20 85 oil pump ?

The outer rotor should be a nice easy fit on the diameter, but not sloppy. More important is the head clearance, in other words the 'slack' or play you have over the width of the rotors. Too much head clearance will dramatically reduce the efficiency of the pump. You may be able to use shims to reduce head clearance to as little as possible without the pump getting tight.

Around a thousandth of an inch should be OK, but be careful.

If there is too much clearance, you create a leak path within the pump, and if there is too little, you chew the shims and spread chewed material through the oilways in the engine - expensive.

Hope this helps. You can get new rotor pair from several suppliers here in the UK, they can post to you.

If you mesh the two rotors and roll the outer rotor round the inner rotor in your fingers, you will be able to identify more easily which tooth pair is causing the problem.

If there is a ding, try polishing it out with a carborundum stone - or a finishing file (if the rotor is metal and not a sintered material which will be too hard to file) - or take it back and ask for a replacement, before you invalidate any warranty.

Also check the inside of the pump body for any foreign material, as this can cause the same symptom. Clean it thoroughly.

The risk of 'letting it all bed in' is that the pump may sieze while running, with potentially disastrous results. The final assembly must be free running, with no contamination, and no tight spots.

You are replacing both rotors aren't you? They run as a matched pair, so don't try to replace only the one that was cracked - you must replace the inner and outer pair together.

Natural gear mesh should be as smooth as silk, with no tight spots, no grittiness, and no noise during the complete rotation.

Hope this helps.

If you get a spray of oil, don't worry what the gauge says. With modern engine oils, the additives reduce wear to an acceptable level.

I have come across people who have had an instant 15psi increase in oil pressure just from changing the gauge.

Good luck in your rebuild, it sounds like you are doing a thorough job of it. The rear cam journal is a favourite for wearing and causing pressure to drop.