Crankshaft balancing question?
Thread Starter
Melting Slicks
Joined: Oct 2000
Posts: 2,019
Likes: 2
From: Na
Crankshaft balancing question?
Can a cranshaft be balanced to a flexplat/damper without the rods, postons, etc.? Reason I'm asking is I need to have my flexplate balanced to my crank (400ci crank) and do not want to remove the engine to do it. Is this possible?
Drifting
Joined: Jul 1999
Posts: 1,337
Likes: 0
From: Brighton, MI
Re: Crankshaft balancing question? (NUckINg FuTS)
I don't think it is, unless you already know the exact bobweight of each piston/ring/bearing assembly. What about the crankshaft? You would need that out too. Do you not have a previous flexplate that is the correct balance that you can have match balanced?
Le Mans Master
Joined: Feb 2000
Posts: 9,715
Likes: 27
From: Kempner Texas
Re: Crankshaft balancing question? (NUckINg FuTS)
Can a cranshaft be balanced to a flexplat/damper without the rods, postons, etc.? Reason I'm asking is I need to have my flexplate balanced to my crank (400ci crank) and do not want to remove the engine to do it. Is this possible?
Are you trying to balance the flexplate to the crank or the crank to the flexplate?
The first part of your question has you balancing the crank to the flexplate, but in the second part you're balancing the flexplate to the crank.
Jake
Thread Starter
Melting Slicks
Joined: Oct 2000
Posts: 2,019
Likes: 2
From: Na
Re: Crankshaft balancing question? (JAKE)
Here's the scoop. I bought this 383 shortblock used. Anyway the engine originally used a flywheel not a flexplate. The original flywheel was not availible with the engine to have it match balanced when I bought it. So the engine has been balanced previously. I bought a 400ci flexplate and bolted that on but now my engine vibrates very badly in the low RPM range. I don't know much about the balancing process so I guess my question is can I have the flexplate balanced to my crank with only taking the crack out??? :crazy: :smash:
Drifting
Joined: Jul 1999
Posts: 1,337
Likes: 0
From: Brighton, MI
Re: Crankshaft balancing question? (NUckINg FuTS)
Don't think so. I'm no balancing expert either, but the rotating mass includes part of the piston weight. I can't remember what all off-hand makes up the "bobweight", but when a spin balance is done they will attach a weight to the crank throws that matches the bobweight, thus simulating a complete rotating assembly. Not sure if that is the only method out there, but is what I have seen. You would need at least one piston/rod/ring set out. To get it perfect, guys will weigh all 8 and have 8 different weights. There probably isn't much difference between them, but you never know.
Le Mans Master
Joined: Feb 2000
Posts: 9,715
Likes: 27
From: Kempner Texas
Re: Crankshaft balancing question? (93Quasar)
I don't think so either. You might want to check with a machine shop to see what, if there's anything they can do.
It would be best if you could contact the shop that actually balanced the engine to see if they still have the bob-weight chart for the engine components.
I've been racking my brain on this point, but can't recall: Is it possible to installed the flexplate on a 400 crank in more than one position?
I know there should be a dowel pin coming out of the back end of the crank so the flexplate can be properly indexed, but if that pin ISN'T there (which sometimes happens), is it possible that the flexplate can be bolted out of sync?
If all the holes in the back of the crank are equally spaced, then the flexplate can be installed in any one of several different positions. This could cause an imbalance and vibration.
I just can't remember how the holes are spaced though. Hope someone will help me out on this one.
Jake
It would be best if you could contact the shop that actually balanced the engine to see if they still have the bob-weight chart for the engine components.
I've been racking my brain on this point, but can't recall: Is it possible to installed the flexplate on a 400 crank in more than one position?
I know there should be a dowel pin coming out of the back end of the crank so the flexplate can be properly indexed, but if that pin ISN'T there (which sometimes happens), is it possible that the flexplate can be bolted out of sync?
If all the holes in the back of the crank are equally spaced, then the flexplate can be installed in any one of several different positions. This could cause an imbalance and vibration.
I just can't remember how the holes are spaced though. Hope someone will help me out on this one.
Jake
Racer
Joined: Mar 2004
Posts: 311
Likes: 0
From: Oakley Ca
Re: Crankshaft balancing question? (JAKE)
With no dowel pin you can bolt on the flex plate or flywheel in six different positions. You must line up the dowel holes. If the original flywheel were available it might be used to match up the balance on the flexplate. With out the original flywheel, the crank, one rod, one piston and one set of rings need to be sent to the balancer to get the bobweights right. Check the harmonic balancer at the front of the engine to see if it is indeed internal or external balanced. External balanced will have one side with extra weight that is roughly opposite the TDC timing mark. Some strokers are internal balanced. :cheers:
