Engine Rebuilding - Flywheel Balancing , Fitting Pistons, Torque ( Excelsior 17/18)

[danf19]

I seem to have a bit of time on my hands nowadays. I've always wanted to learn to rebuild an engine. I have some pretty good components and everything will be original except the pistons (excelsior 17/18) .
Still haven't sorted out if I will in fact do this one myself - Id prefer to bring it to a professional but weighing extra cost and my spare time.

I've been searching old threads on flywheel balancing etc.

I have two questions.... first, can someone explain , in layman's terms the art of balancing a flywheel - assuming all is the same as the original weight (rods, pins etc) except I would assume todays pistons (and pins) are lighter then the original casting iron. does that mean I would remove weight from the flywheel ? . I do have a balancing stand, calipers, milling machine , calipers and lathe although my balancing stand is for a Harley and not quite deep enough for the excelsior flywheel.
Second, where can I order pistons and pins for the cylinders and what are the criteria for sizing. Again I have nice cylinders with a good bore.
Thrid, where can I find proper torqueing specs for crank pins etc. ??

I know many will say bring it to an expert or work with an expert which , again, would be my first choice. But under these extenuating circumstances I don't know when that will be. I'm not aware of anyone local who does this work on a regular basis. Ive gotten burned before when supposed "experts" charge me to learn something they told me they had done before.

Be safe and stay healthy !
Dan

[BoschZEV]

I know many will say bring it to an expert

I won't be one to say that. This isn't rocket science. Far from it. But, there certainly is the potential to screw up. I'm about to re-balance a crankshaft from a BSA Gold Star that has balancing holes drilled in the wrong locations by someone who only understood the concept well enough to make themselves dangerous (unless they were re-balancing for cast iron piston).

can someone explain , in layman's terms the art of balancing a flywheel - assuming all is the same as the original weight (rods, pins etc) except I would assume todays pistons (and pins) are lighter then the original casting iron. does that mean I would remove weight from the flywheel ?

The simple, correct answer is 'yes', you need to remove weight from the flywheel if you install lighter pistons. However, how much to remove, and from where on the flywheel, would require a much longer answer. Plenty has been written about how to do this in books, magazine articles, and on-line so there's no point in someone spending the time to rewrite the process here. Spend some time with google.

my balancing stand is for a Harley and not quite deep enough for the excelsior flywheel.

In other words, you do not have a balancing stand. Without a balancing stand any attempt to rebalance an engine would be silly. If you knew what the original balance factor was (which you could determine if you had a balancing stand and original set of pistons), you could calculate with reasonable accuracy how much additional material to remove assuming no one in the past 100 years already has removed additional material. But, for what it's worth, I'd only advise you to proceed once you have a balancing stand.

[T. Cotten]

Dan!

I made several sets of knife-edges, but if I were going do it again, I would just use two sturdy pieces of ground round stock.
(Just suspend them high enough so you can hang the entire assembly, perhaps even with a piston assembly, 'Indian-style'.)

As BoschZev infers, if you don't know the original factor, you are flying blind.

You might want to review http://virtualindian.org/1techflywheel.htm

....Cotten
PS: If you have existing holes in the wheels close to the crankpin, you can add weight to lower your factor. You can also consider 'stuffing' the wristpins, instead of turning your wheels into 'swiss cheese'.

[danf19]

thanks guys for the response. I have set up the lathe to act as a balancing stand but also started to build a stand with the round stock as was recommended. I do have the original pistons and pins and a digital scale .
I will continue to read up and google. Can anyone guide me in how to determine the original balance factor ??
As always, thanks
Dan

[Steve Slocombe]

Dear Dan, I think choice of balance factor is the key issue. Most of the early literature implies a 50% balance factor because it talks about halving the weight of components in the calculations. But I'm told modern Harleys are balanced to a 58% balance factor for low down grunt, while I have had VLs at 46% for a smoother top end. Balance factor assumptions can swamp different piston weights. Note Harley Shop Dope 112 of 17 Dec 1934 announcing the new aluminium T-slot piston says 'T-Slot piston can also be used in servicing a motor originally fitted with iron alloy pistons...it is not altogether necessary that flywheels be rebalanced...'

[T. Cotten]

thanks guys for the response. I have set up the lathe to act as a balancing stand but also started to build a stand with the round stock as was recommended. I do have the original pistons and pins and a digital scale .
I will continue to read up and google. Can anyone guide me in how to determine the original balance factor ??
As always, thanks
Dan

Lathes are great for truing the wheels, Dan!

But would need an enormous throw to hang the assembly for balancing. (Tapers might not be the "ideal", but with care, probably nearly as sensitive as "rails".)

With the assembled wheels and rods hanging, you can add weight to the rod tops until it achieves balance, and then calculate the percentage of the original.
The mass of the rod tops must be determined first, of course, and frankly, even that can be determined while assembled (attached).

As Dan points out, balancing is enormously forgiving, beware however, felt vibrations are incidental (motors are balanced for the motor, not the rider...)
Face it: With a ~1500g reciprocating mass, you would have to be off on your weights by 15g to amount to one point of factor, and you still wouldn't feel it.

Truing the wheels is far more critical, and that's why I endorse balancing with the final assembly. (My experience with a Stewart-Warner dynamic balancer taught me that just disassembling and reassembling a crank, even with the same bob weight, would give a slightly different result.)

....Cotten

[BoschZEV]

(motors are balanced for the motor, not the rider...)

I have to disagree with that. Motors are balanced for the frame (and rider), not for the motor. Because of mechanical resonances, somewhat different balance factors are needed for the same engine in different frames, for the comfort of the rider, and also for different uses (e.g. high speed rather than touring).

Tapers might not be the "ideal", but with care, probably nearly as sensitive as "rails".

Sorry, but I have to disagree with that as well. A heavy crank puts a lot of pressure on tapers so, no matter what grease is used, there will be a lot of friction. You will be able to balance a flywheel that way to some extent, but not nearly as well as with rails or rollers.

[T. Cotten]

I have to disagree with that. Motors are balanced for the frame (and rider), not for the motor. Because of mechanical resonances, somewhat different balance factors are needed for the same engine in different frames, for the comfort of the rider, and also for different uses (e.g. high speed rather than touring).

Sorry, but I have to disagree with that as well. A heavy crank puts a lot of pressure on tapers so, no matter what grease is used, there will be a lot of friction. You will be able to balance a flywheel that way to some extent, but not nearly as well as with rails or rollers.

Motors are balanced only to keep them from throwing themselves apart, BoschZev!

Yes, the frame design is a critical aspect: http://virtualindian.org/Flywheeltheory3.htm
But the motor doesn't know it has two cylinders, much less what the rider feels.
None of that is in the balancing equation.

Balancing technicians seem to obsess with the insignificant. Its our nature.

....Cotten
PS: I always washed out the rollers thoroughly before any attempts on the edges, no doubt.

PPS: Sorry for the late edit, but v-twin motors are 'only' balanced for one reason.
But the factor tunes for a particular 'performance': Low factors jump like a scalded dog, but higher factors let the motor live longer at highway speeds.

This is the great advantage of a single-throw motor: A forgiving range of factors.

[BoschZEV]

Motors are balanced only to keep them from throwing themselves apart, BoschZev!

Yes, the frame design is a critical aspect: http://virtualindian.org/Flywheeltheory3.htm
But the motor doesn't know it has two cylinders, much less what the rider feels.
None of that is in the balancing equation.

There is no "balancing equation" to determine the balance factor, only an equation that lets you calculate the balance weight with whatever balance factor is assumed as the input.

There are in fact so many consideration involved that it is impossible to quote one figure as being the ideal [balance factor], since it varies with every type of engine, and even for the same engine in different or differently-equipped frames.
Tuning for Speed, Sixth Edition. Phil Irving (Turton & Armstrong, Sydney, 1987)

[Steve Slocombe]

Dear Dan, going back to torque, you'll be lucky to find any factory figures. The VL with a 1" crank pin has the nuts done up 'very tight'. I take this as 100-150 pound feet, enough to get the side float of the con rods between the flywheels close to the factory specs.

[T. Cotten]

There is no "balancing equation" to determine the balance factor, only an equation that lets you calculate the balance weight with whatever balance factor is assumed as the input.

It sounds just like an equation to me, BoschZev!

The countermass equals a percentage of the reciprocating weight. The mainshafts are the "equals" sign.

There are in fact so many consideration involved that it is impossible to quote one figure as being the ideal [balance factor], since it varies with every type of engine, and even for the same engine in different or differently-equipped frames.
Tuning for Speed, Sixth Edition. Phil Irving (Turton & Armstrong, Sydney, 1987)

No doubt, BoschZev! Ever wonder why the Magnacycle never caught on?

And Dan!
If your flywheels are cast, and not malleable, beware when torquing over 75 ft/lbs. I destroyed a 101 flywheel treating it like a Harley.

....Cotten
PS: Some of you may remember losing the top motormount bolt, or at least coming loose enough to be alerted by the vibes.
The motor was suddenly out of balance for the chassis!

[BoschZEV]

It sounds just like an equation to me, BoschZev!

It's an equation to me as well, but to repeat myself, it's an equation that lets you calculate the balance weight with whatever balance factor is assumed as the input.

To the original poster, if you have all the original components, and a balancing stand, you can determine, using an equation, what balance factor the engine originally had (if no one has messed with it in the 100 years since it was made). Then, once you have determined the original balance factor, you can use that number in the same equation to determine how to modify the flywheels to accommodate lighter pistons. So, it's a two step process that uses the same equation both times, except with different inputs in order to solve for a different unknown each time.

[T. Cotten]

It's an equation to me as well, but to repeat myself, it's an equation that lets you calculate the balance weight with whatever balance factor is assumed as the input.

To the original poster, if you have all the original components, and a balancing stand, you can determine, using an equation, what balance factor the engine originally had (if no one has messed with it in the 100 years since it was made). Then, once you have determined the original balance factor, you can use that number in the same equation to determine how to modify the flywheels to accommodate lighter pistons. So, it's a two step process that uses the same equation both times, except with different inputs in order to solve for a different unknown each time.

You lost me, BoschZEV...

I don't believe I've ever calculated the 'balance weight', although I'm not sure what you mean.

The reciprocating 'weight' is what matters (although you have to figure the bottom half of the rod assemblies if you are going to fake them with a bob weight).

It was easiest for me to repeat the process that gave the original factor to measure progress when drilling. Then I could sneak up on it, and place the holes accordingly.

Using slugged wristpins to stack various weights upon, I could get reproduceable trial weights accurate to a thin automotive spring shim: ~1.5g.
Everything had to be perfectly level and centered, of course. A mirror behind my knife-edges helped a lot.

....Cotten
PS: Dan!
Is your crank currently assembled, or apart? If apart, now is the best time to weigh your rod tops.

[BoschZEV]

I don't believe I've ever calculated the 'balance weight', although I'm not sure what you mean.

As I wrote in my first post to this thread, all of this has been written about in a number of places so to write it all again here would be reinventing the (fly)wheel. Personally, I don't want to take the time to do that so, again, I'll refer the original poster to google.

[T. Cotten]

As I wrote in my first post to this thread, all of this has been written about in a number of places so to write it all again here would be reinventing the (fly)wheel. Personally, I don't want to take the time to do that so, again, I'll refer the original poster to google.

I googled 'balance weight', BoschZEV!

Already got plenty.

After balancing motors for decades, professionally, I still don't know what you meant.

...Cotten
PS: Folks, there are only two 'weights' (or masses) in the equation: What goes up-and-down, and what goes round-and-round.