Change flywheel = Crank rebalancing?

[Floddy]

Well, Is this correct?

I'm thinking of getting an aluminium flywheel. I've heard that this would screw with the balancing of the crank?

And, if so, is the old URQ/100/200 flywheel (pictured in my previous thread here) so similar to the 3B unit, that I don't have to re-balance with that one?

[maRS2]

Just need to have a balance one
no need to balance with crank don't forget after the flywheel you got the gearbox holding to it so it not as bad as on the front with the cranck puley.

[Floddy]

Ok, so only reason for rebalancing is when swapping rods, pistons and/or belt pulley?

In that case - Sounds like music to my ears! Plan is to build a new bottom end next year (I know, I'm crazy), so I don't want to rip the engine apart before that...

[mcandmar]

Ok what if you were rebuilding an ABY and wanted to fit a 3B flywheel and pully, will i need to get it rebalanced?

Thanks,

Mark.

[Henka]

Well, yes. I mean, if the old flywheel and crank were balanced togehter, switching to a another flywheel might destroy it all (worst case). Now, if crank and flywheel were balanced separatly, problem, but not that much of a problem. If the original crank wasn't balanced, well, then it won't matter. What I mean is, if you paid to have a dual mass and a crank balanced togheter you'd through that cash in the toilet by replacing the flysheel to a 3B - you'd have to balance it all again... That's why you always balance everything separately.

[Floddy]

Now, if crank and flywheel were balanced separatly, problem, but not that much of a problem.

Why would that be a problem? If the crank is zero balanced without the flywheel, I don't see how a flywheel swap can mess anything up.

[mcandmar]

That was my next question, is the crank & flywheel balanced as a unit in the factory or do they just balance each part separately and then assemble them? ..are they a matching pair if you like?

[AnLe]

you should balance this in normal clutch repair also - no one does this. If you do it right, you balance it, but there is little consern in this matter if car is normal daily driver with little mods. There is reported over 9grams difference in std engines rods&pistons, my believe is, unless proven otherways, is that in the factory engines are built and balanced once whole packet, and differences between parts no longer matter.

When you balance i5 engine, it is done with all parts + counterweights, but before that, balancing the flywheen and dumper to "0" is very wice then you can change parts and remain perfectly balanced.

[Floddy]

Aww crap, I'll get a loan and build a new bottom right now instead!

I've emailed the company that did my balancing, it should be interresting to see what they say.

[AnLe]

dont take it so hard, just change the fly wheel and be done with it I dont think it is dead serious stuff, maybe consult to other builders, has anyone got problems with unbalanced engine, I have not heard anything, but that does not mean anything.

[Floddy]

The engine probably won't go more than 5-10k kilometers, and will probably be unsellable, so I don't really now why I even care. But what the heck, It has cost me some money, so I want it to be right!

[mcandmar]

Can somebody please explain the process of balancing the crank if you are changing the internals?

I'm going to have to go the custom piston route on my build, and will prob buy rods as it would be silly to rebuild everything else and leave the stock ones in there. So how do i do it? Do i need to work out weights for the complete piston/rod assembly, then make weights for the crank, attach flywheel and then balance that?

Thanks,

Mark.

[Billman]

Yes someone please tell us!

[Floddy]

Got the answer from the company that did the balancing on my crank today:
Flywheel is 0 balanced, straight swap if the new flywheel is 0 balanced.

That only applies on my car, though. Don't know how it is on yours.