Should I rebalance it??
+ Reply to Thread
Page 1 of 2 1 2 LastLast
Results 1 to 14 of 24

Thread:
Should I rebalance it??

  1. #1
    Distinguished Member David 519's Avatar
    Join Date
    Jan 2008
    Location
    NorCal
    Posts
    5,754

    Default Should I rebalance it??

    We are going back together with basically the same combo after our rod "mishap". Same pistons and crank, but a new set of rods (Callies Compstars we think). The new rods total weight are within a gram of our old ones. However, the small end is 10 grams lighter and the big end is 10 grams heavier. Seems with the piston/pin/small end total weight around 1170 grams (not counting rings/spiro locks), 10 grams differance isn't much in a 7000 RPM combo... What do ya'll think...

  2. Remove Advertisements
    PerformanceBoats.com
    Advertisements
     

  3. #2
    Senior Member VAMI's Avatar
    Join Date
    Jul 2008
    Location
    srq,florida
    Posts
    282

    Default

    Run It

  4. #3
    Senior Member ol guy's Avatar
    Join Date
    Mar 2008
    Location
    Lake Elsinore Ca
    Posts
    3,814

    Default

    Quote Originally Posted by David 519 View Post
    We are going back together with basically the same combo after our rod "mishap". Same pistons and crank, but a new set of rods (Callies Compstars we think). The new rods total weight are within a gram of our old ones. However, the small end is 10 grams lighter and the big end is 10 grams heavier. Seems with the piston/pin/small end total weight around 1170 grams (not counting rings/spiro locks), 10 grams differance isn't much in a 7000 RPM combo... What do ya'll think...
    I personally would have the rods balanced if that is all that has changed. An average balance job gets the whole reciprocating mass within a quarter gram and normally closer. Its apart why take it apart again because of an odd vibration. CHEAP INSURANCE. IMO. M

  5. Remove Advertisements
    PerformanceBoats.com
    Advertisements
     

  6. #4
    Senior Member MACHINEHEAD1's Avatar
    Join Date
    May 2008
    Posts
    473

    Default

    I would run it. Not that you should.

  7. #5
    Senior Member wagspe208's Avatar
    Join Date
    Apr 2008
    Location
    waterloo
    Posts
    2,034

    Default

    Well, since you take 100 percent of the rotating weight (big end) and 50 percent of the reciprocating weight..you do the math. 10 grams per rod=20 g per rod throw. Now, subtract the 10g for the reciprocating end (5g per rod). (remember 50 percent reciprocating)
    Will this rattle your teeth. Hell no.
    Is it right? Hell no. (not huge either)
    Are you planning on running 8000 rpm?
    Just food for thought.
    Wags
    Oh, and don't forget the black magic of balancing. Some guys like to use 51 percent or 52 percent of reciprocating. Some guys use 3 or 4 g of oil allowance, some use 6 or 7.

  8. #6
    Senior Member VAMI's Avatar
    Join Date
    Jul 2008
    Location
    srq,florida
    Posts
    282

    Default

    not sure i follow your math.when i balance pistion ,pin,rings,oil 3grms,1 small end,2 big ends and 2 sets brg and keepers if apply add up,divide by 2,bob wt is 2200 each half is 1100,sometimes a customer will 1 percent over balance on recricating only high rpm.now v6 with 6 crank pins use 36.6 percent nothing is doubled.iv seen stock rods be 15 grams off and balenced to 25 grams.i get mine down to 5 and depends on the engine and mood iam in sometimes under 1 gram.

  9. #7
    Distinguished Member David 519's Avatar
    Join Date
    Jan 2008
    Location
    NorCal
    Posts
    5,754

    Default

    OK, it took a bit longer to get to the point Steve and Vami are bringing up than I thougt it would; calculating the bobweight. Seems everyone does it differently, yet no one seems to be able to explain which way is best/why. That's where the magic in crank balancing seems to be.... And I hate magic.....
    In my day job/career, I've done lot's of balancing of large plant equipment. And there are accepted standards for residual imbalance of different types of equipment. If a client tells me he ground 10 grams off a rotor of some type, I can do some basic calcs and tell him how much vibration that will result in. Given that there are millions of engines out there, seems there should be standards for calculating the bob weight as well.... meaning no magic to it... Maybe I'm wrong.
    Finally, FWIW, this engine should never see over 7500 RPM...

  10. #8
    steelcomp was here
    Join Date
    Dec 2007
    Location
    n/e TN
    Posts
    26,280

    Default

    If you trust your machine shop to do the balance up to your own standards, then I would guess whatever method they use would be acceptable. I don't see why you wouldn't re-balance unless you have time or financial constraints that won't allow it. Remember, weather it's actually measurable or not, the more imbalance, the more parasitic drag and HP loss. FWIW.
    If God is your co-pilot, change seats!
    Acts 2:38, the perfect answer to the perfect question.

  11. #9
    Distinguished Member David 519's Avatar
    Join Date
    Jan 2008
    Location
    NorCal
    Posts
    5,754

    Default

    Quote Originally Posted by steelcomp View Post
    ......I don't see why you wouldn't re-balance unless you have time or financial constraints that won't allow it. ......
    Man steel, when you put it like that, I guess it seems kinda dumb not to....

  12. #10
    B1 Racing cs19's Avatar
    Join Date
    Dec 2007
    Posts
    6,523

    Default

    I would re balance. Doesnt hurt to double check things.

    Hope to see ya in Sept. David.
    B1Racing.net

  13. #11
    Senior Member ol guy's Avatar
    Join Date
    Mar 2008
    Location
    Lake Elsinore Ca
    Posts
    3,814

    Default

    Quote Originally Posted by cs19 View Post
    I would re balance. Doesnt hurt to double check things.

    Hope to see ya in Sept. David.
    You don't need to rebalance whole motor. Crank, f/wheel and dampner are balanced separate from the rods. As are the pistons. Have the rods balanced and save a buck. Once the pin end and journal end weight the same it's all good. IMO. M

  14. #12
    steelcomp was here
    Join Date
    Dec 2007
    Location
    n/e TN
    Posts
    26,280

    Thumbs up

    Quote Originally Posted by ol guy View Post
    You don't need to rebalance whole motor. Crank, f/wheel and dampner are balanced separate from the rods. As are the pistons. Have the rods balanced and save a buck. Once the pin end and journal end weight the same it's all good. IMO. M
    Exactly right.
    If God is your co-pilot, change seats!
    Acts 2:38, the perfect answer to the perfect question.

  15. #13
    Senior Member ol guy's Avatar
    Join Date
    Mar 2008
    Location
    Lake Elsinore Ca
    Posts
    3,814

    Default

    Quote Originally Posted by steelcomp View Post
    Exactly right.
    Thanks steel. I hate to see guys throw money away.

  16. #14
    Senior Member wagspe208's Avatar
    Join Date
    Apr 2008
    Location
    waterloo
    Posts
    2,034

    Default

    Quote Originally Posted by VAMI View Post
    not sure i follow your math.when i balance pistion ,pin,rings,oil 3grms,1 small end,2 big ends and 2 sets brg and keepers if apply add up,divide by 2,bob wt is 2200 each half is 1100,sometimes a customer will 1 percent over balance on recricating only high rpm.now v6 with 6 crank pins use 36.6 percent nothing is doubled.iv seen stock rods be 15 grams off and balenced to 25 grams.i get mine down to 5 and depends on the engine and mood iam in sometimes under 1 gram.
    Yes...50 percent per throw (rod throw, not per cylinder) of reprocatring. That is what you are doing. Tanking two big ends (100%) rotating per rod throw. 1 piston, 1 pin, 3g oil, 1 set of rings (this is 50% of ther total weight on that rod throw).

    I think we are..no, if I read your post correctly, I know we are on the same page.
    Wags

+ Reply to Thread
Page 1 of 2 1 2 LastLast

Quick Reply Quick Reply

Register Now

Please enter the name by which you would like to log-in and be known on this site.

Please enter a password for your user account. Note that passwords are case-sensitive.

Please enter a valid email address for yourself.

Please select your insurance company (Optional)

Log-in

Tags for this Thread

Digg This Thread

Posting Permissions

  • You may post new threads
  • You may post replies
  • You may not post attachments
  • You may not edit your posts
  •  
 

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95