Falicon Cranks - remove the counterbalancer

[Barkdog]

I need to have some work done to my crankshaft.  Falicon Cranks seem to be the best people to work on it, since they can restore my crank to factory spec.  So, I have 2 questions:

1)  The guy quoted me $275 to do the work.  Its 500 for a new crank.  Has anyone had work done by them before?  Are they as good as they promise?

2)  While I have my engine in pieces, I was thinking of removing the counter balancer and having them re balance it, like described in the racers section.  Who has done this?  Where can you see gains?  What are the cons (I'm sure zuki puts counterbalancers in for a reason)  How much did the operation cost?

[KevinC]

Bob Broussard removed the counter balance shaft on his race bike. I don't know if he had the crank rebalanced. It vibrates so bad he was going to put the counter balancer back in for racing - on the street it would be brutal I expect.

[Blueknyt]

i understand the basics behind how cranks are ballenced and most machine shops should be able to, or atlease know of a shop they farm the work out to for REASONable fee's
basicly, you weigh a rod , piston and  rings as one set, then the other set and see which set weighs less,  the idea is to grind away tiny bits in key area's or add to it, to get both sets the same, then  weights are madeup to same weight as rods pistons, and rings and bolted to the crank throws. the crank is then spun (like tire ballencing) and the machine will indicate where to remove/Add matirial to ballence  the crank out. from that point you should be ready to go removing the counter balence shaft, pluging the holes and assembling the engine. Regaurdless what you may think, its still going to vibrate abit, the counter ballence shaft makes vibrations directly opposite of the crank, but it also acts as a shock dampner through contact in the gears.

[Bob Broussard]

When I had the motor built for my race bike in the beginning, we removed the counterbalancer.
It was pretty brutal. When that crank broke, I replaced it with another stock crank. It was the same!! The crank was supposed to be balanced.
I've run with a counterbalancer and no flywheel since then.
I built another motor lately and had the crank done through Spears Enterprises in Cambell CA.
It cost $250.00.
I was amazed how smooth the motor was. Just like having a counterbalancer. Except it revs insanely quick ( no flywheel either). Unfortunately I blew it up last sunday. Valve to piston contact + a missed shift, NOT GOOD.
I just wish I had my Carrillo rods on the crank. They weigh about 80 grams less than stock rods!
THere is an oil hole missing though so I need to resolve that before using them.
Anyway, Falicon is the main company for repairing motorcycle cranks.
APE only does 4 cylinder cranks.
You should be able to find local shops to balance the crank.
The benefit is quicker acceleration. Especially out of corners.

[JamesG]

Hey Bob- So you had good results with a Spears balanced crank with no balancer?

I've got two cranks laying around that I've been planning to get done for years...

BTW- An asymetrical spinning mass (a crank) will vibrate differently at various speeds. And you can never get one *prefectly* balanced to where it will be stable at every speed. The idea is to balance it so that the distructive vibration freq is either above or below the engines useful rpm range.

[bob]

I removed the C'balancer from one of my engines & it vibrated so bad I could hardly ride it.  When I rebuilt the engine I had Falicon re-balance a crank for me for use without the balancer.   It wasn't much better than before.  I'd be interested in finding out how Spears did it.

Basically, without a balancer, if you weight the crank to compensate for all the vibration generated by the reciprocating pistons, you turn a vertical shaking force into a rotating shaking force (couple).  The way around this is to only compensate for part of the vertical force & then you are left with a smaller vertical force, but you add a rotating force. If done right the resulting forces are smaller than what you would have without any compensation.

The other way to react the vertical shaking force is to react 50% of it in the crank & 50% ot it in a counter-rotating balance shaft.  This way the crank & the balance shaft cancel out each other's for-aft shake & they combine to react the vertical piston shake.  When you remove the balance shaft you end up with just the 50% balance left on the crank.

I had the opportunity to talk to a guy from Falicon at the Performance Racing Industry show in Indianapolis later & asked him about how they decide how to balance a 180 deg twin.  He said that in a case like the GS he would probably put about a 65% balance in the crank so that the vertical part was reduced by about 1/3 but the for-aft part was increased (the reasoning was that a for-aft shake is less of a problem than a vertical one).

Bottom line is, prolly best to leave the balancer in & just try to reduce rotating inertia by removing things like the flywheel & starter.

BTW, it is possible to *perfectly* balance a crankshaft (by itself) but it is not possible to build a crank that does not have a *natural* frequency.  For this reason cranks are designed to have their *natural* frequency either above or below the normal range of firing frequency of the engine.  The natural frequency will change slightly as speed increases, but this is due to loading due to centripetal effects.  The natural frequency doesn't change enough to have any real effect.  The natural frequency is a function of material & geometry, not balance factor.

This ends the physics lecture for today.  There will be a quiz on Monday.  Have a nice weekend...  

[KevinC]

I've posted this link before, but I love looking at their simulations:

http://www.mecc.unipd.it/~cos/DINAMOTO/twin%20motors/twin.html

If you page down to about the middle, there is a 180 degree twin sim. There is an unbalanced force at twice crank speed. That is what the counter balance shaft is for.

[KevinC]

Bob, I have been using a Dyna rev limiter on my GS. It works very well, and isn't too expensive. I'm not sure if it would prevent the miss shift problem (revs rising so fast), but it might be worth a try.

[Bob Broussard]

I have a Dyna rev limiter too.
But I didn't have it set up right.
What do you have the switches set up at. I had 1/2 off and 3 on.
I just reset it at 1 off and 2/3 on.
Greg Spears sends the crank to a local guy for balancing.
There is vibration at lower rpms.
But it's fine at high rpms for racing. Even the counterbalanced motor has some vibes. I don't think I'd do this on a street motor.

[bob]

There is an unbalanced force at twice crank speed...

Actually, in a 180 deg parallel twin like the GS there is a primary (first order) vertical couple plus a secondary (second order) vertical force.  First order means it happens at the same frequency as engine speed & second order happens at twice engine speed.  The GS balance shaft is a first order shaft, because it turns at the same speed as the crank.  It is there to counter the first order imbalance which has a much higher amplitude than the second order vibration, so rather than putting in three balance shafts (which is what they would need to properly balance both first & second order shaking), they just let the second order go & treat the first order.
BTW, the reason the graphic in the link:
http://www.mecc.unipd.it/~cos/DINAMOTO/twin%20motors/twin.html
shows no first order vector because in the view they show there is no first order vertical shake.  If you were to look at the engine from the front or the back you would see a rocking couple trying to twist the engine around the bike's for-aft axis.

I love this kinda stuff!  

[wingbolt]

I like the balancing of the BMW boxer engine.  Cool website, thanks for the link.

[KevinC]

The BMW simulator is a bit decieving. The two cylinders are offset slightly longitudinally because they are on different crank throws, so there actually is a rocking force. Not bad at all, and low frequency, but they do have a vibration to them. I can sit on mine for 12 hours a day though.

Sorry Bob, I forgot to check my Dyna switch positions. I'll do that tonight. The first way I tried it was at half the rpm I wanted, but it works right now.

Was that your GSXR head you broke? That's not good...

[Bob Broussard]

It was the GSXR head I damaged.
The exhaust valves were hitting the edge of the cutouts on the pistons.
They embedded themselves in the aluminum when it got hot and soft enough, So it only made noise when I firt got it running. Sounded like noisy lifters.
When I missed a shift, one exhaust valve broke and wiped out one cylinder.
I bought 5 pistons instead of the minimum 4. So I took the good piston and the extra new one and cut the valve pockets bigger.
Then I took the Carrillo rods I have and drilled the missing oil hole in the base. They weigh 2 oz. less each than the stock rods.
Not to mention stronger.
The whole setup is being re- balanced at Spears Enterprises.
Had to bore another set of cylinders too.
I started to cut down a 90 head I had. First off I noticed the valves were a mm smaller. Then found the combustion chamber was slightly smaller for more compression.
I wasn't sure about piston clearence, so I put it aside for now. I took another 89 head and got things moving along pretty good.
I'm going to have the valve seats replaced as a precaution this time.
I've heard they have a bad habit of cracking and coming loose in the head.
This motor should be unreal.
The way it ran before I broke it was real promising. Just the way it pulled when I was taking it easy made my regular race motor seem weak. I was riding on my street trying to get some time on the motor over a period of a few days.
So I couldn't do it for too long at a time. My neighbors are pretty cool, but I don't want to push my luck.
The jetting was perfect, using an airfuel ratio meter I bought.
I was rolling along in first and just hammered it. It just launched and brought the front wheel up and when I went for second I missed.
I've NEVER missed a gear before.
Well you know the rest of story.
Learned alot, so it won't happen again.

[KevinC]

Too bad about the head, that is a lot of work! It is hard to break in a race bike. I drive mine out to the country and hope for the best.

I have my rev limiter set for 4 pulses per 2 revs, with it hooked up to both coils. The GS has a wasted spark for each cycle. The Dyna switches are 1 - off, 2 and 3 - on.

Mine works right set like that.