Questions on Oil Clearances

Discussion in 'Small Block Tech' started by OddfireV6, Aug 12, 2018.

  1. OddfireV6

    OddfireV6 Active Member

    Hi there, folks. As my username suggests, I have an odd-fire 231 V6 that I am currently rebuilding. I am a member of this forum rather than the Turbo Buick forum because this older odd-fire V6 has more on common with the small block V8 than to the later V6's that the Turbo Buick forum is all about. I'm a mutt stuck between two worlds. Take the Buick 350, cut two cylinders off, and that is me.

    Anyway, my poor V6 fried it's main bearings a couple months ago and damaged the crank quite a bit. I got it back from machining have been test fitting to check my oil clearances. I wanted to check with the forum here to see if my clearances are what they need to be. The service manual is rather vague.

    My main bearing clearance is 0.0020" to 0.0025" on all bearings, which are 0.020" over standard size. That seems about right to me but perhaps some of you have seen better results from running your mains a little tighter.

    The one I am really concerned about is the thrust bearing. My crankshaft thrust faces took a heck of a beating and the machine shop did not treat them. . I'm measuring 0.010-0.012" end thrust, the spec is 0.004-0.008". My options are to run it, send it back to have the thrust ground 0.020" oversize and I'll order an oversize thrust bearing set, or send the crank back and have them weld and grind back to standard size.

    I'm inclined to not cut corners on this engine. Other people cutting corners is why this is the third time in three years this engine has been rebuilt. I'm doing it myself this time because I'm the only person I trust to do it right.
    Last edited: Aug 12, 2018
  2. TrunkMonkey

    TrunkMonkey Well-Known Member

    You never learn anything of value the second time your kicked by a mule.

    I'm with you. Spend the small amount today for insurance, rather than spending more time an money trying to save both the first time.

    I have found, many people can spend your "time and money" for you, when they have no investment in your outcome.

    In the military, it was (and likely is) a saying; "We never have time to do it right, but we always have time to do it over."

    I learned what that meant as a young pup, and never bought in to the false economy again.

    And it has served me well, all of my life.

    You need to figure the best outcome, $ spent, and correctly assess the ability of the welding and machining, vs the oversized thrust bearings.

    I would go with the oversized bearings to avoid a poor welding/change of metal and possible expansion delta from the original crank and the added material, as well as "work" hardening, warping and such. If the machine shop knows their game, then it might be fine. The oversized bearings are less likely to have the same number of variables that can go wrong.

    Hope that helps.
  3. stk3171

    stk3171 Well-Known Member


    I have a 77 regal with a good v6 odd fire. The body is gone.

    This motor runs real good. I installed a 4barrel intake and holley economaster 450 cfm this made it run as good as a small v8.

  4. Stevem

    Stevem Well-Known Member

    Too large a thrust side clearance condition my not be a issue dependent on your rod side clearance and if the edge of the rod Bearings do not ride up on the Crank radius that blends the rod jurnal into the cheek of the Crank.
    You do not want the Rods to take the place of the thrust Bearing because then you will end up cocking the piston and unseating the rings in the least!
    Chech these things out and you may be able to creek by if you have a auto Trans behind the motor, if not then for sure do things the right way!
  5. alec296

    alec296 i need another buick

    I’m not aware of a .020 thrust side bearing. Machine shop should have checked thrust measurement.
    Also, what ate up bearings. Fix that issue too. Drill out block and get a later pickup tube if you can. By 1980 the v6 had a 5/8 passage from oil pickup tube factory.
    Last edited: Aug 13, 2018
  6. Jim Blackwood

    Jim Blackwood Well-Known Member

    If you are at all concerned about oil pressure, do a search on this forum for oiling mods. Check the factory specs for main and rod bearing clearances. I think you will find you have issues there.

  7. OddfireV6

    OddfireV6 Active Member

    It will have a good oil pump, I assure you of that. I know my way around the Buick oil pump, but these bearing clearances are throwing me off.

    I don't care what the oil pressure is to be honest. It could idle at 8 PSI for all I care, so long as it idles at 8 PSI for the next 150,000 miles. What I want is the proper bearing clearance for those bearings to receive proper lubrication and LAST. Whatever oil pressure that produces is fine by me.

    I checked the factory specs several days ago and thought it was completely unbelievable or a typo. That is half the clearance of most engines. Sure, it builds good oil pressure, but there is very little oil flowing through the bearings to cool them. How do the bearings not overheat and seize like they would in any other engine run that tight? How do the bearings not edge-load from crankshaft flexure like they would in any other engine? Any flexing of the crank at all with clearances that tight would bind. I am very hesitant of building an engine with 0.0010" on the mains. It goes against everything I was taught and experienced on other engines I've built.

    This is the fourth time this engine has been rebuilt...three of them in the last two years, though this is the first time by me. There will not be a fifth time if I get the clearances wrong. This need to be done right and it needs to be done right THIS TIME.
  8. Mark Demko

    Mark Demko Well-Known Member

    At .002 you'll be fine, at, its getting kinda large.
    Oil pressure is important, unfortunately all it indicates is a restriction in the oil path..... bearing clearances. The tighter the more pressure, looser clearances = less
    I understand your concern about the clearances, they're VERY important to follow the manufacturers specs.
    I'd be a bit concerned about the crank not having consistent clearances, like I said, .002 is fine/max I'd go with a stock oil pump, at .0025 you might hemmorage oil and end up starving the tighter clearances.
    As far as the V6 crank flexing, I wouldn't worry about that, its a pretty stout, ridged piece, especially yours being a NA V6.
    See if .030 bearings are available, OR find a virgin crank.
    I have an '87 GN, and my thrust was a tad larger than spec, but I've been running it with no issues, and my crank is still original size, never been ground.
    Check TA Performance, see what they may have as far as an odd fire V6 crank.
    Last edited: Aug 14, 2018
  9. 300sbb_overkill

    300sbb_overkill WWG1WGA. MAGA

    Maybe get the block align honed so you can run the proper Buick clearances, have them hone it to the tight side of the tolerance that may tighten up your clearances the .001" you need it to be?

    You're building a Buick engine, not a brand X so adjust your thinking thusly.

    Bearing clearances are measured on the straight up and down axis, 90* from the parting line. Main and rod bearings are NOT round, they are more egg shaped and have extra build in clearance at the parting line so its not like there is only .001 all the way around the journal or whatever the clearance ends up at. All brand engine bearings are egg shaped, not just Buick bearings just so you don't think its a Buick only thing.

    If you want more oil volume to flow through your engine, do like has been said and drill the oil passages in the block, the Buick oil mods.

    Maybe the engine will last this time if it is built to the Buick specs instead of brand X specs? GL
  10. alec296

    alec296 i need another buick

    See if TA performance has a backgrooved front cam bearing for the early v6 . That will help control oil pressure to mains and rods. The odd fire crank is stronger then an even fire crank since rod journals are not split/offset. .0015 doesn’t seem like excessive clearance. Would like to see what your building that has more . A lot of cars that era had similar specs. And the newer cars with harder bearings have tighter clearance.
  11. Jim Blackwood

    Jim Blackwood Well-Known Member

    It ain't a SBC. Like the man said, adjust your thinking. On these engines, if oil pressure is inadequate you do not install an oversized oil pump, as that will wear out the distributor gear. Build it right the first time, build it once. My 340 has .0010"-.0015" clearances, all the oiling mods, and runs 30psi oil pressure at 1500rpm with 10w30 oil fully warmed up. These guys on this and other forums have built a great number of these engines and have long confirmed that the factory clearances are correct. Enlarge the suction galley, radius the corners, use the booster plate and the double groove front cam bearing. That's for a stock street engine, but beyond that all you need is the adjustable relief valve.

    The difference between oil flow through a bearing with .0015" clearance and one with .0020" is way more than you would ever imagine. With .002" you will be running heavy oil and thinking about that high volume oil pump. At .0025" you might as well start over. History proves it. So go ahead and do whatever you want. After you've put in the 50wt oil and it's still thrown a bearing maybe you can swap in an LS that's never had the covers off.

    See that's the corollary to the "always time to do it twice" thing, he that doesn't listen doesn't learn.

    alec296 likes this.
  12. OddfireV6

    OddfireV6 Active Member

    Aside from the bearings, I have a dilemma on my mind that maybe the forum can help me decide on.

    1.) Clean and reuse my old cam and lifters. By "old" I mean 6000 miles, though they were contaminated by bronze shavings as the bearings failed. Really tiny bronze shavings. That is why they'd have to be disassembled and cleaned.

    2.) Use the NOS 1980's Sealed Power cam and new lifters that are sitting on my shelf.

    I know the best thing is to use the new cam and lifters, but I had a heck of a hard time finding that cam. New stock-type camshafts are getting hard to find for these odd-fire V6s. I've inspected my old lifters and cleaned the bronze shavings out of them. They have no scoring or damage inside, outside, or on the cam lobes. I believe they would be perfectly fine to reuse. That would keep my NOS unused cam exactly that: unused. It can remain my spare cam for the future....if there even is another future rebuild in my lifetime.

    What would you do?
  13. OddfireV6

    OddfireV6 Active Member

    Also did Buick stamp the connecting rod position (1 through 6) on both the cap and the rod at the parting line or did they stamp it on the balancing pad on the rod cap? I ask because my rod caps have numbers in both locations...and those numbers don't match on three rods. I think an idiot previous rebuilder added the number on the balancing pad and messed it up.
  14. 300sbb_overkill

    300sbb_overkill WWG1WGA. MAGA

    The factory didn't put on any numbers on the rods except for maybe casting or forging numbers.
  15. Alssb

    Alssb Well-Known Member

    Use the 6000 mile set.
  16. Jim Blackwood

    Jim Blackwood Well-Known Member

    Did you keep the lifters matched to the lobes they were sitting on when you tore the engine down? If you didn't you might as well throw that cam and lifters away and use the new one. If you did, go ahead and use them.

    Match your numbers and have the rods resized.

  17. OddfireV6

    OddfireV6 Active Member

    I addressed the concerns and finished the rebuild. First start was yesterday, first drive was today. It produces 15 PSI at 600 RPM and 45 PSI at 2000 RPM hot with 10W30 so we don't have to worry about that. Runs smooth, no bad noises.

    More questions for successful Buick engine builders:

    1. What brand of timing cover to you use? TA Performance?
    2. What brand and type of gasket do you use between the timing cover and the block? A Fel-pro paper gasket?
    3. Do you use any sealant on the timing cover to block gasket? Copper Coat?
    4. What torque do you tighten the timing cover to block bolts to? The original GM spec of 30 foot-pounds?
    5. Do you retorque the timing cover to block bolts to specification after the engine has run for a while?
    Last edited: Oct 15, 2018
  18. Mark Demko

    Mark Demko Well-Known Member

    #1 I used TA's timing cover
    #2 Fel Pro
    #3 I have used Hi Tack, only to hold the gasket in position, this last assembly I installed it dry.
    #4 Never used a torque spec, just used a 1/4 drive ratchet and tightened 'em
    #5 No, never have.
    300sbb_overkill likes this.
  19. MrSony

    MrSony Well-Known Member

    Make sure to use thread sealant on the long bolts that go into the water jackets upon reassembly. I also use anti-seize on all the timing cover bolts. hate when those break.
    Mark Demko likes this.
  20. OddfireV6

    OddfireV6 Active Member

    I ask because that procedure cracked my timing cover and smashed out the gasket. 30 foot-pounds is the original GM spec but it's apparently way too high. Again, I'm used to building AMC nd Chrysler engines and on them following the OE torque specs has given me nothing but good results. Apparently Buicks are different.

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