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2007 E320 CDI bottom end rebuid questions

Discussion in 'Engine, Drivetrain, Fuel and Exhaust' started by Sully114, Dec 6, 2012.

  1. Sully114

    Sully114 Member

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    2007 E320
    Hi I am in the process of rebuilding the bottom end of my E320 CDI sport on a 2007 (OM642.920) I have been using WIS as a guide for the rebuild and its a little vague about identifying which pistons are left and which are right. When I say vague I mean according to WIS there should be markings on the piston faces which are either 4A or 4B which indicate right and left...I have cleaned all my pistons up to near new condition and there is no 4a or 4b marking :( only a number with a hyphen which is not refered to in WIS anywhere.
    Now I am worried that I will get this part of the rebuild wrong and wreck my engine!! Is there any other way of making sure I get this right? I see the valve indents on the piston face are offset differently on the top and bottom (Exhaust valves and intake valves) and looking at my photo reference the valve indents with the widest gap faces towards the center of the block..

    Also if anyone has any pictures which show this engine with the cylinder heads off or maybe a pic of the bear crankshaft and conrods, this would be a great help to me at this point..
     
  2. DIYMAN

    DIYMAN Senior Member

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    Your Mercedes:
    E270cdi/53 plate/2.7l 5cyl.
    Have you separated the pistons from the con rods? The rods may be marked.
     
  3. OP
    Sully114

    Sully114 Member

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    The conrods are still attached to the pistons, looking closer the rods have a green line on one side near the lower bolts if that helps?
     
  4. MechPhil

    MechPhil Senior Member

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    Since the exhaust manifold is on the "outside" of the V, and the intake in the "valley", the pistons do go with the wider indent (for the intake valves, which are larger than the exhausts) to the inside of the v.

    But, there's a bit of a problem. If you use the old pistons, they really should go back in the cylinder they came out of. it's also quite important for the conrods to be fitted to the same journal of the crank they were previously on. Modern engines that are more precision manufactured are less finnicky about the abovementioned points, BUT, the conrod caps absolutely have to be fitted to the same rod they came off of. The big end of the conrod is machined to size and honed out after it has been matched to a specific cap.

    If theres a chance you may get the rods and caps mixed up, you will have to have the big ends resized professionally.

    As for left and right pistons, I don't think there can be much difference, but I may be dead wrong...

    Phil
     
  5. MechPhil

    MechPhil Senior Member

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    Usually, there's a marking of a sort on the top of the piston. An arrow, or just a little notch somewhere in the rim of the crown. The arrow will point to the front (pulley side) of the engine, and the notch will also face the front of the engine.

    Phil
     
  6. Alex Crow

    Alex Crow Senior Member

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    Your Mercedes:
    W169, W124, w202, W203, KTM 250 EXC, VW T25 camper and a Polo in a pear tree
    As above, the arrows and valve pockets will tell you which bank the pistons go in, but sadly not which location.
    As above, you should really be fitting the pistons, rods and shells in exactly the same location - shame not to have marked them when they came out, I usually use a paint marker on the crowns btw.

    The con rod caps must always be fitted to the same conrod (as said above), and can never ever ever be swapped over to other rods (as they are made as single piece parts, with the caps being 'fractured' away from the rods), and must also always be fitted the same way around with shell location detents on same side.

    Why the rebuild? Was it the main bearing failure?
     
  7. OP
    Sully114

    Sully114 Member

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    Thanks for the replies guys, really helpful! unfortunately I cannot see an arrow on top of the piston crown, I can faintly see the QR code symbol which is where the arrow would be I presume? I have also looked for a notch but cannot see one, but its pretty dark in my workshop so will check again tomorrow...

    I bought the car from an auction and it had ingested water, after stripping the engine down I noticed one of the conrods was bent so I have bought a new rod and piston for the number 3 cylinder. The block and cylinder head and crankshaft/pistons have all been checked at a race engineers, the cylinder walls have been re-glazed. And according to the engineer everything else is fine and not bent. While its been apart I have stripped cleaned and reground all the valves. So if I get the bottom end rebuilt correctly it should run sweet..(I got it running with the bent conrod by the way but it was blowing white smoke, but still ran pretty smooth apart from that)..

    Just a thought but if I scan the QR code symbol would that maybe tell me if the piston is right or left? or at least give me a part number which would give me the same info?
     
  8. MechPhil

    MechPhil Senior Member

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    Your Mercedes:
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    I'll be surprised if the numbers differ on the rods, but if they do, the number may be the way to go as far as identifying which rods go where.

    I've dealt with these "fracture" rods only on Opels (Vauxhalls) before. That should make it easier to match caps to rods, since each cap will only fit in one rod. From threr it may be possible to find some form of mark that indicates the front of the part.

    If you still have no luck, your race engineer friend should be able to help. There HAS to be some form of mark...
     
  9. OP
    Sully114

    Sully114 Member

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    The numbers on the conrods are different which is surprising because I have been told all the conrods are the same, 3 rods read 642 30 37 1 and the other 3 read 642 30 37 2. But if I try to arrange the pistons into right and left bank using these part numbers i cannot get piston face in the right position as the wider valve marks on the piston face needs to be facing the center of the block and they dont in this configuration, some are flipped.. After closer inspection I have noticed a marking on the bottom of the piston which is a little yellow dot of paint and a notch see pic below

    [​IMG]

    Not sure what this is for but its in the same position for each piston..In terms of other markings there are a few faint numbers on the piston face which I couldnt get to show in the pictures. 3 that have a the number "-3" and another 3 that have "-6"..I assume this is supposed to read 1-3 and 4-6 but I cannot see this because of carbinisation..

    Just to help here are few more pictures of the complete piston..

    [​IMG]

    [​IMG]

    [​IMG]

    I found this picture on the net and thought it was quite useful as you can see the Nural writing on the piston is facing towards the front of the engine..

    [​IMG]
     
  10. spock500

    spock500 Senior Member

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    You mention above ' the cylinder walls have been re-glazed', (de-glazed)

    If the cross hatching has been put back in the process I would have thought you would be ok with the location of the pistons?

    I would probably go for new rings and shells to make sure all of the contact parts can bed in to the new journals ect.

    Stagger the rings on assembly and fill with mineral oil for the first 500 miles, also take in few hills under load. This will force the rings out making a good life time seal.

    Bets of luck,
     
  11. OP
    Sully114

    Sully114 Member

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    So after doing a bit research on why there is left bank and right bank piston in a V6. It appears that the pistons heads themselves are all the same but the wrist pin is slightly offset to minimize piston slap and bore wear..I have also read that its to do wth the direction of oil flow thorugh the piston..Could anyone confirm this is the case on a OM642 engine? So taking this into consideration maybe I can measure the offset and find out which is left/right bank from my findings.
     
  12. Alex Crow

    Alex Crow Senior Member

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    The notch in the piston skirt is to miss the oil jet, that will help you along...
     
  13. Uncle Benz

    Uncle Benz Senior Member

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    Alusil cylinder bores require a special process for reconditioning. Cross hatching is exactly what you don't want! It requires the use of special felt shoes and a special type of paste.
    Alusil is basically very hard nodules of silicon cast into aluminium.
     
  14. MechPhil

    MechPhil Senior Member

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    Good of you to mention this... I would certainly have simply honed a decent cross-hatch into the bores if I ever had to do this job, and the result would probably have been catastrophic.

    Is there a sure way to know which MB motors had Alusil sleeves?

    Back to the OP's pictures: I would be tempted to think that the yellow dot should point to the front of the engine. This, along with the valve recesses, and the notch for the oil sprayer nozzle should be enough to place each piston on the right side of the motor.

    Good luck!
    Phil
     
  15. Uncle Benz

    Uncle Benz Senior Member

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    I think pretty much everything with aluminium blocks has alusil bores. I can't recall mercedes being afflicted with the nickasil problems that BMW suffered in the early 90's
     
  16. spock500

    spock500 Senior Member

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    Hopefully we would have noticed there bores didn't have any cross hatching to start with (hopefully).

    Apologies to the OP, I hadn't realised things had moved on so much. The last engine I rebuilt was the OM605 built in 1994 so a bit out of touch.

    Probably the mineral oil is bad advice too, as those bores sound very high tech requiring special treatment to ensure longevity.
     
  17. MechPhil

    MechPhil Senior Member

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    Well, clearly I'm not really an authority on the engine in question, bur mineral oil, as a rule-of-thumb, is the only way to prevent premature glazing of the bores.

    I've seen many overhauls go south (notably 1.9 VW motors) due to premature use of full synthetic oils. The bores and rings never bed in properly, and the end result is oil consumption, excessive blow-by and poor performance.

    After a rebuild, I insist on using mineral oil of "straight" SAE40 viscosity for 1000km (600m). After that, a 15W40 mineral oil for 5000km, and only after that I fill with synthetic. If this regime is followed (once again, I have some experience on VW 1.9TDi's and some Toyota D4D's) oil consumption after a rebuild is always negligable. One customer insisted we use Casrtrol Edge from startup, even though he lost his warranty, and his motor uses a pint per tank...

    Phil
     
  18. OP
    Sully114

    Sully114 Member

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    Hi guys been reading up on wrist pin offsets and major thrust faces and have a few questions... Does anyone know how much the wrist pin offset is for the OM 642 engine? Ive have been trying to measure this and its looking like its about 1mm...Also am I right in thinking the right hand side of the cylinder wall would be the major thrust face on both left and right hand bank because the crank is turns clockwise? One more question, would the side with the smallest offset face the major thrust face?
     

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