How about measuring that cyl for out of round and taper. Maybe you can replace rods and save that block? Just a suggestion but then you would not have to loose that torque and mess with fitting another engine.

BenzD, not sure if I understand your comment. There is supposed to be ~0.8mm of protrusion. The bent rod in the 3.5 manifests as reduced protrusion.

The protrusion spec calls for a measurement of the piston crown above the deck at the very front and very back of the piston (along the pin axis). In the 3.0 block there is almost 1mm front and back. In the 3.5 block there is about 1mm in the back and no protrusion in front. That suggests that the rod is bent forward. I wish it was a half inch low so it's very obvious. As it is I'm still trying to internalize that a 0.7mm difference is significant

I will make a better assessment of the block when it's out of the car. A proper measurement of the bore requires removal of the piston. If I can reuse the 3.5 block, you bet I will!

Sixto
93 300SD

The other thing I have always wondered is if a stronger conecting rod can be had from another engine. Hot Rod engine builders are always doing that stuff.

If the rod weight and center of gravities are different from the original it would effect the balance of the engine. Mercedes must have a solution to the bending rods in the form of updated parts. The big issue will be cost. I know pistons for an OM 603.960 turbo engine are like $1,800. I am sure they are even more for the OM 603.971.

Of course the two ultimate tests will be actually examining and measuring the rods and checking diameter and out of roundness on the cylinders.

__________________
Doug

1987 300TD x 3
2005 E320CDI

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

I found the same zero in front and less than a mm in the back that you found. I also think the egr deposited alot of carbon build up in #1 cylinder, which contributed to the valves not fully seating in the piston grooves because of the carbon build up, which didn't allow the valves to function properly as designed to, which in my opinion could have contributed to my oil consumption (I hope so). I found minimal cylinder wear at the ridges and a couple almost feel completely ridgeless. Have you seen any actual pictures of a bent rod? Anyway, I'm encouraged and will check the head out further tomorrow and see what I find there. Also, it looks like the backside of the gasket was breeched at #1 cylinder and possibly at #6, as well. Anyway, I'm on it.

BenzDiesel

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You checked protrusion with the gasket off, right?

Why is there oil all over the #6 piston?

Your pistons are and head are a lot cleaner than mine. There's deposits all over the place in my engine. Not as much oil, though.

Sixto
93 300SD

That is why it would have been great to see an actual bent rod or a bent rod condition, as it relates to the obvious damage done to the cylinders caused by a bent rod. And yes, the protrusion was checked with the gasket off. Also, in THEORY, a piston is just a big plug that pumps and compresses, so I'm still having difficulty seeing why a slight tilt, possibly indicating a bent rod, can cause so much destructiveness in terms of high oil consumption, when the piston's job is to just plug the hole so that compression can take place.

BenzDiesel

It's a bottom line issue. Total your costs of all parts required plus the cost of
machining and compare that figure to cost of a rebuilt unit from Mercedes with
a 48 month guarantee. I did the same and found that it would not be cost
effective, even doing the work in my own shop and subcontracting the actual
machining.

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

This measuring technique would indicate whether the rod bends around an axis that is transverse to the axis of the engine. This mode of bending seems rather strange to me.

The typical bend of a connecting rod in a gasser is around the axis of the engine. When the rod is at an angle to the piston (nearly all the time), the loading on the rod is not symmetrical and it's failure mode will cause it to compress and twist relative to the engine axis.

Anyone have information as to whether this is true in the 603.97?