I have posted several threads over the past months about this car - incredible smoking and the last post I had checked compression and did a leakdown test. I finally pulled the head today (spring break) - and I have a few observations and some questions and some pictures.

Head gasket looked fine and cylinders 2,3 and 5 valves looked wet and sooty (picture to follow). I have included pictures of the cylinders and what do I do now? I don't want to pull the engine unless I have to, but is there anything I can tell from looking at the cylinder walls and and the pistons? I tried to move the pistons from side to side and all show very minimal movement. The walls look good to me - see pictures.

Car has 185,000 miles and I keep getting mixed advice. Some say to pull the engine, since I'm this far in and others tell me this engine (M130) is practically bulletproof and that the rings last forever. I have taked the head to a mechanic friend and he is going to look it over.

What would you guys do? Obviously, if I have to pull the engine, I'm into a lot more money in my rebuild - which I would like to avoid, if possible.

My most recent post - with compression and leakdown tests is below:
Summary - compression & leakdown results (need some interpretation/diagnosis help)

Thanks, Ryan

Attached Thumbnails

       

__________________
RG Newell

1984 300D
1972 250
1986 560SL
1991 300CE

did you say your smoke is blue?

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.

I'm pretty sure it's oil...

ryan

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RG Newell

1984 300D
1972 250
1986 560SL
1991 300CE

I agree that from what I can see in the photos, the walls look great. I think that I remember that you were having weak #2, #3 cyl. in compression test. Incidently that is the same cyl that we get the best look at.

I would wait to see what the head looks like before second guessing the lower end.

I hope your spring break is treating you well. Don't let the head job get you stressed out. I spent mine doing some interior work on my '72

Before you clean things up, look carefully at the gasket and surfaces for any hint of leakage (combustion). The appearance of the valve stems as seen through the openings to the manifolds might offer some clues to how well your seals were working. I greatly reduced the amount of oil burned by replacing the valve stem seals and eliminated a tendency for #6 plug to foul. Lapping the valves can tell you how well they seat. You can check for leakage by filling the combustion chamber with kerosene and letting sit overnight. If your valves are adjusted too tight it can polish the cam lobes "all the way around" if you know what I mean which can lead to a burnt valve: the seat will probably survive because it's much harder.
My first thoughts anyway, keep us posted,
Basil

Just a little caveat here. I see coolant still in your block - some coolant probably got in your oil during the removal as well. Go ahead and drain the oil out of it now. The coolant will react with the oil to form an acid which will destroy your bottom end bearings if circulated.

When looking at the picture with the carbs I see that there has been a mod. to the secondary vac. diaphram. Did you do that or was it a previous owner?

Since you already have the head out..Here is an easy and accurate way to check the head for leakage. Turn the head sideway and pour mineral spirit into each chamber, and let it sit for over night. Which ever chamber is low on the liquid the next morning, you will know that you need a head recoditioning.

Either way, you still need to have the head recondition so why don't you do that and slap that back on with a new headgasket. If it is still smokes then you can pull the engine later.

The head is still at my indy - but I am going to try and get it on Monday and I'll post some pictures and try kerosens/mineral spirit approach. I really haven't looked it over very thoroughly yet, although I am almost positive the head is leaking.

My dilemma is trying to decide about the motor and what all I should do there. I bought an internal micrometer to measure the clyinder bores and they seem alright, although there is quite a bit of error in the measuring process. The Haynes manual says that there shouldn't be more than .02 mm difference between the top of the bore and the bottom and average measurements are around 86.5mm, which is what it is from the factory. But the piston to cylinder wall clearance looks, and feels too big with a feeler gauge. So I don't know...

The secondary vacs were like that when I got the car...I'm not sure why???

Ryan

__________________
RG Newell

1984 300D
1972 250
1986 560SL
1991 300CE

From my experience working on the INAT is that the origional design has a vac. line coming from the carb base in a tiny metal tube running from the side of the diaphram housing. It is undersized and prone to cloging from pcv residue.

I can see an avantage to rigging up the tops of the diaphrams with a seperate vac line. This would give a stronger "pull" on the secondary. I am tempted to do the same on mine.

You shouldn't worry too much about the block and rings too much. Here are couple of reasons:
1. If rings wear, in which they do. They will all wear the same in every cylinders so thus, the compression numbers should be the same.
2. If the cylinders wall are worn beyond the specifications, oil burning would be the least of your problems..You will hear the annoying piston skirt to cylinder wall tapping, ect...But this is only the extreme cases.

Of courses there will always be a chance of crack rings. But that chance is a lot less comparing to a bad valve guide seal.

Before I got into Mercedes, I was building racing engines to withstand high boosted applications. Sometimes, I would get lazy and not take the engine out (that is if I know everything are good like oil pump, bearings, etc..)..You can remove just the pistons and rods by undoing it from the bottom with the oil pan removed and push it to the top. I have access to a lift so it would be easier.

that would be difficult since it is nigh onto impossible to get the pan off a benz diesel in the car.

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.

Tom,

This is my 250, not the 300D.

__________________
RG Newell

1984 300D
1972 250
1986 560SL
1991 300CE

This is for the M110 so don't take the bore and piston dimensions as gospel for your M130 but it should help with the piston to cylinder gap. Read the whole thing through as it mentions what wear will do to the bore and that you need to clean the crud around the top when you measure.

Some further research has one piston company looking for a .006" gap between the skirt near the pin and the cylinder wall for a normally asperated car.

I don't think you have much of a problem with the pistons and rings. Keep in mind that it is the rings which do the sealing. Compression gasses force the rings down against the bottom of the groove and outward against the cylinder wall. The piston must have clearance or it won't move in the cylinder. You can use an old piston and a new ring to measure cyliner taper. Use the piston upside down to push the ring down the bore and measure the ring end gap. The piston keeps the ring square to the bore.

You could have lost a valve stem seal, it may have been a bit over filled with oil, could be a bad gasket or even a cracked head. It may even have been your intake vacuum leak sucking oil in that leaked out from around the valve cover gasket or chain tensioner which is just in front of the intake. A loose valve stem seal or other bit of debris could have blocked a oil drain back hole and the pool of oil have to go somewhere. If a cam tower came loose or a cam bearing wore enough, would it spray oil on a valve stem?

There is a port in the intake between the carbs. There should be a tube and rubber funnel that fits the underside of the air cleaner. It's just to the right of the secondary vacuum diaphragm for the front carb in your first picture. Could be that if it gets plugged, the crankcase pressure might have gone up.

A broken oil ring will not affect compression much but can lead to oil consumption.

Hope this helps more than hinders or frightens,
Michael

PS, my 250C has the M130 so if you have any Q's about what goes when when you put it back together, let me know. It's also for sale if need a spare car

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Usta haves '69 250/8, '76 280C, 1971 250C 114.023, 1976 450SEL 116.033
Current have, 1983 300SD 126.120

Thanks for the replies - neither hinders or frightens! I am now leaning to leaving the lower part of the engine alone. I know all the arguments for tearing into it - I am already partly there, if I'm going to keep the car I might as well do it right - once! Etc., etc. And .006" is about what my gap is right now.

BTW, can I just rotate the engine to drop cylinder 1 and 6 down to check those bores? The timing chain is suspended by a bungee cord so I have to be careful there and I know that to reinstall everything, i.e. distributor - I would need to rotate the engine back around to #1 TDC.

But, it doesn't sound like that much more work to take the entire engine and transmission - with head intact - from the car. And, if fixing the head doesn't help, then I know for sure.

I will be posting some pictures of the head tomorrow - I hope!

Michael, the M110m link didn't work for me.

Ryan

__________________
RG Newell

1984 300D
1972 250
1986 560SL
1991 300CE