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

craig

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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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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.
 

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craig

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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.
 

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  • 20180410_BSPistonWeight2.jpg
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craig

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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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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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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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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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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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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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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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