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  #46  
Old 04-24-2005, 10:05 AM
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Quote:
Originally Posted by t walgamuth
the machinist's job is to take apart engines that have failed. he has taken apart a lot of them. i suspect that he has seen the results of a starter pushing against a hydrolock or a solid object. from my personal arsenal of sad experince know that a starter pushing against a solid object has enough power to push a hole in a piston... in a '52 cadillac engine... which is a pretty tugged piece, too. the thing is that these parts are designed for a specific job and pushing against a hydro lock is not what a rod is designed to do.
I am going to presume that the solid object was not a volume of fluid. A solid object such as a nut, which has put a hole in a piston, is placing a massive force at a single point on an aluminum object. The result can only be a hole in the piston. You have made an excellent example of my point about machinists. They see a hole in a piston caused by a steel object and make the conclusion that a hydrolocked engine can cause damage to a connecting rod based upon an example that is not at all relevant.

When the machinist can show me the calculations that prove the rod has insufficient strength to support the load, I'll believe him. Otherwise, it's just BS from someone else. I can go ask my mother for an opinion as well, if you like. We can then take a poll of all kinds of folks and see what the majority thinks?? That be OK??

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  #47  
Old 04-24-2005, 01:58 PM
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assumptions

your assumptions are presumptious, i think.
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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.
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  #48  
Old 04-24-2005, 02:07 PM
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44,000 #

i don't know the psi rating of a connecting rod but ordinary structural steel is aobut 60,000 psi. is a rod 1" in section, i believe without measuring it that it is. however an impact load is altogether a different proposition than a static or a gradually applied load. the small angle of the rod is probably the most correct thing to assume, and if the cylinder was very full, perhaps the outcome would be different. i will ask my machinist what leads him to believe that a starter can bend a rod from hydrolock. the examle that i used about the hard object was my personal experience and did not come from my machinist.
please keep the calculations coming but why do you have to dis my machinist?
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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.
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  #49  
Old 04-24-2005, 02:44 PM
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Quote:
Originally Posted by t walgamuth
i don't know the psi rating of a connecting rod but ordinary structural steel is aobut 60,000 psi. is a rod 1" in section, i believe without measuring it that it is. however an impact load is altogether a different proposition than a static or a gradually applied load. the small angle of the rod is probably the most correct thing to assume, and if the cylinder was very full, perhaps the outcome would be different. i will ask my machinist what leads him to believe that a starter can bend a rod from hydrolock. the examle that i used about the hard object was my personal experience and did not come from my machinist.
please keep the calculations coming but why do you have to dis my machinist?
Ordinary structural steel is a bit over 60,000 psi, however, those rods are not ordinary steel in any way. They probably are heat treated and have a tensile strength of well over 120,000 psi. I don't believe they could survive with a tensile strength of 60K.

Agreed. An impact load presents significantly higher numbers. It's very difficult to calculate it. All of the rotational energy of the pistons and crankshaft must stop within a very small time period. This stresses the one rod considerably more. However, at cranking speed, this rotational energy is not all that high.

I am in the business of making complicated tools and parts. I'm very familiar with machinists. They typically have an ego as large as an elephant. They frequently draw conclusions from facts not in evidence. This is a complicated business and their anectodal evidence should not be used for anything more than amusement. It can lead you down a path that is a huge waste of time when you finally realize the error of your ways by calculation.
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  #50  
Old 04-24-2005, 04:49 PM
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machinists

sorry you have had bad experiences with machinists. mine is one of my best friends and if you will stop dissing him i will also leave your grandma out of it.

when i have more ideas about the bent rods i will log back in.
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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.
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  #51  
Old 04-24-2005, 05:56 PM
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Quote:
Originally Posted by t walgamuth
sorry you have had bad experiences with machinists. mine is one of my best friends and if you will stop dissing him i will also leave your grandma out of it.

when i have more ideas about the bent rods i will log back in.
I don't have any bad experiences with machinists. They are the bread and butter of my business. However, I understand their knowledge of turning metal and I respect their input on how to complete a given task using a lathe or a mill. When they start to put forth engineering opinions on things where they have very limited experience and data, and no formal training, then I thank them and tell them that I'll seriously consider their idea.

Fire away. I'd sure like to find the answer to the rod bending issue. However, any answer must address why the 603.961 very rarely suffers from bent rods whereby the 603.970 and 603.971 engines have the bent rod situation all too frequently.
The engines are nearly identical in most respects.
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  #52  
Old 04-24-2005, 07:31 PM
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more bending

i assume the numbers of engines you list are for the 300sd motor and the 350sd motor. i am not familiar enough to know which is which.

same block, same head, same head gasket, right? so what is the difference that makes the difference? well... the bore and stroke are different, so the pistons, crank and rods are different, right? and the motor makes more power and the bore being bigger there is less block to resist twisting. when we built my 617 turbo motor there was measurable permanent twist in the block at 186,000 miles. he decked it before boring it so that they would be perpindicular to each other... so less block, more twisting, that is one negative for the 350 motor. so with a bigger bore there is less material for the head to seal with against the head gasket. that is two... also more power and (presumably) heavier reciprocating mass hence more stress on everything , thats three, and the result is a head gasket problem. i would like to know the percentage of head gasket problems... i am betting most have them. if they don't perhaps they always putt around town and rarely run at high speed on the freeway. btw is the 350 a us only motor?

so i am still on the leaking gasket and hydrolock idea. i can't see mercedes not getting the math right on the rod strength. however with this being the first aluminum head diesel (that i know of) it is possible that their research on the al heads might be thin... this after all being an indeterminate design problem that only can be solved through practical experince.
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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.
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  #53  
Old 04-24-2005, 07:44 PM
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Correct. The 603.961 is in the 300 SDL from 1986-1987. The 603.970 is in the 300 SD and SDL from 1990-1991.

Now you are making the assumptions.

The difference in engine size between the two is 17%. I don't have the specs on the 3.5L, however, I seem to recall it being a lower speed engine. Therefore, I conclude (by sheer speculation) that the stroke is increased from 3.31" to 3.87". The bore remains the same at 3.43.

If this is true, the theory of the head gasket letting go earlier on the 603.970 engine would not be applicable. The head gasket suffers from the same stresses as it's older sibling. The rods, however, are travelling a bit faster due to the longer stroke and are therefore more highly stressed in the larger engine.

Of course, you can conclude that M/B designed additional strength into the rods for this express purpose.............................
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  #54  
Old 04-24-2005, 10:49 PM
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assumptions, etc

i only objected to you assumptions about the character of my machinist.

i am pretty sure that the bore and stroke are both different in the 350. i believe that i got that from the mercedes buyers guide. it could be wrong of course. i dont think that the 350 is a lower speed engine, but dont know for sure.

yes it is reasonable to assume that the factory made the rods stronger, but dont know that either.

talked to my favorite machinist again tonight. forgot to ask why on the cranking with starter idea. but he had two examples of bent rods with engines idling or near idle.

1. a customer with a four cyl. gas alfa romeo had pulled over to avoid being drowned by a large truck coming past in some standing water. as the truck went by it created a big wave (not a tsunami) which raised the level of water enough to get it in the intake. the engine suffered a bent rod and a broken wet sleeve. i believe that engine is still in his shop at present.
2. in his personal olds diesel (about ten years ago) he was driving and came to a large underpass with standing water. he decided to creep through it. bad idea. it sucked water up and bent a rod. the engine still ran but wow! it shook very severely.

so these stories are somewhat antedoctal (sp?) but based on some pretty strong first hand info.

so the question is can a 350 benz bend a rod on a hydrolock upon startup? i still think yes. perhaps some other folks can add personal experience to our facts file.

pleasant pondering
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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.
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  #55  
Old 04-24-2005, 11:04 PM
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specs

in the mercedes buyers guide from 1994 they list the 86 87 300dt at 87 bore 84 stroke and max hp at 4600 rpm, max torque at 2400 with a 2.65 rear end and a top speed of 100 est. (oversquare)

they list the 350 engine at 89 bore 92.4 stroke with max hp at 4,000 rpm and max torque at 2,000 rpm and a rear end of 2.87 and est top speed of 115. (undersquare)

so it doesnt shed too much light on the high speed vs low speed engine... wait... with the lower gear, the 350 will be pulling a higher rev. at a given speed, so it would along with the other three factors that i listed before contribute to a situation where head gasket sealing can become a problem. well of course with a longer stroke comes more piston speed, and presumbably heavier parts.

btw i think that the factory probably knows what the problem is but wont own up to it. i imagine that they quietly replaced a lot of engines when these cars were new... probably head gaskets too. understandable in our litigenous society... no knock on lawyers.
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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.

Last edited by t walgamuth; 04-24-2005 at 11:05 PM. Reason: ideas
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  #56  
Old 04-24-2005, 11:25 PM
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Quote:
Originally Posted by t walgamuth
in the mercedes buyers guide from 1994 they list the 86 87 300dt at 87 bore 84 stroke and max hp at 4600 rpm, max torque at 2400 with a 2.65 rear end and a top speed of 100 est. (oversquare)

they list the 350 engine at 89 bore 92.4 stroke with max hp at 4,000 rpm and max torque at 2,000 rpm and a rear end of 2.87 and est top speed of 115. (undersquare)

so it doesnt shed too much light on the high speed vs low speed engine... wait...
Actually it does shed quite a bit of light.

The older 3 litre engine was oversquare and had max hp at 4600.
The newer 3.5 litre engine was undersquare and had max hp at 4,000.

So, the larger engine is a slower turning engine.

The bore changes between the two engines, but only by .078". I don't think you could attribute the slightly smaller head gasket (larger piston openings) to a generic head gasket problem in the 3.5.

As for bending a rod at idle due to massive water ingestion, I have also heard of this. I suppose the forces at idle are too much for the rod to bear. But, at cranking speed..........................
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  #57  
Old 04-25-2005, 12:07 AM
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head gaskets

according to a catalogue i have the head gaskets are the same.... for what it is worth.

the hydrolock theory doesnt require bending rods at crankover.

my bottom line is the same. if my engine turns out to have a bent rod... and it is not clear yet... i will probably find a 3.0 block and use that. i could do with a little less torque.

it has been fun talking with you, brian.

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.
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  #58  
Old 04-25-2005, 12:34 AM
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Quote:
Originally Posted by t walgamuth
according to a catalogue i have the head gaskets are the same.... for what it is worth.

the hydrolock theory doesnt require bending rods at crankover.

my bottom line is the same. if my engine turns out to have a bent rod... and it is not clear yet... i will probably find a 3.0 block and use that. i could do with a little less torque.

it has been fun talking with you, brian.

tom w
With the same head gasket, it's unlikely that the 3.5 would cause additional failures of the gasket.

How does it cause a hydrolock condition at any engine operation other than crank? Presuming no massive outside water ingestion from diving through massive bodies of water.

I agree with you. If the 3.5 bends a rod, find a good used 3.0 for $2K or less and put that in. BTW, one of the 3.0 engines owned by one of the members just bent a rod in #3 within the past 30 days.
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  #59  
Old 04-25-2005, 09:19 AM
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hydro lock

1. engine weeps fluid into a cylinder, perhaps #1 is prone, on startup, one or more other cylinders fire first and drive the one with fluid up for compression and it hits the fluid lock.
2. with the same head gasket and a bigger bore, there is less contact area for the head block interface to seal against the gasket. when we had mine apart there was corrosion in an area that indicated a probable leak.

i know it seems a little wild, but metal fatigue doesn't seem at all possible to me.

thanks for the tip on the engine for sale.

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.
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  #60  
Old 04-25-2005, 09:28 AM
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Quote:
Originally Posted by t walgamuth
1. engine weeps fluid into a cylinder, perhaps #1 is prone, on startup, one or more other cylinders fire first and drive the one with fluid up for compression and it hits the fluid lock.
2. with the same head gasket and a bigger bore, there is less contact area for the head block interface to seal against the gasket. when we had mine apart there was corrosion in an area that indicated a probable leak.

i know it seems a little wild, but metal fatigue doesn't seem at all possible to me.

thanks for the tip on the engine for sale.

tom w
If the other cylinders fire and the engine gets more rotational speed than crank speed before the final, hydrolocked cylinder reaches TDC, then I agree with you. But, also remember, it's a four stroke engine. Your odds of a few cylinders firing before the culprit reaches TDC, on either the compression or exhaust stroke, just decreased by one-half.

We both agreed that the 3L and 3.5L engines use the same head gasket. Therefore, the head gasket must be large enough so that it fits the 3.5L bores. So, the contact area must be the same between the two engines.
Or am I missing something??

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