Rebuild opinions wanted!!

[trbig]

I am not out for drag racing, but the quicker throttle response and more power to the rear tire is definately an attractive option for me. Read the first couple paragraphs here.
Ape Racing

Some people are concerened with their bikes looking really nice. I prefer to spend the money getting the drive train where I want it instead of getting it all prettied up at the sacrifice of the mechanical parts. I'm the type that would rather ride a turd that ran and performed how I want, than a nice shiny gem that didn't. I'll worry about the paint and replating afterwards. But.... that's just me!

BTW, the guy from that site emailed me back, but he didn't answer my question... he just talked about how precise they do balance the cranks... to within 1 tenth of a gram! I rephrased the question and hope to hear from him tomorrow including price with shipping.

[trbig]

OK, the latest and greatest... here's my last email to APE racing.

Some people think that by removing material from the crank as you do in this process, you are taking weight away that counter balances the weight of the pistons and rods, thus making the motor vibrate more AFTER the crank lightening even though it is balanced. Others are saying that the opposing pistons and rods cancel each other out and a balanced crank whether it's stock or lightened should add no more vibration. Which theory is correct?

Here was their reply.

The "removal of weight effecting the balance" theory is false. The pistons and rods are weight balanced from the factory. The only thing that will throw the rotating assembly out of balance is......if it is out of balance. Just taking weight off will not do so UNLESS the crank is not balanced after the lightening. The OEM cranks are balanced to around +/- 1 gram so when we balance it down to +/-.1 of a gram it is actually 10 times better balance then stock with or without lightening. The only way crank weight ,as mentioned in your email above, effects a motor is in torque and momentum and it has nothing to do with balancing of the rotating assembly. Balancing is the only thing that will effect.........the balance. The better the balance the less vibration.

I then emailed and asked if the magnaflux was a necessity and the time for turn around on the crank, and they wrote back,
"The mag is not really necessary unless 2 things.
(a) The crank has been hurt in some way (spun journal, broken rods etc.)
(b) if it is a 1127 GSXR (they are prone to crack over the course of some time)

Do not know shipping but I can tell you most crank work averages a month."

I like that they didn''t try to "Sell" me on the magnaflux, but a little dissapointed that they couldn't put a price on the shipping. So it looks like $225 plus shipping? I am thinking that there wouldn't be anything wrong with these basically bulletproof cranks. If I can gain some on the bottom end where we all ride, and have to sacrifice some torque on the top end where few of us ride regularly... seems like a cheap/good trade off to me.

[TopCatGr58]

Revisiting topic at my own peril!

Hey Tod,

After rereading "their" reply, I don't think they are saying that you will LOSE torque, just that a lighter crankshaft could affect the torque and momentum.

Torque is the ability to twist something, and with less weight, the amount of power the pistons will be pushing against the shaft to turn it should allow a stronger affect, because there is LESS weight to try to spin, against inertia. This is why the engine will spin up faster, cause it takes less energy to spin the lighter crank. So....I would think the ability to creat torque would be better, and should actually increase the value.

The other item mentioned is momentum, and as was mentioned earlier the XS doesn't have a flywheel persae, the alternator rotor is about the equivalent. The weight of the crank allows for smoothing out of the piston pulses, and helps keep the crank spinning when OFF the throttle....again, inertia at play. The lighter crank will spin down quicker as well, so engine braking affect should also be increased vs. stock. However, I have to admit that with my "little" big bore, mine has a decent engine braking affect due to the increased compression.

But this easier to slow down the spin could also add to a slightly more jerky type of response with the engine, both in revving up and down!? Also the reported increase in vibration may be in the ability to feel the piston surges more since it doesn't have the weight and inertia of the heavier crank to help dampen those powerful strokes, not necessarily due to any actual balance aspects of the pistons, rods, or crank!

Then again, I could be all wet, Ernesto not to blame!
T.C.

[HobbyMan]

These are all valid points. You must also consider the fact that you can not balance the crank enough for the amount of energy that is required to rotated the extra material to make a noticable difference in power Aslo, The fact that the engine does not have a flywheel, as it seems to me, makes no difference. Think about it: When you are above idle going down the road and you let off of the throttle, the direct connection to the rear wheel and the momentum of the bike will keep the engine rotating at an even pace. So, when the clutch is engaged, the bike serves as a flywheel. I just can't see how balancing the crank makes that much of a noticable diffence as claimed, unless it is rotationg at a MUCH higher RPM. In my opinion, the crank was designed that way and if the engineers thought it needed to be balanced, they would have done it. I could be wrong, but the only way to find out for sure is to try it and see what it does.