Quote:
Originally Posted by schoir
Since it is widely accepted that lack of lubrication is the main cause of IMS bearing failure, providing a solution which provides adequate lubrication should solve the problem. Then there is no need to unnecessarily be alarmist about pistons and valves banging into each other.
The above also ignores the additional unknowns that may be introduced by a new design with new parts. All of those parts add a level of complication which is simply not necessary to solve the problem, namely lack of lubrication.
Finally, from my limited understanding of bearings I know that journal bearings don't fare as well as roller element bearings (ball bearings) at the time when most engine wear occurs...at initial startup.
If there are any bearing engineers amongst our members, perhaps they could edify us further.
More time and more real world testing will provide the answer to the question of which approach solves the only problem that we should be considering... lack of lubrication.
In practical terms, I'm not so much interested in the "art", but more in the result. "Art for art's sake" is a good motto for MGM, but not for bearings. This would not be the first time that a less expensive, simpler solution proves to be the best solution.
Regards, Maurice.
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There are many different bearing designs. They each have their advantages and disadvantages. A hydrostatic (oil pressure fed) plain bearing is hard to beat in that the wear surfaces rise off each other and run on a film of oil. This is dependent upon bearing wear surfaces fits, tolerances, and geometrics along with lubricant pressure, flow, film strength, viscosity etc. The trick is to get appropriate oil flow to this location.
Rolling element bearings will have point load contact areas and won't be hydraulically supported to the degree of the hydrostatic plain bearing. You will have more time with metal on metal or ceramic. Without suitable oil feed a hybrid rolling element bearing is your best option. Theoretical cylindrical rolling elements would be a logical choice but they are not yet readily available and harder to make. They will also suffer if there is a thrust load component. Ceramic rolling element balls are now very common and are the standard in poor lubrication environments. Even prior to cermics ball rollers seemed to be favoured in bad conditions even though their load capacity was lower than cylinders; this is something I have found not always to be the case.
One just has to look at the other end of the IMS shaft for proof of concept. If there is suitable oil flow available then the hydrostatic plain bearing will the best option in this case