Mixing bearings
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Mixing bearings

  1. #1
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    Default Mixing bearings

    On a BBC mains. Can a coated bearing half be mixed with a non coated half to get the clearance right?

    Tim

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    mo balls than $cents$ IMPATIENT 1's Avatar
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    i wouldn't do it, the coated bearing will have 2 ledges. try another brand, when clevites are tight, usually a king aceluar(sP?) or other brand will be a tad looser.

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    Senior Member wagspe208's Avatar
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    Or buy a set of x bearings..coated. Then you have two sets of bearings basically. Mix the extra clearance with the standard piece.
    Wags

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    Quote Originally Posted by wagspe208 View Post
    Or buy a set of x bearings..coated. Then you have two sets of bearings basically. Mix the extra clearance with the standard piece.
    Wags
    +1 what he said
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    Thanks guys. I kinda thought thats how it worked. These were Speed Pro. I'm running .010 under and couldn't get a coated x. Put in uncoated and it cam out right. I take it that it doesn't matter which half the x bearing goes in as long as it's consistant?

    Tim

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    With chamfered large radius bearings,(Clevie H bearings for instance) the upper and lowers are marked and must be used in their proper positions or the chamfer will be on the wrong side. On non chamfered bearings uppers and lowers can be installed in any position.TIMINATOR
    MODESTY IS A CRUTCH FOR THE INCOMPETENT!

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    steelcomp was here
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    Quote Originally Posted by River Rat 005 View Post
    Thanks guys. I kinda thought thats how it worked. These were Speed Pro. I'm running .010 under and couldn't get a coated x. Put in uncoated and it cam out right. I take it that it doesn't matter which half the x bearing goes in as long as it's consistant?

    Tim
    I might be misunderstanding this, but if you are running coated/non coated together, put the coated bearing in the rod, and the uncoated in the cap. Like Tim said, make sure uppers and lowers don't get mixed up.
    I'm not sure what I'd do in this instance AFA mixing the two. I know that the coating is very thin and does "wear in" and the edge at the parting line may only be tenths, but I also know that tenths in a bearing can be critical, and parting line issues are considerable when it comes to oil flow. That few tenths may act as a scraper on the lead side of the rotation and completely disrupt oil flow. It also may have no effect at all. I think I'd be tempted to put a set in a rod and torque it down and see just how it feels. If there's an edge you can feel with your finger, that's probably not good. Then the question would be what to do about it.
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    Bostick Racing Engines six-oh-nine's Avatar
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    Stupid question here... but couldn't you line hone the block to the size you need to get the clearance you want so long as it doesn't fall outside the housing range, that way you don't have to mix and match bearings?

    Is that an option?
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    Quote Originally Posted by six-oh-nine View Post
    Stupid question here... but couldn't you line hone the block to the size you need to get the clearance you want so long as it doesn't fall outside the housing range, that way you don't have to mix and match bearings?

    Is that an option?
    Woundn't that limit the block for future use ?

    S CP

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    you can run your clearances tighter with coated bearings. Or you can have your crank grinder clearance grind the the crank.

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    Bostick Racing Engines six-oh-nine's Avatar
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    Quote Originally Posted by Sleeper CP View Post
    Woundn't that limit the block for future use ?

    S CP
    If your chasing a few tenths then... no I don't think I'd worry too much about a block not being able to be reused because it happens to be on the high or low side of the housing spec... in the worse case. Any more than a few tenths... swap out for different bearings or if the journal is too big grind it.


    I've been sitting on this for a while now and guess I'll throw my .02 in...

    Typically what I have done when having a crank re-ground... and I know it is totally wrong because no one else here has ever mentioned doing this so it must be wrong despite never having an issue is:
    Line hone the block to the mid spec... as typically this it what is supposed to be the correct dimension (high and low are the + and - of this), or vary depending on how you wish to have the bearing crush, to make sure each and every housing is the same size... straight... and round (what a concept). Get what bearings you wish to run (-.010 for example) install them... measure the hole... subtract out the clearance you want... and have the crank ground to that size. If your crank grinder is worth a damn they can cut it to size and keep it to size. Now not only is everyting round and to size... but you have not artificially altered the crank centerline with mix and match bearings.

    Despite knowing or know of many people who do it on a regualr basis without issue, to the point of being a well accepted practice, I have never been a fan of the bearing swap around on mains unless it's done to all the journals the same. The main reason (no pun intended) is that you theoretically change the crank centerline on on the journal you mix the bearings on. Simplified example... #1 main you use std/std bearings... then #2 you use -.001/std... then #3 you use std/std. even though you dimensionally on the hole have each with the same clearance, lets say .002, you have altered the centerline of one journal in that instead of having .001 clearance on both sides of the journal as in journals #1 and #3, journal #2 now has .0015 on one side and .0005 on the other, despite all measuring out as having .002 clearance. Granted it doesn't work out EXACTLY like this as the bearings do have oil clearance and the crankshaft is not FIXED in place, with a fixed centerline, and my example doesn't address lateral clearance... but I believe this explains my point.

    I don't know if this is a machinest's view on an engine building practice or what... but I believe that when you have situations like this, in addtion to not line honing (because a 20,30,40 year old block should be straight, the factory holds "tolerance", and the crank turned nice when it came out) having crank grinders cut cranks all over the spectrum around, above, or below specs... so on and so forth all adds up to needing to run gobs of clearance to have an engine live.

    Sort of a long winded rant I suppose... but

    Btw Sleeper... You'd hate to know how much main clearance I run on the gullwing...
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    six is right on, he describes the proper conditions. With a new stroker crank, try different bearing brands to get correct clearance, or as we prefer, use.001 or x bearings in Clevite. TIMINATOR
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    Quote Originally Posted by six-oh-nine View Post
    If your chasing a few tenths then... no I don't think I'd worry too much about a block not being able to be reused because it happens to be on the high or low side of the housing spec... in the worse case. Any more than a few tenths... swap out for different bearings or if the journal is too big grind it.


    I've been sitting on this for a while now and guess I'll throw my .02 in...

    Typically what I have done when having a crank re-ground... and I know it is totally wrong because no one else here has ever mentioned doing this so it must be wrong despite never having an issue is:
    Line hone the block to the mid spec... as typically this it what is supposed to be the correct dimension (high and low are the + and - of this), or vary depending on how you wish to have the bearing crush, to make sure each and every housing is the same size... straight... and round (what a concept). Get what bearings you wish to run (-.010 for example) install them... measure the hole... subtract out the clearance you want... and have the crank ground to that size. If your crank grinder is worth a damn they can cut it to size and keep it to size. Now not only is everyting round and to size... but you have not artificially altered the crank centerline with mix and match bearings.

    Despite knowing or know of many people who do it on a regualr basis without issue, to the point of being a well accepted practice, I have never been a fan of the bearing swap around on mains unless it's done to all the journals the same. The main reason (no pun intended) is that you theoretically change the crank centerline on on the journal you mix the bearings on. Simplified example... #1 main you use std/std bearings... then #2 you use -.001/std... then #3 you use std/std. even though you dimensionally on the hole have each with the same clearance, lets say .002, you have altered the centerline of one journal in that instead of having .001 clearance on both sides of the journal as in journals #1 and #3, journal #2 now has .0015 on one side and .0005 on the other, despite all measuring out as having .002 clearance. Granted it doesn't work out EXACTLY like this as the bearings do have oil clearance and the crankshaft is not FIXED in place, with a fixed centerline, and my example doesn't address lateral clearance... but I believe this explains my point.

    I don't know if this is a machinest's view on an engine building practice or what... but I believe that when you have situations like this, in addtion to not line honing (because a 20,30,40 year old block should be straight, the factory holds "tolerance", and the crank turned nice when it came out) having crank grinders cut cranks all over the spectrum around, above, or below specs... so on and so forth all adds up to needing to run gobs of clearance to have an engine live.

    Sort of a long winded rant I suppose... but

    Btw Sleeper... You'd hate to know how much main clearance I run on the gullwing...
    Wow James,

    That seems like a lot of extra work for small investment like a boat engine

    That would seem to be the "Correct" way to do it but I'm not an engine builder so take that for what it's worth.

    S CP

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  16. #14
    steelcomp was here
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    Quote Originally Posted by six-oh-nine View Post
    If your chasing a few tenths then... no I don't think I'd worry too much about a block not being able to be reused because it happens to be on the high or low side of the housing spec... in the worse case. Any more than a few tenths... swap out for different bearings or if the journal is too big grind it.


    I've been sitting on this for a while now and guess I'll throw my .02 in...

    Typically what I have done when having a crank re-ground... and I know it is totally wrong because no one else here has ever mentioned doing this so it must be wrong despite never having an issue is:
    Line hone the block to the mid spec... as typically this it what is supposed to be the correct dimension (high and low are the + and - of this), or vary depending on how you wish to have the bearing crush, to make sure each and every housing is the same size... straight... and round (what a concept). Get what bearings you wish to run (-.010 for example) install them... measure the hole... subtract out the clearance you want... and have the crank ground to that size. If your crank grinder is worth a damn they can cut it to size and keep it to size. Now not only is everyting round and to size... but you have not artificially altered the crank centerline with mix and match bearings.

    Despite knowing or know of many people who do it on a regualr basis without issue, to the point of being a well accepted practice, I have never been a fan of the bearing swap around on mains unless it's done to all the journals the same. The main reason (no pun intended) is that you theoretically change the crank centerline on on the journal you mix the bearings on. Simplified example... #1 main you use std/std bearings... then #2 you use -.001/std... then #3 you use std/std. even though you dimensionally on the hole have each with the same clearance, lets say .002, you have altered the centerline of one journal in that instead of having .001 clearance on both sides of the journal as in journals #1 and #3, journal #2 now has .0015 on one side and .0005 on the other, despite all measuring out as having .002 clearance. Granted it doesn't work out EXACTLY like this as the bearings do have oil clearance and the crankshaft is not FIXED in place, with a fixed centerline, and my example doesn't address lateral clearance... but I believe this explains my point.

    I don't know if this is a machinest's view on an engine building practice or what... but I believe that when you have situations like this, in addtion to not line honing (because a 20,30,40 year old block should be straight, the factory holds "tolerance", and the crank turned nice when it came out) having crank grinders cut cranks all over the spectrum around, above, or below specs... so on and so forth all adds up to needing to run gobs of clearance to have an engine live.

    Sort of a long winded rant I suppose... but

    Btw Sleeper... You'd hate to know how much main clearance I run on the gullwing...
    I have the same problem sometimes looking at an engine from a (non automotive) machinist's point of view, and I agree in theory with everything you said fom a numbers on paper, static point of view, providing the crank and main bore is perfectly straight. However, that's seldom the case, and engines don't sit there with tolerances that cooperate like that, as miuch as we'd like them to. It's a dynamic environment and everything is constantly moving/changing.
    Just something to keep in mind.
    If God is your co-pilot, change seats!
    Acts 2:38, the perfect answer to the perfect question.

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