I opened the can of worms known as a rear main seal replacement, and now I have questions pertaining to the connecting rod bolts.

Currently, the engine is mounted in a stand upside down and I just set the crankshaft into the engine last night. I have not installed any rod or crank caps yet. Prior to tearing this thing open, I was careful to mark the timing chain and sprocket locations and I made sure that the chain stayed put on the injector pump sprocket. I did not remove the cam or the head and I'm hoping to put everything back together without upsetting my timing. I'm REALLY hoping that I do not need to dig any deeper into this project, but I will in order to do things the right way if necessary. I'm at the point of contemplating installation of rod caps and torquing everything down which leads me into the current conundrum...

The FSM states that the rod bolts should be replaced, yet I found another factory service procedure stating that the bolts can be reused unless the necked-down portion is less than 8.0mm. So, which is it?

Have others re-used the bolts with good results? Catastrophic results?

Assuming that I do need to replace them:
1.) Can they be removed/re-installed without removing the pistons? If not, can the pistons be removed from the bottom (in order to avoid head/cam/timing issues)?
2.) What is the correct part number, and where is the best place to buy them? I'm finding that several MB part vendors are not stocking the rod bolts. I'm also finding two part numbers referenced for my vehicle (1985 300TD-T) on various online parts look-ups; 6150380271 and 6150380571. Which number is correct, or if neither is correct, what is the right number?

Thanks in advance for your help! I'm stuck until I consult with all of the experts.

Do not remove and replace rod bolts yourself. This is a machine shop operation. Upon changing rod bolts, rods should be resized. This means rods removed from engine.

If you found a spec for 8MM then check that and reuse the bolts if they meet spec. I have overhauled several 616/617 engines and have yet to touch the rod bolts.

Hope this helps.

__________________
2001 SLK 320 six speed manual
2014 Porsche Cayenne six speed manual

Annoy a Liberal, Read the Constitution

Is this the same engine from back in 08 when you were trying to pull the upper pan with engine in car? As you mentioned in that thread you really are a procrastinator.

I have the same job coming up to replace the rear seal, and was wondering the same thing about the bolts. easy to replace the seal, just everything you have to do to get to it.

Charlie

__________________
there were three HP ratings on the OM616...

1) Not much power
2) Even less power
3) Not nearly enough power!! 240D w/auto

Anyone that thinks a 240D is slow drives too fast.

80 240D Naturally Exasperated, 4-Spd 388k DD 150mph spedo 3:58 Diff

We are advised to NOT judge ALL Muslims by the actions of a few lunatics, but we are encouraged to judge ALL gun owners by the actions of a few lunatics. Funny how that works

I've reused connecting rod bolts on a 616/617. They came within spec at the neck. So far I haven't thrown any rods yet..... knock on wood!

But they are easy to replace. Just tap them out with a hammer.


.

__________________
1983 123.133 California
- GreaseCar Veg System

I don't see way the Rod would need to be resized after replacing the Con Rod Bolts.

Once they are replced torque them properly and measure the ID of the lower end of the Rod and see if it is round. If it is there should be no issues that need resizing.
That is one of the things that is done on other Engines.

__________________
84 300D, 82 Volvo 244Gl Diesel

Yup, that's me!!! Was it really 2008?!?!? Wow... And you remembered me?

Although pulling the upper pan w/ the engine still in the car seems to be an ongoing urban legend, I can testify that the engine did indeed need to be pulled.

Now, back on task. This is the re-use procedure that I referenced in my original post:

Checking, renewing and tightening connecting rod bolts

I will measure the bolt necks tonight. I'm keeping my fingers crossed that they are within spec.

I too am wondering about that. A&R, can you elaborate?

My understanding is the rule of thumb is that you "should" resize the connecting rod when you replace the bolts. The big end gets distorted in terms of roundness in relation to the clamping down of the specific bolt. When you introduce a new bolt, the relation of the clamping down force has changed.

But resizing requires having the rods and pistons removed and taken the a machine shop. At that point it is "Might as Well" rebuild the whole motor as you have to remove the head to get the pistons out.

My opinion is you would get by fine without resizing on a stock motor and a used crank.



.

__________________
1983 123.133 California
- GreaseCar Veg System

I'm not too sure I'd be that worried about timing. I would just remove the IP, set the timing on the crank and cam and then re-install the IP using the correct procedure.

__________________
Jim

+1

__________________
I choose to be happy, even when the Mercedes is being awkward, lol

I wouldn't recommend pulling the pistons out the bottom; there may be a ridge at the lower limit of piston ring travel that would break the rings on the way out. Normally, they exit up top, after checking for a ridge and using a ridge-reamer if req'd.

__________________
I choose to be happy, even when the Mercedes is being awkward, lol

Changing rod bolts without resizing is risky business. When the rod is retorqued with different bolts, the very slightest of mis match will distort the bore and reposition the bearings ever so slightly. As long as the small diameter portion of the rod bolt is within spec so that it can stretch safely, you will be much better off leaving them be.

If this is the first time the engine has been apart they will almost certainly be within spec.

__________________
2001 SLK 320 six speed manual
2014 Porsche Cayenne six speed manual

Annoy a Liberal, Read the Constitution

Just in case anyone reading this thread hasn't seen them chapter 03-310 and 03-313 in the FSM describes what Mercedes says you should do!

__________________
1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

Everyone, thank you for answering ALL of my questions.

As someone pointed out, being the first time this engine has been cracked open, all of my rod bolts were well within spec, so I just left them alone.

I carefully torqued each pair a little at a time up to the specified 40-50 N*m (I went with 50 actually), and then my heart sunk when a few of the bolts spun a little (~15-20 degrees) during the additional 90-100 degrees of angular torque which makes me really question the integrity of the rod/bolt interface now. They all took the initial 40-50 N*m and they all got "most" of the extra torque so I think I've decided to just roll the dice and hope for the best. This is my first time working on an engine, so I'm second guessing every action at this point. I apologize for all of the questions, but I've got more now.

Is it normal for these bolts to spin like that? Should I attempt to correct this somehow? I thought about removing the rod bolts and re-installing them with red locktite near the heads (not on the threads), but that would mean a third "stretching" of the rod bolts upon re-torque and I'm not sure how many rounds these things have in them. I was measuring 8.15-8.2mm on the necks, and the spec is 8.0mm so removing them at this point might mean new bolts...which means machining the rods...which means a total disassembly...grr! Any advice?

I don't know the answer to your question but I recommend you not proceed until you are 100% certain you have torqued them correctly.

I am pretty sure spining bolts is a red flag.

__________________
[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.