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Old 07-24-2012, 12:34 PM
Air&Road Air&Road is offline
Posting since Jan 2000
Join Date: Sep 2011
Posts: 6,228
Originally Posted by spinsession View Post
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.
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