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I purchased a dissassembled 3869942 4 bolt mains block with a 454 crank and balanced pistions. I bought it in pieces with 1 bad pistion which had detonated. If I reassemble this can I use the factory correct balancer and what does the correct balancer look like? The 66 judge manual says 1 3/4 x 8 inches in diameter and nothing else, I have 1 with those measurements am I correct? Should I buy a new 427 crank or can I use this crank with my blancer or should I get the correct balancer?? Thanks for any advice.
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Re: 66 427/425 Crankshaft Balancer Identify??
Bill-----
If you use the 454 crankshaft, then you have to use a counterweighted balancer. From the front and side it looks just like the 8" 427 balancer. From the rear, it looks different. The balancer hub will have a cast-in weight which will appear as a "hump" for about 1/3 of the balancer hub's circumference.
If you change the crank to a 427 crank, then you would use a 427 balancer which has no counterweight.
There are various balancers for both 427 and 454 engines. However, the balancer that you should use will have the same, basic dimensions regardless of whether you use a 427 or 454 balancer. Both will be 8" OD and have a thickness of 1-3/4".In Appreciation of John Hinckley -
if you want to keep the 454 crank you can
get the rotating assy internaly balanced and then you could use the 427 balancer and flywheelComment
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Re: 66 427/425 Crankshaft Balancer Identify??
Thanks Joe, I am going to check that, would the engine have run with the wrong balancer. Would my corect balancer have any part #'s on it?Comment
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Re: 66 427/425 Crankshaft Balancer Identify??
Bill-----
Sometimes, the balancers will have a 4 digit derivative of the full part number stamped on the face somewhere. You can look for this. However, the counterweighted balancer is very easy to identify whther the balancer is on or off the engine.In Appreciation of John HinckleyComment
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Re: 66 427/425 Crankshaft Balancer Identify??
My engine machinest said that the crank and pistons had been previously balanced, he is going to double check that. But my crankshaft balancer does have an extra casting hump inside the circle. Could I not use that and buy a correct balancer and it would then judge correctly? What would be the correct part number and is it still avaliable from gm?Comment
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Re: 66 427/425 Crankshaft Balancer Identify??
if the engine has a damper with a offset weight on the back side it is a external balanced set up and you also need a flywheel with a offset weight to complete the setup.Comment
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Re: 66 427/425 Crankshaft Balancer Identify??
Bill------
If the balancer has the counterweight (i.e. "hump"), then the engine is likely an externally balanced engine. All PRODUCTION 454 engines were externally balanced. The fact that the engine was previously balanced probably just means that it was precision balanced, but as an externally balanced engine. Both internal and external balanced engines can be precision balanced as part of an engine "blueprinting". In order to maintain the precision balance, you have to keep all of the balanced components together. That means the whole reciprocating assembly----crank, rods, pistons, harmonic balancer, and flywheel. If you change any of them, then you have to have the whole thing rebalanced.
As clem mentioned, you can convert an externally balanced engine to internal balance. This would allow you to use the internally balanced harmonic balancer and flywheel with a 454 crankshaft. However, doing this is expensive since mallory metal usually has to be used to balance the crankshaft. I would say that it's not worth it just to use a balancer without the counterweight. You could, of course, convert the engine to a 427 by changing the crankshaft and pistons. That might be a big expense, too, just to get rid of the counterweighted harmonic balancer. But, that could be done.
Anyway, the 8" SHP 427 balancer is GM #3860010 and remains available from GM. The L-88/ZL-1 balancer is also available and is GM #3879623. This balancer is physically identical to the 3860010 except that it is tuned for the different crankshaft and higher RPM operation of the L-88/ZL-1.
The 8" 454 balancer is currently GM #10216339. It's identical to the above except for the counterweight.In Appreciation of John HinckleyComment
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Re: 66 427/425 Crankshaft Balancer Identify??
If you use all the old parts, you can keep the previously blanced parts and have the one new piston and rod balanced to the rest.
You cannot use the correct '66 425 hp balancer for judging because you need the 454 balancer for the engine to run without trying to tear itself apart.
Clem mentioned internal balancing. Your machine shop guy can do that, however, it is much more expensive because it involves drilling the crankshaft and installing heavy metal. But it is a way to build a 454 on the inside that looks like a 427 on the outside.
If you are concerned with judging, that is one way to go. The other is to build a 427. To do that, you need the 427 crank and the 427 pistons, so it is probably cheaper to internally balance the 454 to look like a 427 at this point for you.Comment
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