Quote:
Originally Posted by Pladi
again you are missing the point.. You have a headache you take Tylenol and no more headache you are not dealing with the root cause. Your headache will return. If you know for sure that the bearings are bad thats when you do that type of work.. who here has proved that. So replacing bearings "proactively" does not necessarily solve the root cause. Your new bearings will have the same potential of failure if you have not dealt with the root cause..
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I see BMW spec'd these motors for rod bearing clearances of .00135". Most engine builders would spec a 20wt oil for that tight of a tolerance... S65 engines have the same type of pre-mature bearing wear with the same tight clearance spec and they change their bearings every 60k as a preventative measure. BMW is now putting 30wt oil into those motors vs their old recommendation of 60wt.
I think this may become a future recommendation with N55 motors too... Many engine builders are grinding down cranks and running .002" - .003" rod bearing clearances which is better suited to 40wt oils and high load engines. We very well could be seeing intermittent oil starvation causing bearing wear over time. Particularly, in left hand sweepers. Once the bearing get's worn down past its hard out layer, which we have seen plenty of motors show bearings down to the copper, they will over-heat and melt to the crank. Not much you can do about oiling except maybe run a thinner oil, but you can surely polish the crank and throw in new bearings in a few hours as a maintenance thing for <$150.
Changing rod bearings is not rocket science. I think we would see 100x more engines have this work done if it didn't involve so much work to get the oil pan off. Once the pan is off all you have to do is remove the rad caps and swap the bearings. There is nothing to "get wrong" except mixing up the rod caps or something. The only reason why rod bearing clearance would be out of spec is because you have a rotating assembly problem. This is hardly something someone swapping rod bearings should encounter, but it would damn nice to catch an out of spec rotating assembly before a seized motor!