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Old 01-23-2010, 10:49 PM   #1
Manic Machinist
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Default On-line Bob-weight calculator?

Any body know where there is an on-line bobweight calculator ?
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Old 01-24-2010, 01:57 AM   #2
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Default Re: On-line Bob-weight calculator?

I don't know of any online, but I'd be happy to help if you like. I've balanced over 10,000 engines, or I can send you a copy of my work sheet, so you can easily do it yourself
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Old 01-24-2010, 08:31 AM   #3
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Default Re: On-line Bob-weight calculator?

10,000 engines? That's one a day, every day, for over 27 yrs. You've been busy....LOL. How or what is a bobweight calculator? How would someone know what your particular piston, pin, rod, rings weigh?
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Old 01-24-2010, 09:10 AM   #4
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Default Re: On-line Bob-weight calculator?

The inline 4 & 6 cylinder cranks we have balanced have needed no bob weights.
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Old 01-24-2010, 09:25 AM   #5
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Default Re: On-line Bob-weight calculator?

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The inline 4 & 6 cylinder cranks we have balanced have needed no bob weights.
My only experience with balancing a crank is paying someone like you to do it for me. My understanding was you always had to have a bob weight. What is it about the 4 & 6 cylinder cranks that doesn't require a bob weight? I think I know but am curious if I am correct or not.
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Old 01-24-2010, 10:01 AM   #6
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Default Re: On-line Bob-weight calculator?

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My only experience with balancing a crank is paying someone like you to do it for me. My understanding was you always had to have a bob weight. What is it about the 4 & 6 cylinder cranks that doesn't require a bob weight? I think I know but am curious if I am correct or not.
The throws are 180 degrees apart but rods and pistons should be weight matched..

We have balanced some pretty big deseil cranks and I can't imagine making a bob weight to fit those cranks.
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Old 01-24-2010, 12:27 PM   #7
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Default Re: On-line Bob-weight calculator?

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Originally Posted by CNC BLOCKS View Post
The throws are 180 degrees apart but rods and pistons should be weight matched..

We have balanced some pretty big deseil cranks and I can't imagine making a bob weight to fit those cranks.
Did you think he said in line bobweights when he said on line bobweights or were you just saying in line needs no weights.
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Old 01-24-2010, 01:57 PM   #8
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Default Re: On-line Bob-weight calculator?

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Did you think he said in line bobweights when he said on line bobweights or were you just saying in line needs no weights.
Good catch!!
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Old 01-24-2010, 02:57 PM   #9
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Default Re: On-line Bob-weight calculator?

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Originally Posted by CNC BLOCKS View Post
The throws are 180 degrees apart but rods and pistons should be weight matched..

We have balanced some pretty big deseil cranks and I can't imagine making a bob weight to fit those cranks.
That's what I thought. Thanks!
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Old 01-24-2010, 04:49 PM   #10
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Default Re: On-line Bob-weight calculator?

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Originally Posted by toolmakeron View Post
I don't know of any online, but I'd be happy to help if you like. I've balanced over 10,000 engines, or I can send you a copy of my work sheet, so you can easily do it yourself
Man, that would be great.

2350 grams seems a common rough balance point, and I wanted to figure out what type of recipricating assembly it takes to make up a 2350 gram bob weight. I would guess that 2350 grams is slightly more than a typical H-beam rod/ forged piston bobweight. Would that be correct?


toolmakeron, could you send me the file or pic of a worksheet or let me know where its available?


How much do you guys add for the weight of the oil. Isnt this a theoretical value?
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Old 01-24-2010, 04:54 PM   #11
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Default Re: On-line Bob-weight calculator?

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Did you think he said in line bobweights when he said on line bobweights or were you just saying in line needs no weights.

LOL, that was ON-line, like, www.bobweightcalculator.com.

It would be cool if there was a bobweight calculator like Diamond Pistons compression calculator. Just fill in the blanks, and it spits out the answer.

.....but hey, I dont mind doin' it on paper.
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Old 01-24-2010, 10:07 PM   #12
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Default Re: On-line Bob-weight calculator?

Hi Maniac Machinist.I will send the worksheet to you as soon as I can . Basically,you add up the rotating weight of the con rod with the weight of the rod bearing set.Now multiply it by 2, then add 4 grams of oil allowance weight (6 grams for bbchev )to this .Put this # aside for now. Add the piston/pin weight with the reciprocating rod weight, also add the ring set weight & pin clips or oil ring support ring (if used). This weight is added to the rotating #'s previously saved. this will be your bobweight #'s to be used. Hope I haven't left anything out. Any questions, please don't hesitate to call me (403) 277 0505 .Consider checking out my website,at custombalancing.com Thanks
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Old 01-24-2010, 10:20 PM   #13
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Default Re: On-line Bob-weight calculator?

Hi Real McCoy, yes I have balanced over 10,000 engines, from go-karts, to funny cars.My record to date is 13 balances from Fri.night through the weekend to Mon. a.m..Not 1 easy small block in the bunch.I have just finished balancing a weird cummins 8 cyl diesel/ compressor (oilfield) engine . The crank weighs 200 lbs.I had to make up the bobweights to (are you sitting down?) 10,500 grams! This has been my longest , hardest balance to date. Including some r&d , due to huge imbalance problems, I've got about 70 hours into it.It was so badly out of balance, that the crank was bouncing up from the machine , more than 1 inch! Talk about shitting your pants! Can't show pictures of it without customers permission.I'll ask them this week if they mind. Some of you guys might have a good laugh.
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Old 02-05-2010, 03:48 PM   #14
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Default Re: On-line Bob-weight calculator?

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Originally Posted by toolmakeron View Post
Hi Real McCoy, yes I have balanced over 10,000 engines, from go-karts, to funny cars.My record to date is 13 balances from Fri.night through the weekend to Mon. a.m..Not 1 easy small block in the bunch.I have just finished balancing a weird cummins 8 cyl diesel/ compressor (oilfield) engine . The crank weighs 200 lbs.I had to make up the bobweights to (are you sitting down?) 10,500 grams! This has been my longest , hardest balance to date. Including some r&d , due to huge imbalance problems, I've got about 70 hours into it.It was so badly out of balance, that the crank was bouncing up from the machine , more than 1 inch! Talk about shitting your pants! Can't show pictures of it without customers permission.I'll ask them this week if they mind. Some of you guys might have a good laugh.
Far out! That's something I'd like to see!
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