1) The dimetrical clearance between the body and gears: With the bottom cover off, push the drive gear (one on the shaft) toward the pump body. Measure that clearance with a feeler guage. Do the same with the idler gear. This measure tells you if the pump body is worn and allowing the drive gear shaft or idler gear to move side to side. It probably means the shaft is worn too - but either way the pump body has to be replaced.2) Endplay can be measured with the cover off. Push the the shaft gear assembly up from the bottom. Use a feeler guage to measure the gap created between the oil pump drive pinion (the top gear that meshes with the cam)and the pump body. This measure is often out of spec. The result is that the pump gears can now contact the oil pump cover plate, cutting circular indentations into the plate through which oil is allowed to escape producing low oil pressure. Look at the bottom of the cover plate if it isn't smooth or nearly so, you have excessive endplay. Three things must be done to affect a fix: 1)eliminate the endplay by removing the drive pinion and place the appropriate shims under it to make up excessive play, 2) have the coverplat refaced so it is perfectly smooth, 3)replace the gasket with a new 0.005" thick gasket. This seems to be the most common reason for oil pressure loss at the pump. You must fix the endplay to fix the problem - smoothing the cover is not enough. 3) Gear backlash: that is the gap between the drive and idler gear teeth when they are meshed together. You already know that yours are out of spec by over 100%. The only fix here is to replace the gears. Some people get into spec, or close enough to get pretty good oil pressure by replacing only the idler gear. The pinion drive gear is a bit of a pain to remove, and some folks don't like to mess with it. If you have to fix endplay, however, you may as well replace both gears if you can afford it. To find NOS parts try posting a new message asking where others go for parts, and also put an add in the classifieds. I got mine sometime back and I can't remember the gentleman's name, but his screen name is NOSIH. The other alternative is to find a good used pump. Even if your cam bearings have to be replaced in the end (and I hope not), you will want a great functioning pump to protect all those new parts you worked so hard to get in. So either way the pump is time and money well spent. Good luck, let us know how it goes.
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