1977 300D threw a rod. Now what? - PeachParts Mercedes-Benz Forum

keywitt · #1 09-29-2014, 09:14 PM

My car died yesterday. I've learned a lot from posts on this forum over the years, lots of good advice, but I guess I didn't follow enough of it.

I changed the oil around 1800 miles (5 months) ago and checked the level just last week. It was a little low, but not terribly so, about what would be expected of a 35 + year old car. I've had to add a quart or two a month for as long as I've had her.

Yesterday, I was on the highway for about 15 minutes when I noticed the oil pressure gauge reading between 1 and 2. Uh oh. The temp gauge read just over 80, so I wasn't too worried. Start to change lanes to exit, stop, and check it out when the knocking starts. 30 seconds of knocking, progressively louder, and then the bang and smoke. f**k.

I got the car towed home, marveled at the gapping hole in the bottom/side of the block, had a beer, poured some out for the recently departed, and now I'm wondering what to do.

I cannot tackle dropping an engine in myself right now, though I would love to do a project like that one day.

Is it worth it to pay the local euro shop to do the job, or would I be better off selling the car? If the latter, should I part her out or try to sell her whole? How do I price? Should I just hold on to her till I have time to do the work she deserves?

She died with about 220,000 miles on her. I drove her across the country, and she's been my daily driver for the 5 years she's been mine. Only three hubcaps, one door ding, faded paint, but no rust or leaks. The seats lost most of their stuffing long ago, but you get used to the vinyl hammock feel. I definitely got my moneys worth, and I knew she wouldn't last forever, but I sure didn't expect her to go so soon and so catastrophically.
What now?

CTD · #2 09-29-2014, 09:24 PM

I wonder what caused the engine to throw a rod? Did it lose oil pressure from the failure of a bearing or did oil suddenly leak out from someplace?

I always wondered a bit about the health of the bottom end of the motor in my old 220d since the oil pressure is a little bit on the low side-- drops down to about 10-15 psi at idle after a hot day's highway travel, whereas the two other old Benz motors I've seen do about 25-40psi.

Junkman · #3 09-29-2014, 10:25 PM

Just get another motor for a few hundred, change the gaskets so it doesn't leak oil. Do some minor touch up on the trans and be rolling again. See if a 617 will fit - probably but I guessing.

leathermang · #4 09-29-2014, 10:30 PM

The problem comes in little things like the linkages.... it might seem straight forward to just get another engine... but only if you find the same year.. otherwise some real time will be used up with small but important stuff...

Diesel911 · #5 09-29-2014, 10:50 PM

I have read that the non-tubo Engines have issues with the Oil Pump. The Pressure Relief Spring Breaks or the Valve Sticks.

Aslo the drive on the Oil Pum is like a Gasser Distributor; worm Gear and little teeth.

I am not sure what Engine it was on but I think I have read of the Oil Pump Pickup Tube cracking or coming loose.

mach4 · #6 09-30-2014, 12:31 AM

You don't say where you are, but you should be able to get a replacement 300d for a lot less than sourcing an engine and paying someone to install it. Junk it, part it or sell it and move on.

vstech · #7 09-30-2014, 06:55 AM

Quote:

Originally Posted by mach4

You don't say where you are, but you should be able to get a replacement 300d for a lot less than sourcing an engine and paying someone to install it. Junk it, part it or sell it and move on.

+1
Where are you located?
Lots of good w123's out there cheap.

barry12345 · #8 09-30-2014, 09:54 AM

Just curiosity mostly. What rod went out #1 or #2? These are the only ones that proper fuel pressure maintenance might help reduce failures.

Proper fuel pressure maintenance includes keeping the fuel filters free flowing. This lower pressure otherwise seems to occur easier as the naturally aspired engines have a weaker lift pump pressure wise. Of course the state of the lift pump and filters has no effect if the relief valve spring on the injection pump has seen its internal spring tension sag way down with time.

As the fuel pressure in the base of the injection pump sags with time one way or another. More engine loading progressively goes on to the first and second cylinders. Increasing bearing wear on them faster than the other bearings. Actually the other bearings are receiving less wear in this situation than normal.

The four cylinder 616 engine seems even more notorious in this fashion.

For any other rods in those engines there is fundamentally nothing much can be done about their service life . Other than regular oil changes to maximize bearing life. In my opinion it takes lower fuel pressure of long standing to create the negative bearing failure situation if it occurs.

These lower blocks are built like tanks. in my opinion. I trust them almost totally unless certain things are not checked and maintained.

Installation of a turbo cars lift pump is a cheap update on a N/A car. Or a lift pump pressure spring installed from one.

The true answer is to install a convienient way to measure the pressure based on some kind of millage. Perhaps every ten K.

There should always be fuel out the return line on the injection pump is a simple semi test. It is not a conclusive test because the relief valve may be weak. Still better than nothing.. If there is no output the injection pump is operating at less fuel pressure than designed is pretty obvious.

I only post this once again because a member asked me years ago why it appeared only certain rod bearings always seemed to be the ones that failed in these engines. It took me quite some time to figure out as there was an accepted ideal it had to do with oiling passages. Plus many rod bearing failures are preventable.

For a long time I was not absolutely certain. Since then I have only found incidents that tend to support my concept. Too much information to ignore.

I still feel that too many owners still take this area with a grain of salt. At the same time the engines actually run and perform better with good fuel pressure as well. So in my simple mind why not make sure you have it? It is just maintenance of a preventative nature to me.

Eventually I also picked up that periodic checking of the fuel pressure was part of the factory maintenance schedule on these engines. Although the manual did not mention the why to do it for the mechanics. When the manuals were written It is my belief what I describe was an unknown effect as it takes a lot of miles to do the damage. They probably knew the injection pump changed its sequential calibration a little. Not that it could ultimatly wear out certain engine bearings. It may take 100k of low fuel pressure operation to do it though. Probably depends a lot on how low the pressure is the injection pump has been operating at.

I am also starting to believe if an individual wants the maximum lifespan out of a 123 engine they should have the fuel injectors checked every 100k. Many 123 type cars out there probably have never had theirs checked. A properly maintained engine of this type with todays superior oils changed out often enough may see 500k. An improperly maintained one perhaps only half of that.

leathermang · #9 09-30-2014, 10:18 AM

The problem I have with the low fuel theory is that the range... upper AND LOWER... is controlled by springs... at a certain ' low ' you get no fuel... as when you have air in the system which just gets compressed instead of opening the valve allowing fuel flow . So how you could have low enough pressure for it to affect the engine I do not see happening.

Another problem is that if it were true that less fuel was getting to number one and two... that would mean less power.. thus less pressure being applied to those front two pistons...

I have read about oil passages being the cause on some engine designs... and I believe it...

One thing which I think may can counteract the danger... is switching to straight 40 wt oil after about 100 k . I use straight 30 wt before that. The bearings have worn enough to have more space and the higher viscosity provides more support there. I use STRAiGHT oil wt because manufacturers of small air cooled engines .. one of the most severe tests for oil.... used to mandate the single weight for warranties to apply....
I do also believe in 3000 mile hot oil changes....no matter how many testers say it is good beyond that... it is cheap insurance compared to an engine rebuild.

barry12345 · #10 09-30-2014, 11:17 AM

If it was not important the fuel pressure that injection pump is calibrated at would not matter. It matters very much. It has to be checked before an attempt at injection pump calibration is started at any pump shop.

I have suggested adjusting the relief valve to 19 pounds when a low pressure situation of long standing is encountered. This may shift the calibration of the injection pump slightly to favor the rear cylinders a little more than was intended. Equalizing wear existing perhaps over time.

Also the concept that the maker wanted the fuel pressure checked even way back when is signifigant on a well running car otherwise.

The lift pump recharges once per injection pump rotation. Since the fuel is non compressable as elements load the pressure perhaps drops a little each time an element fills. This would make their injectors fire just slightly later.

Whatever it is the equality of element fill that is changed just enough that the first element to load gets serviced the best in a sub standard pressure situation.

It is hard for me to explain still my belief is the intended volume of loading in a sequaential fashion is just distorted a very little with abnormal fuel supply pressure. There may be some answer in the vicious loading of element pulses impacting lower fuel supply pressure even to consider.

Anyways there is far too much evidence indicating that low fuel pressure is damaging long term. The idle even smooths out at proper fuel pressure reflecting more equal power loading of the engine has been restored. My guesses about exactly what is occurring and how are just guesses and estimates. That they where occurring in some form is pretty well absolute to me some time ago.

Still I think the sequential fall off is not completely linear in nature. The end result is injection is slightly delayed or retarded on the bulk of cylinders after number one I think. So the only element to be loaded properly or the best established in the the sequential reload is number one. This changes the engines power balance just a little favoring the loading of the first cylinders element.

barry12345 · #11 09-30-2014, 12:05 PM

Quote:

Originally Posted by leathermang

The problem I have with the low fuel theory is that the range... upper AND LOWER... is controlled by springs... at a certain ' low ' you get no fuel... as when you have air in the system which just gets compressed instead of opening the valve allowing fuel flow . So how you could have low enough pressure for it to affect the engine I do not see happening.

Another problem is that if it were true that less fuel was getting to number one and two... that would mean less power.. thus less pressure being applied to those front two pistons...

I have read about oil passages being the cause on some engine designs... and I believe it...

One thing which I think may can counteract the danger... is switching to straight 40 wt oil after about 100 k . I use straight 30 wt before that. The bearings have worn enough to have more space and the higher viscosity provides more support there. I use STRAiGHT oil wt because manufacturers of small air cooled engines .. one of the most severe tests for oil.... used to mandate the single weight for warranties to apply....
I do also believe in 3000 mile hot oil changes....no matter how many testers say it is good beyond that... it is cheap insurance compared to an engine rebuild.

It has to be More fuel not less getting loaded in number one and two with a probability almost certain now that number two gets only slightly less. Or at least in relationship to number one.. More fuel loaded means an earlier injector release compared to any other element with a reduced loading.

Any lesser amount of fuel being loaded after that will produce a delayed injection but similar volume. That is the damaging component. Leaves the first two cylinders working harder than the others.

The sequential timing of some of the injectors is retarded. Upsetting the power loading of the engine. I never saw it as a fuel volume problem at injection. Rather a timing issue. The lower the injection pumps fuel supply pressure the more the retardation effect of injection down the sequential line.

I almost brought into the oil passage thing on these engines as it was almost gospel by the time I came along. Many engines I have to agree it is still the cause. Not the 123s though.

To tie the cause of the rod failures to fuel supply pressure would not have come along had not that member asked me If I knew why the rods where failing. . It was not the easiest thing I ever did. Afterwords it did seem pretty obvious even simple. This hindsight thing.

As a random thing I also observed there were some other items that required serious investigations in this area. Without a lot of testing it would be insane to try them out. Or discuss them openly as someone may try them and do harm.

One of them I suspect to still have some promise perhaps. I have discussed more semi retiring after this year with the wife. Just to enable hopefully enough time to get to many things in my remaining able time that interest me. The work ethic is so well entrenched it keeps me at it when there is no financial need. Some of it is still the challenge but I want to change my ways.

As for oil. Oil film strength will always be important. You do not wear fixed grade oil out. Just contaminate it basically. Accumulated soot in these 123 diesels is the killer.

I suspect the viscosity enablers with multi grades do degrade with milage. I have also reciently came to the conclusion that perhaps the molecular size of synthetics is substantially greater by the way. Too expensive perhaps for the frequently required changes on 123s.

This molecular suspicion was indicated by some of the lower viscosity grades in recient cars. Where I am going with this is I would think long and hard substituting a dino oil of a similar viscosity in an engine that recommends synthetic of at say a 0-20W as the wives Toyota does. . The side thrust loadings on the pistons would contact the walls perhaps.

I suspect that some of our newest cars have specific manufacturers recommendations of oil product brands based on large molecular additive packages. These may have replaced viscosity ratings as we know them to some extent ..Or present an illusionary picture.

Incidentally straight 30 weight is considered a little on the light side in eastern Canada on these old diesels. Part of the viscosity package on multigrades I suspect again have a larger molecule presence. That is the only way I can think they could quote equivelant protection to straight oils. They temperature react.

What many of my thoughts in these areas are based on. You burn a quart of oil a thousand with a 15w 40. You may only burn half a quart on straight 40. I suspect the difference is not the viscosity weight. The thinner component of the muligrade is getting past the rings while the viscosity increaser is not. It is truly amazing how little besides the sales hype engine oil sellers tell us about there products.

The base weight viscosity wise of a 15-40 of the oil itself may only be a twenty weight. Actually I suspect it has to be a fifteen weight. Small engine manufactiures have some time ago went over to multigrades in numbers. We older guys continue to use straight 40 in them. One now has to understand that there is more going on of a marketing nature. The 10-30 recommended because of additives may be more than its equal. Like yourself though I stick to the heavier viscosities in straight grades in our lawn tractors etc. I am satisfied with the lifespans I am seeing. As for some of the newer stuff there are indications this approach does no longer work out well.

vstech · #12 09-30-2014, 12:32 PM

the OP has stated his vehicle loses a "a quart or two a month"... and 5 months ago, the oil was changed around 1800 miles... so, he's going through 1-2 quarts every 360 miles...

I'm guessing, he missed a check or two, and or the oil consumption got worse, and he starved the motor of oil... if the oil pump had failed, he would not have had 1-2 bar of pressure under load, it would have been zero...

I seriously doubt it had anything to do with fuel consumption.

the fuel pressure issue affects the piston, more than the rod I'd think...

barry12345 · #13 09-30-2014, 12:47 PM

Quote:

Originally Posted by vstech

the OP has stated his vehicle loses a "a quart or two a month"... and 5 months ago, the oil was changed around 1800 miles... so, he's going through 1-2 quarts every 360 miles...

I'm guessing, he missed a check or two, and or the oil consumption got worse, and he starved the motor of oil... if the oil pump had failed, he would not have had 1-2 bar of pressure under load, it would have been zero...

I seriously doubt it had anything to do with fuel consumption.

the fuel pressure issue affects the piston, more than the rod I'd think...

Possible low oil of course but that depends on the rod that failed. For example an abnormal amount of wear in the first rod existing might help it go out first on low oil. If he threw any other than the number one or two rod it was not fuel related. Or the chances were probably very low because of a bad injector lets say over time.

Of the course the piston transferring different loadings on the rod bearings relates to the difficulties with low fuel pressure. The number one cylinder with these difficulties is always working harder than the others. So its bearing and piston will be as well. Over the miles the wear of the bearing is increasing over the others. It is one of these silent killer situations.

I would expect the piston or/and rings or bore may have some additional wear as well. That's my thought of why on an engine with low fuel supply pressure it is best to go to 19 pounds pressure when restoring. There is a slight chance to not only reduce the loading by additional transferring even a slight amount more loading than it would normally see elsewhere.

Going much higher fuel pressure wise is one area I thought about experimenting with. The injection pump should be recalibrated for that pressure unless you can prove otherwise that you are not messing up the calibration. Appears to be a substantial power increase. But you might just be advancing the injection timing in effect.

You have not changed the volume processing in any way I can think of. Other than maybe squeezing a little more fuel into the elements. This only makes the injectors open a little early and closed perhaps a little later as pressure inside the element increased longer. Still this is kind of not borne out by reports of similar fuel milage in one case I saw of elevated fuel pressure. At the same time the car was much faster though.

Risk of pre detonation damage is there unless Mercedes was playing it very safe. There would have to be a lot of thought given to the celane rating of the north American fuel. At revs can the engine stand some advanced timing on our poor fuels? The better approach might be to respring the centrifical advance mechanisim.

Lots of work first though to calculate celane against advance curves. Funny that no member has gotten into that on our site that I am aware of. There seems to be some indication there is some benefit because of our poorer north American fuels. Although with all the noise these engine make could one hear a moderate problem? Mercedes probably has the information we need somewhere. Modern Diesels of course automatically compensate timing for poor fuel.

barry12345 · #14 09-30-2014, 02:12 PM

Quote:

Originally Posted by vstech

the OP has stated his vehicle loses a "a quart or two a month"... and 5 months ago, the oil was changed around 1800 miles... so, he's going through 1-2 quarts every 360 miles...

I'm guessing, he missed a check or two, and or the oil consumption got worse, and he starved the motor of oil... if the oil pump had failed, he would not have had 1-2 bar of pressure under load, it would have been zero...

I seriously doubt it had anything to do with fuel consumption.

the fuel pressure issue affects the piston, more than the rod I'd think...

I use oil consumption with no obvious leaks to get some handle on wear. It is not conclusive but a thousand miles a quart of oil is about the lowest I feel comforatable with on 616 and 617s . Below that depending on where the wear is matters more. You know it is there usually and wear increases more rapidly the more it is underway. Wear is not a linear but exponential component with engines usually. It is far more probable to have a major failure with an engine processing too much base oil than one that is not.

leathermang · #15 09-30-2014, 04:46 PM

As an ' older guy' I have only used straight 40 wt in the 240 and my Ford 5600 tractor... Delo 400...
' side piston ' wear... many a time people ' rebuild' engines and do not use the proper shims to set the end play on the crankshaft.... too much will wear OUT an engine..
I think the car manufacturers suggest things like 20 wt to get their fleet MPG ratings to what they need for the Govt... they really do not care long range about the life of the engine.. and few of their engines have the potential of what ours do when properly built... or rebuilt...