So I now the 2.8's (at least the earlier ones anyway) are externally balanced. I always thought that meant that the flywheel is balanced with the rest so that you cannot just replace the flywheel. Is this true or can you actually replace the flywheel if you have a prblem with it??

I noticed on mine (85 2.8) it also has a lot of drill holes around it too.

So can you replace them with no balancing issues??

 

I would think you can't... let us know what you find out!

 

A guy at one of the machine shops said you can as the new one has the weight on the back too. He had an explanation for the drill holes but I couldn't quite get the jist of it. I find that kind of weird that every one would have the exact same weight on it.....wouldn't there be variances on the weights of the internals from one to the other? Not quite sure, I don't understand it enough yet.

 

its just a difference of whether the crank is balanced or the flywheel is balanced, i believe. its not engine specific, all 2.8 mills have the same balance requirements, 87+ handle it internally, pre 87 are balanced through the flywheel. so ordering a direct replacement flywheel for your year and model will provide you with a correctly balanced flywheel.

 

ok, cool, thanks. I did not know that.

 

not really clear on what you are asking, but you can replace the flywheel with another as long as you replace it with the same one, whether you have an internally or externally balanced engine. If you have an internally balanced engine, but have an externally balanced flywheel just grind the counterweight off and take it to a machine shop and make sure it's balanced.

 

I'm confused-

If the 81-86 2.8's were externally balanced on the flywheel, then how could you just order up another 81-86 flywheel?

Wouldn't that flywheel then have to balanced with the crank?

I can't see them off-balancing every 81-86 crankshaft the same way from factory... it's gotta be unique to the engine ... ?

 

THat's why I am confused about the drillholes too I wouldn't think that they come pre-drilled like that from the store, because then why the weight on the back??

 

every factory engine component is created as a clone of an original prototype. they are made within certain specifications, and so each engine is identical to some level of statistical significance(probably around 97.5% or greater). create a prototype crankshaft that is balanced to all the prototype engine components, and recreate all those components exactly, and you will create more identically balanced engines. theoretically (and practically) all the engines are balanced within the oem tolerances. Now you would have a very hard time finding a factory 2.8 that was precisely balanced(it would take quite the stroke of inordinate luck), but it is possible, and all the 2.8's you will find will be balanced within oem tolerances.

creating an unbalanced engine works the same way, all the factory pre-87 2.8s will be identically unbalanced(within tolerances), therefore a prototype flywheel that balances the prototype engine will yeild production flywheels that will adequately balance any production 2.8.

If all engines came precisely balanced from the factory, there wouldnt be much point in blueprinting and balancing an engine yourself would there? and if gm was paying people to balance each and every individual engine it put out . . . well, it wouldnt be a mass producer, thats for sure. Ferarri may do it, but you dont pay 300k for a pontiac firebird, now do you?

youre right, they couldnt offbalance every crankshaft the same way, they just made them all exactly the same as the first one.

 

Naft,
So if I understand you correctly, the weight on the back of the flywheel would be the same on every flywheel (up to 86), right??

What about the drill holes and holes where they added weight. Would that be the same on every one too? You should see mine, it has probably at least 15 drill holes on it. I am just confused as to why the holes when there is the weight on the back. From your explanation is sounds like they would just have to make a flywheel with a certain weight on it and then make them all the same. Wouldn't the holes kind of defeat the purpose of the weight??

 

the holes in the back are what balance the crank, if its off balance you have to take weight off a certian area to balance it out, same thing with a car rim, why do they only put a wight on 1 spot?

because it balances it out

 

Yes, but on a car rim the balancer tells you that you need "x" grams at "y" position on the wheel (one weight). On the flywheel there is one weight on the back (same principal). However, on the front there are several drill holes around the diameter in several different locations and even a couple holes where they plugged them with heavier material. Almost as if the thing was balanced again???

 

you just answered your own question, they did the exact same thing they did to your rim, just on the flywheel in different way

 

my neutrally balanced flywheel has those same holes, some just drilled holes, some drilled holes filled with material. Theoretically if they made my flywheel perfectly round, it should already be neutrally balanced. For whatever reason, that obviously didnt happen, otherwise my neutrally balanced flywheel wouldnt be covered in irregular holes/fillings. Those holes are not to balance your flywheel with the crank, they are to balance the flywheel itself.

This allows flywheel manufacturers to create one base flywheel, and modify it to use with a variety of applications. So your pre 86 flywheel is exactly the same as mine, but with weight added on the back to balance it to the crank on your engine. This way the flywheel manufacturer can use that flywheel and modify it for any application that requires the same diameter flywheel.

id be willing to bet $$ that if i took a picture of the front of my flywheel and you the front of yours, they would have identical holes/fillings.

 

So THe weight on the back is in relation to balancing with the crank.....gotcha, that makes perfect sense.......but are you saying that the holes then neutrally balance the flywheel itself?? Sorry, but I am still confused. If you need 10 grams at 6 o'clock to balance it with the crank, then you go and drill holes at 9 o'clock and 3 o'clock taking out material, won't this affect the original balancing with the crank??

 

they do all the frontside drilling and stuff before they ever balance it to the crank. i'm not sure why they need to put all those holes in it(it seems like they could get the job done with just 1 hole or weight), but im sure they know what they are doing, and im sure they are all the same.

 

Ahhh, never thought of it that way, balance it first and then to the crank. That makes sense.

Do you happen to have a pic of yours?? It would be really interesting to see if they are indeed the same.

 

i dont . . . clutch and bell are all torqued down and everything, its too late now(well, has been too late for a week or two). i could take a picture of the picture on the box, but i doubt the picture on the box is the actual unit, its just a reman flywheel.