After replacing the orings on a 1995 e300 the car seems to idle much louder than before. It runs well, but at idle it sounds like the older benzs.
What could have caused this to happen? copper seals?

Do a search for some of the threads; it is a frequent comment. Ask one of the folks that had the same problem if it cleared up for them.
I have always wondered if people got used to the softer sound while the "O" rings were leaking and now that the leak is fixed and the injectors are getting the full amount of fuel they are not used to the louder sound. But, I have not read a conclusive reason for them being louder.

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84 300D, 82 Volvo 244Gl Diesel

I have heard reports of this when the copper washers have not been changed. The copper washers are the seats for the valve spring, and the spring wears a seat into it. When removed for DV seal replacement, the spring ends up in a different position.

I replaced the seal and washers in my car a few months ago, and it also sounded louder for the first 200 odd km, and then the noise mysteriously went away.

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'98 E300 DT
'87 190D 2.5 turbo RIP
'92 S500 Sold
'03 3.2TL-S A-Spec

Just finished doing the delivery valve seals on my 96 e300d, and ended up with similar results. Prior to the job, engine was quiet at idle, but after doing the job, it sounded like a diesel...with minor clacking. No problems with smoke, power, performance or sounds at highway speed, just made a sewing machine sound at idle, or when driving about 15 mph and taking your foot off the throttle. I read most of the posts regarding this issue, and hoped that it would go away with time. The one thing I did notice was the fact that when the engine is started from dead cold, the sewing machine sound will not be present while the glow plugs are engaged. Once the after glow process is finished, the sewing machine sound is immediately noticed. When I first did the job, I did not change the crush washers, just the rubber seals. After driving about 400 miles, I decided to redo the delivery valves, only this time changing both the rubber seals and the crush washers. Torqued them down to 32 N/M, and the noise issue was resolved. My thought is this, when I first did the job without changing the crush washers, I believe that extra fuel was being sent to the injectors. When the car was first started from cold, as long as the afterglow process was in effect, this extra fuel did not cause any problem. Once the afterglow process ended, the extra fuel caused the "nailing" issue. This is just a hunch on my part. Good luck with your vehicle.

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96 E300d

where is a good place to get the washer and the o rings? Would it be better to get Viton o rings?

Fastlane had both the "O" rings and the crush washers. When I purchased mine, Viton was not an option at Fastlane. If you are interested in Viton, Fryerpower.com has kits with the various "o" rings and crushwashers.

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96 E300d