1980 W116 300SD OM617 Front Crank Seal Replacement

[Squiggle Dog]

This is a write-up on replacing the front crankshaft oil seal on an OM617 5 cylinder turbo diesel engine in a 1980 W116 300SD with over 315,000 miles. The procedure should be nearly the same for the W123 and W126 chassis with this engine. Many of the principles can be applied to nearly any of the older Mercedes models.

I cannot stand oil leaks! My front crank seal leak has been gradually getting worse, now leaving a spot of oil in the garage.


Since I have free time and the parts are cheap, I decided to try replacing it myself. First, the alternator bolts are loosened so the belts can be removed (17mm for mounting bolts, 13mm for tension nut).


Then remove the 10mm fan bolts and remove the fan and pulley. There is a high risk of rounding them. It is best to use a box wrench with the outer edge ground down so it will slip over them. I did not have one and yes, I rounded them. One was so bad I had to use clamping pliers to remove it.


The 8mm bolts on top of the fan shroud come out next.


Then the fan shroud comes out. Yes, it will come out, but you have to turn it on its side as pictured.

[Squiggle Dog]

Now the power steering pump is loosened (all 13mm nuts and bolts) and the belt removed.


Despite what others have told me, I did not believe it was necessary to remove the radiator. I would also have had to remove the condenser and oil cooler with it. I found that I was right; there was plenty enough free space and having it out wouldn't have done one bit of good. I didn't even come close to damaging it.


As a safety precaution, I flattened out a small cardboard box to act as a shield. I found it isn't necessary if you are reasonably careful.


I held onto the crank bolt with a 27mm socket while I loosened the 6mm hex key pulley screws (make sure the heads are clean or the socket won't fit in all the way and it can round them).


This became awkward, so instead I took a socket extension, wrapped it in a paper towel as a cushion, and wedged it between the cutout on the harmonic balancer and the air conditioning compressor to keep the crank from turning backward.

[Squiggle Dog]

Once the six pulley screws are out, the pulley and balancing disc will come off, so it is important to hold them to prevent them from falling and causing damage to anything or themselves. I don't know if it's necessary, but I marked the original position of the pulleys, balancing disc, and harmonic balancer to each other with punch marks. As you can see, once the pulleys are off, there is plenty of space to work around in.


No need for the extra headache to drain fluids and remove the radiator and oil cooler.


The 27mm crank bolt is torqued to at least 270nm (200 ft-lbs), so breaking it free after many years is very difficult. I did it the easy way--make sure nothing is blocking the crank from turning (remember the socket extension that was wedged in to keep it from turning?--remove it). Then I positioned a breaker bar wrapped in cloth against the frame rail and bumped the starter. Make sure the socket is fully seated on the bolt. This breaks the bolt loose with minimal effort. The breaker bar did fall back and rest on top of one of the transmission cooler hoses, but it didn't cause any damage.


Here is what the harmonic balancer looks like with the fixing pins. Make sure to mark the position of the balancer on the crank with punch marks on each. If it is installed 180 degrees off, the engine will be out of balance. If the old balancer is damaged, the replacement must be match balanced to the old one.


I didn't have a harmonic balancer puller, so I rented one for free from my local auto parts store. I used a generic one and it worked great. There was plenty of room to use it. The balancer came off slowly but smoothly. Make sure it doesn't fall to the ground.

[Squiggle Dog]

Excuse the blurry photo; I forgot I had my camera under the car when I hosed off the engine! The crank seal is now visible.


A seal puller is supposed to work well, but I used a screwdriver to pry out the seal--just make sure to not score any machined surfaces.


There is a spacer ring that rides between the crank and seal. It is a replaceable wear item and should be replaced every time the seal is replaced. I have heard that these should come off with your fingers. This did not work. I also tried prying from each side simultaneously with a screwdriver. This also didn't work. I had to resort to drastic measures and remove the upper seal cover. I split the seal ring apart from the sprocket by hammering a screwdriver between them, then rotating the crank and prying around circumference with larger and larger screwdrivers until it came off. It was a struggle the entire way.


My spacer ring had a deep groove cut into it from the crank seal. It wouldn't have sealed well even with a brand new seal in place; too much material was missing.


I protected the inside of the engine from debris by placing a plastic bag in the opening as I cleaned the mounting surface. Changing the oil is not necessary if you are very careful, but planning this right before a scheduled oil change is a good idea.

[Squiggle Dog]

As I was looking at the aluminum seal top cover, I noticed that one of the threaded holes was stripped out and the threads were stuck on one of the upper oil pan screws, both of which were too short! I went to the wrecking yard and removed one from a 1983 W126 300SD, having to remove the pulleys and harmonic balancer on it in order to access the part--there is just as much room to remove the parts on a W126 without removing the radiator.

When I got the part home, I noticed that it was a different part number (617 014 05 33) than the one from my car (617 014 03 33)! Apparently, this part supersedes the old one.


One of the differences can be seen on the backside.


I made sure to get the proper length screws for mounting it to the upper oil pan (size difference of one from my car vs. proper length on lower left). I am glad that I also got the block mounting screws as they were longer in length, due to the replacement part being thicker than mine!


I cleaned the mounting surfaces of the block and cover by carefully scraping away the old sealant and then using 800 grit sandpaper with brake cleaner as a lubricant. Then I did a light parallel directional scuffing with 220 grit sandpaper to give a bit of a bite and help keep oil from seeping across a too-smooth surface. I was extra careful to chip away old sealant from around the pin on the block and cleaned the mounting surfaces with brake cleaner applied with a rag.

With the surfaces clean, I applied Reinzosil Anthracite 300+C Silicone Sealing Compound (003 989 98 20 10) to the block and exposed portion of the upper oil pan. I quickly placed the cover onto the block and installed the two lower screws slightly snug, put some sealant on the bolts on the smooth portion near the heads, then inserted them into the block. The centering tool is nice, but not necessary. I just made sure to feel that the top cover was centered perfectly over the upper oil pan as I was torquing the bolts to 10nm (lower ones get torqued first as they have to fight the upper bolts).

I found a 1 1/4" PVC union from the plumbing section of a hardware store makes a great installation tool for the crank seal and spacer ring.


I added a small amount of Reinzosil just around the forwardmost lip of the new crank seal where it wouldn't fall into the crankcase and pressed the seal in a ways by hand. Then I used part of the PVC union and tapped the seal in some more. For further seating I used the crank bolt with a washer and another part of the union inside, and tightened it just enough until it was fully seated, but not too far.

If you left the spacer ring on the crank, you'll have to make a sleeve out of a plastic drink cup, lubricate it, slide it over the spacer ring, then insert the seal and slide the sleeve out. Otherwise the seal will flip inside out when it is pushed against the spacer ring.

[Squiggle Dog]

I made sure the seal was fully seated and square with the crank.


After the seal was on, I lightly greased the crank and tapped on a new spacer ring using part of the PVC union. I put a good amount of grease on the outside diameter of the spacer to help it slide into the seal without tearing it. This type of hammer without the claw at the other end is the way to go; you get more swinging room and if you need to pull nails, that's what a crowbar is for. I stopped tapping on the spacer when the PVC tool touched the seal as I didn't want to damage the seal lip. From there I tapped it in the rest of the way with a flatblade screwdriver.


The harmonic balancer gets placed back on the crank (I used a very faint amount of grease, but any large amount and it could possibly cause the balancer to rotate on the crank during operation). Position it with the punch marks matching and the bores for the pins as closely aligned as possible. The crank bolt can be used to press it into place. Remove one or two of the cupped washers if necessary to get enough threads to start the bolt. It is a good idea for the bolt to be as clean as possible and with a light amount of grease on the threads. Use a socket extension wedged between the balancer and the upper oil pan to keep the crank from turning. I have read of people heating the balancers in the oven at 250 degrees Fahrenheit to get them to slide onto the crank, but this seems overkill.

Tighten the balancer onto the crank until the bores for the pins are a good ways into each other. Chances are they will not be perfectly aligned with each other, so using an extension or block of wood, tap on one of the cutouts in the balancer (without the extension wedged and the crank free to turn) to get it to rotate on the crank so that the pin bores line up. It may take sharp blows to move it a good distance. When the bores look perfectly aligned, go back to pressing on the balancer some more and recheck. You want the bores to be perfectly aligned when the balancer is tightened fully on the crank. The slightest misalignment will cause the pins to not go into place without shaving off too much metal.


Once you are absolutely sure that the bores are perfectly lined up on both sides, carefully tap NEW pins into the bores. Take your time and make sure they go in straight. These are an interference fit and there will probably be small metal shavings that come out. Once they are fully tapped into place, they will set about 1mm above the balancer face.


Using a rotary tool, carefully grind the excess material off of the pins until they are flush with the balancer face. Be careful as you could realistically grind too much material off of the balancer very fast. Alternatively, you could shorten the pins before driving them in, but you would have to be careful to not mushroom the heads by hitting on them too hard.

[Squiggle Dog]

A new crank bolt (grade 10.9 pictured) and cupped washers should be used because of the high amount of torque to which these are tightened, and the potential for breakage due to vibration. These are to be installed with the threads lightly greased and tightened up to 270nm or 200 ft-lbs. I do not have a torque wrench that goes this high, so I rented one for free from my local auto parts store. You'll need to use an extension wedged in the balancer to tighten it up this much. I placed a rag around the extension so it wouldn't dent the upper oil pan. 270nm is a lot of force (sometimes it looks like you are lifting the engine out of the car). It's best to pull the wrench toward you as you tighten, making sure to not let the socket on the crank bolt slip.


I used 80 grit sandpaper on the belt surface of all of the pulleys while they were off, making perpendicular lines to discourage belt slippage.


Crank pulley screws should be used only once. I ordered new ones. The originals were grade 8.8. The replacements are grade 10.9. Supposedly the early engines used grade 10.9 and a bulletin was put out to replace them with 8.8 because they had a tendency to shear off. Now I see Mercedes went back to grade 10.9. I would not recommend using grade 12.9 found at the hardware stores because even though it is a higher tensile strength, it is more brittle than a grade 10.9 or 8.8. I would recommend using grade 8.8 if available. I ordered new spring washers, but since January 1979 they were no longer installed on OM617 engines. I used blue thread lock compound on them and tightened them to 30nm (25nm is spec for grade 8.8, I went a touch higher due to higher grade screws plus 25nm didn't seem tight at all).


I had a nice-looking spare fan clutch, so installed it.


I put the radiator shroud, fan, and belts back into place. After things were tightened up, I started the car and let it run for a while. So far, no leaks! It seems my repair was a success. It's one that I had been dreading and I think it went rather well. It only cost me about $50 and several hours of time. I'm sure this would be an expensive job to have a shop do. Let's hope my rear crank seal and upper oil pan hold up for a while!

[KenM]

Nice work as ever Squiggle, surely a job as a Merc mechanic is in your future somewhere mate.

Thanks for taking the time to post the pics and write it up, very informative. One comment on the score marks you put on the pulleys to stop belt slip, I would think all this will do is increase belt wear and that

the marks would soon wear away, could be wrong though, haven't seen this approach before.

Cheers,

[jbrasile]

Superb write-up Squiggle! I see you have adopted nitrile gloves as well to work on the car! I began using those a couple of years ago and cannot live without them anymore.

BTW, your engine looks really nice from underneath.

Tks,

Joe

[Squiggle Dog]

Thanks for the comments. I've heard that sanding the pulleys is the recommended procedure when the pulley surfaces become polished from belt slippage. I use 14mil Thickster gloves, which last several uses; I got tired of the normal ones breaking.