Topic: Do engines need to be balanced


MOXIE    -- 10-14-2009 @ 4:00 PM
  I’m trying to decide if I should spend the extra bucks to have my 21-stud engine balance. I remember 10 years ago I had a small block Chevy engine balanced and I could not tell a dime’s worth of difference. Do most of you balance.




CharlieStephens    -- 10-14-2009 @ 4:35 PM
  I had the 21 stud in my '37 balanced. The shop said it was way off but I didn't run it before. When it was finished it was one of the smoothest early Ford motors I have ever had and I assume that balancing was the reason.

Charlie Stephens


ford38v8    -- 10-14-2009 @ 10:06 PM
  I'm kinda far afield here, as I'm not a machinist nor an engine builder,
but I'm going to wing it: Engine balancing is a relative term, which
applies to several different operations. A crankshaft can be balanced
by means of drilling on the heavy side of the counterweights. Flywheels
in much the same way, but with clutch mounted. an altogether
different type of balancing is done with the piston/rod assembly, in
which piston/rod assemblies are matched by weight in pairs. This is a
careful mating of similarly weighted parts, involving only a scale and
patience. these mated pairs are then mounted to offset each other's
weight in the spinning engine, thus eliminating excessive vibration. I
believe that any good re-builder would not consider assembling an
engine without performing this operation.

Alan


51f1    -- 10-15-2009 @ 3:31 AM
  No, it doesn't have to be balanced. However, I had my 8RT balanced, and it runs extremely smooth. I wouldn't rebuild an engine w/o having it balanced.

Richard

This message was edited by 51f1 on 10-15-09 @ 3:35 AM


47Fordor    -- 10-15-2009 @ 4:15 AM
  Forgive my ignorance: I'm just getting into the engine rebuild game. What exactly are you referring to when you say "ballance"?

Chris


trjford8    -- 10-15-2009 @ 7:59 AM
  It's not that much more monney to balance a motor. I had two flatheads balanced and the both ran so much smoother it was well worth the money.Make sure they balance the flywheel and pressure plate as a unit.


supereal    -- 10-15-2009 @ 10:02 AM
  At our shop, we balance all engines that we rebuild as a part of the complete job. Each piston and rod assembly is weighed, and a "bob weight" with an equal amount is placed on the rod journal. The crankshaft is then spun as a gauge measures for any out of balance condition. A drill press mounted on the machine is used to modify the counterweights until the vibration disappears. Any off balance of a rotating part will likely show up as a periodic vibration in a completed engine. Some require little adjustment, while others really shake. Be sure to ask the place offering engine rebuilding if they include balancing. If they say it isn't necessary, I'd look elsewhere.


CharlieStephens    -- 10-15-2009 @ 11:44 AM
  Chris,

When you balance an engine you (probably the shop you hire to do the work) go through and weigh each moving part and then grind or machine off or weld on weight. When you finish all of the pistons weigh the same (how close they are to the same depends on how much money you spend). You balance each end of the rods separately. You balance the counterweights on the crankshaft. When something rotates like the flywheel clutch and pressure plate you must add or remove weight based on how far the weight is from the center of rotation (a good analogy is balancing the tires on your car). If you are really thorough you balance the crankshaft pulley. I wouldn't build an engine without having it balanced.

Charlie Stephens


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