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E: Engine What's my Black Shadow balance factor?

craig

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VOC Member
#1
I have a Black Shadow project to finish and it came with a finished, rebuilt crank containing new Carrillo rods.
Also supplied are new standard cylinders, new piston assemblies, and renewed heads.
I want to determine what the existing balance factor is please, so I moved the uprights on my Pit Posse wheel stand to accept a crankshaft and started recording weights.
So here is step 1 , crank heavy side down, Carrillo rods up.

20180409_ShadowCrankBalance1.jpg
 

craig

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VOC Member
#2
So next step is to counter balance the crank so it stops in any position.

Here is weight added to balance rods out, crank is holding position at anywhere 360 degrees.
As you can readily see, I have a very sophisticated stack of highly accurate weights to use for counter balance.
This weight set, including all pieces, is 220gms.
 

Attachments

craig

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VOC Member
#3
Here is one of the pistons for this Shadow renew.

Piston, rings, circlips, wrist pin...maybe a little tissue paper.

Weight of one piston assembly is, lets say, 465gms.
Times two is 930gms.

My previous post numbers -
Here is weight added to balance rods out, crank is holding position at anywhere 360 degrees.
As you can readily see, I have a very sophisticated stack of highly accurate weights to use for counter balance.
This weight set, including all pieces, is 220gms.
Small end of both rods, together, weigh in at 374gms.
 

Attachments

craig

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VOC Member
#4
Here is the catalog info for Carrillo Vincent rods.
Rod total weight 567gms each x 2 = 1134gms
BE = 1134-374=760 - big end
PE
= 374 - pin end
CarilloCatVincent1.jpg
 

craig

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VOC Member
#5
I found a chart/form online leading to something. I estimated the BE bearing weight, maybe others have a more accurate number.

So can balance factor be estimated from these numbers?

BobweightSheetEx1.jpg
 

vibrac

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#6
I take it that its being fitted to a standard Frame
Many say the % depends on the frame
Certainly I used a lower % on an Egli twin
 

Magnetoman

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#7
An article in MPH by Neville Higgins (date unknown, because it's missing from the photocopy in my notebook) says "The Works recommended a balance factor of 46 per cent for the Twins... I followed their advice for many years, being satisfied with the vibration levels experience by my engines, even up to 7,500 rpm on my racers... Bob Dunn... had recently done a check on a number of engines, finding those having a balance factor around 50 per cent were good, 45 per cent were OK, at 40 per cent they began to vibrate, and down to 30 per cent they were really bad. Some people running Norvins claim that a 60 per cent factor gives them a smooth engine."
 

timetraveller

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VOC Member
#8
If you want to use the standard Vincent twin balance factor of 46% then with the figures you have provided I make it that you should have had to add 226 gms (sorry Vibrac) to the small ends. You are actually using 220 gms which is near enough. Using your exact weights, and assuming that everything is weighed accurately, then you have a balance factor of 45.55%.
 

Magnetoman

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#9
addendum: the next photocopy in my notebook is Part 2 of Neville Higgins's article on balancing, which says it is continued from page 27 of MPH 700,
 

craig

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#10
so the Bobweight is the total of -
2 rods total = 567 x 2 = 1134
balance weights = 220
big bearing est = 140

1134+220+140 = 1494 ??
 
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craig

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VOC Member
#11
If you want to use the standard Vincent twin balance factor of 46% then with the figures you have provided I make it that you should have had to add 226 gms (sorry Vibrac) to the small ends. You are actually using 220 gms which is near enough. Using your exact weights, and assuming that everything is weighed accurately, then you have a balance factor of 45.55%.
Thank you, It would be best for me to see the math, as I don't understand how to get the percentage.
 

timetraveller

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VOC Member
#12
You can ignore the big end weights. What matters is the weight of the small ends and the weight of the two piston assemblies (complete). You are trying to balance some percentage of that total weight in such a way that the flywheels will not rotated when that percentage weight is applied at the small ends. So to take your figures; the two small ends weigh 374 gm. The two piston assemblies weigh 930 gm. Total 1304 gm. 46% of that is 600 gm. However, you cannot change the weight of the small ends so you subtract that weight, 374 gm from the 600 gm figure which gives 226 gm and that is the weight which you would have to add to the small ends in order to obtain a 46% balance factor. You were adding 220 gm. which I would consider near enough but if you want to work out exactly what balance factor you have then use 220 rather than 226 in the above calculation and work backwards. If this is not clear then you will have to do what I did about sixty years ago and read a book on engine tuning for motor cycles and in there you will find the whole thing explained better than I can in a brief item here. It is good to have an enquiring mind.:)
 

craig

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VOC Member
#13
So the bob weight is only important to the balance altering activity. I thought this was much more complicated and involved with math, science and measuring devices, or something beyond my comprehension. I get this, Thank you.
With a crankshaft out and recip components, you can quickly determine an existing balance factor.
I see 46% for Vincent twins, and 66% for Vincent singles, as quoted in Paul Richardson - Vincent Motorcycles, pgs 60&63.

I filled in the bob weight sheet, I am not sure of this bob weight due to unverified BE bearing weights.

BobweightSheetEx1.jpg
 

craig

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VOC Member
#15
How do you accomplish this increased (46->55) balance factor?
Lighter weight reciprocating pieces (pistons, pins, rods)?
Or removing weight from flywheels? More holes that a home shop could accomplish?
Thank you
Craig

PS I need better brakes, maybe I should buy a ticket.
 

Vincent Brake

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VOC Member
#16
i did the top 3 holes:



Static Rebalanced:

Small end weight When levelled:

Pri side 203 gr, timing 200gr = 403 gr

Pistons complete each 457 gr

Formula: free to The Man:

Weight to balance (where we take the % from) = small end + pistons complete

1317gr = 403 +2(*457)

Test: % of wieght - smallend=FG (FG: being weight to the smallend when in balance)

638 - 403= 235gr

So 638 is 48,4 % of 1317 (being 100% reciprocating weight)

To balance to about 55%

By drilling the 4 top holes to 13mm and the middle top holes milled 12,5 and milled bit to the top

After some extra drilling FG became 303gr leaving the balance weight to 706

this being 53.6% balance factor from 1317gr

that worked for me,
although still not Dynamically balanced, (one need to make a bob wieght exactly running in true, let allone the weight....) have to say i did frist both flywheels on a knife edge, bit cumbersome but one gets them more or less the same, when done in two axis.

well of course this is all shit so may god and good luck be with you, when finally you start her and she jumps like a horse:D
 

Bill Thomas

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VOC Member
#17
How do you accomplish this increased (46->55) balance factor?
Lighter weight reciprocating pieces (pistons, pins, rods)?
Or removing weight from flywheels? More holes that a home shop could accomplish?
Thank you
Craig

PS I need better brakes, maybe I should buy a ticket.
Craig, I did these holes in my home shop, After having the wheels made more narrow !.
I see your wheels have extra holes already !.
Good Luck, Bill 002 (4).JPG
 

craig

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VOC Member
#18
I looked in my "Another Ten Years" Jeff Bowen, and found numerous articles on balancing published in MPH over the years. My interpretation or collective on all this MPH info seems 46%-50% is the range most used for Vincent twins, and Neville Higgins quotes these numbers on page 75.

So, as I really didn't want to pursue more crank work, my crudely confirmed "about 46%" is good enough for me. If 46% doesn't suit me, I will pull this BS apart and file away.
 
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