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Crank balancing

tractorman414

Well Known and Active Website User
VOC Member
I built up a Shadow some years ago, the engine parts being from a number of sources, but I never had the crank balanced, I naively considered at the time this was a racing refinement, not really necessary for the road. The bike never ran well, slow, vibrated badly. So I have decided this winter to totally pull it apart and check the basics, crank alignment and balance.

After reading about Paul Norman’s crank assembly balancing experiences on www.racingvincent.co.uk I am pretty sure the balance is going to be a similar challenge. I too have Carillo rods and may have to look at "adding" weight to wheels opposite to the pin, rather than further reducing weight near the pin.

Paul’s work was undertaken by a specialist via The Maughans who inserted heavy metal plugs into the wheels. My assumption being that these inserts would be a tungsten alloy, which I understand is quite machinable, but I have been unsuccessful in sourcing a supply of small pieces of the this alloy. Darts are a bit small and the only other item using tungsten I could think of is A golf clubs head!

Anybody been in this situation or help with a supplier of tungsten alloy and best engineering practise for added the weight to the flywheels

Bernard
 

Tom Gaynor

Well Known and Active Website User
VOC Member
Simon Linford made me a new crank (he machined the flywheels from better material) using with club parts and my Carillo rods, and balanced it. It took less than a month from my being advised that the rods had arrived with Dave Nourish.
It works.......
 

bmetcalf

Well Known and Active Website User
VOC Member
Balancing

The hot rodders call it Mallory Metal, but I googled that a few years ago, with no results. Maybe you could try again. Maybe save some money by buying in the US, with the "new lira".:)
 

Pete Appleton

Well Known and Active Website User
VOC Member
VOC Forum Administrator
Dynamic or static?

I have been waiting for someone to mention dynamic balancing of cranks. It is all very well to balance the crank statically but you stand a good chance of setting up a rocking couple. Taking this to extremes if you imagine adding a weight to one flywheel you could add another weight diametrically opposite on the other flywheel and this would appear to make everything balance although what you have in fact done is un-balance both flywheels in opposite directions.

I had my maughan crankshafts with corillo rods dynamically ballanced by j & J Engineering 01793 740169 cost about £90

Pete
 

Tom Gaynor

Well Known and Active Website User
VOC Member
Balancing cranks

There's a piece in FYO about dynamic crank balancing and the benefits thereof. There's a lot about crank balancing theory and practice in a series of articles by The Prof.
I believe the name of the (UK) company who did the Vin crank was Basset Down Engineering.
 

andygbsmith

Website User
Non-VOC Member
I have used Basset down (Swindon in Wilts) and can fully recommend his work.
On the last crank he did for me I wanted to change the balance factor and he added Tungsten to the fly wheel by drilling and screwing it in.
His number is in old bike mart.
 

tractorman414

Well Known and Active Website User
VOC Member
The story so far.

Many thanks for your comments and advise

Have stripped the engine, made up a set of parallel knife blades to measure the balance, following Neville Higgins’s articles in MPH 700/702. All set to add weights to the rods in order to obtain balance and we find they are already rolling to put the crankpin at the bottom !! I had to add Bluetac to the wheels opposite the pin to get balance. About 15 gms. So using Neville formula with X as -15 I end up with a balance factor of 32.2%. Think this explains my vibration!! To get to 50% factor I will need to remove 216 gms.

I had a discussion with J & J engineering and they confirm earlier reports that its not practical to remove that much weight from the pin side, so its the heavy metal option opposite the pin and with so much weight involved I will leave it to the experts to fit
 

Pete Appleton

Well Known and Active Website User
VOC Member
VOC Forum Administrator
Balance factor

To get to 50% factor I will need to remove 216 gms.

Steve at Maughans advised 46% balance factor for a Vin with standard frame although apparently the Egli and Norvin fraternity prefer other figures. All to do with the different frame angles I am told.
Anyway with 46% and standard 'C' setup I am vibration free

Pete
 

clevtrev

Well Known and Active Website User
VOC Member
The dart material is a copper/tungsten alloy available is various percentages used as a spark eroding electrode. It is not easily machined, but with good tips will machine to fine tolerances.
So I ask the question, where do you want the balance to occur ?
 

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