Oil pressure drop

[57larry]

I have a fresh rebuilt 350 Chevy bored 30 over. upon start up, it has 60 lbs of oil pressure, no knocks. 2 minutes  later the oil pressure drops to zero., knocking in the valve cover area.

changed oil gauge, dropped oil pan, no metal in pan, changed oil pump.  started engine up, same problem with oil pressure dropping.

where should I start to look? thanks, Larry

[kb426]

lifter galley plugs behind cam gear

[57larry]

pulled timing gear, plugs are new and tight, no leaks. my 1st guess also. thanks

[enjenjo]

Check here  

[chimp koose]

Is the distributor too deep or too shallow? I had an engine do that before and the relief where the oil passes by the distributer body was not in the right spot and oil was returning to pan before getting to rockers . It never made as much oil pressure as yours does on start up though .

[57larry]

finally got around to pull the intake. lifters look good. what's next? pull the engine, main/cam bearings? thanks, Larry

[UGLY OLDS]

Larry ... This explanation will take some time but it works ......
 1..... Lay the intake manifold back in place , ( It doesn't need to be "installed"), & put the distributor back into place .....

 2.....Above the oil filter mounting area , you will find a 1/4" pipe plug ....( It's on the side of the round part of the block).. Remove this plug ...

 3....Using whatever combination of fittings necessary, (nipples, elbows, etc), work up a way to hook your shop air hose to the hole where the plug was removed from .... Hook up your shop air hose ...This will pressurize your complete oil system in the engine with compressed air....
By looking & listening around the engine, you soon will find where the pressure is being lost .....

I have used this method multiple times to track down internal oil leaks .......

 The plug in Enjenjo's video & the vertical distributor placement is also very critical ....  As has been said ... The distributor being to high in the block will allow a severe pressure loss ....

Please let us know what you find .....

Bob ...  

[wayne petty]

a few images.. you did not mention which generation it is..

 oil pressure bypass valves...  


the oil flow from the pump and into the block.




a better view



how much clearance do you have with the oil pump pickup?  click the link.. the picture is too big..

http://i.imgur.com/AwxRF22.jpg

and lastly.. do you have one of the Fuel pump Vacuum gauge that reads 30 inches of vacuum and 15 inches of pressure.  cheap over at HF..  hook that up to the engine oil dipstick tube..   start the engine .. if you get vacuum or pressure..you have a crankcase breather blockage problem...    what..  if you don't have a crankcase breather that will flow.. you can create almost manifold vacuum in the pan and that will really screw with the oil pressure readings.. it may also suck the pan up tight against the oil pump pickup tube.   i have found 2 pvc valves on motors and no breather.. i have found no pcv valves and no breather and a vacuum leak from the bottom of the intake manifold gaskets..  i had one issue where the guy hooked up a vacu sump set up.. first he blew the seals out.. then he sucked them in.. i ended up giving him a tube of black super weather strip adhesive and flanged seals i picked out of the seal spec guide for him.  i got him to hook a turbo boost vacuum gauge for his dashboard.. he ended up using a chevy electric smog pump with the hidden plunger removed.. i tried to tell him i could wire it up to work..  he would turn the pump on as he staged the honda..

[57larry]

pulled the crank, all main & rod bearings parts of the crank are grooved. main & rod bearings are smooth. machine shop says crank was not harden. this was a new Eagle crank, all bearings new, new pistons & rods from Eagle. Eagle sent a replacement crank & bearings.

will assemble probably next week. wish me luck. thanks, larry

[kb426]

Hope that's it. I'm not an expert at aftermarket cranks but I'd think any crank would run for a while before that happened. Because you have the engine all apart, I'd look very carefully at everything.

[chimp koose]

Seems odd that the bearings are fine when the crank is messed up . Cast cranks are not hardened , you can easily mark them with a file or nick them with a rod bolt . Bearings are usually softer than the crank and more easily scratched . I wonder if you have some sort of harder faced bearing in there . And yes do a thorough check for debris , maybe toss a magnet in the corner of the oil pan too .

[wayne petty]

pulled the crank, all main & rod bearings parts of the crank are grooved. main & rod bearings are smooth. machine shop says crank was not harden. this was a new Eagle crank, all bearings new, new pistons & rods from Eagle. Eagle sent a replacement crank & bearings.

will assemble probably next week. wish me luck. thanks, larry

 invest in a set of oil galley brushes..

please pull the cover off the oil pump..

do you have the oil that came out of it.. i am hoping it was in a clean pan.. run it slowly thru a coffee filter.. look for sediment that might have caused the failure.. cut open the oil filter..

i have found engines with tiny bits of sand blast media in the nooks and crannys..

if you can.. pick up an IS-55E oil pump drive from the parts store. $8. . drill a piece of bar stock to mount the chevy pump to it.. make it long enough to go across a 2 or 5 gallon bucket... with 1 bolt mounting the pump.. a hole drilled next to it for a pressure gauge..  you can dip the end of the pump screen in oil and spin up the pump to check the internal bypass valve ..  sediment can effect these and hold them open.. as can damage from driving the screen into the pump body..


look up oil pump dyno.. these are really easy to make..

i might have mentioned.. did you have a crankcase breather vent installed in one of the valve covers.. there were issues where only a PCV valve was installed.. the breather blocked. the vacuum thru the PCV pulled the pan in slightly.. blocked the pickup screen opening..  i have been thinking about welding some 1/4-20 nuts to the bottom of the pickup screens to prevent this from happening.  actually i would love to build a spring steel snap around the pickup screen flange to do the same thing..

[57larry]

thanks for all the tips guys. I used a Melling 55HV oil pump with a moroso pickup. the oil in the pan was gray in color. PCV valve was good. the block is at the machine shop being cleaned & checked out. I'll get one of the kids to come over & I'll post pics of the crank & bearings

[wayne petty]

this is an easily duplicated oil pump dyno. http://pitstopusa.com/i-23909361-percys-oil-pump-dyno-chevy-v8-chrysler-ford.html

[Ohio Blue Tip]

Always check out a new oil pump before installing.  Last year I installed a new Melling HV oil pump in a SBC and it cost me an engine.  After tear down the pump had no bypass valve in the pump.  Melling replaced the pump, I rebuilt the engine including a crank.  Lesson learned. $$$$