Low pressure on Rebuild

[slowride]

Just had my 1977 Honda CB750F rebuilt  from bottom up.  Shop put in during rebuild a 836 kit.  Got bike back and oil pressure at start-up is running 73psi.  After riding the bike for about 30 minutes at 80 degrees Fahrenheit, the oil pressure on my 100 psi analog gage drops to 0. Low oil  pressure light does not come on and no internal noise in engine, though I don’t wait but a second then turn bike off. I have checked the bike with 2 oil filled 100psi analog gages and get the same readings. No help from  shop without more money.

[TOOLS1]

My first thought was that the gauge was defective. Where is the gauge plumbed into the system at? Are the oil lines from the oil tank reversed?
TOOLS

[slowride]

Will check oil line configuration.  Gage is inline with the low oil pressure sensor.  Gage kit is on right side of engine.  Thanks for the help!  

[slowride]

Marshall  oil filled pressure gage replaced with new one.  Both accurate within 3 percent, and both reading 0 PSI after 30 minutes of riding.  Oil tank seems to be extremely hot, but do not have device to verify.  My RTD only reads too 300 degrees Fahrenheit. Oil tank hoses are in proper configuration  

[TOOLS1]

If you have ridden it for 30 minutes and it has not blown up. it must have oil pressure. Maybe those fancy hi-tec gauges do not read when hot. What application are they designed for?
TOOLS

[slowride]

I shut the bike down when the oil pressure drops to zero on my motorcycle oil pressure gage made by Marshall. I'm sorry for not going into detail on time for oil pressure to drop from 73psi too zero.

[Re-run]

Is it one of those liquid filled gauges? Looking at a couple of the marshalls, and they are liquid filled and compare pressure to the liquid inside the gauge, not to atmospheric pressure. That might be your issue. It may be that your pressure, especially at idle, isn't enough to register. Does it change when you bring the RPMs up? Maybe contact the company and see how sensitive the gauge is at low pressures.

[slowride]

Pressure does go up when I increase RPMs.  At 3K I am pushing 20psi

Thanks for input

[Re-run]

Ok, so we are a bit further. Without knowing the model of gauge you got, I can only speculate. However, these engines don't move a lot of oil at high pressure. It could be the gauge you have is meant for bigger engines, or ones the move more oil at higher pressures. It could be meant for a v-twin, and a 1000 cc engine. If this is the case, what is happening is when the RPMs are up, the engine moves more oil, obviously. It is able to register then. At low rpm, not enough oil flow.

When cold, oil is thicker and engines idle a bit higher till warmed up.