Powerplus or Bust, Eh?

[T. Cotten]

Kevin!

I'm ignorant of your cylinders, as the only blind ones that I have honed oversize were Lycomings.

But metal moves.
The thinner a casting becomes, the more fastener stress will distort the bore.

I suggest making a stressplate to simulate the motorcase, and install the cylinders at the same torque as when the piston is fitted.

....Cotten
PS: I am also ignorant of your chassis; Is there a top motormount?
This would weigh heavily (sorry for the pun) in a choice of balance factor.

[Shaky Jake]

Kevin!

I'm ignorant of your cylinders, as the only blind ones that I have honed oversize were Lycomings.

But metal moves.
The thinner a casting becomes, the more fastener stress will distort the bore.

I suggest making a stressplate to simulate the motorcase, and install the cylinders at the same torque as when the piston is fitted.

....Cotten
PS: I am also ignorant of your chassis; Is there a top motormount?
This would weigh heavily (sorry for the pun) in a choice of balance factor.

Yes - I agree with using a torque plate. There is no top motor mount. I'm about 3/4 of the way through your VI compositions on crankshafts, then I'll start on Spacke2speed's links. I strained my back earlier this week, so reading is a good activity while I recover.

BTW - I agree with your earlier assessment that the original designers probably knew what they were doing. My plan is to rebuild as closely as I can to stock, because my experience has been that you can't change just one thing without potential unanticipated consequences somewhere else. One possible exception may be the carb.

Kevin

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[T. Cotten]

Kevin!

Matt E. in the VI discussion put it simply: "A motor with low balance factor thus vibrates up and down a lot and vibrates fore and aft a little."
Without a top motor mount, I would predict you will find an original factor that is quite high.

And you're right, carbs are enormously forgiving!
(But manifolds ain't. If yours is anything like the attachment, they are diabolical.)


....Cotten

[Shaky Jake]

'As Found' Balance Factor

All of that reading today inspired me to measure the "as found" balance factor of my crankshaft. I would say "original" balance factor, but I don't know what has been done in the last 100 years.

The first thing I needed was a static crankshaft balancer. Since my flywheels are about 8 1/2 inches in diameter my first plan was to put the crankshaft between centers in my 9 inch lathe and use it as my static balancer. Here's the problem I had:








I could go to the trouble of drilling a center in the end of that junk shaft, but I got to thinking, why can't I use my cheapo wheel balancer that I bought on eBay instead?








The answer to that question is that the bearings in the wheel balancer are too far apart. Each tower is fastened to the base with four screws and there are two positions provided for each tower, but even with both towers bolted to the innermost position they were too far apart. However, I found that if I move them in to the point that each one is only held by two screws like this:








Then the crankshaft fits perfectly in the bearings:








There's a piece of tubing that you put through some holes to make sure the towers are lined up before you tighten the screws:








It has adjustable feet so you can level it:








So now I have a static crankshaft balancer. In the next post I will take some weight measurements, do some balancing, and see if I know how to calculate the balance factor.






Kevin

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[Captk]

One way of looking at it is that it is dependant on the rings as they are the true circle item. It is easier to get the bore to match a standard dimension because rings will be available. The people who make the pistons will usually cam grind them to the appropriate clearance. So the bore might be 3", so the rings will be for a 3" bore and the pistons made with (example ) .004" clearance for the bore.

[Shaky Jake]

Measuring the 'as found' balance factor, part 2

The balance factor is defined as the percentage of the reciprocating mass being balanced by the flywheel counterweights. The reciprocating mass is defined as the mass of the pistons, rings, wrist pins, wrist pin retaining devices, and the small ends of the connecting rods. Since this is all taking place on the surface of the earth, we can assume mass and weight are equal, so next I'll measure the weights of the reciprocating masses. I started with the small ends of the connecting rods. I sat the crankshaft on blocks and blocked up the scale as shown so the rod being weighed was level. I used a lamp shade to hold the other rod vertical, so that it wasn't affecting the result:



The weight of the small end of the rear (male) rod was 198.0 grams.
The weight of the small end of the front (female) rod was 193.7 grams.






I weighed each piston together with it's rings, wrist pin, and cotter all in one swell foop:



The rear piston assembly weighed 596.3 grams.
The front piston assembly weighed 594.0 grams.







I put the crankshaft in the parts washer and used mineral spirits to clean the bulk of the carbunckles off of it, that might affect balance. After it dried, I put it on the balancer. I was expecting the crank pin to settle exactly to the top, but I was surprised to see that it was a few degrees off from that. No matter how I rocked it, it settled back to this position:








I decided to hang the rear piston, rings, pin, and cotter on the rear rod, but leave all the front piston stuff off, and see if it balanced. It did not (too much weight) as shown in this video:








Since the front piston was a little lighter I tried it next, but it was still too heavy:








So then I hung the front piston and rings from both rods using a piece of bailing wire of a scientifically calculated length, and it balanced very well. I could turn the crankshaft to any orientation, and it pretty much stayed there as shown in this video:








I weighted the piston, rings, and bailing wire that balanced the crankshaft, and they weighed 524.0 grams:








In the next installment we will find out if I can still do math.

Until then,


Kevin

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[T. Cotten]

Kevin!

Sounds like you are going to get a Panhead factor..
And I am surprised that the male rod top weighed more than the female.

....Cotten

[Shaky Jake]

Kevin!

Sounds like you are going to get a Panhead factor..
And I am surprised that the male rod top weighed more than the female.

....Cotten

I was expecting the factor to be higher too. I'll double check the rod end weights after church.


Kevin

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[rwm]

why do you want the rod end weight? Don't you wont the whole rod weight?

[T. Cotten]

Rob!

The tops of the rods are arbitrarily considered reciprocating mass, and the bottoms to be rotating mass.
(Please remember that motor balancing is only an applied technique.)

Of course the bottoms also move up and down with the stroke, so that's why it is conventional to "hang" the rods while weighing, as some of the bottom will still affect the scale: One end on the scale weighs one half of the rod.
(As a check, the bottom is weighed to add to the top weight for a total, that should match the whole rod on the scale.)

This is why I would always expect a female rod top to weigh more than a male,... but I'm clueless about the PowerPlus.

Kevin may well get different results after dis-assembly, but probably not significantly.

....Cotten

[Shaky Jake]

Measuring the 'as found' balance factor, part 3

OK. I went back and re-checked the rod end weights, and it turns out I had made an error. It happens. The male rod still weighs in at 198.0 grams, but the female rod weighs in at 198.7 grams. Maybe I wrote the 8 down as a 3 the first time around. I promise I wasn't drinking much when I took the data. The 5 gram error does shift the answer in the expected direction, but only by a few tenths of a percent. To be honest, I think that in this case the difference in rod end weights probably has more to do with the fact that the wrist pin for the male rod is 0.010 inch oversized, so there has been some meat removed from it's bushing. Note that the rear piston assembly is slightly heavier, which you would expect because it includes a slightly larger wrist pin. I also re-checked the weights of the piston assemblies, that check out the same.


Here is the math, way I see it:

The amount of reciprocating mass that is being balanced by the flywheel counterweights is equal to the mass of both small rod ends plus the amount of weight I had to add to get it to balance in the third video. Arithmetically, that is 198.0 grams + 198.7 grams + 524.0 grams = 920.7 grams.

The total reciprocating mass is equal to the sum of both piston assemblies plus both small rod ends, or 596.3 grams + 594.0 grams + 198.0 grams + 198.7 grams = 1587 grams.

The percentage of the reciprocating mass being balanced by the flywheel counterweights is 920.7 grams / 1587 grams = 0.580

My as found balance factor is 58%.


Discussion and corrections are welcomed!




Kevin

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[T. Cotten]

Like I posted, Kevin,

It wouldn't be significant.
With nearly 1600g of reciprocating mass, you would have to error by sixteen grams to make a point of factor.

And upon assembly, the factor could vary as much as eight points without notice (based upon H-D's ever-changing dogma.)

Balancing is fun, but its often flatulating in a hailstorm.

....Cotten
PS: Are there any balancing holes in the flywheels?

[Shaky Jake]

...

PS: Are there any balancing holes in the flywheels?

No, there are no existing balancing holes. I guess I'm going to have to make some though; the new piston assemblies are about 215 grams lighter. Man, I hate drilling on old parts.



Kevin

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[T. Cotten]

Ooh, that's a lot...

(...but it would get you up only slightly higher than the 64% range of Chiefs with 67%!)

Perhaps it would be easier to slug weight within the wristpins; Top end parts are temporary, the flywheels are not.

It would still be prudent if we had other samplings of original PPs' existing factors.

....Cotten

[rwm]

. Man, I hate drilling on old parts.



Kevin

.

then make the wrist pins heavier