I am putting a 425 together. I installed a new Melling oil pump. Using a drill to to test the oil system I can get 38 pounds at a 1,000 RPM's but no more when I turn it faster. So the pump is bypassing. Is a maximum 38 pounds OK? I would like to see 60 pounds.
Normal oil pressure is regulated to 40 psi. Maybe you can replace the bypass spring on the pump, not sure on the Nailhead.
you will never get full oil pressure till 2400 rpms. you can shim the spring. but the stock pump should only be about 40-44 lbs anyways. something else might be going on, loose bearing clearances,. you don't need or want 60 lbs with a nailhead.
I've gotten 55PSI. But that's with a blueprinted pump & massaged pretty heavily. The engine is shifted 62-6500 with NO related oiling problems. Most "Nails" from the factory produce about 38PSI. For normal driving it's more than enough.
Ok I will not worry about the oil pressure. Maybe I can get this thing started in a couple days. And Tom those pistons are beautiful, the man who fitted the wrist pins to the rods said those were probably the best finished he had ever saw.
Mine spun up to 40 psi with drill and ran 40 psi for about the first 500 miles at operating speeds and temps. (about 23 psi at idle) It settled, and now reads 38-40 above 1200 RPM, and about 20-22 psi at idle when hot. That is about as close to perfect as you can get (or need) for a nailhead. It's sort of like blood pressure, higher is not always gooder.
At what pressure ( hot / cold ) would you start to think something's not quite right here and need to stop engine and / or investigate ?
Way back in the day I got as low as 15 psi at idle, maby even a bit lower as i'm thinking close to 10 psi, I can't remember exact but never more than 40ish psi when pushing 90,000 mile 401 GS, I put the gauge in at that mileage. It was a cheapo gauge though that had a plastic line No issues what so ever with the motor and sold the car at 118,000 miles.
If you have a baseline already established for that engine, any drop of 20-25% from that norm for more than a few seconds, should be noted and watched. What matters is what is "normal" for your engine. And then anything that deviates from that. Any "change in engine sounds/noise" is a need to stop the car, open the hood and identify if it is internal or something external. (fans hitting shrouds small animals or a cow in your fan belts, or flywheel inspection cover coming loose, etc). If the pressure drops and the valvetrain starts making noise, time to stop, check oil level. The cam and lifters are oiled by "splash" from crankshaft slinging oil, too low oil and high speed, hard acceleration can bring damage quickly to bearings or cam/lifters (the baseline being within factory specs to begin with and a healthy running engine). I understand a used car, or having an engine built by someone and then you taking ownership of it can be a bit of a challenge to "know" what is correct. So, no one should dismiss asking these questions. The point is to enjoy your car and it's hard to do with doubts in your mind. The "rule of thumb" is 10 psi for every 1000 rpm. Since nailheads factory idle from 450-650 (depending on engine displacement and transmission type) 5-6 psi is still in that range, and the pressure relief is set to 40 psi, I have heard of some nailheads with hot oil pressure in the 6-8 psi range and it was not a concern (of a pretty well respected nailhead guy). One person said 5 psi at idle all day long. As long as pressure rises when the RPMs increase and is steady 30-40 above 2500. I use an oil pressure switch to regulate relays to my EFI fuel pump, and one of my concerns was oil pressure dropping to a point that the switch would close the relays. That was how I came across the low pressure numbers. Tom Telesco (teleriv, above) would be the one to be definitive on all of this.
if you start noticing significant pressure fluctuation you might want to pull the oil pan and check to make sure the idler pin is not working it's way out of the pump body. apparently this is common on the aluminum pumps. if it works out far enough the crank counterweight hits it.
I just disassembled a Nailhead which showed evidence of this on the crank counter weight and I found a piece of metal which looked like a piece of the old oil pump. I think the crank conter weight broke off the oil pump casting at some point. Tom Mooney
