My 82 300sd was doing the shakes, the valves are recently adjusted so I went to adjust the dampener bolt. The shakes became smoother but not completely. I ordered a new bolt and installed it this evening. The engine is much smoother. Here is my question. when I took the old bolt out and unscrewed the lock nut I put it down in my tool box. I put the new bolt on the lock nut and installed it. When I looked in my tool box there was a small O ring next to the old bolt, is this O ring part of the assembly? or is this from another repair.

That "o" ring needs to be on your bolt, ensure it's correct place, IIRC, it is seated in a slot "inside" the nut maybe. Anyway, that goes on the bolt. You may run fine for a little bit, then back to the shakes. Done that, been there.

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83 SD

84 CD

thanks

Explain further- you're saying that o-ring needs to be there and properly seated or the engine shakes?
I just replaced engine mounts and shocks and shock mounts, now my car shakes. Didn't shake before. All the new parts were dealer items. I tried adjusting the rack bolt, which incidentally is new also. It's a gold one. Engine shakes quite miserably. Although - I have noticed that it decides when it's going to shake and when it isn't. Doesn't shake all the time, just about 90% of the time. I've tried to figure this out with no luck. So, I've decided to just live with it, because other than that it runs great. Injectors are fine, no nailing, no smoke. Good power. At idle though, 750 rpm, you could mix cake batter on the hood.
What size o-ring is it? Would it happen to be the same size as the ones that go on the oil filter housing cap stem?

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'02 BMW 325i
'85 300D 450k
'93 190E 2.6 170k(killed by tree)
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'06 Ducati S2R800 14k(sold)