Slant Six Forum :: Paging Doc or SSD

Quote:

you will also have to send them at least one piston / con rod assembly so they can get the weight. (unless you already know the "bob-weight" value)

I've heard all about doing this when rebuilding a motor, but is it really that critical to pull one or could my bro just let this float as is without them knowing the weight? Would it really screw thing up and what would be some consequences be? I'll pass this along, Thanks!

Wait a moment, this seems way too obvious. Isn't the purpose of the counterbalance to offset the effects of piston / con rod assembly? So, if you don't know the bob weight, how in the world would you be able to know what your counterbalance weight should be? The shortcut you're proposing seems a bit like flying blind.- Erik

Author:	69a100 [ Tue Aug 30, 2011 11:33 pm ]
Post subject:	Paging Doc or SSD
A couple years ago one of Doc builds had pics of where he ground the snot out of a crank and I'm trying to find that topic with the pics of before and after and not having much luck. Please help. Thanks

Author:	raPoM [ Tue Aug 30, 2011 11:37 pm ]
Post subject:
Did you check this http://www.slantsix.org/forum/viewtopic.php?t=23314

Author:	Doc [ Wed Aug 31, 2011 8:15 am ]
Post subject:
Are you trying to lighten a crankshaft? DD

Author:	69a100 [ Thu Sep 01, 2011 1:32 am ]
Post subject:
No, not really Doc. My brother has a 383 that the moron builder put different pistons in than what my brother wanted, and through the course of doing other stuff getting the engine ready he discovered that the block would stop at a certain postion with a clunk. Took the both of us forever to figure out what was up. Come to find out that the counter weight was hitting the piston skirt on a piston. After tons of tallk with people they said just grind the journal till you get .050 clearence, we did grind till we got clearance, and took another swipe just to CYA for clearance. I figure we ground less than a Oz. if even that off the edge of the weight to get there. Brothers worried that upon fire up the amount of mis-balance from grinding will cause the motor to garnade or just vibrate to death, I can't blame him for that. He's thinking on spending tons of bucks for different parts to make this all work. Should he not worry about it, fire it up and go? Should he yank the crank and grind all the slag, flashing, etc from it and have it spun balanced for his piece of mind? Buy new crank and pistons so he knows it's right? Go with whatever advice you say? Thanks BTW- I found the pics I was looking for finally, it's these. http://www.slantsix.org/forum/viewtopic ... ing+cranks

Author:	Doc [ Thu Sep 01, 2011 8:33 am ]
Post subject:
Me... I would pull-out the crank, tape-up all the journals and do a complete deburring job on it, then have the crank rebalanced. Here is the "pain".... you will also have to send them at least one piston / con rod assembly so they can get the weight. (unless you already know the "bob-weight" value) This applies to "V" engines only, not our in-line six. Send the stuff to Motor Warehouse in Sac., they do good work. ( say "Hi" to DK for me.) DD Link to MW Contact info. Link to a "Shop Tour"

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Author:	69a100 [ Thu Sep 01, 2011 9:08 am ]
Post subject:
[quote="Doc"]Me... Here is the "pain".... you will also have to send them at least one piston / con rod assembly so they can get the weight. (unless you already know the "bob-weight" value) [quote] I've heard all about doing this when rebuilding a motor, but is it really that critical to pull one or could my bro just let this float as is without them knowing the weight? Would it really screw thing up and what would be some consequences be? I'll pass this along, Thanks!

Author:	mpgFanatic [ Sat Sep 03, 2011 10:02 am ]
Post subject:	have i had enough coffee yet?
Quote: Quote: you will also have to send them at least one piston / con rod assembly so they can get the weight. (unless you already know the "bob-weight" value) I've heard all about doing this when rebuilding a motor, but is it really that critical to pull one or could my bro just let this float as is without them knowing the weight? Would it really screw thing up and what would be some consequences be? I'll pass this along, Thanks! Wait a moment, this seems way too obvious. Isn't the purpose of the counterbalance to offset the effects of piston / con rod assembly? So, if you don't know the bob weight, how in the world would you be able to know what your counterbalance weight should be? The shortcut you're proposing seems a bit like flying blind... - Erik

Author:	69a100 [ Sat Sep 03, 2011 10:49 pm ]
Post subject:	Re: have i had enough coffee yet?
Quote: Quote: Quote: you will also have to send them at least one piston / con rod assembly so they can get the weight. (unless you already know the "bob-weight" value) I've heard all about doing this when rebuilding a motor, but is it really that critical to pull one or could my bro just let this float as is without them knowing the weight? Would it really screw thing up and what would be some consequences be? I'll pass this along, Thanks! Wait a moment, this seems way too obvious. Isn't the purpose of the counterbalance to offset the effects of piston / con rod assembly? So, if you don't know the bob weight, how in the world would you be able to know what your counterbalance weight should be? The shortcut you're proposing seems a bit like flying blind.- Erik .. I don't think so! I've rebuilt a few other V8's in my day and never had a problem before worring about anything being balanced. I don't the factory ever worried about it that much either in the history of making engines! Besides, tell me what is the job of a harmonic balancer????

Author:	Jeb [ Sun Sep 04, 2011 5:54 am ]
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Generally if you change pistons, rods, etc you have to get your rotating assembly rebalanced. The job of the "harmonic balancer" is to absorb minor vibrations, it can't handle the big vibration that comes from an out of balance rotating assembly. I know I had to get my 383 rotating assembly balanced. Changing the pistons alone throws off the factory balance job. Yes, the factory engines were "balanced" to a certain extent. They knew the bob weight of the pistons and rods they were installing in the engines.

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