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#1
02-17-2016, 01:14 PM
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Harmonic vibrations
1979 Mercedes 300 SD - 116 - 617 Engine - 315 thousand miles - burns 1 quart of oil every 1500 miles.
I have a very strange pulsing vibration at 1500 RPM that diminishes above that rpm, while in drive only. My mechanic tells me it could be harmonic resonance connected with the sync in the crankshaft. I have replaced the motor mounts, Transmission mount, checked drive shaft, had a engine compression check with the following results: Cylinder #1- 400 - wet 475, #2- 400, #3-350- wet 475, #4- 380 - and number #5- 370. Performed power balance test, and it appears all cylinders dropped equally during balance test. Performed turbo output test, and found low boost 6-7 lbs (spec calls for 10-11 lbs) At speeds of 60 to 70 mph, there is no noticeable vibration, and there is plenty of power for passing. Any one want to take an opinion as to what, where or why ? Open to all suggestions. Have studied Harmonic vibration etc. but it is a little over this Captain's head. Thank You 
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#2
02-20-2016, 11:24 AM
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Harmonic Vibrations
Unbelievable situation, after months of this pulsating rumbling vibration which would repeat and repeat itself over and over again, we have found the solution. This occurrence was only noticeable at speeds of under thirty mph, about 1500 rpm.
I say we, but it was the Italian marvel Marcello owner of "marcellosluxuryautorepair@hotmail.com". Automotive repair in Boca Raton, Florida. Because I had all the motor mounts and transmission mounts just changed less than a year ago, it was hard to believe that the engine was not isolated from the frame. After a few hours of road testing and thinking that it could be an engine cylinder that was losing power, ( went through an expensive power and compression test, both wet and dry which showed the numbers were acceptable) from another mechanic two months earlier. He found that the problem was a bad transmission mount. Even thought it was less than a year old. It does pay to find that right mechanic who knows what he is doing........... 1979 Mercedes 300 SD Turbo - 325 thousand on the spedo and no major expenses on the engine except for valve adjustments. That's It for now. Captain Naselli USCG.
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#3
02-20-2016, 12:21 PM
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glad you sorted this out...
seems like a tedious process of elimination. but well worth the time
__________________
1983 300CD Turbodiesel
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