamping force on something like a head gasket, as parts change dimensions from thermal expansion. Since the camshaft towers have no gasket, that seems unneeded here, but perhaps they used them due to mixing aluminum and steel parts. Most head bolts don't need a neck-down since they are long enough to be elastic. Torque-to-yield bolts are torqued to a value, then marked and turned an exact angle from there (ex. 1/2 turn). That is because the turning torque can decrease once the bolt starts yielding, so if you kept trying to reach a higher torque value, you would just neck down the bolt and break it. This bolt is thus not a torque-to-yield assembly.

Perhaps M-B got reports of snapped bolts so changed to a stronger straight-shaft bolt. Personally, I would have gone to Ace Hardware and looked for a Grade 8 bolt (not sure they have in metric). 28 ft-lbf is nothing, almost 1 hand on a 3/8" socket wrench, so little worry about snapping a quality bolt. Insure you use 2 hands when torquing, keeping one pushing against the head of the torque wrench so you apply a pure couple load and not also a bending load like you would by just pulling on the handle, though unlikely that caused this bolt to snap.

__________________
1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans