They Said it Can't be Fixed - A Journey to the Inside of a Mercedes Bluetec

Thanks to the advice from The Gang here, I'm going to proceed with that scratch in place.  So tonight, I spent an hour or so getting things ready to bolt together.  I wiped the cylinders down with copious amounts of ATF until my rags were coming back pink with no grey stains.  It took a lot of wiping, but eventually I got it all and proceeded to the pistons.

I was going to just put the pistons in as they were but I decided to spend a couple minutes cleaning the carbon off.  Good thing I did, too, because my rag got caught on the oil control ring and a bit of it snapped off.  Glad that didn't happen when it was assembled and in the car!  The oil ring is what made the scratch on the cylinder so I assume that when it was banging around on the loose rod bearing the ring got compromised.  I'm going to order up some fresh rings for this piston and I'll get back to it.

Using some vintage gage blocks, a micrometer, and a bore gauge, I checked the cylinders and the rods for roundness today.  The cylinders are all looking good, but the #2 rod big end has a variation of just over a hundredth of an inch.  The other five rods are more like a 5 thou range.  Given how consistent the 5 rods that didn't have mostly missing bearings were, I'm inclined to think that this rod got a bit damaged from banging around.  A new rod is about $300 (gulp), so I think I'm going to go ahead and replace the #2.

I'm not sure how it happened, but the reason that I haven't received the ring set yet is that I failed to actually order it.  Which is actually kind of good, because I can save myself a couple bucks on the shipping by ordering the rings and the rod at the same time.  Except that the rings were already in my cart, so I wound up ordering two sets instead of just one.  Hopefully idparts can figure that out for me and modify my order to reflect just the one set.  So now we wait on parts....

Woohoo!  A rod and a piston's worth of rings on the way!

Wow...  looking at that rod makes me want to buy 5 more of them.  You honestly can't tell where the rod end was fractured!  It's just so damned pretty!  I don't think I've ever actually seen a brand-new rod before, come to think of it.  Plenty of used ones, of course, and I've even got a couple bent ones hanging around.  But this is beautiful.  Oh, and a box of rings.  Neat packaging.

I should have what I need to get the rotating assembly re-installed in the block now.  Tonight is Bingo night, but tomorrow sounds like a nice day to work from the shop and put this together. 

The more I ponder the oil pump, the more I'm concerned about having FOD-ed it.  A new one with the Merc logo stamped on it is about $500.  The same pump with Febi's logo is half that.  I don't really trust that there are any used ones out there that have not also been FOD-ed so I'm not interested in going that route.  Maybe I can open it up and see if it's scored or damaged in any way and then decide from there.

Haven't even looked at the oil pump yet, but I did decide that I want to replace the valves in the #2 pot, so I'll order those up when I get the head install kits.  I'm still wondering how far I should go on that, but I'm thinking that I'll stick to just the four valves in #2 since I wasn't having any other problems.

I finally got some time last night to go out and start with the crankshaft.  I lost a little bit of work time because my brother and sister-in-law came out and we wound up sitting around drinking beers instead of doing actual work, but the thrust bearings are in place, the main bearings are installed, the caps are in place, and the new bolts are all finger-tight.  Plus everything is assembly lubed.  Oh, actually, one of the bolts isn't in - there are bolts that go through the block and into each side of each cap.  The left-rear side bolt hole is blocked by the super-long bolt that I'm using to mount the block on the stand, so I need to pull that bolt out so I can put this one in.  I also need to get a 1/2" set of e-torx sockets so that I can set the torque appropriately.  But, hey, at least I did SOMETHING!

Good news!  I got the main bearing caps installed and torqued down to the specifications in WIS.

Bad news!  The crank will not turn.

I've double-checked that the part number they sent me for the main bearings are indeed .5mm oversized, and the report from the machine shop indicates that the main journals were ground down .5mm.  I found it odd that they would grind the mains more than the rod journals since all the damage was on the rod journal and now I'm wondering if they flipped the measurements on me.  Or if they just didn't grind down the mains at all. 

Time to pull it all apart and mic it?

In reply to eastsideTim :

Yep, I think that's what I'm stuck doing.  I'll have to look again, but I don't recall seeing the dimensions in WIS anywhere which is why I didn't check it before I dropped it in.

I found the specs for the bearing clearance and the journal dimensions.

Bearing clearance, radial is .029mm-0.56mm or .00114173"-.00220472"

Bearing clearance, axial is .1mm-.254mm or .003937"-.01"

Crank journal is supposed to be 75.940mm-75.965mm or 2.9897637795"-2.99074803"

Main journals on the crank are ~ 2.9809"

The paperwork from the machine shop says that they were ground down 0.5mm.  .5mm ~ .0197"

2.9809 + .0197 = 3.0006

If the shop had actually ground the crank by .25mm the math looks like:

.25mm ~ .00984"

2.9809 + .00984 = 2.9907

3.0006 would be too big for a main journal, but 2.9907 would be right there at the top end of the spec.

I think they did a .25mm cut on the mains but since they told me it was .5mm, I bought a set of .5mm bearings.

Now I'm questioning if the rod journals are actually .25mm or if they reversed it when they wrote out the invoice.  Problem is that I cannot find the spec for the rod journals anywhere.

wae said:

Main journals on the crank are ~ 2.9809"

The paperwork from the machine shop says that they were ground down 0.5mm.  .5mm ~ .0197"

2.9809 + .0197 = 3.0006

If the shop had actually ground the crank by .25mm the math looks like:

.25mm ~ .00984"

2.9809 + .00984 = 2.9907

3.0006 would be too big for a main journal, but 2.9907 would be right there at the top end of the spec.

 

I think they did a .25mm cut on the mains but since they told me it was .5mm, I bought a set of .5mm bearings.

Now I'm questioning if the rod journals are actually .25mm or if they reversed it when they wrote out the invoice.  Problem is that I cannot find the spec for the rod journals anywhere.

 

You can't grind down by adding.

Maths:

2.9809-0.0197=2.9612

or

2.9809-0.0098=2.9715

Your confusion is that the bearing thickness has to increase to make the same oil clearance dimension for a now smaller bearing journal.

In reply to Ranger50 :

I think I'm computing that correctly.  I'm taking the actual size of the crankshaft, after the grind and adding back what they told me they ground off, the .5mm.  when I do that, I get a theoretical original crank diameter that is almost exactly .25mm larger than what the MB spec says the crank should be.  If, instead, I add back in the .25mm that I think they actually ground off, I get a theoretical original crank size of almost exactly what MB says it should be.

That 2.9809 is after the grind, not what the spec says the crank should have started with.

In reply to wae :

Then just mic it. Eliminate all confusion 

In reply to Ranger50 :

Oh, I did.  But I can't find the spec for what the rod journal is supposed to be before a grind.  They have the main journal data in WIS, but the rod info isn't anywhere I can find it.  I know where it's at right now, but I don't know if it's .25 smaller or .5 smaller.  And the bearing set is expensive enough that I don't want to just plastigage what I have - I'd rather return the unopened rod bearing set for the right size if I need to.

Could you contact the machine shop to see if they have the before/after measurements from the job or is that hoping for too much if they couldn't put it on the invoice correctly?

In reply to EvanB :

My assumption is that if I call them and ask, the most effort they'll do is look at their copy of the invoice and say "yep, did a .5 grind on the mains and a .25 on the rods.  Says so right here".  My plan instead is to take the thing back out to Tom and have him mic it and compare that to whatever reference he uses for what the sizes should be.  Again, an assumption, but I would guess that he has some source somewhere that probably costs them a bunch of money every month that has the dimensions that Mercedes failed to put in WIS.

Just left the machine shop.  They miced it out and apparently the rod journals are .25, but for some reason the mains got ground to .3.  They're going to re-grind it to .5.

Now I need to mic out the bolts to see if I can reuse them or if I need to buy another $150 set of bolts.

In reply to wae :

I'm not sure about your relationship with the shop, but I feel like they should be paying for new bolts. They gave you a product with certain spec, that spec was incorrect which is causing you to incur additional charges. Not to mention all the time wasted....

It is really cool to see things moving right direction finally though!

In reply to Misha_ :

...slowly but surely, right?  heh!

I agree - and if the bolts are stretched past spec, then I'm going to chat with them about it.  I want to be prepared for them to tell me to get stuffed, though.  What I might do is see if they'd knock the $150 off of cleaning up the heads and installing new valves in #2 and new seals and guides all around.  The original plan was to just do that myself, but since finding time to work on this thing is apparently more difficult than I thought, it might speed things up a bit to outsource that work.

First I have to find something that's long enough to measure these bolts, though!

Okay, so I'm really confused here.  I was getting all set up to measure the bolts for stretch, but the spec says the max length is 67.8mm.  they reference a picture for how to measure and it's the length of the bolt minus the head.  Except these bolts are all about 6" long and the heads aren't 3 inches long.  A 67.8mm bolt wouldn't be long enough to reach the block through the bearing cap. 

Thinking that they might have been talking about the side bolts, I checked those but they're under the 66mm minimum size by a decent margin.  They call for M11 (?) bolts and while I don't have a thread gauge for M11, these bolts are too big for the M10 and too small for the M12, so that seems like a good guess.

So I'm a bit lost on this one now.  Does "crankshaft bearing cap bolts" mean something different in the specs versus the EPC, assembly diagram, and instructions?  Is the diagram they reference to show you where to measure wrong? 

Just go thread to thread, comparing two bolts against each other.  The part that stretches is almost always right above the threads in whatever they are going into.  You will easily see where the thread pitch changes/gets skewed at the part where it stretched.

Fig.1: Stretched Volvo rod bolts.

Yep, using that method, there is definitely some stretch going on.  Sounds like I'm going to have to have a fun conversation with the folks at the shop.  I wouldn't sweat it ordinarily, but the set is about $125 because Mercedes....

Picked up the crankshaft on Monday and had Tom look at the bolts and bearings.  He tells me that they are still within spec and should be good for two or three torque cycles. 

Just wanted to say thanks for documenting this rebuild. I am about to dive into my own OM642 in my GL. It burns more oil than fuel and leak down test shows most if not all rings are probably stuck. fortunately it does not make any bad noises or show any signs of bearing failure yet, so I hope to get away with just replacing rings/ honing cylinders. There is so little information around about rebuilding these engines your thread is really helpful.