My 180.000km 3.5 was running good before I swapped new standard size rod bearings as preventive maintenance, 1000km after that, engine started to develop knocking sound when warmed up, only when light throttle is applied, say after 2500rpm at cruising speed or idling in same rev range or when accelerating above 4500rpm, when I push piston down with spark plug removed, i feel play between piston and crank on ALL cylinders, I got oil light when idling, etc.. I've been driving the car 30.000km's since knock started, redline it cold/hot almost everyday with saturday burnouts and it just runs.
Does anyone have an explanation behind this?

 

Those bearing are obviously shot. 30,000 km of daily redlining cold and hot and Saturday burnouts could very well be the cause. You didn't specify whether they were OEM or aftermarket parts, but the next set should be of higher quality to sustain that kind of driving. Better use plastigauge to determine the correct size as you might be needing oversize bearings by now.

 

Hi, I thing we have misunderstanding here, I was driving very carefully after changing bearings, soon later it started knocking, but in last 6 months I drove it hard and knock is still there not getting worse.
Bearings are brand new by Mopar, std size.
Just got home from 1000km trip and lot of uphill and highway road. Nothing happend

 

When you replaced rod bearings as "PM" did you inspect the bearing wear condition of the originals and plastigage or mic the crank journals for trueness? From your original post, sounds like you did not. There is much more involved in the "bottom end" than just slapping in replacement bearings.

 

I asked my my mechanic, he said he didnt measure the crankshaft, I think that new bearings were not run-in properly. Should oil be changed day after new bearings were istalled?

 

By the info in your posts, that would be of little help now to take care of your concern. When I was actively rebuilding motors, I would have the oil changed after 500 mile "break in"time.
You said bearings were replaced with std. size bearings, but without micing the crank journals or plastic gaging , the needed bearings MAY have needed a set of +.010 (example) sized bearings. OR at least a set that matched the part#/size stamped onto the con. rod side of each bearing.
Either way you are looking at "opening up" the bottom end again to find and fix your concern.
Good luck, and keep us informed on how things go.

 

I skipped that oil change part after break-in
Anyway, i have another crankshaft with bad number 2 rod, I would like to machine it and put oversized bearings on it. Do you know where can I get ones?

 

First of all ..WHERE is HR that you reside? Second if putting in a different crank, you need to know(measure your OD and ID) for sizing of needed MAIN bearings, a bit of work to do properly..but it is the very heart of your motor! A good auto machine shop will know and tell you how much has been machined off the cranks rod journals after they are done to get the proper connecting rod bearings.
This is posted under GENERAL TECH, what car is this motor installed in?

 

My car is 1998 300m, another crank I have is from 2001 300m, I think that block(mains) size should be same in both engines, right mate?

 

While the cranks are the same part number they may be machined slightly differently. As are the engine blocks. There are codes on both the crank and block that indicate the correct bearing for each position. These engines are precision fit when assembled and must be precision fit when repaired. You need a technician that measures rather than a mechanic
Link Below is to Main Bearing information and contains a link to Rod Bearings also
http://300mclub.org/forums/viewtopic...t=Main+Bearing