Flywheel balance

Almost everything I read says to make sure and mark the flywheel in relationship to the crankshaft so it can be replaced in the same position it was removed.

If I remove a flywheel take it and have it resurfaced and I assume (possibly in ignorance) this would include balancing Why would it have to be replaced in the same position (o'clock let's call it) as it was removed? What other relationships am I leaving out of the equation?

Also is there a difference between the 71-75 258 flywheels and the 76 - up 258 flywheels?
KSA

 

Some flywheels help to balance the crankshaft (external or "Detroit" balance) and some don't (internal or "neutral" balance). It depends on the design of the engine. The AMC V8s have Detroit balance flywheels that are specific to their displacement. The AMC inline 6s have neutral balance flywheels that will work on any AMC inline 6.

AFAIK if you remove a Detroit balance flywheel, there's only one way that it will go back. It has to be indexed to the crankshaft somehow. I don't think it's neccessary with a neutral balance flywheel, but they too may be indexed.

Re this issue, I would do what the factory service manual tells me. If it says nothing about indexing the flywheel, then there's only one way it will go on, or it doesn't matter.

 

One thing I'd like to add is during a flywheel resurface they do not re-balance anything. Because they are remove a very slight amount of material evenly from the surface of the flywheel it doesn't affect balance. Nickmil

 

Well I'd like to call an "oops" factor to mine and not having done that. But... I just dropped off my engine at the machine shop and the fella told me that it's possible to rebalanced the crank to the wheel. This is correct right?

 

My 74 AMC manual has a note

"On manual transmission equipped cars, (sic) the fly wheel is balanced as an individual component and also as part of the crankshaft"

and then further more states:

"Do not attempt to duplicate original flywheel balance holes when installing a service replacement. Service flywheels are balanced during manufacture.

Now the first note does provide some insight into the "system" but if it's balanced as a component what do they do to further balance it as part of the crank.

The second part is sort of scary. If you have to say it somebody must have tried it!!

KSA

 

From the 40 or 50 clutches I've changed out over the years, my opinion is that marking the flywheel keeps you from fumbling around with 40 pounds of iron dangling over your head while you're trying to figure out how to get the bolts back in. At one time the flywheel may have been balanced to the crank, but I bet that hasn't been true, outside of racing, for 50+ years.

 

With regards to "balanced to the crank" I'd have to agree. Thinking about the mass production process and quality control (especially, AMC I owned several in the 70's) I would find it hard to believe that there was that much attention paid to such niceties as that. I had a 78 232 new off the lot that had a casting fault in the block and seeped oil out the side of the engine. I'll bet the guy that put that engine together wasn't too concerned about matching crankshaft to flywheel.

But; you never know!!

KSA

 

I was just rereading my reply and I'm sure there's more than one person wondering about the bolt comment. I've never seen a flywheel that has a symmetrical bolt pattern. There's always one bolt hole that is a bit off. Marking the flywheel and crank makes it a lot easier to make sure the flywheel is rotated correctly on the first try.