Barnsh wrote: ↑
Sun Sep 22, 2019 9:31 pm
Naqshejahan wrote: ↑
Sun Sep 22, 2019 7:26 pm
I have written confirmation via email that it is a modified balance shaft which they are now using. Will see how it develops. I hope this fixes it.
I cant see how you have arrived at a correlation between oil dilution and rate of balance shaft failure.
The ECU would recommend oil change once dilution hits 6%. At this level, I would imagine that load bearing surfaces like crank shaft would be more susceptible to damage. I think the balance shaft is a separate issue, but I may be wrong.
Sure is hard to define exactly what it is , but lubrication is favourite looking at the balance shaft video of the strip down.
The balance shafts are rotating at twice the speed of the engine , do any lack of oil or poor viscosity won’t do them any good.
My concern with changing just the shafts has always been the fact the outer race of the bearing is part of the engine and is not changed when the shaft is changed- effectively changing half a bearing . The inner race and rollers being pressed to the shaft.
Hope your new shafts work out well for you .
The only oil spray nozzles in the sump are the four piston cooling oil jets located adjacent to each cylinder and secured into the cylinder block with a bolt (2, 3, 4, 5 below) . These jets provide piston and gudgeon pin cooling and lubrication through a single outlet nozzle which sprays oil into the cooling chamber in the piston. In addition to supplying oil to the piston cooling gallery the oil lubricates the small end bearing and gudgeon pin.
The balance shaft bearings are not specifically served by the piston cooling jets and rely on the general "oil mist" present in the crank case for their lubrication.
From the maintenance manual.
Dynamic Balance Shafts
The engine balance system consists of two eccentric weighted dynamic balancer shafts which oppose vibrations created by the engine's reciprocating components. The dynamic balancers are mounted into machined bores inside the cylinder block. The two dynamic balancers rotate in opposite directions, driven at twice the speed of the crankshaft by a dynamic balancer gear pressed onto the crankshaft. The equally sized eccentric weights are phased so that the inertia reaction to their counter-rotation cancels out vibration caused by the engine. One of the dynamic balancers is driven off an 86-teeth dynamic balancer ring gear located on the crankshaft which rotates a 43-teeth driven gear on the driven dynamic balancer. The second dynamic balancer is driven off the same ring gear through a 45-teeth idler gear which rotates the 43-teeth driven gear on the driven dynamic balancer.
The idler gear is mounted on to the cylinder block using a steel idler bush which is pressed into the cylinder block. Driven gears on one of the dynamic balancers and the idler gear are anti-backlash “scissor” gears in order to minimize noise. All the gears are helical to ensure smooth operation. The dynamic balancers are located on needle roller bearings which run on outer races installed in the cylinder block machined bores. The bearings are lubricated by oil mist during engine operation. It is important to make sure that each dynamic balancer is timed correctly in respect to the crankshaft using alignment tool(s).
There are several conditions that could result in inadequate lubrication reaching the needle roller bearings and we can all imagine one or two for ourselves. Here was my first thought when I looked at this: where does the oil mist originate?
At least some proportion of it must come from the piston cooling jets. But digging a bit deeper reveals that these jets don't operate all the time: they are switched on and off according to the engine temperature. Again, the maintenance manual provides the details:
The jets are supplied pressurized engine oil from the variable flow oil pump with integral vacuum pump via a drilling in the cylinder block. The oil supply to the drilling is controlled by a piston cooling oil jets solenoid which is controlled by the Powertrain Control Module (PCM). The solenoid can open and close the oil supply depending on engine speed and load.
The implication is that the "piston cooling oil jets solenoid" turns these jets on only when the engine is hot or working hard. Light bulb moment....
Might balance shaft failures be occurring more frequently in cars that are driven in a more "relaxed" fashion?
Is there always a delay in lubrication reaching the bearings at start up?
Could the cooling jets be tricked into staying on?
Any brother/sister engineers out there care to comment?