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Thread: Oil Pressure Problem

  1. #1
    StealBlueZ
    I have an oil pressure problem, and could sure use some ideas.... I rebuilt a 502 w/6-71. It was bored (+.030) and had the crank checked and polished. Installed a new pump, and of course rod, main and cam bearings. The cam and lifters are new, with a Pete Jackson drive, and on the initial startup, in the garage I ran it maybe a minute, on two occasions. I also primed the pump before cranking it. When all was complete, I ran it on the ramp at about 1600rpm for about 15 mins, then back to the garage to tighten a few bolts and hoses, then back to the ramp for more break-in. Now for the prob: I have great pressure (60-80) at start up thru warm up, but when I take it off the trailer and the motor gets hot, the pressure at RPM is still high, but at idle is in the 10-15 pound range, maybe lower. NOT GOOD. Now, I 've already pulled the motor out to investigate, but what can I look for. Plans are to grind the crank and get another pump. Any ideas????
    Thanks,
    Randy

  2. #2
    BlownCole
    There is a piece that goes in the oil passage where the oil filter spins on and with out it the oil goes thru the oil cooler to fast to properly cool it. If you had it in a machine shop they may have taken it out. Cheap part but without it it could get expensive.

  3. #3
    hulshot
    check your oil temp into the cooler and out of the cooler. It may be too hot, or you could have a clearance problem. what weight oil are you using. Was it you that had another post and a guy named Ray was builking the motor??

  4. #4
    StealBlueZ
    Thanks HS & BC....I'll look for the "piece" that you mention. I plugged the NPT hole next to the filter, but unsure of any other part that goes where the filter is--will look into it in the AM after work.
    HShot, I used Valvoline 40wt for starters, and I do not run an oil cooler. As for clearance, I may check it with plastiguage. And no, this is the only thread on this board that I have posted on this subject. On DBR.com, a guy said that low pressure is not that uncommon at idle, with good pressure at RPM. I can accept that, but I'm just not too comfortable with maybe 10 pounds.

  5. #5
    gnarley
    Originally posted by BlownCole:
    There is a piece that goes in the oil passage where the oil filter spins on and with out it the oil goes thru the oil cooler to fast to properly cool it.
    BlownCole, on which BBC are you refering? IV, V, VI ? I don't remember it on a mark IV & haven't done any V's or VI's. It sounds like you are describing a restrictor of some type which does not sound at all good in an oil gallery if it is slowing the oil flow down.
    StealBlueZ, I bet you run a elec guage? If O/P is in question make sure that you Tee in a mech guage and check it against your elec unit. The sender could also be bad!
    [This message has been edited by gnarley (edited June 07, 2002).]

  6. #6
    StealBlueZ
    Originally posted by gnarley:
    StealBlueZ, I bet you run a elec guage? If O/P is in question make sure that you Tee in a mech guage and check it against your elec unit. The sender could also be bad!
    Nosir. It's a mechanical that's run from the port by the oil filter

  7. #7
    gnarley
    OK Got it, good! So what was the clearence on the mains? And which BBC year is it?

  8. #8
    BlownCole
    BlownCole, on which BBC are you refering? IV, V, VI ? I don't remember it on a mark IV & haven't done any V's or VI's. It sounds like you are describing a restrictor of some type which does not sound at all good in an oil gallery if it is slowing the oil flow down.
    It is on a V and yes it is a restrictor of some type the true tech name escapes me at the moment. We did 6 pulls on the dyno and kept picking up a knock on the knock sensor. About pulled our hair out trying to figure out what the prob was. I have built several motors but this was the first GM so it was new to me as well.

  9. #9
    gnarley
    Ok I would appreciate the info on the mystery part. I have a mark V that is coming out in the fall for work & will be my first mark V block, so share the info please. So far it sounds weird to me, I have worked on a lot of wet & dry-sump systems in the past and have never seen a restrictor in a main gallery that would be going out of a pumps flow before or after a cooler. Not to be confused with a cam gallery where you can install restrictors.

  10. #10
    US1Fountain
    the "mystery part" is the oil bypass valve. It is not a restrictor, but a saftey protection item. It allows oil to return into the motor in case of a plugged filter. Any oil that goes thru the bypass valve does not get filtered. On the GenV motors, this valve is pressed into the block filter pad right next to the filter mount screw. On the Gen IV (Mark IV) the valve is in the filter adapter.
    Many guys remove these valves and plug them to force all oil thru the filter. But if the filter does get plugged, the motor will starve of oil. Bang, bang, boom
    Don't think you will find anything wrong with the motor. The oil temp is just getting to hot from not having a cooler. Ideal oil temp is around 230 from the pan during hard runs. 280 is to hot.

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