About those balance shafts!

[Chris]

Hey,

I just adjusted my balance shafts and that got me to thinking... Anybody care to provide answers to the following?

1. How do balance shafts work to reduce engine vibration?

2. When properly adjusted, do they lower horsepower by increasing friction in the engine (that terrible whining noise when tightened a bit too much makes me think they use friction).

3. Even after adjustment, in neutral my bike rattles unless the clutch is pulled. Balance shaft adjustment made no difference. Is this the clutch or engine rattling?

Thanks,
cb

 

[Blrfl]

1. How do balance shafts work to reduce engine vibration?

They have lopsided weights on them, and when perfectly adjusted, they're positioned to counter the engine's lopsidedness. That's why they're called "counterbalancers."

2. When properly adjusted, do they lower horsepower by increasing friction in the engine (that terrible whining noise when tightened a bit too much makes me think they use friction).

Probably not. I don't know what causes the whining when they're out of whack.

3. Even after adjustment, in neutral my bike rattles unless the clutch is pulled. Balance shaft adjustment made no difference. Is this the clutch or engine rattling?

That's the clutch basket. On this bike it's noisy.

--Mark

 

[MileHigh]

Hey,

I just adjusted my balance shafts and that got me to thinking... Anybody care to provide answers to the following?

1. How do balance shafts work to reduce engine vibration?

2. When properly adjusted, do they lower horsepower by increasing friction in the engine (that terrible whining noise when tightened a bit too much makes me think they use friction).

3. Even after adjustment, in neutral my bike rattles unless the clutch is pulled. Balance shaft adjustment made no difference. Is this the clutch or engine rattling?

Thanks,
cb

1. Like Mark wrote "they're positioned to counter the engine's lopsidedness."

Take a look at the engine diagram on STWiki

Then, take a look at this thread. Post 9 shows the firing order and crank rotation of the V4 used in the 1300.

Your power stroke is 90, 270, 90, 270. Not the best configuration for vibration canceling. Ideal combination on a V4 would be every 90 degrees.

To do that, they would have to place a rod journal on the crank every 90 degrees. You would need a much longer, heavier and, expensive crankshaft.

The rod journals on the crank in the 1300 are in the same location. Crankshaft up, all 4 pistons up. Crankshaft down, all 4 pistons down. At any given point, all 4 pistons are in the same vertical position in the bore.

Counter balancers are an inexpensive and lightweight alternative to offset the natural imbalance of the 1300 crankshaft and, lopsided firing order.




2. Properly adjusted, no power loss. When you adjust the balance shafts, you are changing the lash on the gears of the counter balancers - when the teeth on the two gears engage with each other.

Too early or late, whining gears. In the middle, nice and quiet.

It's more noticeable since the gears are straight cut. Straight cut gears are much stronger & accurate. When set correctly.


3. Like Mark wrote "clutch basket." The metal discs & friction plates doing their normal thing in the basket, in an unloaded condition.

 

[Blue STreak]

Here's an interesting article on counterbalancers:

http://dansmc.com/counterbalancers.htm

 

[Chris]

Great info guys.

I appreciate your help!

Thanks,
cb

 

[jack d]

At any given point, all 4 pistons are in the same vertical position in the bore.

This would be true on an inline 4 but not on the 90 degree V4 of the ST1300. At any given crank position the pistons on the left are in the same position and the pistons on the right are equal to each other but 90 degrees displaced from the left. i.e left side both pistons at TDC, right side both pistons 90 degrees away from TDC. It would also be difficult to make a 4 cylinder 4 stroke cycle engine fire every 90 degrees as it needs 720 degrees of crank rotation to complete a complete cycle.

 

[Gonzo]

IMHO, they should really be called "counterIMbalance" shafts, but that's just me.

The whining of the straight-cut gears is the price we have to pay for it versus having angle-cut gears which may be quieter but require a thrust washer and have a little more power loss.

 

[jack d]

It takes 2 complete rotations of 360 degrees to complete the firing cycle. That is 720 degrees.

Yes, that is what I said. And on the ST1100 and the ST1300 it is physically impossible for all 4 pistons to be at Top or Bottom Dead Center at the same time because of the 90 degree separation of the left and right cylinder banks and the inline crank journals. Therefore the engine cannot fire at equal intervals of 180 degrees. But maybe you are saying that also. I am not clear as to what you were saying in the last part of the post.

 

[jack d]

This is a missunderstanding of terminology. No one is saying they are all at top dead center together. They are on a 360 degree common crank pin design that puts all the crank throws on one side of the center of rotation. The counter balancers are set up to offset that weight, and power pulses, being on one side of the crankshaft. Each set of pistons move up and down together, but not kept in position relative to top dead center together. They are however close to being at bottom dead center all at the same time, when the crank throws are at the bottom. And all four pistons are close to being at the top together, but 2 are past top dead center and the other bank is before top dead center, with respect to their cylinder heads, when the crank is at the top of it's rotation.
11-29-2009 01:18 PM

Total agreement. We were both saying the same thing all the time but I misunderstood your posts.

 

[CABINPETE]

And they do all go up and down together

Not on a V4. At times one bank is moving down while the other is moving up and vice versa.

On an inline (1 - 3) and (2 - 4) move together. If 1 and 3 are moving up 2 and 4 are moving down and vice versa. The only time the pistons on an inline (with a standard crank) are equal in the bores is when the rod journals are 90 degrees to the bore center (right or left of center)
If it uses a big bang firing order all bets are off.

On topic I think the noise you note with the clucth out but not in is due to the trans input shaft turning with the clutch out in neutral and is normal due to the transmission gear lash and mesh.

 

[Byron]

See respone in blue below.

Hey,

I just adjusted my balance shafts and that got me to thinking... Anybody care to provide answers to the following?

1. How do balance shafts work to reduce engine vibration?

Counter-weights are set to oppose the mass/vibration of the pistons/crank.

2. When properly adjusted, do they lower horsepower by increasing friction in the engine (that terrible whining noise when tightened a bit too much makes me think they use friction).

What you are setting is the lash in the gear that drives the counter-balance weights. It doesn't change the position or timing of the weights only the fit between the drive gears. As stated in the linked article, "Gear drive Counterbalancers do not change or go out of adjustment, . . .".

3. Even after adjustment, in neutral my bike rattles unless the clutch is pulled. Balance shaft adjustment made no difference. Is this the clutch or engine rattling?

It's noise from the clutch basket/friction plates. Nothing to do with the counter-balance adjustment.

Thanks,
cb

 

[CABINPETE]

Hey,

I just adjusted my balance shafts and that got me to thinking... Anybody care to provide answers to the following?

1. How do balance shafts work to reduce engine vibration?

Counter-weights are set to oppose the mass/vibration of the pistons/crank.Short answer yes but it?s done more through harmonics. Most balance shafts spin at twice the speed of the crank

2. When properly adjusted, do they lower horsepower by increasing friction in the engine (that terrible whining noise when tightened a bit too much makes me think they use friction).

What you are setting is the lash in the gear that drives the counter-balance weights. It doesn't change the position or timing of the weights only the fit between the drive gears. As stated in the linked article, "Gear drive Counterbalancers do not change or go out of adjustment, . . .".
They can go out of adjustment, reason they allow you to adjust them. They can go out of phase with excessive lash but it would be minute.


3. Even after adjustment, in neutral my bike rattles unless the clutch is pulled. Balance shaft adjustment made no difference. Is this the clutch or engine rattling?

It's noise from the clutch basket/friction plates. Nothing to do with the counter-balance adjustment.I?ll stick with transmission gear noise, when the clutch is out the plates are locked together in the basket so I don?t think you would hear them rattle.
Thanks,
cb

 

[MidLife]

See respone in blue below.

What you are setting is the lash in the gear that drives the counter-balance weights. It doesn't change the position or timing of the weights only the fit between the drive gears. As stated in the linked article, "Gear drive Counterbalancers do not change or go out of adjustment, . . .".

Just like drive train lash allows the rear wheel to move back and forth an inch or two, CB lash will allow free play of the CB.

The more lash, the more CB free play. Lash results in various positioning of the CB within the range of the lash.

Tightening the lash will tighten (change) the angular position of the CBs.

 

[George]

Just like drive train lash allows the rear wheel to move back and forth an inch or two, CB lash will allow free play of the CB.

The more lash, the more CB free play. Lash results in various positioning of the CB within the range of the lash.

Tightening the lash will tighten (change) the angular position of the CBs.

Expanding a little more on this topic, MCN has an article in their current issue about slack in the timing chain changing (retarding!) the timing with age and wear. Quite significant with only a small % change in chain length. Unlike our 1100 belt (recommended change at 90,000 miles) there is no change interval for the cam chain on the 1300. Wonder if any of the high-mile 1300s are experiencing this anomoly?