Flywheel/Crank Balancing - Ducati.ms

italianpower · Jan 12th, 2011, 11:08 pm

So I decided (after convincing from a few other members) to try out a lightened flywheel. Bought a stock one from another member so I will machine down the diameter.

Anyways, I saw in the photo of it a hole drilled in the side. This has to be for balancing, right? So they balance the crank assembly by drilling the flywheel?

Has anyone done anything to re-balance after machining it down?

Decreasing Dave · Jan 12th, 2011, 11:56 pm

Yes. Well, not me per se, but it is done.

You need to speak with mark at DucShop. You should probably just let him do it for the $75.

Dave

italianpower · Jan 13th, 2011, 12:04 am

Quote:

Originally Posted by Decreasing Dave

Yes. Well, not me per se, but it is done.

You need to speak with mark at DucShop. You should probably just let him do it for the $75.

Dave

I'm not afraid of doing the work. I was just curious how people are rebalancing the crank assembly. The whole crank would have to be removed to do it right, which seems like too much work.

Decreasing Dave · Jan 13th, 2011, 12:20 am

Quote:

Originally Posted by italianpower

I'm not afraid of doing the work. I was just curious how people are rebalancing the crank assembly. The whole crank would have to be removed to do it right, which seems like too much work.

See now, you didn't say that specifically.

They/we are not balancing the crank assembly when we install new flywheels. Nothing changes on the crank except the flywheel so as long as it is balanced, everything should be as it was before you took the old flywheel off........except the bike will be more fun to ride, but that's a mere technicality.

Dave

italianpower · Jan 13th, 2011, 12:50 am

I did, last line of my OP. I'm definitely machining it down, just wanted to open up this topic because I have not seen anyone discuss it yet.

That's where I don't follow you though. You machined down the diameter, right? So that means the hole the factory drilled to balance it was machined off.

Of course the flywheel is balanced after being machined, it is round. But it appears Ducati is making the flywheel out of balance to account for the crank being out of balance, and cancel the two out. So by making the flywheel perfectly balanced now the whole assembly is not. But it is probably out of balance by so little it may not matter.

Decreasing Dave · Jan 13th, 2011, 1:08 am

Now I think you may be over-thinking this.

Your tires are round, are they balanced naturally??

Besides, it's not just taking down the diameter, you're taking meat out of the flywheel as a whole. The diameter actually stays relatively close to what the stock one is. it has to, your rotor has to bolt up to it. You are right in a way though, the heavy outer ring of the flywheel pretty much gets removed and of course that is where the balance hole is drilled.

This is where Mark can best help you. They machine them, and they balance them, so he should have the best explanation of "why". He has helped others before by giving them advice even though they did their own machining.

Plus, there is A LOT of posts on this subject so go get yourself a coffee and hit the search button. The posts from the guy that machined his own is out there somewhere too. I'm sure he'd be willing to offer any help you needed. I just can't remember who that was off the top of my head.

Dave

Johnb250 · Jan 13th, 2011, 6:43 am

The hole on original flywheels is for the ducati tool to lock it when removing/installing don't think its anything to do with balance.

Ducshop · Jan 13th, 2011, 9:10 am

Assuming the stock one is balanced. First thing is to make sure your Lathe is centered when clamping it, if it is off then it will start removing material off one side before the other throwing it off balance. As Johnb250 stated, they are holes for the holding tool.
We use a "shop" balanced crank, add the flywheel and re-check the balance.

The stock one is about 150mm in diameter and machined down to 110mm

italianpower · Jan 13th, 2011, 12:06 pm

John and Ducshop, thanks for the info. That's exactly what I was looking for.

08hyper · Jan 13th, 2011, 10:24 pm

When building my "Motor of Death II"

I had my crankshaft lightened, used lighter stronger Carrillo rods and had the crank assembly balanced, they did not use the flywheel during the balancing as Ducati flywheels are usually spot on, and since your cutting down the OD of the flywheel to lighten it, balancing of the flywheel becomes even less of an issue, & is not needed. Aloha Alex