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Hi there, I 'am really...
Hi there, I 'am really impressed with your site.
I have a question I need verifying.
I'm a yacht engineer on a motor yacht with D348 Main Engine CATS and 3304 Gensets. One of my gensets oil blackens within 40 or so hours of use. The sump is always flushed clean prior to re-filling with fresh oil. I only use 30W Rimula as per manufacturers recommendations. What I find is when ever I remove the Rocker cover I notice that it has a black varnish covering on the valve side of the head. Now, I have checked crankcase pressure and it seems fine, I wouldn't ay there is much blow past at all. It is the same as the other Generator. I'm thinking that it might be valve stem seal by-pass. What do you think? I haven't carried out a compression leak down test but would consider it. I do have a spare head to bolt on though. Also, My other Genset's oil only darkens towards its 250hr service limit but still remains relatively transparent.

Hope this helps.


Troy
Submitted: 8 years ago.Category: Boat
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Answered in 1 hour by:
6/20/2010
Marine Mechanic: Yachtwork, Marine Engineer replied 8 years ago
Yachtwork
Yachtwork, Marine Engineer
Category: Boat
Satisfied Customers: 1,048
Experience: MEC3 and RYA Yachtmaster Ocean
Verified
Thanks for asking. Black oil means carbon is filling the oil and carbon comes from combustion. So, one of the cylinders has to be blowing by into the sump. So, how to find what cylinder and why.

Why? A broken compresion ring could cause black oil. Also a bad injector. You could pull the injectors and look at the tips to see the one gummed up.

While the injectors are out you could borescope to get a look inside the cylinders. The one with the bad ring should be gummed up a little more as it would have a little bit lower compresion.

So, reasons the oil is building up with carbon, and a few methods to track the cylinder.

Hope that helps.

Scott
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