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1981 xj650 bearing sizes crank and conrod

Discussion in 'XJ Technical Chat' started by mervyn, Jan 27, 2014.

  1. mervyn

    mervyn New Member

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    Hi I have tried to find out the various oversize specs for main and big end bearings from Yamaha ,but they can only order them via the manual which states green, yellow etc but cant tell me what size a colour represents .

    This is a project bike and if I cant sort the bearings and crank chrome and regrind Ill have to sell off as spares. the barrel has been rebored already with 0.o5 over size rings pistons etc and head done already ... just waiting to assemble . Bike was in storage for 11 yrs till I bought it this month .. spare carbs , drive shaft, new filters , gasket sets..everything waiting till crank and bearings are sorted . Can any one help with the standard oversize specs so I can give to engineers so they know how much to build up and re grind .
    Is there another motor that will bolt straight in and work with the shaft drive. Has anyone replaced main and big end bearings in the xj650 and are their oversize bearings if crank can be reground.?

    I live in S Africa --Durban Thx
    Mervyn
     
  2. TIMEtoRIDE

    TIMEtoRIDE Active Member

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    It's my understanding that the various colours refer to a VERY slight difference in dimension, not to an undersize spec. These are to fine-tune the main bearing clearance.

    Check with Chacal (XJ4EVER - upper right corner) for new bearings.

    I would think welding and re-grinding an XJ crank would be horribly expensive. You could just get one shipped in from Europe's E-Bay.

    You should consider re-assembly with your used bearings on your un-turned crank, if you don't exceed your maximum oil clearance.

    XJ750 "Seca" engines should drop in with little fuss, add 12 HP too.
    You would need to re-jet the carbs.
     
  3. mervyn

    mervyn New Member

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    Hi Thx for prompt reply. My research locally with fundi's and engineers contradict ea other . one says re-chroming and grinding wont last 100kms , others say they don't know what to work from cos we cant get the original measurements of the journals not even from Yamaha..
    Gets very technical.
    Apparently the diff colour codes in the manuals refer to each big end bearing ie no1, 2, 3, and 4 etc , Same applies for the main bearings of which there are 5 .
    Any way unless I can get another crank looks like I'll have to sell it off as spares , but there are very few owners here in SA.

    Do you know if its collectible by now and worth restoring to original or customise it . If it was original and cleanly painted here , would be in the R15000 price range which at R11 to the $ and R19 to the pound is peanuts.

    Any idea of how much a crank(standard, unworn ) would cost?. Suppose shipping would also be expensive. Bloody heavy.
    Thx
    Mervyn
     
  4. TIMEtoRIDE

    TIMEtoRIDE Active Member

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  5. chacal

    chacal Moderator Moderator Supporting Vendor Premium Member

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    Basically, engine bearing sizes were the way that Yamaha "blueprinted" the crank to the engine cases, and then the rods to the crank. This "blueprinting" is why the engines live so long and will happily run at 10K+ rpms all day.

    I've never heard of anyone "re-grinding" these cranks because:

    a) they rarely need it, and...
    b) as Mervyn mentions, the lack of specific crank bearing dimensions. But, even if you were to obtain those dimensions, there is still the issue of nominal crankcase bearing saddle and rod big-end dimensions that would also have to be obtained, as the two go together to determine clearance.

    You might possibly get away with a crank (or rod) swap by simply measuring (plastigage) clearances and adjusting to specified oil clearances (.04 - .064mm for the crank and .03 - .09mm rod) via trial-and-error (and an assortment of each size ("color") bearings), but that is a tough row to hoe.

    Of course the first thing to do is to measure the crankshaft run-out, which should be .04mm maximum.

    All of the above numbers apply to the 650 and 750cc engines; other engines may have different specs (the factory service manual will guide you in these numbers).


    Crankshaft Bearings:

    Yamaha used a unique way of "sizing" their engine bearings, both for the crankshaft main journal bearings and the connecting rod big-end bearings.

    The factory coded, via a series of numbers indicating a "size code", numbers onto the crankcase, the crankshaft, and the connecting rods.

    The crankCASE has numbers hand-scrawled onto the upper (and possibly the lower, also) engine case(s) ---typically, behind/below the stamped pad where the engine ID number is, behind the clutch cover opening, but, in reality, could be anywhere on the case(s) --- that specifies the main bearing saddle sizes for that particular engine case.

    The crankSHAFT will have two grouped sets of numbers on one end. The first set of 5 numbers are the main bearing journal size numbers for that crankshaft, and the second set of 4 numbers which denote the rod bearing journal numbers for that particular crankshaft. Both sets of numbers refer to the crank journals starting at the left side of the crankshaft (the #1 cylinder side).

    Each connecting rod also has a number that is stamped (with ink) on the rod itself, right where the upper and lower shells meet.

    To calculate the correct bearing sizes to use in a particular engine, you will go through the following process:


    Crankshaft Main Bearings:

    The correct main bearing selection is made by subtracting the crankshaft journal number from the engine case main bearing saddle size number, for each main bearing journal position.


    Connecting Rod Big-End Bearings:

    The correct bearing selection is made by subtracting the crankshaft journal size number from the rod size number, for each rod/crank journal position.


    For both the crank main journal bearings and the rod bearings, you will then use the numbers calculated above to realize a "bearing color" as outlined in the chart below. You would then order the correct "color" bearing for each crankshaft main journal or connecting rod big-end position:

    Bearing "Color Codes":

    #1 = Blue
    #2 = Black
    #3 = Brown
    #4 = Green
    #5 = Yellow



    Example:

    - Crankshaft is marked 21223 2111
    - Engine case is marked 34534
    - Rods are marked 6, 4, 3, and 3

    The first set of 5 numbers on the crankshaft (21223) are the main bearing journal sizes for that crankshaft, and are sequentially #1 to #5 as read. The corresponding 5 numbers scratched onto the engine case (34534) are the main journal saddle sizes for that engine and are sequentially #5 to #1 as read. For the #1 main journal position (the far left position), we would have 4 (on the engine case) - 2 (on the crankshaft) = 2. The #1 main journal bearing is a "size" 2, which is a "black" bearing.

    NOTE THAT THE HAND-SCRAWLED NUMBERS ON THE CRANKCASE READS JOURNALS #5 TO #1 as you read them left-to-right, and thus in a 5/4/3/2/1 sequence for the main journal bearing sizes! They are actually "backwards" from an intuitive approach (and "backwards" from the sequence they are coded onto the crank itself), but are "correct" in spatial orientation and sequence for the top crankcase half (since they are scrawled "reverse" in relation to the crankshaft position within the crankcase). Make SURE you (or your machinist) understands this paragraph completely before you start turning wrenches, buying bearings, etc.....it is easy to become confused (especially in regards to the mains).


    For the #1 con-rod, using the example above, you would use the 2nd set of numbers on the crankshaft (2111), and the ink-stamped number on the rod itself. So the #1 rod is stamped as 6, and the #1 crank rod journal is 2, and 6 - 2 = 4. Thus the #1 rod was use a "size" 4 connecting rod bearing, which is a "green" bearing.


    Notice that it is NOT unusual for a single crankshaft to use a variety of different "size" or "color" bearings.


    NOTE: The yellow "size" bearings are used only for crankshaft main journal bearings. Rod bearings were never made nor available in the yellow "size".

    IN ALL CASES YOU SHOULD REFER TO A FACTORY SERVICE MANUAL OR A SKILLED, EXPERIENCED MACHINIST AS TO HOW AND WHAT SIZE ENGINE BEARINGS THAT NEED TO BE PURCHASED AND USED DURING AN ENGINE REBUILD! DO NOT PURCHASE ENGINE MAIN OR ROD BEARINGS BASED ON THE "NUMBERS" ALONE----ALWAYS PLAN YOUR ENGINE REBUILD PARTS NEEDED ONLY AFTER ENGINE DIS-ASSEMBLY, PARTS MEASUREMENT, AND CONSULTATION WITH A MACHINIST.
     
  6. bmarzka

    bmarzka Active Member

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    Good Ole Len. Tells you everything you need to know and more. You're the best, dude. If it weren't for xj4ever, we would be a hurtin' bunch of puppies.
     
  7. bigfitz52

    bigfitz52 Well-Known Member Premium Member

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    Unfortunately, that's NOT everything you need to know which is the problem; and it's not Len's fault by any stretch.

    What was explained above is exactly what the factory manual says, explained so that you can halfway understand it. The PROBLEM is that nowhere, and that's NO freaking WHERE, in any book, does Yamaha let on as to what a #3 bearing is except "brown" or that a "brown" shell is a "#3." Oh I'm sorry, did you need a #2? That would be a black one.

    The other thing Len left out (probably out of sheer humility) is that he HAS most of the bearing shells available if you can figure out what you need.

    BUT: As soon as you "massage" a crank journal, does it still use a brown bearing? Or does it now need a black one, or a green one or ??? If it's a rod journal, do you have to paint a different number on the rod? :?

    Quite honestly, I don't know why Yamaha bothered. You could probably count the number of XJ motors that ever had "big-end" bearings done on the fingers of one foot (or the toes of one hand.) I think they were just trying to torture us.
     
  8. silversan

    silversan New Member

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    hi all . I new here ..want to ask ? do i need change this all crank bearing or do plastic gauge to check tolerance still in range .I want to replace all of this
     

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  9. a100man

    a100man Well-Known Member

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    Platigauge first and keep your fingers crossed. can you identify the colour codes on those shells - if not Len (above) summarised the situation with the immortal line..

    'that is a tough row to hoe'
     

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