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petermerle
Expert
Date registered: Apr 2006
Location: Cape Town ( deep south )
Vehicle(s): W460 *1, W123 *2, W124
Posts: 1315
| OM 617 piston protrusion - limitation
Handbook specfies a maximum piston protrusionof +0.9mm. Mine is currently at 0.8mm so is within spec even though the block has only been skimmed once by about 0.1mm. Am wondering what is the limiting factor - the valves hitting pistons or prechambers hitting pistons - has anyone made clearance measurements.
Peter |
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Boy G
Expert
Date registered: Feb 2007
Location: Bushveld, South Africa
Vehicle(s): Diesel G's: 617A and 602
Posts: 1683
| Re: OM 617 piston protrusion - limitation
Peter,
You mention the handbook. Is it the SA Atlantis Diesel one as that is a short form version? I have the MB engine manual for this motor. PM me if you need more info but in short both of your speculations are correct. The valve protrusions must be: NEW :MIN Intake +0.03 to -0.43mm and exhaust -0.38 to -0.78mm and MAX with overhaul for both intake and exhaust -1.5mm and then says" The maximum distance drops by the same amount as the cylinder head parting surface is refaced" As far as the sleeves are concerned they must be level on top and the height of the block must not be less than 242.5mm (new is 242.8 - 242.9) and the gap between piston crown and top is +0.50 to +0.90mm (ie protrudes). The pre combustion chambers vary depending on which type of engine you have. If it is the 617.912 with slanted chambers the clearance is +5.5 to +5.9mm. If your pistons are the ones that have a star shape on the crown and your PC chambers are rounded then the clearance should be +7.6mm to +8.3mm. Please confirm this last measure elsewhere as there are a number of different combos here.
Thanxanrgds |
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petermerle
Expert
Date registered: Apr 2006
Location: Cape Town ( deep south )
Vehicle(s): W460 *1, W123 *2, W124
Posts: 1315
| Re: OM 617 piston protrusion - limitation
I am using the same specs as you are referring to as obtained from OM617 engine manual published by Mercedes benz AG. I am referring to piston protrusion not valve seat depth.
Thanks
Peter |
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hipine
Date registered: Jul 2006
Location: US, CO, Bailey
Vehicle(s): 460 1980 280GE w. 617A
| RE: OM 617 piston protrusion - limitation
Hey Peter, I haven't measured, but I'll tell you I'd be a lot more worried about the valves. Once the prechambers are set, they're set and only effected by thermal expansion of the metals. Valves are a whole different, and very dynamic, story. Crack a spring, over-rev a little and get some float, a bad lash job, over heating, sticking, timing chain wear, what have you. So many things can eat into the valve to piston clearance. That's the one I'd be most concerned with. Exhaust would be the one to be wary of as it's the one that will foul most readily with float or overheating. Intake is always on the cam when piston is near. Exhaust is coming off the cam when the piston's coming up. If it sticks or floats or lags a little - SMACK Stick by the book and you should be okay. -Dave G. |
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petermerle
Expert
Date registered: Apr 2006
Location: Cape Town ( deep south )
Vehicle(s): W460 *1, W123 *2, W124
Posts: 1315
| Re: OM 617 piston protrusion - limitation
Thanks, I still within specs but am thinking about next time arround!.
PEter |
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