Its not smaller. The cylinder is bored 10 thou over. Im not sure if the rings are the same or not. Probable reason is that temperature regulation is not as good adjascent to the timing chest. This is also the case with 617s.

Fuel filters made a huge diff, valve adjust coming and two new tires on Monday but still bugging me was that the trans would shift hard 1-2 and then rev kind of high to shift into 4th near 45-50. Poked around the vac lines after reading about how the trans is mostly vac controlled and voila, found a metal vac valve on in the far left (as you face the car) engine area just behind the headlight was bumped loose. Have yet to figure out what it does.

Secondly, the vac control valve was buggered up with dust and found another rubber line all crackly (the one circled in white in the pic). Till I find the "y" rubber replacement vac line I cinched it up with a mini zip tie, dusted, silicone sprayed, wiped, put some white grease on the cam and she no longer shifts hard nor revs up real high to shift. The difference is nothing short of amazing..
So between clogged fuel filters to a bumped vac line and a crackly vac line fitting, this Gretel- the 240d-has changed her ways big time. Baseline maintenance continues, thanks for all the pointers!

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I do not doubt your expertise, or your recommendation, but as a point of trivia I'm curious if you've actually seen this happen on a diesel.

It can happen very easily on a gasoline engine, of course -- but I've had people assert to me that you can't have a tight valve get burned on a diesel, because if the valve doesn't close fully, the cylinder will not fire due to lack of compression.

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1981 Mercedes 300TD, 1994 Honda Civic Del Sol
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Mmmmmmmm, I have never seen it but I would tend to think it would still occur. Even if the valve is tight enough to just hold it off the seat a tiny bit, the piston moves really fast and the compression is very high. After the fuel ignites the pressure spike is powerful and would push that hot gas right past the valve.

The acceptable compression number in the manual is very low, as long as the numbers are even and close across the entire engine.

I've never seen it, but just running a thought experiment I'd say it's very possible.

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'84 190D 2.2 5MT (Red/Palomino) Current car. Love it!
'85 190D 2.2 Auto *Cali* (Blue/Blue) *sold*
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Low fuel pressure over a period of time takes it's toll by making the engine run in a less balanced power fashion. Because the lift pump only cycles once during all the injection needs down the line so to speak. The first element gets loaded better than the others. You start with little pressure and it decreases fast while filling the elements. Then the lift pump recharges. Really it is somewhat more complex than this but who wants to read a book.

That is why normally when you correct a low fuel pressure problem the engine sounds better usually as you have restored a better power balance. Without it over the years the first cylinder has worked harder than any other cylinder and the rod bearing wear reflects that. I could seriously elaborate on this but it would be very long.

Proof of concept is no issue as using the milli volts application system. You would see at low fuel pressure the hottest cylinder running would be number one. A little less voltage on the others.

Raise or restore the fuel pressure and either the number one cylinders temperature will drop or the others increase.

They all become more equal running temperature wise than they were. Or power balanced if you wish. I like to see the fuel pressure at 19 pounds for reasons I will not go into right now. Simply because some are speculative.

It takes years of low pressure abuse in my opinion to take the first rod bearing out. There are some probable design defects as well.

For example the 240d has a weaker lift pump. This makes filter choking effect occur earlier on fuel filters. Lowering the fuel pressure in the base of the injection pump.

The lift pump should be tested and rebuilt if low in output pressure and also have the pressure regulating spring upgraded to one out of a turbo model lift pump. Not an expensive or big deal. Some way of monitoring the condition of the fuel filters periodically should also be employed.

Now when you aquire a new to you 240d there are some preventative measures you can undertake. First make sure the fuel pressure is good. Or if not repair it. Almost always really cheap to do.

Then consider going in and plasti gauging the first rod bearing. My problem is these engines are so noisy it may not be that obvious when the point of it should have been changed out is passed.

This is not that hard to accomplish thanks to the oil pan design. I think the four cylinder engine can make 500k but probably not if it has been exposed to long periods of low fuel pressure.

Anyways running a 240d not knowing what fuel pressure you have may reduce power you still need. As another benefit some of these engines are quieter on the highway with good fuel pressure.

You are still not going to break the sound barrier though.

Please humor me or put the effort in to prove what I believe wrong. I was requested by a member years ago for an explanation of why the first rod bearing fails in 240ds.

It was pretty hard for a simple guy like me to establish the probable causes when everyone was screaming oiling problem. I have never seen one instance yet that has caused me to question my assumptions. Not even one to cause the slightest doubt and I have tried.

Then when I worked on the milli volts system I realized the concept could even be proven. I never put the final nail in the coffin and posted it simply because some people still want to hold on to whatever they wish to believe.

To take that away from them would be wrong and anyways over time they would come to accept the obvious. The fuel pressure present in the base of the injection pump is too important to ignore as it once was.

Especially on the 616 but still to a lesser degree on the 617 engines. There you have it and take it as you wish.

If the car is in almost cream puff condition and you wish to own it for a long time. I would critically look at the two hoses to the oil cooler. Basically inspections rather than absolute change outs.

I believe the vast majority of the 240ds exported to north America have the oil cooler. This is one item that can prove terminal to the engine if either hose to one ever lets go.

Probably 100.00 a pair for original type replacements. I do not know if age or milage or a combination of both is why they let go. They usually fail during highway usage if they fail.

In probably ninety percent of cases it costs you the engine. If the motor mount gets in terrible shape on that side of the engine. The belt can slice into the oil cooler hose as well. At least on the five cylinders and it is too late for me to slip out to the garage to see if this also applies to the 616 engines.

Another two items just to inspect very carefully is the flex disks on the driveshaft. When they become cracked change them. If a driveshaft ever gets loose on one of these it is something else. Also inspect the boots on the drive axels carefully for condition.

Also I have suspected that the 240ds will become the first collector type cars of this era for the diesels. They just do not make anything like them at all anymore and are not likely to.

Sounds like you got a good one hopefully at a fair price.

Often forgotten.

Thanks Barry, will add these to the list, fuel pressure check, motor mounts, flex disc and the boots on the drive shaft. Got tons of tinkertime planned with the 240d. I plan on doing the hoses and will check the oil cooler hose which it has. Some of the work I will do but have a local shop that is great for the non deisel stuff if I want to 'punt' on the harder stuff.
Although here in ne IA weather is willing and it would be great to get more done on the car but after getting a couple new tires today (goodyear says they are phasing out the 195 70/14's btw) the deisel shop doing the valve adjust told me in a german accent that 'it should be done by the end of the week' ..I think he saw my sad face and said if it is done sooner, he will call.. Never thought I would have Gretel the 240d separation anxiety but guess I do!
Think I did get a good deal, Positives: rustfree, interior/exterior amazingly nice but drove crappy because of the crackled vac hose and some other vac hoses which got bumped off their fittings and the clogged fuel filter diatribe alluded to earlier. I took a little risk and turned out quite nice and plan on keeping it for the long haul, whatever that means at age 50!

On my 83 240D, the vac relay/valve behind the passenger side headlight inhibits/enables the EGR valve... and gets it's vacuum from a 17°C coolant temp valve (screwed into the top of the thermostat housing), which in turn gets it's vacuum from the cam driven valves you cleaned up... and possibly from the A/C circuit (mine has 3 vac lines and an electrical connector).

I've been chasing vacuum leaks in those valves/lines for a couple months now, and I've just about read enough to convince myself I can remove the whole mess up there...

Thanks for the update, will look for that post when you decide to undertake the removal! The merc. vac line logic -and overuse?- seems kluge-prone now (it has been working though for 30+ yrs) but luckily is relatively easy to fix.. I locked the drivers door the other day and then the car took some time shutting off so for now I wont touch that till I can remove door panels and fix that part of the vacuum riddle etc etc..

Great result on the fuel filters. I have never changed one and noticed a difference. You can buy a diesel bio-cide at truck stops that is supposed to kill and remove "black slime" that can grow. It is pricey but you the bottle lasts a long time. The slime grows when water (even condensation) gets in the tank. The bio-cide is most used by boat owners who have a tank sitting for years and helps them use 200 gal of slimed diesel.

The vac hoses you show on top of the valve cover are part of the EGR controls I think. Many here have removed their EGR valve and controls, using a $15 block-off plate kit (see Rollguy). I will let your consience be your guide. Many feel that a poorly working EGR system makes pollution worse, and it is very hard to maintain these 30 years later. At least we aren't hiding our NOx emissions like newer VW diesels. For the other vac lines, I have been using 1/8" silicone hose for replacements since should last much longer. I have seen enough cracked rubber hoses.

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1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans

Biocide will kill and prevent future growth, but not remove, the existing black slime. The only ways to remove it are to (1) drain the tank and replace with fresh fuel, (2) run it and change fuel filters frequently until the slime is out of the system, or (3) "polish" the fuel by pumping out, filtering, and pumping back in. #3 is done by some commercial outfits, but really only makes economic sense with a large boat with a lot of contaminated fuel that would be otherwise be difficult to dispose. (I know these things because of 90 gallons of algae-ridden fuel in my diesel RV; as an aside, the slime is commonly called "algae" but it really isn't algae)

Thanks so much for the detailed explanation! That was EXACTLY the type of answer I was hoping to get. The way my mind works, I have an easier time of understanding mechanical things if they are explained in a good amount of details and with layman's terms sprinkled in as well. I really appreciate you taking the time to answer my question. Thanks again.

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2007 Dodge Ram 3500 Cummins Turbo Diesel 4x4
1994 GMC S-15 pickup 4.3 5MT
1985 300 SD
1978 300 CD
1962 220-S Fintail - awaiting restoration