Thread: oil pressure problem on a rebuild

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just rebuilt a 305 out of a 88 firebird formula. refurbished heads crank, all new bearings and oil pump. 10 oversized rings and all the normal seal and gasskets. Any way heres the question, when she first started she had awsome oil pressure. Now the gauge only reads like 20 psi when Im at 2000 rpm when im at idle its like 6 psi according to a manual gauge. The engine now has 1700 miles on her I can lifter one of my lifter tapping. What are the odd that the pump could have messed up verses that I am on my way to destroying a bearing or two. Oil pressure reading was taking at the top of the block. I put a stock pump in the car. I also notice that if I rev the car up pressure will come up but as soon as I back off the pressure drops real low. Could this be a weak spring in the oil pump? Any opinion would be appreciated????????????

Kenny

I am on the virge of dropping the oil pan to check all the tolerances on the bearings and rods. But my first test will be to see if the oil pump is putting out the propper pressure by tapping the oil sensor above the oil filter. My understanding is that right out of the filter before it hit the bearings.... if thats low then i have an oil pump issue if not then its time to pull the pan down and use the old plasti gauges. Truthfully we did not check the clearances. The crank was cut .10 under and I had a matched set of bearing for them. If I pull the pan down and find that they are out of tolerance............ What would you suggest........ pull it out and send it to the machine shop to be checked..........
Or is possible to try and correct the clearance problem while the engine is still in the car........ I'm hoping I don't have to cut the crank again but hell if I have to I have to.

Kenny

Just check the oil pressure by taking out the oil pressure switch(above the oil filter)and running a manual gauge. Engine started up with 20 psi At 1200 rpm and worked it way down to ten psi in a matter of seconds at the same rpm. If I'm not mistaken if the pump was working well shouldn't it be pumping more psi from that point and then it would decrease through the slop in the bearings if there was any. Could the oil pump be screing up..... Maybe loose pickup or the spring messing up. Or a defective oil pump? What would be the signs of a bad pump? What I want to know is my assumption correct? Shouldn't this pump start up cold should be putting out like 45 to 60 psi and run at like 30?

Im reading the same psi at the top as the bottom???????????
I'm going with defective oil pump.
which would be better if this is the case. High volume or high pressure????? oil pump?
Kenny

http://www.clubhotrod.com/forums/sho...4&goto=newpost

according to chevrolet a stock oil pump for a small block pumps sufficient oil for all lubrication purposes up to 6500rpm

Did you prime the engine at all, sounds to me that if you did prime the motor and you did the biuld that maybe one of your galley plugs worked ther way loose and is leaking , witch is not comon at all but i have seen it happen,I think that your bearing clearances are very loose ( cam, rod ,crank and maybe even lifter bore) High oil preasure robs horsepower but a small chevy will be safe at 10 psi for every 1000 rpm's, some guys don't like to hear that but it's true,I have a 600 hp 383 that idols at 800 rpm.s and 15 psi and it sreams!! but to get this preasure i installed a soft spring in my pump. I hope you solve your problum before it's to late ! GOOD LUCK

yeah always remember that the lifetime warranty on an oil pump does not cover the engine it just destroyed, it only covers the $35 oil pump

I was wondering if u changed the cam bearings, and did u use a good assembly lube, and how did u prelube and what weight oil ?

new cam bearings, lubed it with lithium grease, primed the engine before starting. Using 10w 30 oil... I know there is a check valve by the oil filter in the threads. Or that if the spring goes in the pump it would do something like that as well. If its as bad as I think bearing are wiped. But this simple fact tell me other wise. pick up to oil pump- oil filter-check valve- pressure switch(where I tapped in) - main bearings and rod bearing- lifters and cam bearings, rocker arm case finally oil pressure gauge.......................... reading at the top was crap and the reading before was the same.......... so its a pressure prob right at the source.......... worse case senario she's coming back out going right to the machinist. but if I'm lucky oil pump might have something up with it or the pick up. Plus Im gonna check the rod and main bearing with a plasti gauge.......... and change the check valve. Maybe upgrade to A high volume and or pressure pump...........................
will find out tomorrow
Kenny

well the engine bearings were wiped..... have since sent it a machinist to have everything checked. Got a new crank cut .10 .10 and new set of bearings all around. Re honed the cylinders, got a high volume pump and a new pick. Had the machinist pess in the pick up. New rings as well............................

only thing that sux is that the gasket kit i purchased came with a ripped gasket for the rear main seal plate. what difference would it make if I installed that gasket with permatex or gasket glue??????????

the prob was the oip pum was sucking air $10 part wiped out my bearings......... plus I ordered a new set of crane lifters

thanx for all your help
Kenny

you can use sealent if you want... but i prefer just to exchange the set and get one without a torn gasket... or if you've already starting using the gaskets... tell them to replace the one for you.... better to not use sealant where you dont have to... less chance of leaks that way