>>But, not to be a pain,

Thanks Jim, until you posted that, I didn't really understand your position.

The local strain effects which are going on when a crack is being intitiated are a part of the fatigue process that I have never been too involved with - there's nothing much to see or measure without extremely elaborate equipment which I've never had access to.

I'm not sure that he bending will actually work to change the stress regime and protect an area of the rod. I think there are two reasons for this - 1) the fluctuating stress would remain unchanged 2) as bending is an anti-symettrical deflection, any area that could claim a benefit would have a counterpart on the opposite side of the rod where there would be a detrimental change.

I've had a few dealings with materials like Inconel - I was involved in a project with Rolls-Royce to develop tooling and processes to enable the material to be ground at high material removal rates. Awful stuff!

The rods on my 1991 300SD engine that bent were found by removing the head and measuring the difference in height at TDC for each piston, relative to the block head gasket seating surface. In my experience, I was so startled by the diagnosis I asked to see the engine. Still in the car (they only took the head off to do the diagnosis) the difference in height was visually apparent. I don't believe the shop actually measured the height differences, because the condition was so obvious. Which I will guess was more than 0.015" short on the two pistons with bent rods.

That kind of difference will reduce compression loading significantly. Which should reduce the loading on the rod and possibly push the load point away from the fatigue limit, putting an end to the conditions that caused the rod to bend. The work hardening aspect may or may not contribute to pushing the actual operating loads further from the material's endurance limit.

The other consideration is we don't really know when the actual bending of the rod takes place. I think it is possible it happens earlier in life than we suspect and the symptom we detect is the oval shaped cylinder, the resulting high oil consumption and performance degradation (noisy, loping idle, and smoking as it burns oil, for the most part). A bent rod by itself won't smoke or cause the loping idle problems. How long between the bending of the rod, and the onset of noticed smoking and idle changes may well be dependent on other regular maintenance intervals and quality of oil.

And Tom, I have seen a side by side photo, on this forum I believe, of the two rod designs. Unfortunately I think they went through more than one rod design change and have never seen all the iterations side by side. The more than one changed rod design may just be a rumor, though. Jim

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Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)

Read that there is 50% possibility that the engine may be ok...how can I acutally tell if there is a problem or not. Also what do you consider a cheap price (or worth buying it)? for a 175K miles 1994 S350
Thank you

The only immediate way is to know the oil consumption, in number of quarts per mile, using proper diesel-rated (Cx) oil. Most sellers will have no idea so this is often hard to find out. A good engine should use a quart in 4-6000 miles, or better. If it's using a quart ever 2000 miles, that's a bad sign. Every 1000 miles, you've got a rebuild or engine swap on your hands before too long. The only way to tell for sure if the rods (and cylinders) are good is to pull the head, and measure the piston protrusion, and cylinder bores. If you REALLY want a W140 diesel, this could be a great car, but just prepare yourself for the worst just in case.

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Check out my website photos, documents, and movies!

Oil use is a warning sign but leaks and the turbo seals can cause oil use too. A bad compression test is a sign that you have to take the head off to see if the rods are bent.

My car was using oil, but I could see it under the car! It turned out to be the oil line to the turbo.

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1991 350SD (updated rods)
Biodiesel B100 when I can find it.
Dino when really cold outside

Mine registered 420 - 450 psi across all cylinders, but is using a quart per 300 miles.

I think you have to assume the engine is a time bomb waiting to go off. The idea that there are some that are just "good" and some that are just "bad" does not wash for me.

What is a fair price? If it is really really clean take the nada book and deduct $3000 to $4,000 for a motor conversion to 3.0 liter, IMHO.

For myself the 140 is too big and way too complicated.

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.

Exactly. This *could* be a head gasket issue but on a 3.5L it's the lesser probability.


But for other people the 140 is the perfect size, and although it's much more complicated than a 123, 124, or 126... it's far less complex than a 210, 211, or 220. You can still service a 140 yourself when armed with the FSM and/or WIS. I too think the 140 is a bit large for my taste, but on a long road trip with 4 people in the car, I'd take a 140 over a 124 any day. My sister has a 140 (S500) and it's an incredible vehicle, except for the 15mpg. The S350 offers the same experience but with roughly 50% more fuel efficiency, in exchange for less power. But anyway, it's always good to factor in at least $4k in fudge factor for when (not if) the 3.5L goes belly-up.

In the case of the engine I took apart, #6 had the same piston protrusion uneveness as #1. Obvious head gasket breach in #1, I found no traces of a breach in #6. That said, this was a -20- head on an early block so #6 could have been bent by an earlier gasket failure.

That reasoning still suggests poor or marginal rod design because the rest of the 60x family is subject to the same head gasket failures but not the subsequent lower end effects.

Sixto
87 300D

You regularly see them with replaced engines. Here's another one: "Engine was replaced with factory long block at 158,000 miles" http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=230246767219&ih=013&category=6330

Wonder if having a replacement engine represents an iron clad "stay free of future rod issues" guarantee. If yes, then a purchase of one of those would be a best buy - the biggest most luxurious last generation 126 with the smoothest gas like diesel and the potential of 500,000+ miles as a select few on this board enjoy.

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'83 SD, 2x '85 SD
You are entitled to your own opinions, you are not entitled to your own facts.

I am proud to be one of the few. The 350 can always be rebuilt with updated rods. The engine is sleeved. New sleeves, rods, bearings, rings, and pistons will be required if the rods were bent. Otherwise you can do rods, rings, and bearings. Not cheap, but if you want the good stuff, you have to pay.

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1991 350SD (updated rods)
Biodiesel B100 when I can find it.
Dino when really cold outside

Yes, that would be excellent..........but, we've concluded beyond any doubt that it does not have any sleeves. There is no room in the block.

You sure? This doc from the FSM indicates that non-sleeved engines (from the factory) can have the block bored out to accept sleeves, no?

Good explanation but it doesn't address the propensity for #1 to go bad long before the others.

And what exactly is knock that doesn't make untoward noise? What does low cetane knock sound like?

Sixto
87 300D

A comment. I test drove several 350s before buying the one I had. A slight miss at idle which was not noticable while driving was present in all of them. I think an engine with a bent rod will miss at idle for sure and maybe run pretty well at high rpm.

Unfortunately there are other common causes of a miss too.

For me buying a diesel with a miss at idle, unless cheap enough to cover the cost of a new engine is a red flag.

diesels shoud not miss at idle.

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.