Dynamic Balance

Since you have all of the components, why not see what the existing BF is?
It might be close enough right now.
 
Naahh!
Well yes to buy the scale, it's cheap and you will find it very handy.


 
Last edited:
Hm, interesting. Realise I should check my 100 mm stroke crankshaft I bought from Terry Prince a few year ago before I put it in the crankcase. I have bolted up my standard stroke Shadow with the Terry Prince crankshaft already. Not sure I want to dismantle it and check the balancing though.
Anyhow, found this read interesting:
https://www.cycleworld.com/2016/02/...d-flat-twin-engine-tech-sound-insights#page-2
 
Last edited:
This is a guy that's done calculations on a Brough JAP KTO engine (a 50° V-Twin crankshaft, so like the Vincent).
Says it has a relative rod length of 2.32 (2.32 times the stroke). The rod length is stated as 7.75" so stroke should be 3,34".
To get the lowest peak force and lowest mean force he concludes that a balance factor of 53% is best. Any thoughts on this?
http://www.brufnut.de/SS100/ENGINE/CRANK_BALANCE/crank_balance.htm
 
There are just so many opinions as to what the ideal BF is for a Vincent .


Terry Prince likes 60%. R&R Cycles, who spent half a million on the only rods on Hines dynamic balancer in existence, also like 60% for Harley engines. They also use 60% for their 150 cubic inch R&R engines

They came up with this number via a combination of trial and error plus science.
They fitted vibration sensors to v twin bikes and tried a variety of crank balance factors
The vibration meter showed 60% to be the best balance factor for rider comfort at normal cruising speed.
So it seemed a good number to go with.

Glen
 
Thanks Glen, 60% seems like a very good figure!

Would it be possible that a BF of 60% compared to 40% would give similar results? Same with 65% and 35%, 70% and 30%. I haven't investigated this but just a thought. I'm thinking these pairs are centered around 50%. As BF 0% and 100% give equal results but in different directions?
 
Perhaps. Im a bit bewildered on the question of the ideal Balance factor for a Vincent. I wonder if Nigel ( Tricatent) has it right that there could be different equations at work, hence the wide range of " best" numbers.

I put a fair bit of hope in R&Rs research and experience, even though it wasn't with Vincents.
They seem to have gone to a lot of trouble and expense to reduce the vibration problem with VTwins. I guess they had to in order to make their 150 cubic inch bikes rideable!
Old, handed down Vincent folklore gives us all of these numbers -35% ( the man himself, Phil Irving) ,46% ( Richardson) 54%( John McDougall)
62%( Maughans for an Egli type frame) Maughans use Richardsons 46% for a standard Vincent.
I do know that 90 % BF with a porkchop crank and hi compression 1360 motor in a stainless monoshock oddball, sort of Egli frame, does not work!
60 % and dynamically balanced seems to be a very good number for this particular bike.

Still waiting for weather to improve so I can give it a real good tryout.

Glen
 
Last edited:
jimbo said:
more

http://www.lindskog.com/automotive-balancing/

http://houseofbalance.com/serv03.htm
Click to expand...

My machine shop, Coleman in Linthicum, used House of balance to rebalance my Norton P11 crank to a new balance factor. Coleman did not have any data from "House of Balance" about this radical BF change, 90% to 56%, so I called HoB to ask for data. The balance man, at HoB, said they keep no data, they only balance to balance factor provided. I am not sure who or how component weights were provided. I was very disappointed.

Currently have a Shadow engine in progress with a crankshaft renewed years ago thru Canada Ken.
New pistons recently thru Coventry spares. I will set up crank in my wheel balancer and check weights.

P11 seems to vibrate the same as before.

Dynamic Balance
 
Sadly, stories of balancing ‘experts’ getting it badly wrong seem to be more common than ever recently.

Previously I would never rebuild an engine without having it dynamically balanced as a matter of course.

These days though I’m inclined to leave it be if it seemed to run smooth before hand.
 
Once more - dynamic balancing (this is, without altering the BF) should not involve touching the flywheel.
Some material is usually removed from both cheeks. If only one cheek is touched the the BF will change.
Usually very little material is removed as the dynamic balance is usually not too far off - otherwise the engine vibes beforehand would have been horrendous.
My 650 had 21 grams removed - the equivalent of a 8mm deep 20mm dia hole.
It was removed from my crank by setting it up in a lathe and skimming material around the outside top of one cheek and the outside bottom of the other.
I assume the House of Balance tech was wearing a blue & white striped apron while destroying that flywheel!
 
I just noticed in the pic above that the owner seems to have fitted JS rods (and therefore pistons) so presumably that’s why so many holes.

In which case, rather than dril so many holes, why not add heavy metal in t’other side.

Rob, so, if I understand you correctly, I could take my crank to a dynamic balancer and say ‘the balance factor is perfect, leave that as is, please just dynamically balance it’.

Is that right?
 
Sometimes the added heavy metal comes loose and goes thru the engine.
There were remains of such an engine at my balancer's shop.
This was a V8 race engine that the owner had taken to a specialty shop to have the heavy metal added ( up the bF) The cost to add the heavy metal was $900 but the damage done to the expensive engine was many times that.
We do love to screw around with stuff, don't we:)

I realize that adding heavy metal to a crank doesn't always result in destruction of the engine, but it does add a little spinning liability to the equation.

Glen​
 
I had to have heavy metal added to a Norton crank cos some half wit had ‘lightened’ and it was the only way to bring it back into balance. I didn’t try lightened a crank again :oops::rolleyes: !

That was with Basset Down doing it, it was a Norton crank in a unit Triton and it was surprisingly smooth.
 
Here is a stock Shadow crank with Carrillo rods sitting in my wheel balancer with no counter weight added.
Small end of both rods, together, weigh in at 380gm
Heavy flywheel sides are down, rods at top.


Dynamic Balance
 
Last edited:
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.

Anyone have a crank to compare?
What is the balance factor?
What would be allowed for piston, pin, rings, circlips?

I will explore for my new pistons, pins and such.
Might be in the attic.


Dynamic Balance
 
Last edited:
Rob ss said-Once more - dynamic balancing (this is, without altering the BF) should not involve touching the flywheel.

Not sure how one can dynamically balance a Vincent crank without touching the flywheel(s)
Flywheels, big pin and mainshafts make up the entire crank. You have to touch ( drill a hole, or machine some thickness away ) in order to get rid of the side to side imbalance or rocking couple, should one be found to exist.
If no other work is done, this will change the bf a little, probably not enough to worry about.
If you were absolutely set on the existing bf then you could maintain that number by splitting the difference. One could then add half the error in heavy metal to the correct spot on the light side and drill half from the corresponding location on the heavy side.

Can't touch the diameter tho, it works against an oil skimmer cast into the cases.

Glen
 
Last edited:
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.

I don't have a weight for big end rod, but can these known numbers calculate to some balance factor?

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 380gms.



Dynamic Balance
 
You must log in or register to reply here.
Back
Top