So I have a 71 400 block and matching heads that was "recently" built as far as know bored over cam piston heads and balanced. Bought the car with the stuff already done. my concern is low oil pressure, it runs at about 5psi at hot idle around 1000 rpm or so. Has mechanical oil gauge that has been changed since I had it. Old gauge's glass was busted but worked and read the same. The oil responds to the rpm. Id say 30 psi or so around 2500. Had a Melling high volume oil pump in it and just bought a new exact one and put it on and all psi reads the same. 50 psi cold idle. I know the difference between pressure and volume. I fear of putting a hv and hp pump in because no head work. Also id like to not worry about it being that's a terrible job and I do not want to do it again being its a 82 Camaro. I was told that as long as the psi responds to rpm I should be fine. Is 5 psi enough at idle. Thank you for your input.
Low oil pressure concern.
1 - 20 of 28 Posts
Joined
·
8,828 Posts
I replied. Maybe they didn’t like what I said.
5psi doesn’t sound good.
What filter and what oil?
5psi doesn’t sound good.
What filter and what oil?
Joined
·
8,828 Posts
You have to go all the way up to peanut butter 20/50 to see it.
Where is the gauge hooked up on the engine?
Where is the gauge hooked up on the engine?
Joined
·
8,828 Posts
Any build sheets or bearing specs?
Absolutely nothing unfortunately, guy who I bought it from knows nothing about cars and failed to ask when he bought it. He had it a few months and sold it to me. I know him personally so I know for a fact he bought it for the looks and sound. Also doesn't have the number to the previous owner.
Joined
·
1,955 Posts
Too bad you didn't shim that spring when you put the new pump in but I will tell you that we recently had a problem that we traced to the line feeding the gauge. Had a slight, almost invisible kink in the line. Pressure was low, bring up the rpm and the pressure would increase, then slide off again.
Joined
·
8,828 Posts
Okay.
I don’t know what to say here beyond it’s likely bearing clearances or lifter bore clearances.
The only way to know for sure is tear it down and get to measuring stuff or drive it and fix it later. How much later we shall never know until it tells you at the least convenient time. I working on a 3rd Gen z28 right now myself. They are a pain in the butt. This one has problems. Pretty much all the problems actually. Its a basket case of bad hacks.
if you pull it out to shim the pump, I’d pulla couple of rods and couple of mains and plastiguage them for peace of mind. If they check out okay it’s probably the cam bearings and lifter bores. I’d probably end up bolting up a HVHP pump like the Melling ST.
I don’t know what to say here beyond it’s likely bearing clearances or lifter bore clearances.
The only way to know for sure is tear it down and get to measuring stuff or drive it and fix it later. How much later we shall never know until it tells you at the least convenient time. I working on a 3rd Gen z28 right now myself. They are a pain in the butt. This one has problems. Pretty much all the problems actually. Its a basket case of bad hacks.
if you pull it out to shim the pump, I’d pulla couple of rods and couple of mains and plastiguage them for peace of mind. If they check out okay it’s probably the cam bearings and lifter bores. I’d probably end up bolting up a HVHP pump like the Melling ST.
Joined
·
4,426 Posts
Bummer, but not uncommon from an unknown source motor.
Cut up the filter and see if it's full of shiny stuff. If it's not, then you might as well do a leak down test before tearng the motor down to confirm that you have good cylinder seal. As long as you don't find an obvious failure during the visual inspection with the pan removed you need to pull the heads,crank, cam and lifters. Look closely atr the pickup tube. Measure everything and inspect as you go. You need to check all of the soft plugs behind the cam gear, check for the soft plug in the rear oil bore, and then start measuring cam. lifter and crank clearances.
Personally, if you don't have the tools, then take the short block directly to a reputable machine shop and give them fuk detail of what you know to be accurate about the motor. Expect an $800-1500 bill + parts.
Cut up the filter and see if it's full of shiny stuff. If it's not, then you might as well do a leak down test before tearng the motor down to confirm that you have good cylinder seal. As long as you don't find an obvious failure during the visual inspection with the pan removed you need to pull the heads,crank, cam and lifters. Look closely atr the pickup tube. Measure everything and inspect as you go. You need to check all of the soft plugs behind the cam gear, check for the soft plug in the rear oil bore, and then start measuring cam. lifter and crank clearances.
Personally, if you don't have the tools, then take the short block directly to a reputable machine shop and give them fuk detail of what you know to be accurate about the motor. Expect an $800-1500 bill + parts.
Is it drivable?
Joined
·
1,137 Posts
Before you take the motor apart, use a distributor primer, and use an a electric hand drill. If it reads at least 70psi you have a bad distributor. My 406 sbc did the same thing when I rebuilt my 400.
Joined
·
1,137 Posts
Yes, that is exactly what I ment.
1 - 20 of 28 Posts
Join the discussion
