How to Inspect an Oil pump
Mazda BP 1.8L
First thing is to have the oil pump off the engine.
Some of the tools needed
Impact driver with a #3 phillips bit
#3 phillips screwdriver
Needle nose pliers
Start by using the impact driver and hammer and loosen the oil pump back plate screws.
Once all the screws are loose, use the screwdriver and remove the screws.
Now lift away the oil pump back plate.
Look for scoring and excessive wear on the plate.
This one looks good with just a minimal amount of wear.
Now look for wear and scoring on the back of the gears.
Now reach in a remove the oil pump drive gear.
Flip it over and inspect the front.
Now reach in and remove the driven gear.
Now flip it over and look for wear and scoring.
Now inspect the pump housing.
So far this oil pump looks good. No scoring, and minimal wear lines have been found.
Now time to check the oil bypass
First is to straighten the cotter pin.
Use the needle nose pliers.
To remove the cotter pin, use the needle nose pliers and press down on the spring seat.
The cotter pin should pull out with your fingers.
Try not to let the spring seat and spring fly out!
Remove the spring seat and spring.
Now remove the plunger valve.
Inspect the plunger for wear.
This one had wear on the same side as the bypass hole in the oil pump housing.
Inspect the plunger bore in the housing.
I did not see any wear, even below the bypass hole in the oil pump housing.
I measured the plunger. .628 dia.
The bore in the oil pump housing measured .6295
So the clearance is .0015
Any amount of grit or trash in the oil pan stands a good chance of locking the plunger valve.
I did not notice any strange wear patterns on the bypass spring ends.
The bypass spring, by my math, holds the plunger closed with a installed pressure of 10lbs @ 1.430” and 20lbs @ 1.130
Free length is 1.770
Dia. of the spring is .440