Bob weigth
Thread Starter
Drifting
Joined: Jun 2001
Posts: 1,625
Likes: 1
From: Zagreb, Croatia
Bob weigth
I was calculating bob weigth and this is what I came up with
piston - 495g - reciprocating weigth
pin - 130g - reciprocating weigth
spirolocks - 2g - reciprocating weigth
ring set - 28g - reciprocating weigth
rod small end - 191g - reciprocating weigth
rod big end - 431g - rotating weigth
bearing - 46g - rotating weigth
I was using this formula: rotating weigth + 50% of reciprocating weigth
So I came up with bob weigth of 910g but since there are two pistons
per journal total bob weigth = 1820g
Can somebody verify my numbers?
I found some strange software, Maverick racing crank balance assistant
and according to it, my bob weigth shoul be 1600g????
Here is link to Maverick page and if somebody is interested, scroll
all the way down and download the software.
http://www.maverickracing.co.uk/crankbalsoft.htm
EDIT: It looks like my calculation was OK.
In software, piston weigth should be input
together with pin weigth.
piston - 495g - reciprocating weigth
pin - 130g - reciprocating weigth
spirolocks - 2g - reciprocating weigth
ring set - 28g - reciprocating weigth
rod small end - 191g - reciprocating weigth
rod big end - 431g - rotating weigth
bearing - 46g - rotating weigth
I was using this formula: rotating weigth + 50% of reciprocating weigth
So I came up with bob weigth of 910g but since there are two pistons
per journal total bob weigth = 1820g
Can somebody verify my numbers?
I found some strange software, Maverick racing crank balance assistant
and according to it, my bob weigth shoul be 1600g????
Here is link to Maverick page and if somebody is interested, scroll
all the way down and download the software.
http://www.maverickracing.co.uk/crankbalsoft.htm
EDIT: It looks like my calculation was OK.
In software, piston weigth should be input
together with pin weigth.
Last edited by Sliding; Jan 19, 2010 at 01:55 PM.
Drifting
Joined: Dec 2005
Posts: 1,360
Likes: 3
From: NORTHEAST
I was calculating bob weigth and this is what I came up with
piston - 495g - reciprocating weigth
pin - 130g - reciprocating weigth
spirolocks - 2g - reciprocating weigth
ring set - 28g - reciprocating weigth
rod small end - 191g - reciprocating weigth
rod big end - 431g - rotating weigth
bearing - 46g - rotating weigth
I was using this formula: rotating weigth + 50% of reciprocating weigth
So I came up with bob weigth of 910g but since there are two pistons
per journal total bob weigth = 1820g
Can somebody verify my numbers?
I found some strange software, Maverick racing crank balance assistant
and according to it, my bob weigth shoul be 1600g????
Here is link to Maverick page and if somebody is interested, scroll
all the way down and download the software.
http://www.maverickracing.co.uk/crankbalsoft.htm
EDIT: It looks like my calculation was OK.
In software, piston weigth should be input
together with pin weigth.
piston - 495g - reciprocating weigth
pin - 130g - reciprocating weigth
spirolocks - 2g - reciprocating weigth
ring set - 28g - reciprocating weigth
rod small end - 191g - reciprocating weigth
rod big end - 431g - rotating weigth
bearing - 46g - rotating weigth
I was using this formula: rotating weigth + 50% of reciprocating weigth
So I came up with bob weigth of 910g but since there are two pistons
per journal total bob weigth = 1820g
Can somebody verify my numbers?
I found some strange software, Maverick racing crank balance assistant
and according to it, my bob weigth shoul be 1600g????
Here is link to Maverick page and if somebody is interested, scroll
all the way down and download the software.
http://www.maverickracing.co.uk/crankbalsoft.htm
EDIT: It looks like my calculation was OK.
In software, piston weigth should be input
together with pin weigth.
ROD ROTATING 431
ROD ROTATING 431
ROD BEARING 46
ROD BEARING 46
OIL ALLOWANCE 4
PISTON AND PIN 625
LOCKS 2
RINGS 28
ROD RECIPROCATING 191
__________________________________
TOTAL BOB WEIGHT IS 1804
You left out for oil but this should help give me a fax number and I will fax a BOB WEIGHT card to you
Everything on the pin end is singular and everything on the big end is double, Oil allowance may very between engine builders on SBC we use 4 grams and on BBC we use 6 to 8 grams depends on the size of the pistons.
Hope this has helped
Carl
Last edited by BLOCKMAN; Jan 19, 2010 at 03:04 PM.
Drifting
Joined: Jun 2007
Posts: 1,261
Likes: 2
From: Prather, California -1990 ZR-1 White/Flame Red- -SOLD!!-
Thread Starter
Drifting
Joined: Jun 2001
Posts: 1,625
Likes: 1
From: Zagreb, Croatia
Our BOB WEIGHT CARDS ARE AS FOLLOWS
ROD ROTATING 431
ROD ROTATING 431
ROD BEARING 46
ROD BEARING 46
OIL ALLOWANCE 4
PISTON AND PIN 625
LOCKS 2
RINGS 28
ROD RECIPROCATING 191
__________________________________
TOTAL BOB WEIGHT IS 1804
You left out for oil but this should help give me a fax number and I will fax a BOB WEIGHT card to you
Everything on the pin end is singular and everything on the big end is double, Oil allowance may very between engine builders on SBC we use 4 grams and on BBC we use 6 to 8 grams depends on the size of the pistons.
Hope this has helped
Carl
ROD ROTATING 431
ROD ROTATING 431
ROD BEARING 46
ROD BEARING 46
OIL ALLOWANCE 4
PISTON AND PIN 625
LOCKS 2
RINGS 28
ROD RECIPROCATING 191
__________________________________
TOTAL BOB WEIGHT IS 1804
You left out for oil but this should help give me a fax number and I will fax a BOB WEIGHT card to you
Everything on the pin end is singular and everything on the big end is double, Oil allowance may very between engine builders on SBC we use 4 grams and on BBC we use 6 to 8 grams depends on the size of the pistons.
Hope this has helped
Carl
I made a mistake and wrote 28g for rings, instead of 48g. Plus 4g
for oil should be 1824g total.
This is the weight that I gave to my machinist.
I live in Croatia and experience with SBC's here is almost zero.
So I'm trying to help my machinist, plus I'm making sure that everything
gets done right.
I'm really sorry that my poor spelling hurt you. I'm sure that you know
what I was refering to, as I'm sure that you know what g(gram) is
unit for.
Perhaps it would be less painful for you if I write it down in Croatian?!
Here you go:
Racunao sam koliki mora biti "bob weight" i evo do cega sam dosao:
klip - 495g - pravocrtna masa
bolcna - 130g - pravocrtna masa
spirolocks - 2g - pravocrtna masa
karike - 48g - pravocrtna masa
mali kraj klipnjace - 191g - pravocrtna masa
veliki kraj klipnjace - 431g - rotirajuca masa
lezaj - 46g - rotirajuca masa
Koristio sam slijedecu formulu: rotirajuca masa + 50% pravocrtne mase
Tako sam došao do "bob weight" 910g, ali posto su dva klipa na svaki
dosjed, totalni "bob weight" = 1820g
Moze li netko potvrditi moje brojeve?
Better?
Racer
Joined: Sep 2007
Posts: 351
Likes: 1
From: Marysville OH
I know you are in Croatia, but it doesn't matter if you are in Mexico, Iceland, or the far side of the moon, the proceedure for figuring bob weight is the same for cross plane crankshafts no matter where you are.
If I had to tell my machine shop basically how to do their job I would sure as hell find a different shop.
How are you going to trust them for anything else?
If I had to tell my machine shop basically how to do their job I would sure as hell find a different shop.
How are you going to trust them for anything else?
Thread Starter
Drifting
Joined: Jun 2001
Posts: 1,625
Likes: 1
From: Zagreb, Croatia
I know you are in Croatia, but it doesn't matter if you are in Mexico, Iceland, or the far side of the moon, the proceedure for figuring bob weight is the same for cross plane crankshafts no matter where you are.
If I had to tell my machine shop basically how to do their job I would sure as hell find a different shop.
How are you going to trust them for anything else?
If I had to tell my machine shop basically how to do their job I would sure as hell find a different shop.
How are you going to trust them for anything else?
properly and to specs that I want. I love building engines and I like
to know as many details about it as possible.
One of them is how to calculate bob weight.
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Michael S. Palmer
Race Director
Joined: Apr 2003
Posts: 17,700
Likes: 1,667
From: moraga ca
Racunao sam koliki mora biti "bob weight" i evo do cega sam dosao:
klip - 495g - pravocrtna masa
bolcna - 130g - pravocrtna masa
spirolocks - 2g - pravocrtna masa
karike - 48g - pravocrtna masa
mali kraj klipnjace - 191g - pravocrtna masa
veliki kraj klipnjace - 431g - rotirajuca masa
lezaj - 46g - rotirajuca masa
Koristio sam slijedecu formulu: rotirajuca masa + 50% pravocrtne mase
Tako sam došao do "bob weight" 910g, ali posto su dva klipa na svaki
dosjed, totalni "bob weight" = 1820g
Moze li netko potvrditi moje brojeve?
Better?
Drifting
Joined: Dec 2005
Posts: 1,360
Likes: 3
From: NORTHEAST
Thread Starter
Drifting
Joined: Jun 2001
Posts: 1,625
Likes: 1
From: Zagreb, Croatia
this matter. You probably give whole rotating assemblly to machine shop,
or whole engine, or even the whole car and they just call you when it's
all done. Don't get me wrong, that's OK. Most of people do it that way.
I don't do it like that, but I'm sure that a lot of people on this forum also
don't. Why? For me it's two main reasons.
1. I enjoy working on my car.
2. It's easier on my finances.
When I wrote that I'd like to help my machinist, I didn't mean that I'll
tell him how to balance. But if I give him just bob weight, he'll have
less work to do and I'll save some money, plus I'll enjoy while doing it.
I have tools needed to do some of the work, so why not to do it?
I've weighed pistons, pins, rods..... and used the lightes parts as
reference for bob weight, and I'll do some work on other parts to get
them all to same weight.
That's really not similar to telling doctors what to do. At least not to me.
Racer
Joined: Sep 2007
Posts: 351
Likes: 1
From: Marysville OH
That is hardly the same thing. You obviously have a different view on
this matter. You probably give whole rotating assemblly to machine shop,
or whole engine, or even the whole car and they just call you when it's
all done. Don't get me wrong, that's OK. Most of people do it that way.
this matter. You probably give whole rotating assemblly to machine shop,
or whole engine, or even the whole car and they just call you when it's
all done. Don't get me wrong, that's OK. Most of people do it that way.
LOL.....I have built more engines than most of the posters here combined.
And I would never just drop off a crank at the machine shop with a note on bob weight.
Whatever floats your boat.
Instructor
Joined: Dec 2009
Posts: 111
Likes: 1
if you have the tools to measure weight whats the difference between you doing it and the guy who gets $12 an hour to do it.
