Featuring quality restoration help for Mercedes 300 SEL 6.3 owners and enthusiasts. Includes Mercedes Classic Car Hire

Rear crankshaft oil seal

The rear crankshaft oil seal on these engines is a two piece impregnated rope seal with a rubber backing. Unfortunately in common with many two piece rope seals they often drip oil after a few years. As technology moved on this two piece seal was replaced with a neoprene one piece circular seal. This type of seal is often used elsewhere such as oil seals for axles, power steering boxes and pumps etc. I have replaced the two piece rope oil seals before on V8 engines with no problem. I replaced the one on the 6.3, unfortunately it still drips a little oil. Having spoke to other people who have replaced these seals they have encountered the same problem after replacing it.

To remove these engines and fit the seal is a major job and I certainly would not advise anyone to just have a go without prior mechanical knowledge. The fact the seal still leaked prompted me to look into designing and having a seal made. After some investigation the idea I had to make one was already being used mainly by the Americans.

In short it is basically the same design as the modern type one piece seal except it is split to allow it to pass over the crankshaft. The garter spring is also split with a connection hook to re join it together. Unfortunatley I have not had chance to test this seal as it off course means taking the engine out and quite a major strip down, and the very small oil drip is not a problem.

It is important that the journal area on the crankshaft where the seal sits should be perfectly smooth and not groved through wear. If it is then you can have the area 'metal sprayed' by a decent engine reconditioner which is what I had done. This is basically having new metal fused on to the journal and then dressed down to the correct size of 75mm.

I have sent Kienle in Germany one of these with the instructions and there head mechanic has said it should all be ok. Please see the seal below and the fitting instructions I wrote to go with them. If anybody is interested I have these seals for sale. Please see below the fitting instructions which I wrote.

End view of oil seal with garter spring separate and unconnected.

Rear view of oil seal with garter spring separate and connected.

Front view of oil seal with garter spring separate and unconnected.

Please click images to enlarge.

Guidance notes for the replacment of the rear crankshaft split oil seal for Mercedes 6.3 300 SEL (M100) engine.

1. When fitting the seal ensure the split is facing upwards towards the top of the engine. That is to say that the split should be approximately in the middle of the engine block recess.
   
   
2. It will be necessary to drill six small holes in the sides of the seal casing where it comes into contact with the outer edges of the top bearing case and engine block recess. This is to allow the seal to sit correctly in position over the six prongs, which are in the top bearing case and lower engine block.
   
   The holes may also penetrate the outer section of the rubber seal where it sits against the seal casing. Before drilling the holes make sure that the hole near the split in the seal is slightly to the left or right and not in the middle of the join. Ensure that the holes are drilled accurately in the seal casing. The six holes should be drilled slightly larger to allow enough play for the seal to go together tightly and the garter spring to go into position.
   
   
3. Once you have drilled out the holes make sure they all line up by fitting the seal in position with the garter spring and replace the top bearing cap. If everything lines up remove the top bearing case and proceed to number 4.
   
   
4. When fitting the seal slightly roughen the outer edges of the seal and ensure that the top bearing case and engine block recess are cleaned with thinners then generously coat with black automotive silicone sealing compound. This is to stop any possible leak of oil between these surfaces and to bed the seal in position.
   
   
5. Lightly lubricate the seal with engine oil before placing over the crankshaft. The garter spring side of the seal should be facing in towards the engine block. Ensure that the garter spring is fully together before locating on the seal. With the seal on the crankshaft and garter spring still fitted gently lower the crankshaft in position and the seal onto the silicone in the engine block recess, wiping away any excess. Ensuring that the holes in the seal line up with the prongs in the engine block recess.
   
   
6. Apply silicone in the top bearing cap and bolt this down, again ensuring that the seal goes over the prongs. Use a little jointing compound on the two mating bearing surfaces.
   
   
7. When bolting the top bearing case down make sure any excess silicone is cleaned away whilst still wet.