Slant Six Forum :: Balancing bottom end

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Balancing bottom end https://slantsix.org/forum/viewtopic.php?t=27104	Page 1 of 1

Author:	Jopapa [ Sun Feb 10, 2008 1:24 pm ]
Post subject:	Balancing bottom end
When I return stateside, I'm planning to buy a '66 slant to install in my Duster. To mate it to a late model lockup 904, I'm going to swap out the crank with a later forged unit. Since I'll have the bottom end pulled apart, I'm going to have the "new" crank balanced at a local engine shop and I want to balance the pistons and conrods too. From what I've read, it's best to have a shop do the crankshaft, but since each piston and connecting rod assembly has to have the exact same weight, this can be done at home as long as you have an accurate scale (which I'll buy when I'm ready to start the work). Is this true, or will I save myself some aggravation by taking the piston and conrod assemblies to the shop to be balanced as well?

Author:	slantzilla [ Sun Feb 10, 2008 2:06 pm ]
Post subject:
A good shop will not balance one part without the rest.

Author:	Aggressive Ted [ Sun Feb 10, 2008 3:29 pm ]
Post subject:	Crank balancing
Jopapa, I tried that but the shop wanted everything. So they did all the balancing. I stood there and watched them.

Author:	runvs_826 [ Sun Feb 10, 2008 7:35 pm ]
Post subject:
If your good you can give them the numbers of each rod and piston combo weights. They than put that much weight on their balancer. It might be easier just to give it to them. The only way I would balance them myself is on the super cheap and not balance the crank dynamically.

Author:	Jopapa [ Mon Feb 11, 2008 7:04 am ]
Post subject:
Quote: A good shop will not balance one part without the rest. Makes sense. Can it be safely assumed that they'd want the complete rotating assembly from the engine, including flywheel, etc.?

Author:	66aCUDA [ Mon Feb 11, 2008 7:47 am ]
Post subject:
Dont forget to take your Harmonic Balancer in too. Thats how I found out I had a bad one. Unlike Charrlie who has them chase him accross the floor. Frank

Author:	Jopapa [ Mon Feb 11, 2008 7:55 am ]
Post subject:
Quote: Dont forget to take your Harmonic Balancer in too. Thats how I found out I had a bad one. Unlike Charrlie who has them chase him accross the floor. Frank That's the funniest picture I've had in my head all night. Running like hell from a posessed harmonic balancer...

Author:	66aCUDA [ Mon Feb 11, 2008 7:56 am ]
Post subject:
You ought to here Charrlie tell it. LMAO Frank

Author:	Doc [ Mon Feb 11, 2008 9:32 am ]
Post subject:
Just so we have all the facts... A SL6 crank is like a lot of "neutral balanced" cranks used in inline engines, this type of crank does not care what the piston / con rod assemblies weigh. (but these assemblies should all weigh the same or you defeat the purpose of balancing the crank) A crank in a "V" engine is different, you must know the weight of the piston / con rod assembly and add this amount of weight to the rod journals (bob-weights) before you balance the crank. It is true that most shops want to balance all the parts for you, mostly because that is how they have the job priced... doing all the parts as a group. This is done mostly because of the "bob weighting" needs on a V engine and the "do all the parts as a group" thinking carries over to all other applications. Bottomline... you can have a SL6 crankshaft dynamically balanced by it's self, I do this all the time. For an engine using a factory dampener, that item needs to be sent with the crank. Also the flex plate or flywheel should be balanced with the crank. Here is an interesting side note, you need to tell the shop to balance all the parts separately and you may need to pay a little more to have the balancing done this way. If you do not ask for this, the shop will do what I call a "Detroit balancing job" where they bolt all the parts together and balance the assembly in one shot, instead of first balancing the crank, then adding the dampener and balancing that part, then adding the flexplate / flywheel, and balancing again. You can see that the "add a part and rebalance" process will take more time but if you ever have to swap out a dampener or flywheel, you will be less likely to throw-off the engine's balancing. Truth is that on race engines that run an aftermarket dampener and an automatic trans (flex plate) I just send-out the crank for balancing seeing that the aftermarket dampener is already balanced and the flex plate has so little mass that it does not have much influence on the crank's balance. DD

Author:	Wizard [ Mon Feb 11, 2008 10:00 am ]
Post subject:
While running along with the balancing, what about the 4 cylinder crank? Balance with bob weights or neutral? Cheers, Wizard

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