Bearing Clearances

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

  1. Jim Weise

    Jim Weise EFI/DIS 482

    Probably a little of both Ben... factory tolerances and block that has gone thru many heating and cooling cycles, could have been overheated at one point, and we do know that stuff moves around a bit.

    The main impact of lifters not being 90* square to the block is contact pattern, and the ability of the lifter to spin properly. The cam tilted in the block will impart a forward or rearward force into the block, depending on which way it's tilted. If the cam bores are not all on the same centerline, then that imparts force into both the camshaft, and the bearings, and can be a factor in cam bearing life.

    We have not set the block up in the boring machine yet, to tram the holes, to see how straight they are.. so that could be yet a third issue.

  2. Staged70Lark

    Staged70Lark Well-Known Member

    Hey Phillip,

    The more I read through the responses, the more questions I have.

    There are some very good articles written that discuss the variables to take into account when setting up your rod and main bearing clearances. I suggest you google engine bearing clearances to see what the bearing manufactures and other engine builders suggest.

    Ideally you want high volumes of oil to go through the engine at appropriate pressures to minimize friction and keep the engine and oil temps cool.

    That being said, getting the oil to the right places in a 455 Buick iron block engine is very important. As Gary explained, 7&8 get oiled last unless you modify with an oil equalization line. There are other important oil mods outline in other threads on this site.

    I know others have had success with tighter clearances but my only concern is main bearing wear at the parting line. If you go with .0025 then you only have .00125 on each side of the crank journal. When you start making real HP you will distort the block enough to see the wear.

    I personally run all my engine at .00325 to .0035 on the mains with a 3.25 crank journal and on my 2.100 rod journals they are set at .002 and .0021 but I will only run 20/50 penzoil racing oil.

    Good Luck and hope to pit next to you again!!! It was fun!
    Last edited: Feb 19, 2018
  3. 8ad-f85

    8ad-f85 Well-Known Member

    There's extra clearance at the bearing parting line. You can measure it easily with a caliper.
    (Not sure I understand the comment fully?)
    If you are having wear problems there, things are really getting jacked out of shape and you are about to have bigger problems. That's a sure sign that more rigidity is needed.
    All of these engines that have flex/distortion problems, crank counterweight/mass issues, that benefit from girdling and harder parts are happier with tightening the clearances back up...not just Buick.
  4. Jim Weise

    Jim Weise EFI/DIS 482


    That depends on what bearing your using.. a Clevite P series bearing is on average, .007 to .0015 thinner, on each side of the shell at the parting line, than it is vertically. The term used to describe this is bearing shell eccentricity. Production P series bearings are somewhat more inconsistent in shell thickness variations, than most race bearing sets. Partially by design, partially by execution in manufacturing.

    Huge parting line clearances are the number one reason we lose rod bearings, not uncommon to have .005 or more at the parting line, even in a motor that is set at .0025 vertically, if your housing is not dead round. I have fixed several stockish type 455 builds, sent to me with rod bearing failures, and huge parting line clearances are what I have always found. Line hone the main housings, set the vertical clearance around .0025 and the rod bearing failures disappear.

    As you said, oil pressure equalization lines, and thick oil, go hand in hand with running larger vertical clearances. Not so much because of the extra .001 at the vertical, but the the parting line clearance is really starting to get big.

    The federal Mogul race bearing is more round, but that is a hard bearing, and I am no fan of hard bearings. They are unforgiving, and require that you surface harden your crank. I like a bearing with higher imbedablity, and I have yet to see a p series clevite 77 melt out in a BBB, not even a forced induction one, at over 1000 HP. I don't believe durablity is an issue with the P series bearing.

    That being said, I wish King would make a HP series main bearing for the BBB. It's what I use exclusively in the 3" main Tomahawks. I use the King HP rod bearing in all the stroker BBB motors, with the 2.200 to 2" rod pins.

    Have had excellent success with that bearing.

    Your right, there are reams of information on the internet on bearing optimization, bearing types and eccentricity variations in bearing shells. Here is one of my favorite write-ups.

    My conclusions are what I originally stated.. .0025 +/- .0002 is the sweet spot, with a Clevite P series bearing (high eccentricity) in our factory iron block engines. Our selection of bearings at the 3.25" size is limited, compared to other performance engines. I would lean harder toward larger vertical clearances, if we had a King HP series main bearing.

    Last edited: Feb 19, 2018
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  5. Philip66

    Philip66 Well-Known Member

    John I've been wearing out my search button!
    Reading an EngineLabs article and they quote an early saying:
    " If it's too tight, everybody knows. Too loose, and you know."

    I guess that means that you're better off with looser clearances because if they're too tight, everyone will know, when your engine comes apart.

    They also talk a great deal about the current trend toward tighter clearances and using a -0 weight or 5 weight oil.

    I've always leaned towards heavier oil 20W50 Brad Penn. When I bought Ricks car he said he blends in half 10W30. But this is a girdled engine so I imagine it's a little more stable. It also has all of the oiling mods and a balance line.

    And I too look forward to Norwalk John!!
  6. buicksstage1

    buicksstage1 Well-Known Member

    The oil is the cushion, wider bearing clearances require higher viscosity engine oils to maintain hydrodynamic oil wedge period! Before good oil mods and TA timing covers we tried to keep a balance between keeping the bearings alive by getting room for these flexi BBB blocks to move around and oil pressure. Now that we have great flowing heads we have 650+hp 10.5:1 small cam pump gas engines vs not too many years ago a 650hp BBB was a all out big compression drag engine. When it comes to bearing clearances look at a Nascar engine, to begin with it has a very ridged block that does not flex at all and pinch the crank bearings like our BBB's, rods and main journals are very small compared to our BBB's also. 1.850 on the rods and 1.999 mains set with .001 bearing clearance so they can get away with oil as thin as 0W5 they are everything our BBB's are not. Our mains are HUGE, the block flexs all over the place, our cranks are stupid heavy, same with pistons and rods, our parts are all heavy in a thin wimpy block that most buick guys externally balance so there is unsupported weight hanging off both ends of the crank. I groove main saddles as often as I can because in my opinion the only way to keep the hydrodynamic oil wedge with a large main bearing is to reclock and give it 3 oil feeds vs 1 as long as I can get a big enough oil pan on it they pretty much all get grooved saddles when they are performance builds. I do not like filled blocks on the street, the oil in the pan is a extension of the coolant system, when you put all that concrete fill in the block your oil temps take longer to rise and when they do the operating temps are also substantially higher. Joe Gibbs rates there oils by the bearing clearance for good reasons.

    Attached Files:

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  7. Philip66

    Philip66 Well-Known Member

    So are you looking for precise consistency across all main bearings and all rod bearings? Or is a close range of clearances acceptable?

    Is it possible with variations in prior crank turnings and polishes to have a range of clearances that vary from main to main and rod to rod? What about the thrust bearing, is it preferable to have it looser or tighter than the other mains?
    If you gather a particular series of bearings from TA and after installing them you end up with mains at .0027 but the thrust ends up at .0029. Are you going to adjust the bearing pack to bring the thrust down to be in line with the other mains?
  8. Bens99gtp

    Bens99gtp Well-Known Member

    I'm no builder, but if machining is done correct. And all the holes( mains and rods ) are made to be the same size, and the crank is well machined to the same size, the crank isn't bent, and the bearing company did it's job and all the shells are the same size. The clearance should be able to be different. I think if the machine is all done correctly, the bearing shells become the mass produced part that has the veriences in it. I think this is why you some ppl buying several bearing sets to make 1 having to go through 3 or 4 sets of lifters to get the clearances they need. The window of acceptable range in these outside purchased parts that us out of the builders control.

    But in theory you could get the clearances all the same if you cycled through enough parts. I guess it depends how much you want to chase that .0002 differance.
  9. Jim Weise

    Jim Weise EFI/DIS 482

    I would not worry about an extra .0002 on the thrust, because of the flanged thrust surface on the crank, it will leak a whole lot slower than the other four bearings.

    As Ben said, no excuse for the machine work on the crank not to be spot on in size.. the block is a bit trickier, it takes a talented guy, who is willing to experiment, to be able to get all the housings exactly the same size. This is because we have 3 different thicknesses of bearing surface.. number 1.2 and 4 are the same, but 3 is narrower, and 5 is wider. The hone takes out more material on thinner holes, less on wider ones, per stroke, just how it works... so your machinist has to find the sweet spot, on how much to take of the caps.. and most guys that do a few a year are not going to bother.. So you will most likely have size variation in the housings, as well as in the manufacturing process of the bearings.

    Which is exactly why most guys wait till the block is finished, they torque it up with the bearings, and then call out a size for the shaft.. and my grinder will actually do an exact size grind, with individual specs for each main... I assume all shops will do this, they just charge extra.

    I use this if I am working with a previously machined block, and get involved with someone else's problem child.. if the main housings are round, but not near the same size.

    Mart likes this.
  10. TA Perf

    TA Perf Member

    My job title is not engine builder but I have been building Buick engines for 44 years and the current builder at TA Perf. Interested folks may apply. I have run bearing clearances as tight as .001 and as loose as .004. In an aluminum block the mains could get as loose as .006 at temp. If I remember Rod Hendrickson's engine is over .004 on the mains. For the most part I have settled in at .0025 / .0025 on a 455. I do take in consideration as to what the engine will be used for, so clearance may vary a bit. There is a possibility towards this fall that we may have a HP style main bearing available for the 455 Buick, for sale. Years ago I for one was into tight oil clearances, I ran .0015 on my aluminum rods in the wagon and was somewhat successful until I pulled into the water box on a cold Bowling Green KY day after sitting in the staging lanes to long. That's when oil temp gauges started showing up on Buick race cars because I pushed it on everyone. As time went on I realized that this wasn't the only answer. I started on the cam bearings which evolved into what we have today. Most of you don't even know the trouble we had with keeping cam bearings in one of these engines. The current TA1559 cam bearing doesn't dump the oil like a stock bearing, leaving more oil heading to the crank. I started installing what I called a rear bypass line. It tied the pressure sender port into the passenger rear lifter gallery creating a loop. Poston wanted me to make those for him, I never did. Poston not being an engine builder or ever seeing what I was doing thought because I called it a rear bypass line he started selling kits that connected the two lifter galleries at the rear of the block. This was during the time there was a lot of cam bearing failures and if you installed one of his kits you would have no idea if you lost the cam bearing's in the engine. Without his line the driver side lifters would not oil and get noisy, you would know. Otherwise with his line you could run the cam down to the block without hearing noisy lifters. I don't recommend tying those galleries together by the way. My findings on some of this discussion have been a little different. I have found some FM HP bearings to have more eccentricity than some Clevite's. On one engine I was testing on I was able to pick up 10 lbs of idle oil pressure installing a Clevite over an FM. I think I tried two different sets of FM std and .001 and two styles of Clevite as well. I had a low idle oil pressure thing going on. Ended up with the Clevite's. The TA timing cover has helped us a tremendous amount in the oil pressure department. I have tried the others, both V6 and V8 and they are not holding the machine tolerances that are held at TA and it shows. On the aluminum turbo V6 Buicks I was setting the mains up at .0016-.0018. After inspection / after a few 750 hp rear wheel dyno pulls. The bearings looked dark grey in color. I ball mic'ed them and they were exactly the same thickness as a new FM set off the shelf. NO wear at all. I really didn't care for the way they looked though so I added another .001 to them, now I'm at .0027-.0028. This is a 2.500 main journal. Once the car was back together I thought the idle oil pressure would be a lot less but it wasn't. This engine had one of our timing covers which could have made that happen. The reason I added clearance to this engine, even though the bearings measured perfect, they were getting burnished as I call it. I was concerned that the owner may get excited one day getting on the freeway with the oil not up to temp and want to feel 750 hp. Remember, these things run well when there cooler. Anyway thats when a bearing can get hooked and I wanted to prevent that.
    If your interested in more defined information, feel free to call me at the shop.
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  11. Thumper (aka greatscat)

    Thumper (aka greatscat) Well-Known Member

    Great explanation Mike, and info from years of experience. We also run the tighter clearances,have been for years. By the way,those cam bearings were a Godsend, after a season of racing with stock bearings we typically had to replace them to stay on the safe side.Especially the front one,the higher oil pressures would wipe it out,then the noise on the driver side would occur.
  12. Staged70Lark

    Staged70Lark Well-Known Member

    Has anyone ever checked a main journal cold vs hot? For example... a journal when the block temperature is at 30 Fahrenheit verses 120 Fahrenheit?
  13. TA Perf

    TA Perf Member

    You will need to do that, never gets that cold here in SUNNY, WARM, DRY Scottsdale Arizona. I don't have a fridge or a freezer that large. I have check pin clearance at 18 fahrenheit, you better have .0005 to be safe.
  14. Staged70Lark

    Staged70Lark Well-Known Member


    I had a feeling that comment was coming! And deserved lol. But dont ask for any of my Great Lakes water.

    I actually have done this test. The clearances were .0007 to .0008 tighter when the block is cold. The April, May, September, October months can be very cold here in Ohio!

    Great discussion by all. I have learned quite a bit reading the responses! It seems the design phase is quite important when building an engine.
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  15. race0

    race0 Active Member

    Out of curiosity, what kind of clearances are you guys running for aluminum rods with a 2" rod pin..
  16. TA Perf

    TA Perf Member

    Well, I will tell you I'm running .003" in the wagon and it has a 2.100 pin.
  17. LARRY70GS

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

    This is the bearing clearances in my 470. JW takes the time to put a "Motor book" together for every engine he builds. It's a really great resource to have for reference. I realize not every shop does this. Thanks Jim.

    StagedCat and Julian like this.
  18. Bens99gtp

    Bens99gtp Well-Known Member

    That's great info to have for ones motor for sure. Great to know where you exactly starter when it comes apart too see if or how much wear it has undergone
  19. Jim Weise

    Jim Weise EFI/DIS 482

    Your welcome Larry..

    Aluminum rod clearance depends on a lot of factors.. and those are best discussed with your engine builder. Some of those factors are oil weight used, how you run the car at the track (starting line temps) and how much power your making.

    Rods are generally pretty forgiving, I have ran between .0023 and .0028 successfully on a 2.200 journal over the years.

  20. Philip66

    Philip66 Well-Known Member

    Ok, it has been well established that as the clearances go up or down then the oil chosen should do the same. Is there a set starting point to help guide that decision? Kind of like the formula for figuring clearances based on journal diameter...

    .0010" of clearance per inch of shaft diameter

    Looser---Thicker Tighter---Thinner

    As usual there is probably the same variables: intended usage, fill or no fill, compression, rollers or stamped steel, roller cam or flat tappet, induction type, fuel type, oil pump style, etc. But it would still be nice to have a place to start for viscosity choice.

    Tell me what you use for oil with your bearing clearances, maybe also include the type of oiling system you use or prefer...

    As always, I appreciate everyone's input, I value your opinions, and I thank you for your time!


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