340 oil pressure ( Help )

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jkent5368

jkent5368

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I built a 68 340 got it the car prime the motor and it had 70pds oil pressure. Fired it up and it went up did the brake in on the motor for the rings and cam after doing this went down the next day and fired it up it ran for about 20 min. and the pressure went from 70 to 0 . i went back and checked the oil pump, the bearings, all the oil plugs in the block and the oil filter. I'm at the end can anyone help. One question I put a windage tray in it and put the stock oil pan 5qt. will this work or not :banghead:

Thanks
 
have you pulled a VC to see if your getting any oil up top?

are you sure your gauge is functioning properly?

do you have and electric oil gauge or a mechanical? if its mechanical,do you have the style with the semi clear plastic oil line? if so can you see oil flowing through it?

did you by chance leave a rag inside the engine?

what oil filter did you use? reason I ask is because there have been alot of fram filters that collapse ....also...some filters use a check ball valve inside of them and lodge in place.

not saying any of this is your problem, just trying to help pin point.

when at "0 psi" do you hear anything out of the norm? at 0 psi your top end of the engine should be chattering and it would be kind of hard to miss. so if everything sounds alright after running for a period of time at 0 psi I would guess you have a fault in your gauge/kinked feed line/disconnected feed line (you would notice a puddle of oil somewhere)....possible a cut/pin hole in the line letting it suck air giving an inaccurate reading. Also possible that a chunk of debris floated its way up in to the galley of your oil gauge feed line and it blocking oil flow to the gauge.

those are all mostly easy fix's.

of course there are more severe things that could be wrong with it.....but being that it had good pressure before ...I am assuming all your bearings are clocked correctly.....and you didnt mention hearing any noises or anything so i am assuming there was no mechanical failure. hopefully its something simple.
 
Also, is the oil pressure any different when the engine is cold...versus at operating temp? and is there and change when raising the rpms?
 
oil is coming to the top, mech. gauge and it's working ( put it on nother motor and checked it ), when you take the rpm's up the pressure goes up and when its at 0 at idle you can hear a knock in the bottom end when the rpm's go up the knock goes away. when its cold 68pd and as it warms up it goes away
Thanks for helping
 
I rechecked all crank bearings,rod bearings and the cam bearings. checked the plugs at cam plate, plug at the dist. gear and at the oil filter
 
what about the W. tray and stock oil pan with a high vol. pump. I'm thinking that's ok right
 
How about the Oil Pump Driveshaft, I've seen them round off at the hex end and only build oil pressure while the engine is cold. Usually happens if the oil pump wasn't seated all the way/cocked to the side slightly when bolted on. It will either snap the end off the shaft, crack the pump or round the hex end off the shaft.

Also if it wasn't seated the whole way, it could build oil pressure when cold, and as the engine warms up the oil gets thinner and could be blowing past the block & pump body.
 
with the money that's involved and the way your describing everything do your self a favor and pull it out and check it..i'm sure the wind age tray has any thing to do with it they used them from the factory.the knocking sound isn't good..sounds like a rod is loose........I hate to be the bare of bad news but it can be fixed if you do it now...........Artie
 
the noise sound is scary. i have put a brand new oil pump on a 383 once were there was a piece of garbage stuck in the oil pressure relief, when it was cold good pressure and hot none hot revved up ok oil pressure.i really don't think that the windage tray would have anything to do with this if its a stock type don't know much about after market types if they interfere with any moving parts or the oiling system
 
Are you sure the oil gallery plug is installed INSIDE the engine just below the distributor? Remove the distributor and shine a light towards the front of the engine. There should be a plug inserted about 5 inches from the top of the distributor platform.
 
Did you check the oil pump pickup tube? You never want to turn it backwards to position it roperly because it's pipe thread. If it was loose ,it might be sucking air. Also, did you disasseble the pump and inspect it before you ran it? This should be standard operating procedure during assembly. I agree with the "pull it out" advice. If the pressure goes to zero, you have a problem. Pull it, and fix it where it's easier to see and do everything.
 
If oil galley plug was not installed he would be building 0 oil pressure even when cold. Are you running the rite size bearings. Sounds crazy but a buddy of mine not paying attention to detail put .020 under rod bearings in his HEMI w a .010 undercut crank. Oil pressure was 70ish cold and then droped to 0 when it warmed up when you could then hear a light knock. Luckily he cought it quick before it hurt to much.
 
Thanks everyone for the help. i have worked on it all day got it out and started over.put it on the engine stand turn it over and started checking the bearing's and I found that the crank was cut wrong at 1 and 2 rod bearings. the crank was cut 10 / 10 at 1 and 2 was cut 20 how do you do that and what do you do just put 20 in 1 and 2 rod or have it cut again.that is the question??
 
How did you find this out? Are you measuring it? How does the finish on the journal look like?
 
i would take that crank to someone you trust and have them check to see if that thing is ok. not from the noise, but because if a shop did that it would worry me. if they say the journals are sized right and are round and not tapered i would use the different size bearings maybe you could do that yourself but i don't know your skill level
 
I built a 388 lt1 stroker for a firebird I had a few years back and bought all new bearings for it......put it all together and it ended up having a mean knock to it.

turned out that the cam that was in it had progressively been machined. (standard,next journal was .010 under, next was .020 under ect...ect...) and the cam was just bouncing around in there. sometimes its hard to see how some people can justify having machine work done that way.

Then again, it was my fault for not checking the sizes prior to installing......stuff happens lol
 
Some motors came off the engine line with a funky rod journal, the crank would have a character on it noting the special journal. You can run different rod bearings, but your balance would be the slightest bit different unless they detroit balanced it as a assembly ala 360. Sounds Ghetto to me, but short on funds,(like Ramen for a month short) it can be run.
 
I had the same experience with a slant 6 years ago. I didnt mike anything on the rebuild and put std bearings in it. The engine pad had a maltese cross on it an I didnt think too much about it. Turns out that the cross meant that the rods or mains I forget which one, were 10 under from the factory. Over the period of a couple days the oil pressure dropped frpm 60 to zero, As it turned out, the crank was scored from this experience and I had to start all over because of all the metal particles that were created. This was a very expensive lesson that I will not forget.
 
I know my machine shop guy good and for years but he is human so I check my bearing clearances and rings!
 
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