When switching to a longer crankshaft stroke, they just redesign the piston to put the piston pin a little higher in the piston, just the right amount so that at TDC, the top of the piston is in the same position as it would have been in the shorter stroke design.

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Numen tibi adsit!

So, they're gaining an incremental increase in the length of the stroke without redesigning the block?

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" We have nothing to fear but the main stream media itself . . . ."- Adapted from Franklin D Roosevelt for the 21st century

OBK #55

1998 Lincoln Continental - Sold
Max 1984 300TD 285,000 miles - Sold
The Dee8gonator 1987 560SEC 196,000 miles - Sold
Orgasmatron - 2006 CLS500 90,000 miles
2002 C320 Wagon 122,000 miles
2016 AMG GTS 12,000 miles

I have been lurking as a reader only on this forum for about 6 years and as I have a '91 350sd with now 175K I have followed the threads about the 350sd(l)s. A very early thread about these engines included an opinion by Benzmac, one of the founders of the forum. His theory was that the intake plenum gets hard carbonized deposits from the EGR and this intake arrangement was an add on in the US models. The hard chunks break off and get into the intake manifold, get sucked into the cumbustion chamber, fail to compress and cause the rods to bend, ovalling the cylinder and generally ruin the engine. Benzmac's advice was to clean the plenum and intake manifold and block the egr. Good advice! These are great cars. Unfortunately Mercedes had to put an egr on the US models which I believe in the long run causes severe smoking from the crap in the intake and eventual engine failure.

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'91 350SD 118K
'85 Lincoln Town Car 92K
'73 F100 Ford Pickup w/ 351C 240K

It's an interesting theory, however, there's no evidence of hard carbon deposits on the inside of the intake manifolds. It's usually a soft oily mixture that accumulates on the inside walls of the manifold over time. It takes quite a bit of work with a brush and some fuel oil to dissolve all the deposits.

If there were hard carbon deposits on the inside of the intake, you would not be able to remove them and you'd need a new manifold to prevent the problem that you are describing.

Furthermore, the bend is always the same...........very slight and barely noticeable to the eye. If it was a solid piece of carbon.........of varying size.......it would probably cause a catastrophic problem with piston or a valve at some point. This never happens.

So, it's another theory without any basis in fact.

Why would the EGR on this engine cause problems but not on other earlier diesels? Was EGR not included on the OM617?

- Peter.

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2021 Chevrolet Spark
Formerly...
2000 GMC Sonoma
1981 240D 4spd stick. 347000 miles. Deceased Feb 14 2021
2002 Kia Rio. Worst crap on four wheels
1981 240D 4spd stick. 389000 miles.
1984 123 200
1979 116 280S
1972 Cadillac Sedan DeVille
1971 108 280S

Exactly........

i am pretty sure the later ones had an egr....or was it an air pump?

tom w

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[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.

why would you compare a 617 to a 603?
point it they both have the egr,but the turbo charger seals are different,i see on the later ones that the carbon seal fails on the 603 turbo and the piston ring seal on the 617 turbo hangs tough. so i think that the additional oil that flows past the carbon seal causes more problems with carbon build up on the head and piston,at least thats what i see as the units are disassembled.
take a non turbo unit apart and it will look really close to a gas engine,hardly any carbon build up.
just another opinion
larry perkins lou ky

I am the original owner of a 1991 350SDL that now has 189K miles on it. No indication of rod problems and the engine continues to perform as expected. My engine was built 12/90 and I don't know if it has the updated rods or not.

I have maintained this car well and it is still a genuine pleasure to drive, it still looks great.

The one scare I had was when the windage tray in the oil pan dropped due to loose bolts and that caused oil pressure to drop somewhat because it blocked the pump pickup some, I caught it before any damage was done.

If anyone is buying one of these cars there is the possibilty that the rods were updated somewhere along the way unless you can confirm with the car's various owners otherwise.

AFAIK, it doesn't matter either way. Stronger internals or not, they can fail.

If your 350 engine is running great, save up for impending failure, just in case, so you're not caught short-handed.

Another one is going south, the second one I've personally known and driven (out of a total of two). It is a 1990 350SDL. Mine had an engine replaced in July of 1995. Its been through two engines, the third is a 3.0 liter and its got plenty of oomph. The 350 engines can potentially last for YEARS burning oil.....Tens of thousands of miles. Plenty of time to save up for another, IMHO. Just recognize it for what it is. Always assume the worst.

So far for me, failure rate is 100%.

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1987 300SDL (324000)

1986 Porsche 951 (944 Turbo) (166000)

1978 Porsche 924 (99000)

1996 Nissan Pathfinder R50 (201000)

I have never heard of or read any posts where any of these 350SDL engines with the updated rods installed by MB have experienced rod failure.

After as many miles as I have (189K) and 17 years of ownership of this great car it is a moot point to me regarding engine faliure in terms of it being a "disaster". This car has has more than paid for itself in the pleasure it has delivered to me. I feel like it makes me money every time I start it up now. If it fails tomorrow or sometime soon yes I will disapointed but I will not be upset, after all 17 years of service is darned good for any piece of mechanical hardware, nothing lasts forever.

My EGR was blocked off after cleaning the intake at around 75K miles.

If and when this engine fails I will most probably explore a crate motor replacement if it's available because i really dig this car. As of now there is no indication that I will have to do this any time soon.

The main reason for the rod bending is because of hydrolock. The front oil gallery would leak into the first cylinder and cause the engine to hydrolock even if you put titanium rods in there they would bend.

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Have you ever noticed that anybody driving slower than you is an idiot, and anyone going faster than you is a maniac?

As long as they would add one additional commandment for you to keep thy religion to thyself.
George Carlin (Wonder where he is now..)

1981 240d (engine donor 1983 240d) recently rebuilt engine hurray! - No more.. fought a tree and the tree won.

pearl black 1983 240d 4speed (Converted!@$$%) atleast the tranny was rebuilt.

........and your data supporting this conclusion is...........

several folks here have reported failure with the updated rods.

i lean toward the partial hydrolock and or carbon lump myself. no hard data to support it though.

afik no hard data to support any of the theories yet.

tom w

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[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.

Just knowing there's a problem is good enough for me. The fact that the cause and/or cure has elicited so many varying opinions tells me to steer clear of the 350. Thanks for all of your responses.

__________________
" We have nothing to fear but the main stream media itself . . . ."- Adapted from Franklin D Roosevelt for the 21st century

OBK #55

1998 Lincoln Continental - Sold
Max 1984 300TD 285,000 miles - Sold
The Dee8gonator 1987 560SEC 196,000 miles - Sold
Orgasmatron - 2006 CLS500 90,000 miles
2002 C320 Wagon 122,000 miles
2016 AMG GTS 12,000 miles