Exceeding recommended RPM with cold oil

A highly respected expert with these engines once told me that a primary concern is that cold (thick) oil can side load the crankshaft as it’s pushed into the bearing journals. When the oil is cold it will not flow easily between the crank journal and the bearing, so the side of the crankshaft journal that is opposite the oil passage gets pressed tight against the bearing with higher RPM. The concern is that with repeated instances this can wear the bearing unevenly.  This is of course not going to happen quickly or from just a few instances.  

We are not talking about "Cold " Oil here.
100°F is almost at operating temp and giving it a good blast of power probably pushed it over 120° very quickly.
The problem with Cold oil is the elevated Oil Pressure that accompanies it.
At 100°F it would be hard to exceed the 70-80 PSI range.

I agree with the others here.
If any damage occurred, it has more likely due to the Baha excursion in the grass than revving the engine.
I would look for a physical problem in the Airframe instead of the Engine.

Please describe the 'Unpleasantness' in more detail.

I don’t think 100f is considered cold, just not quite at operating temperature.

He was able to speak with a Rotax expert, who had him do some testing, pulling the engine through,… We think it’s ok. The rough running turned out to be some fouling of the front plugs we believe. All good. 

Thanks for all the replies and info. 

Many/most don't get an essential point of conventional oil systems: the pump is a constant displacement unit, that is, it pumps a certain constant *volume* of oil per revolution. Higher oil *pressure* indicates only a higher resistance to the flow of that volume through the system and, within reasonable limits, neither good nor bad on its own. The faster the pump spins, the more volume it delivers. Manufacturers gear the pump to the crankshaft to deliver sufficient volume for the speed of operation. More rpm requires more volume. More volume/sec increases the oil pressure (OP). The majority of engines using warm oil of the manufacturer's specified weight run with approximately 10 psi OP per thousand rpm.

Now, enter the problem: cold oil resists being pumped. The pump pumps volume, regardless. The high oil pressure/rpm of cold oil is a *result* of this resistance and can easily far exceed 100 psi, which can not only blow seals but shear the pump drive shaft. Hence, a pump bypass is added to avoid such disaster. (this is *not* the bypass built into the filter, which serves different purposes). For Rotax and many other engines, that is set to about 80 psi.

Cold oil then results in a disaster waiting to happen. Assume a couple minutes warmup, followed by high power. The pressure builds far too quickly and reaches that 80 psi at say, 3,000 rpm. The bypass opens. At this moment the pump is still supplying the correct *volume* of oil for 3,000 rpm. However, as the rpm builds, the volume supplied *does not increase*. You have an engine running at 5,800 rpm with half of the oil supply it needs. This is bad.

A better measure of readiness for full rpm operation is, within reason, not the oil temperature, but the oil pressure. It's ready to go when the pressure does not hit the bypass limit at or near full rpm. The magic 120 deg, 50 deg C number is sampling only one point and may also be miscalibrated. OTOH, the OP reflects the entire oil system and if mis-calibrated, still tells you with cold the point at which the bypass open (the reading where the indicated pressure stops rising.with rpm).