Bearing Clearances

Discussion in 'Race 400/430/455' started by Philip66, Feb 16, 2018.

  1. Dave Mongeon

    Dave Mongeon Well-Known Member

    If your going to turn your buick 7500- 8000 rpm regularly you better have more than .0025 ! iron or alum!
  2. Thumper (aka greatscat)

    Thumper (aka greatscat) Well-Known Member

    Yep, but I never spin that high,my butt would be puckering at the stripe, 6500 usually at most.
  3. Jim Weise

    Jim Weise EFI/DIS 482

    Yup, 7500+ with and iron block is a whole different kettle of fish..
  4. Tom Righter

    Tom Righter Well-Known Member

    I spin my race block to 7500 regularly, .004 clearance on the mains .0032 on the rods external Peterson oil pump bearings look great.on any motor that Sees 6500 I wouldn't want any less than .003 on the mains. Look at people who run big block Chevy's with 2.750 mains turning 75 two 8000 RPM they're running .003 on the mains
  5. TA Perf

    TA Perf Member

    Here's a tid bit for most of you and for those who think they know. In the Federal Mogul Engine Bearing book, this one was in arms reach. On the 455 Buick the designed bearing clearance spec's are,
    Rods .0005"-.0027"
    Mains .0005"-.0035"
    If you are just rebuilding an engine shoot for around .002", rod/main. The tighter you go the better the machine work needs to be. Tight will help idle oil pressure.
    Now if were going to build a street strip car I would shoot for around .0025" rod/main.
    Race engine around .0027" - .0030" rod/main.
    Understand that the main bearings are designed to run at .0035". If you are going to run your engine at full output power, put some clearance in it, get the book out and read. Heck, you could put a TA1531B/TA1533A timing cover on, new TA1520A 5/8 pick up tube, because the mesh is not as fine as a factory tube and way more less restrictive. Put the clearances at max book spec's.0027" & .0035" and go. It will live. We do know that the mains could be closer to .003", but I'm just saying. If it's over .003" and you asked me, I would say "Just put it together" and there are some of you that heard those words from me.
    Remember I stated I was running tight clearances. I'm sharing my failures without the carnage. The most important thing is to know and understand what the engine will be used for. If that's not totally clear .0025"/.0025". If the stock GM or Proform timing cover has low idle pressure with those clearances then install a TA1533A assembly.
    Julian likes this.
  6. Philip66

    Philip66 Well-Known Member

    Mike, that's great information!! And as usual, it generates more questions for me.

    So if we go to .0030" on the mains in a race application, which viscosity oil would you recommend?

    Would the oil choice be different for a Tomahawk as opposed to a factory iron block?

  7. TA Perf

    TA Perf Member

    From my time running these engines I will tell you what I have run. On the last wagons iron block with a girdle and after looking through what notes I could find. It looks like we were between .003"-.0035" on the mains. On that 532 engine I ran 0-30w AMS oil.
    Current 560 aluminum block I'm at .0031", running Lat 15-15w oil.
    I have run other oils as well Brad Penn 10-30, 10-40 in the 560.
    I had run 20-50 Castrol for years in the 532 but I found that I needed to make sure the oil was up to temp before I started a burn out. I still make sure temp is up with any oil I run today. Install a oil temp gauge. You know the only oil I would say to be really careful with is Royal Purple. I have taken more calls from folks loosing engines that had been together for sometime, RIGHT after they changed to Royal Purple. Most, first time out with that oil in there engine. Make sure that the oil and weight fits your application before you run it. Royal Purple has choices. I do not know this product, only what I have heard from customers. DO YOUR HOME WORK.
  8. GS Kubisch

    GS Kubisch THE "CUT-UP" BUICK

    I was afraid of being "wrong" when I shared my experience but it sounds like I'm on the same page with Mike.

    My oil used to start with 20/50 on a fresh engine and then after several runs I would change to 30wt Redline. I went so far as to do this oil change at the track once. As I expected the car picked up several hundredths in the 1/4 mile which was in a 3400 LB , 9.60 car.
    Last edited: Feb 28, 2018
  9. Jim Weise

    Jim Weise EFI/DIS 482

    Mike, when they lose a motor, is it rod or main bearing failure?

    In the 3 tomahawks I have built to date, I have used .0021-.0022. on the very first one... that one did not fail number 2 main, but the bottom insert was pounded out, which coincided with what I believe was detonation on number 2 cylinder, that cost us a camshaft, as it damaged number 2 exhaust lobe.

    The bearing was not blackened but there was just enough heat in it to deform it, it fell out of the cap when I removed it. This was after 425 1/4 mile passes and 2.5 seasons. It exhibited no symptoms, the motor was here for a fresh set of alum rods, and a top end upgrade.

    It had Federal Mogul bearings.

    Interestingly, when I torqued it back up to measure the housings, all 5 had shrunk since the initial build. I went thru the whole torquing and measurement process 3 times... just to be sure.
    Can't recall how much, but it was a couple tenths, and they were slightly out of round. I chalked that up to heat cycling, and that aluminum is different than cast iron in how it reacts to heat cycling.

    That one went back together at .0028, it was the first use of the King HP main bearings, and I was pleased to see that no work was required to achieve acceptable end play, which I recall was a real PITA the first time around.

    The next two were street motors that used the King bearings and .0025 to .0028 in clearance.

    All 3 are in the 750-850 HP range.

    I have another one of those on the stand now, with the same bearings and clearances.. a bracket motor.

    The other one going together is the supercharged one, which will spin harder, and may make nearly double the HP of the previous ones, that one has the mains right about .003.

    All of these motors used the stock timing cover oil pump housing, the first had the TA scavenger setup, the next 2 had the stock buick oil pump, with HV gears, as do the current ones on the stand.

    20W50 in all... I tried 10-30 in a couple of them, was happier with pressures with the thicker oil. The bracket race motor had an oil heater in the SRE pan which I recommend for drag race engines.

    Other than the lower insert on number 2 with the first motor, all the other bearings in that engine looked great. That motor saw 6800rpm in the traps regularly.

  10. Philip66

    Philip66 Well-Known Member

    JW had said in an earlier post that he would prefer a King HP series bearing for the mains. But since they don't manufacture that bearing...

    That leaves us with Mahle/Clevite bearings. More specifically, P-Series Clevite-77 tri metal. Federal Mogul, and I'm sure there are probably other bearing manufacturers but I don't know if they are of a consistent enough quality.
    Just wondering what the consensus is for bearing brand of most of the builders here...

    Most are recommending .0025-.003 on rods and mains. With appropriate oil mods to supply adequate pressure and flow of enough oil to lubricate, cool and maintain the hydrodynamic wedge of protection.
    Choose oil viscosity to give adequate oil pressure at idle with the selected bearing clearances.

    Does anyone prefer a harder surface for their bearings, like an "H" series?
    Would you choose a harder bearing with tighter clearances?

    Would that eliminate only one element of the tri-metal design? Clevite-77 has the shell, then the copper-type bearing material, and then the "soft" coating.
    Does the "H" series eliminate one of those layers?

    I realize that this may be splitting hairs, but I am really digging the learning part of all of this.

    Last edited: Feb 28, 2018
  11. Bens99gtp

    Bens99gtp Well-Known Member

    We ran royal purple 20w50 mostly, sometimes 15w40 when we were out early or late or the store didn't have it on the a motor built by AMP, 464 stk rod motor, don't remember the clearances, but went 2200 plus passes b4 the block got a pinhole in #4 cylinder, we always did long warm up cycles, never let it sit more than a hr with putting heat back in it some ever 20 mind on cold days. Didn't have a temp gauge then

    Only ran regular oil for break in, lived on RP, I only changel oil start of year and late july

    Pulled that assembly out, built new block and rods went 500 more passes till I couldn't get royal purple one day used a buddy's Brad Penn but it was 50wt, 3 passes later bad rod bearing's 6,7,8, had the bottom end repaired, used Brad Penn again but 20w50 3 passes later lose the mains on 2,3,4, but rods look reasonable considering, but I think this last one was more an ignition system faure with the new mad grid not a oil flow, brand, weight, clearance issue. I think.the first failure wit BP was a flow issue with the 50wt
  12. Thumper (aka greatscat)

    Thumper (aka greatscat) Well-Known Member

    Lots of guys bad mouth Royal Purple, maybe they had issues I don't know. Me and my son use the same RP that you do.Never had a problem,so we continue to use it, don't fix something that doesn't exist. We race every week,you all know how many passes we make in a year.Of course we only run high 9's and don't spin over 6500 rpm, clearances are .002" to .0025" ,again contrary to others,but it works for us.
  13. TA Perf

    TA Perf Member

    Normally a rod bearing will go. Heavier oil and low oil temp, not good. I feel the oils travel to the mains is clear, continuing on to the rod has a few more corners and passages to address. When the oil is of a heavier weight, cold and sticky these obstacles will slow its travels up a bit. I would make sure your oil temp is at least 130' before rpm.
    Remember folks, the oil starts and stops moving while its trying to oil the rods. This is because the groove in the main bearing is only 180'.
    (Full groove main bearing reduce load carrying ability). The main thrust of oil to the rod is when the rod oil passage lines up with the feed hole in the main bearing/block. I also feel that when the oil is on the cooler side it has much harder time flowing through the groove in the upper main bearing shell against the rotation of the crankshaft. This will limit the effectiveness of oil being feed to the rod once the rod feed alignment occurs with the groove in the main bearing shell. So reducing the oil to the rod bearing even further. Most rod oiling will be from 12-3 o'clock, prim time being 12. Again, once the oil warms up much of this personal problem start to go away.
    By grooving the main saddles in the block like the Tomahawk. This allows the engine builder to add two more 3/16 oil delivery oils to the bearing. Normally at the 10 and 2 o'clock position. Now the oil doesn't need flow against the rotation of the crankshaft and the rods passageway will get pulsed 3 times instead of 1, plus the groove is now pressurized much better allowing more oil to feed to the rod.
    There is still more that can be added to this story, but out of time for now.
    Julian and StagedCat like this.
  14. Philip66

    Philip66 Well-Known Member

    So is it preferable to have a block heater/oil heater, or just idle and lightly flutter the throttle until it gets to the desired temp?
  15. Staged70Lark

    Staged70Lark Well-Known Member

    81439E19-415C-4989-BAB2-FFFD2F5F7BCB.png When comparing the 455 Buick main bearing to others, I realized the size of the oil trough is much smaller than others. Adding the holes at 10 and 2 o’clock as Mike explained, is what I do to help oil to the rods.
    I have often thought about trying to machine out the top of the main bearing similar to the one pictured above. Maybe even make the opening larger but not all the way to the 10 and 2 o’clock positions.
  16. Staged70Lark

    Staged70Lark Well-Known Member


    I have an oil temp gauge. Your engine water temp will be at 160-180 for quite some time before the oil temp even moves. Using an oil heater is a wise option!
  17. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    I just watch my pressure gauge. There is a very big drop off in pressure as the oil heats up. Doesn't take long. Obviously, street and track are 2 different scenarios. I never romp on the engine when the oil is cold.
  18. Bens99gtp

    Bens99gtp Well-Known Member

    We just put a temp gauge the last motor we had the ignition issue, took a lot of idling and light driving g to get temp even up near 140.......on our run when we notice the oil pressure drop and shut down, I was 160 pretty burn out, ran an 1/8 miles with 3 very bad main bearing, idled back to the pits and oil temp was still only 165. But we have an AL poston oil pan too
  19. Dave Mongeon

    Dave Mongeon Well-Known Member

    when we ran the hawk with the iron block and std buick mains. I tried tighter clearances to improve idle oil psi
    when we went below .003" we would often scuff main bearings . We spun those motors 7650 in top end regularly.
    and with the birdcatcher being more of an on off switch than throttle, burnout rpm often exceeded that. thats usually
    when it would pick up a main. in the end we just turned the pump up till we had 100psi at idle and 135 downtrack with about
    .0035 clearence we ran 15-50 oil . That was around 2004 , never lost a bearing after that, ran the car regularly till 2010. The Tomohawk in NBF is running very similar rpms and the first time we asembled it we again tried tighter main clearance . dejavu
    scuffed #2 main so we opened them up to .0035 , no problem since doing that the only real diff is oil psi avg about 75 psi could probably go lower. I havenot seen much diff with clearance required iron vs alum
    Staged70Lark likes this.
  20. Staged70Lark

    Staged70Lark Well-Known Member


    Same here... it was always #2 that was scuffed. Was there a specific spot on the bearing that was scuffed? Mine would scuff near the 7 to 9 o'clock area of the bearing.

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