[AMC-list] Match Balancing

["Bruce Hevner" <scramblr@xxxxxxxxxxx>]

First of all I don't mean to inflame,, only inform,, so I hope all on the
list take my comments that way.

 

Of course you all can do with your motors as you wish,, it's the American
way. BUT to make a blanket statement that match balancing is always reliable
just isn't so in my book. 

 

But when it comes to balancing I think I've probably got as much info as
anybody to put out there and do it for the good of others who don't.

 

There are simply TOO MANY UNSEEN VARIABLES when it comes to balancing. How
about these,,, 350 or 305 crank?? These cranks carry THE SAME PART NUMBER
since they are the same stroke. Visually THEY LOOK THE SAME. USUALLY the 350
usage has deeper holes on the end counterweights,,, but not always,, how ya
gonna know if that STOCK crank is 350 or 305?? Boy I've seen plenty of those
be wrong over the years.

 

How about that 302 ford setup,, are the balancer and flexplate 28oz or50oz,,
for use with the heavy counterweight or lightweight crank? These can USUALLY
be told apart by sight but are you sure?? If anything rebuilding a stock
motor (unless ALL the parts are reused or checked for balance against the
replacements) can be just as "iffy" as HP stuff. 

 

Got a bad rod that needs replacing?? How close is the "reman" rod to the
original?? I have seen reman rods be as much as .035+ shorter than the
others in the set. That should make it lighter, and usually does, don't know
till you check it.

 

Had a customer bring in a 455 Olds from a jet boat. Someone else had built
the engine , he had bought it as is. After running it for awhile it started
having some bearing knock at idle "and always ran kinda rough". Oil looked
good so he didn't suspect bad bearings. Tore it down and the rear bearing
had a LOT of wear on it. This thing used what looked like a regular straight
drive flywheel probably at least 40lbs but had special adapter to drive the
propulsion unit. . I imagine that was to smooth it out at idle and help keep
it from revving up to quickly if it got out of the water. I checked all the
parts and got ready to spin the assembly up but WHOA!!! This thing would
find the heavy spot all by its own in the balancer!! A little investigation
showed they had the wrong flywheel on it! It should have had an light spot
for the external balance but was straight up. I HAD to do some machine work
on that flywheel do to unavailability of a correct one. The customer was
informed and gave the go ahead. He was amazed at how smooth that thing was
when finished and took my shop out for an afternoon ski trip on the local
lake!!!

 

You are right that some engines are drilled in the balancer at the factory
to get engines into final spec for balance. It's called "force balancing" if
I remember correctly. They attach a sensor to the motor which measures
imbalance and then "tweak" the assembly by drilling the balancer. Once again
there's no way to know if this has been done without checking your assembly
and in this case a replacement balancer could actually make it worse but
they don't take enough weight out to cause major headaches.

 

In my shop we BALANCE EVERYTHING or have the customer sign a waiver that he
has declined a balance check and accepts the engine assembly as is. It just
not worth NOT doing it. Heck with the availability of inexpensive digital
scales it's not as expensive as it used to be to set up at LEAST for
checking rods and pistons. Couple of hundred bucks will do it. Good profit
center and shows customers you are into "the balancing act".

But HEY,,, that's just ME!

Bruce Hevner

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