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How did AMC balance our motors?

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rang-a-stang View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote rang-a-stang Quote  Post ReplyReply Direct Link To This Post Topic: How did AMC balance our motors?
    Posted: Oct/18/2018 at 2:22am
So, out of curiosity, how did AMC balance our engines during assembly? I am assuming they did not match piston and rod weights, did not spin up each crank with dampers, flexplates/flywheels, and weights attached. I am assuming they weighed a certain amount of piston/rod/pin/rings and came up with an approximation of the reciprocating mass, then just calculated how much counterweight they had to deal with, right? Maybe made some adjustments when piston/rod/crank lots changed?

When I had my 401 balanced, a couple months ago, I was pretty amazed at how much work my bottom end needed to come into balance. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Fluffy73 Quote  Post ReplyReply Direct Link To This Post Posted: Oct/18/2018 at 3:38am
Pistons and rods were weighed. Approximate weights were sorted into groups.
Cranks were balanced separately to be within a certain tolerance.
Flywheels/Flexplates and Harmonics were within an allowable spec.

These engines were mass-produced, not blue printed. As long as weights were within a certain range, "Good Enough" was the order of the day.

That's why most engines are externally balanced or, "Detroit Balanced".  To my knowledge, only Chrysler had internally balanced engines.  But even then, everything was within allowable spec.
I am genetically incapable of being Politically Correct.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Lucas660 Quote  Post ReplyReply Direct Link To This Post Posted: Oct/18/2018 at 6:44am
Originally posted by Fluffy73 Fluffy73 wrote:

Pistons and rods were weighed. Approximate weights were sorted into groups.
Cranks were balanced separately to be within a certain tolerance.
Flywheels/Flexplates and Harmonics were within an allowable spec.

These engines were mass-produced, not blue printed. As long as weights were within a certain range, "Good Enough" was the order of the day.

That's why most engines are externally balanced or, "Detroit Balanced".  To my knowledge, only Chrysler had internally balanced engines.  But even then, everything was within allowable spec.



Gen 1 V8's are internally balanced.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote farna Quote  Post ReplyReply Direct Link To This Post Posted: Oct/18/2018 at 7:54am
The engines were spun up after assembly for a final balance. Then the dampener was drilled if necessary to get a close balance.  Flywheel could be drilled on a manual car, or even the flexplate. The engine was cranked and run, it was attached to a machine that spun it with an electric motor at the crank (not the starter!) and spun. Someone who worked at the engine plant told me about this once, can't recall who or when now. No clutch or torque converter attached. Don't know exactly how the Gen1 internally balanced motors were done, assume something similar (but crank was drilled to balance).  As noted, most of the machined parts are within a few grams of each other in weight. You can do a "mini balance" just by weighing pistons (with rings and wrist pin) and matching all to the lightest within a couple grams and each end of the rods the same. That helps.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote FSJunkie Quote  Post ReplyReply Direct Link To This Post Posted: Oct/19/2018 at 4:38am
For considering yourselves AMC fanatics, you certainly don't give the company much credit. American Motors built some of the best engines of any company in this country. This isn't General Motors where engines were slapped together and close enough balance was good enough balance. 

From the 1956 SAE technical paper titled, "The New American Motors V-8 Engine" describing the design and production process of the Gen-I AMC V8: 

"The crankshaft is then assembled in the engine with connecting rods, pistons, piston pins, piston rings, flywheel, and crankshaft pulley attached. This assembly is then corrected for the 7.5 oz-in. left by the initial balancing, plus variations due to weight and balance tolerances of the attaching parts. The correcting is done by drilling two 15/16 in. diameter holes radially into the periphery of the No. 1 and No. 8 cheeks, with the location and depth of the holes varying with the amount of correction needed. The left portion of Fig. 17 (above) plots the vectors representing the various corrections obtainable due to location and depth of drilling, and a 3.66-oz-in. circle to cover the permissible component variations. This final operation balances the engine assembly to within a maximum tolerance of plus or minus 1/2 oz-in."

From the 1967 SAE technical paper titled, "American Motors Typhoon V-8 Engines" describing the design and production process of the Gen-II AMC V8: 

"Among the "quality built-in" features of this engine
are two in particular that merit attention.....our "mass-balancing" of the
engine assembly. In this system, final balance is accomplished
on an engine assembly containing all
rotating and reciprocating weights. This is accomplished
on automated equipment; and final total engine
unbalance is maintained at less than .5 oz.-in.,
front and rear."


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Post Options Post Options   Thanks (0) Thanks(0)   Quote 401MATCOUPE Quote  Post ReplyReply Direct Link To This Post Posted: Oct/19/2018 at 6:31am
Matthew (FSJunkie) sure glad you stepped in here...AMC did a fantastic job of balance on the Gen 2 engines...I have little expereince with Gen 1 engines.....after disassembly of several NOS engines, the latest being a 1973 401, they use paint daubs for weight selection of parts internally.  After discussing this process with one of the operators of the balancing equipment in the 1970's, he said they had pretty strict requirements to the amount of "trim" balance they were allowed to do on the rotative balancing machine.  That was to make sure that replacement front dampeners and flywheel/flex plates that had to be field replaced could be done and the engine would still be in balance limits.

My personal experience after building and balancing over 100 Generation 2 engines is aftermarket pistons, poorly ground crank shafts (not ground on exact crank pin centerlines...I can tell you horror stories on that alone), internal timing gears, replacement Chinese flywheels, flex plates, dampeners...even rebuilt dampeners all CAN build up to make an AMC engine require a lot of crank mallory metal to get back.  Plus our 50+/- year old engines have had some sinful things done to them, parts swaps, conversions...all back when no one really cared about anything but the engine running.  I can't tell you how many seemingly "Dead" AMX/Javelin's I have bought with major vibration problems and every single one was after a clutch change....only to find out the flywheel was replaced with a 6 cylinder unit....swap the correct flywheel from known source back in and down the road she goes.

If you really have interest in build methodology and quality, as Matt is quoting from, those SAE papers are worth the read...you will find out that AMC had the dog leg head port design in work in 1967!!!!   That have a ton of great detail, that I have seen no other manufacture ever come close to letting out the door.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote farna Quote  Post ReplyReply Direct Link To This Post Posted: Oct/19/2018 at 6:50am
My description follows what the SAE paper says, more or less. The paper doesn't say how the front and rear corrections were made, only that everything was spun on automated equipment. The short block was assembled then spun. I don't know for sure if the cam and timing set were installed, but the SAE paper seems to indicate it was, as that is a "rotating weight".
Frank Swygert
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Steve_P Quote  Post ReplyReply Direct Link To This Post Posted: Oct/19/2018 at 9:45am
Many years ago, the CACI newsletter had a really good article on this which described the process, who built the balancing machine, etc- but the quote from the SAE paper sums it up.  And like Ross said, they could not go wild drilling the flywheel and damper because they had to be close enough so that a new replacement could be installed and be satisfactory.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote White70JavelinSST Quote  Post ReplyReply Direct Link To This Post Posted: Oct/19/2018 at 10:09am
I'm curious how the oiling was achieved for the short block assemblies that were spun balanced by the factory.

Cam and lifter oiling before crank and cylinder bore? How did that work to spin up a short block assembly?

If the lifters weren't in?? If they were in, could they move out of their bore ?

?????
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Post Options Post Options   Thanks (0) Thanks(0)   Quote FSJunkie Quote  Post ReplyReply Direct Link To This Post Posted: Oct/20/2018 at 5:00am
I had a machine shop balance my last 360. Virgin engine that had never been apart. I installed new pistons, rings, bearings. Rods reconditioned, crank polished on the rod journals, .010" on the main journals. Reused original balancer and flex plate. 

They didn't remove much material from the crank but they sure removed a lot from the big ends of the rods. Kind of scary, actually. I worry it makes the rods weaker. I wonder why they removed so much material. Surely the rods could not have been that far off each other in mass. Surely the new rod bearings could not have ben that much heavier. I don't think you're supposed to remove material from the rod big ends to correct from the different reciprocating weight of new pistons. 

I think I'll call and ask. 


'66 Marlin: 327/T10/3.54 Twin Grip
'72 Wagoneer: 360/TH400/3.31
'73 Ambassador: 360/TF727/3.15
'77 Hornet: 232/TF904/2.73
'84 Eagle: 258/TF998/2.35
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