BBB oil pressure dropping

Discussion in 'Race 400/430/455' started by 71bskylarkk, Mar 21, 2021.

  1. 71bskylarkk

    71bskylarkk Vroom Vroom.

    Gonna try to make this short,

    486 build, girdle, all block oiling mods done, SRE pan, Internal pickup, ta grooved cam bearings. Ta cover, booster plate, stock pump housing. Lifyer valley epoxy plates with holes drilled for returns, .020 restricted pushrods.

    Primed it on the stand with no intake on and drainback seemed fine.

    Fast forward a few days, get the engine in the car, oil pressure seems fine, notice a oil leak from back of engine (I was half expecting that) with the engine running, I put the car up in the air to investigate, while it idles, see what I needed to see, and when the car gets back down I go to turn it off and notice the oil psi was less than 10. Immediately shut it down. (Was idling with 25-30ish. Mechanical gauge btw)

    Check oil just because. Its fine. Crank it back up, no noises, pressure is good. So I Rev it up to 2k rpm and hold it. Pressure stays at 40lbs. Holding rpm I notice the pressure go from 40 to less than 15 gradually and I shut it down.

    Pulled the engine today, noticed a slight amount of material in pan, so I pulled #1,#4, and #8 rod cap off, and all show obvious signs of wear. Mains were tighter than we wanted but all .0028-.0032 and rods .0035-.0038

    Any suggestions? Oil drainback? Before I pulled pan I did prime the engine with a drill (max 1k rpm) to see if I could get the pressure to drop and it held a steady 50lbs for 2+ minutes with no drop. Checked oil and stick and it showed about 1qt low but still plenty of oil (trying to see if drainback was an issue)

    At this point all I've torn apart is the 3 rod caps, no mains, nothing else. Less than 10 minutes of run time.

    Looking for any, and all, constructive advice or recommendations. Thanks in advance.

    Attached Files:

    Last edited: Mar 22, 2021
  2. Brad Conley

    Brad Conley Super Moderator Staff Member

    Looks like another rebuild is in your near future. I have no expert advise, but that looks nasty for only 10 minutes of run time.
  3. 71bskylarkk

    71bskylarkk Vroom Vroom.

    Yea, I figured that part out already.
  4. Brad Conley

    Brad Conley Super Moderator Staff Member

    Well then, tear it down and see where you screwed up. We're not standing there to look over your shoulder to see what you did wrong.
    TrunkMonkey likes this.
  5. Stage 2 iron

    Stage 2 iron 472 IRON HEAD STAGE 2

    It may have been because it was a quart low and you were running it for 2500 for 10 minutes and the oil started foaming. Better to have more oil than not enough on break in.
  6. 71bskylarkk

    71bskylarkk Vroom Vroom.

    Obviously. Didn't think it would hurt to get the opinions of others by posting here. It'll get torn apart tomorrow, in the meantime, maybe someone here has ideas or comments that are useful.
    GS464 and buicksWILD like this.
  7. 71bskylarkk

    71bskylarkk Vroom Vroom.

    Had 8 qts in it.
  8. 71bskylarkk

    71bskylarkk Vroom Vroom.

    Stock gear with booster. Ran this same cover etc on another combo with no issues for a while
  9. Stage 2 iron

    Stage 2 iron 472 IRON HEAD STAGE 2

    Dam i’m sorry to hear that, I’m sure if Jim Wise sees this he will chime in if not I would send him a conversation.
  10. Bens99gtp

    Bens99gtp Well-Known Member

    Wow that looks nasty,

    I had main caps walking b4 and ate the center 3 mains out and the rods looked almost perfect.

    Lost a cam in bbc where 4 lifter we beyond ate out and the bearings didn't look that bad..........some how they didn't get oil.......
  11. Brad Conley

    Brad Conley Super Moderator Staff Member

    ok. What were your clearances? Rods and Mains? Clearance on booster plate? We'll start there and see if we all can't help you find the cause. I know you're frustrated. I would be too.
  12. Stage 2 iron

    Stage 2 iron 472 IRON HEAD STAGE 2

    I know on the motor I build a couple years ago that we had to run the high volume gears because of the clearances stock pan modified 8 quarts with pick up F3AF064F-F606-4178-B1F3-B9C139352E04.jpeg
  13. Briz

    Briz Platinum Level Contributor

    I have an unused HV pump set up if ya wanna go that route
  14. BrianTrick

    BrianTrick Brian Trick

    What are the bearing AND side clearances on the rods. I’ve seen multiple combinations of how people come up with the correct combination,but there are also some that will direct result in failure. Too loose of a side clearance will let too much oil out and not enough cushion to ride on. Yes,pressure is important,but I always focus on volume with these engines. Different builds also require different oil weights. What were you running?
  15. That's some big rod bearing clearance.
    m louk and 1973gs like this.
  16. Thumper (aka greatscat)

    Thumper (aka greatscat) Well-Known Member

    My opinion,for whatever thats worth, is too much bearing clearances unless you use a peterson pump system.Those are chevy specs. I run .0025-.0027 mains and .0023-.0025 rods on race engines, .002 and .002 for street motors. Thats tighter than many others run but no issues. Also,as Brian stated,excessive side clearance could be hemorrhaging a lot of oil. And lastly, filling the lifter galley slows oil return, what looks good on the stand is not the same as in practice. We filled a galley in anticipation of a solid roller, oil returned great on stand, at the track at the 1000' went to 5psi, added 1 quart same result. tore it down and found worn bearings. Right now we're adding additional holes for better return.
    Buicksky and Stage 2 iron like this.

    BUICKRAT Torque Rules!

    Those rod clearances seem awful big for a BBB. Also, did you find/correct the oil leak from the back of the motor?

    FWIW, this forum is free for all to use, so if someone tells you something that you don't deem useful, just keep your mouth shut about it and move on. Lots of valuable info on here, and smart a$$ replies will keep others from responding. If you posed that question on yellow bullet, about a dozen guys would have told you you are a dumbf... for setting your Buick rods at .0038. Remember, beggars can't be choosers.
    Last edited: Mar 22, 2021
    Staged70Lark and TrunkMonkey like this.
  18. Brad Conley

    Brad Conley Super Moderator Staff Member

    He did state his clearances in his first post but I missed bad. I should have paid better attention.

    Your main & rod clearances are way off, almost double what they should be for a street car. I don't know what you started with rotating assembly wise but all of that is going to have to be re-done or replaced. Let us know when you round up parts/machining work.
  19. standup 69

    standup 69 standup69

    With no load even with loose clearances it's doubtful IMO that it wiped the bearings out first thoughts are some trash went through it from the build and or oil starvation from a drainbacks issue ...I get the impression the clearance was set big for NOS ? I could be wrong about that ....001 too big isn't going to wipe out an engine in the driveway
    71bskylarkk likes this.
  20. 71bskylarkk

    71bskylarkk Vroom Vroom.

    Still haven't torn it further apart, had my boss, engine builder whatever you want to call it, look back on his notes where we built it and i was off on the rod clearance by a few, all .0030 - .0035, side clearance on the rods was .0015-.0020 across the board.

    correct me if we're wrong, but I have a hard time believing bearing clearances is causing this issue at near idle. I would think that it would be something on the suction side of the pump to cause a pressure drop. OR a drainback issue. If clearances are too loose pressure would low from the get go and stay low. Again, just my thoughts.

    We always run clearances looser than tight, I am going to beat the dog **** out of this engine, not a cruiser where i may see 4k rpm every now and again. Street driven, drag raced often, and abused and sprayed with a 200 shot of nitrous. I pulled the timing cover off today and made a blockoff for the pickup tube, and put a vacuum pump on the main feed passage and it is holding vacuum fine, also air checked it. so nothing there (o ring in girdle not sealing etc)

    I'm at a loss, engine is coming all the way apart to triple check everything, but so far now damage is minimal, no scores on the crank, replace rod bearings, polish crank, and hopefully that's all. Also drilling more holes in the valley, OR going to block drainbacks in the head and run lines to the pan. But once again I'd be surprised and shocked if at 2k rpm the oil is all stuck in the valley/top of the engine unless around the lifters is hemorrhaging excessive oil. solid lifter with restricted pushrods there shouldn't be that much oil up top.

    The leak seems to be coming from a spot that the silicone didn't hit from the girdle,pan,block area. Not to mention when I pulled the pan some of the silicone was still wet even after sitting for 5+ days. Grr.

    So after priming it on the stand for a few minutes, then checking the oil, and then moments later draining it (after pulling engine out, obviously) I noticed the oil was super aerated, So that's the next thing that leads me to believe suction side.

    The timing cover/pump etc was all on my previous build and worked fine with great pressure. I appreciate all the feedback.
    Sorry this response was jumbled. Been a long day at work !

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