Maybe the rod is bent forward and is the problem. Did you check to see if the other pistons had 1 mm clearance at both back and front and that the front of #1 was the only piston to have 0 protrusion? Regardless, the protrusion check is new information for me and I will check my pistons when I get the head off. I was really hoping that the head gasket was the problem. But the protrusion has been explained more clearly than I've read it explained before. Which ever way you decide to go, good luck.

BenzDiesel

now granted I haven't tried it but if its only #1 can't you just drop the pan and remove the rod and piston to inspect and replace if necessary?

__________________


1980 500SE/AMG Euro
1981 500SEL Euro
1982 380SEL
1983 300TD
1983 500SEC/AMG Euro
1984 500SEC
1984 300TD Euro
1986 190E 2.3-16
1986 190E 2.3
1987 300D
1997 C36 AMG
2003 C320T 4matic

past: 1969 280SE 4.5 | 1978 240D | 1978 300D | 1981 300SD | 1981 300SD | 1982 300CD | 1983 300CD | 1983 300SD | 1983 380SEC | 1984 300D | 1984 300D | 1984 300TD | 1984 500SEL | 1984 300SD | 1985 300D | 1986 300E | 1986 560SEL | 1986 560SEL/Carat | 1987 560SEC | 1991 300D 2.5 | 2006 R350

I notice the same lopsidedness in pistons 1 and 6, not in piston 2. I haven't checked the others.

I hear a set of custom rods is not a cheap alternative to dealer rods at ~$200 each list. Then there's pistons and sleeves and whatnot depending on how they measure when the engine comes apart. $4800 for a short block from Metric Motors starts to sound like a bargain. I'm working on getting more solid quotes on what a set of custom pistons and rods will cost.

I'm not sure I can drop the pan without lifting the engine. Now that the head is off it's not a lot more work to yank the block. Fortunately I have the 3.0 block to keep the car on the road so I can take my time deciding what to do with the 3.5.

Sixto
93 300SD

If you just want to do it on the cheap, I'd re sleeve that cylinder, replace the piston rings, and replace the rod and bearings. Measure the piston to make sure its in spec first. Then put on a new head gasket and button everything up.

How many miles? If the rest of the engine is tight this is probably nota bad option. If its got like 300k+ miles on it then its short block time.

__________________
2016 Corvette Stingray 2LT
1969 280SE
2023 Ram 1500
2007 Tiara 3200

It is improbable although not impossible that both #1 and #6 would bend rods identically based on the angle of the piston from back to front theory or diagnostic method. And seeing your head gasket DEFINITELY BLOWN in your pictures at #1, around the main oil channel, which if a breach is there, could easily justify why so much oil was being consumed by the engine, but still allowed the engine to perform well in all other aspects, at least in my case (couldn't hold good compression at #1 and allowed excessive oil to enter the chamber from the gasket breach, simultaneously). Anyway, I'm way more motivated to open that engine and hope to see a blown head gasket. And am glad that #6 was angled forward in the bore, just as #1 was. This is really like a roller coaster ride, up one minute, down the next, then back up.

Question Sixto??? What does the ridge look like at the front of #1? Is it excessively more worn than at the ridge point at the back of the piston's cylinder or at any other place? Can you detect any ovalness or out of roundness, is what I'm asking?

BenzDiesel

Using only my fingers I can't detect any difference in the ridge around the circumference of the #1 cylinder. For that matter the ridge of the #1 cylinder doesn't feel any different than the ridge in the other cylinders.

Sixto
93 300SD

the bending might be very difficult to see visually. when they bend they twist. the twisting is the source of the problem as now the piston is wanting to bind a bit.

no matter how strong a rod you install, a hydrolock will bend it. so imho it is futile to try to go with stronger rods to solve the problem. you leaked oil into number 1 and when you get more than 1.5 cu in, the volumn of the combustion chamber the rod bends. you see it could be 1.55 cu in and the rod would not bend much. but any bending will cause trouble.

if it were mine i wouldnt be afraid to sleeve it and replace the rod and probably the piston and rings and go as long as the other cylinders looked fine.

but if it were mine i think i would go with the 3 liter block since they are not known for bending rods.

imho it is the flex of the too much bored and stroked engine that is causing gasket seal failure and the following hydrolock.

good luck in however you decide to go.

tom w

__________________
[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.

Has anyone else who's seen a bent rods 603 noticed an oil leak near the #1 exhaust runner?

Sixto
93 300SD

Sixto,

I've been watching intently, but quietly. I think I am in the same situation. My car has gone from using / leaking a quart every 2500 miles to a quart every 300 over the past year. I had a few leaks fixed by a good independent hoping that was the issue. It wasn't. The mechanic really cleaned the engine to see where the oil was going. He showed me a leak right at the head/ block joint in front of #1 exhaust. That would match your pictures.

The MB stealership did a quick look and their next step was remove head and measure piston height, to the tune of $2000. I passed and called Noels. For $8000 ( $6500 long block and $1500 installation) I could be cooking again. I was considering making reservations and literally was looking at flight costs from FL back to NC. Then the next week my ignition switch started giving me a fit, and the stealership quoted $1000 to fix that. That was it for me.

Forgive for I have sinned. I had no time to mess with it and debated the financial wisdom of investing in an engine and ignition fix. I bought an Infiniti I-35 for a song and have been driving that since July as my primary car. I expect it will be my daughters car in a year or so when she starts driving.

The Mercedes still runs wonderfully, even at a quart per 300 miles. Not many flying bugs in the area lately.... 8). I drive it occassionally to keep all the parts working. I hadn't driven it more than around the block in the past 3 months. I had to make a 30 mile trip and back the other day so I decided to take it. Along with following Sixto's inspiration and ambition fixing all his issues, I fell in love again driving it. There is no comparison to the small Infiniti and I miss the diesel clatter. It is time to fix it once I can save a few $. Well more than a few...

So I am at the same decision points as Sixto... new 3.5 longblock? Find a 3.0 to drop in? I did locate a place that has 3.5 sleeves for $35 a piece. But that is probably past my skill level. An engine / head swap, sure I could do that.

Sixto, if you get the 3.0 into the 300SD and it works, that might be my preference. My 87 SDL had nearly 300K on it and was still running well. I can live with a little less performance for the longevity.

FYI.. in discussion with Noel, he thinks the issue is glow plug failure causing hydrolock. To me it looks like it may be headgasket / oil leak leading to hydrolock.

And then I still need to fix the ignition lock.. 8(
Chuck

It's my understanding that the .97 engines are not sleeved like the .96, hence the need to spend $$$ on a factory replacement, or swap in another "good" engine.

Cold fuel condenses and causes hydrolock? I don't think the volume of liquid fuel can do that unless you crank until the cows come home. Or does he have something else in mind?

I've been offered 606 long blocks for $4000 plus shipping. Maybe the 603.96 won't have enough torque to put a smile on my face and $4000 won't seem so bad. I can't imagine a 606 has more off-the-line torque than a 603.96. The rods are the same length and breathing isn't an issue at 1500 rpm. Does combustion chamber design make that much difference in off-the-line torque? If so why does a 617 pull harder from 0-10 mph?

Sixto
93 300SD

Probably because of the lower rear end ratio and/or more displacement per cylinder.

The EPC shows .97 liners for $80 list each. Not cost prohibitive but who knows what the machine work costs. The FSM talks about resleeving the .97 by boring the cylinders out by 3mm (IIRC) to take the new liner.

Again, $4800 for a Metric Motors short block starts to sound attractive...

Sixto
93 300SD

I drove a Camry from when Matt bought the SDL to when I found the SD. Darn thing held its value as well as a Diesel.

Sixto
93 300SD

i think forced has it nailed here.

the combustion chamber and valve design will flow more air at high rpm so the total horsepower will be more and at higher rpm. at low rpm four valves really dont do anything. in fact they could actually lessen the take off torque.

i would go with the 3 liter for sure if i were planning to keep the car.

tom w

__________________
[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.