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Balance #711578
10/14/17 9:12 pm
10/14/17 9:12 pm
Joined: Aug 2015
Posts: 1,244
Bolton Lancs UK
A
Andy Higham Online content OP
BritBike Forum member
Andy Higham  Online Content OP
BritBike Forum member
A

Joined: Aug 2015
Posts: 1,244
Bolton Lancs UK
I wonder how many people consider crank balance?
Years ago I had my A10 crank reground at a local engine remanufacturing workshop, they asked me if I wanted it balancing. I said ok and took my rods and pistons in. They static balanced it and dynamic (end to end) too
The result was a very smooth free revving engine
When I ordered a crank for my B31 Phil pearson wanted to know the weight of my piston assembly so he could balance it, I weighed it to the nearest 0.1g on a digital scale.
The result is an engine that is as smooth as Guinness and will happily cruise at 70 to 80MPH


BSA B31 500cc "Stargazer"
Greeves 200cc "Blue Meanie"
Greeves 350
Greeves 360 Challenger
Suzuki GSX1100 EFE "Sorcerers Apprentice"
GM500cc sprint/LSR bike "Deofol"
Jawa 500cc "Llareggub"
2003 Aprilia RSV Mille "Lo Stregone"
'35 OK Supreme
'36 OK Supreme
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Re: Balance [Re: Andy Higham] #711606
10/15/17 1:49 am
10/15/17 1:49 am
Joined: Mar 2014
Posts: 625
Denver CO
J
Jerry Roy Offline
BritBike Forum member
Jerry Roy  Offline
BritBike Forum member
J

Joined: Mar 2014
Posts: 625
Denver CO
Did Phil say what balance factor he used? The manual says 58% on a DB34, if I remember correctly.Others say more and less.

JR

Last edited by Jerry Roy; 10/15/17 1:52 am.
Re: Balance [Re: Andy Higham] #711630
10/15/17 9:53 am
10/15/17 9:53 am
Joined: Aug 2015
Posts: 1,244
Bolton Lancs UK
A
Andy Higham Online content OP
BritBike Forum member
Andy Higham  Online Content OP
BritBike Forum member
A

Joined: Aug 2015
Posts: 1,244
Bolton Lancs UK
I didn't ask him. I assumed it would be classified information.


BSA B31 500cc "Stargazer"
Greeves 200cc "Blue Meanie"
Greeves 350
Greeves 360 Challenger
Suzuki GSX1100 EFE "Sorcerers Apprentice"
GM500cc sprint/LSR bike "Deofol"
Jawa 500cc "Llareggub"
2003 Aprilia RSV Mille "Lo Stregone"
'35 OK Supreme
'36 OK Supreme
Re: Balance [Re: Andy Higham] #711690
10/16/17 1:54 am
10/16/17 1:54 am
Joined: Nov 2011
Posts: 186
Nova Scotia, Canada
K
koncretekid Offline
BritBike Forum member
koncretekid  Offline
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K

Joined: Nov 2011
Posts: 186
Nova Scotia, Canada
Why don't you ask him? At the worst, we won't know any less than we do now.

I've tried 65 and 60% on my BSA singles race bikes, and both raise blisters at full song. Other road bikes I've rebuilt with Carillo rods and JE pistons and no re-balancing, and I can't tell the difference at legal road speeds.

Tom


Life's uncertain - go fast now!
Re: Balance [Re: Andy Higham] #711756
10/17/17 12:25 am
10/17/17 12:25 am
Joined: Aug 2001
Posts: 4,522
Owego, NY, USA
Mark Z Online content
BritBike Forum member
Mark Z  Online Content
BritBike Forum member

Joined: Aug 2001
Posts: 4,522
Owego, NY, USA
I've never owned a single, but I can attest to the benefits of balancing a twin (A65), based on direct "before and after" experience with the same engine. In that regard, it has been posited that, more important than achieving a particular balance factor, is getting both sides the same, which doesn't apply to a single.


Mark Z

'65(lower)/'66(upper, wheels, front end, controls)/'67(seat, exhaust, fuel tank, headlamp)/'70(frame) A65 Bitsa.
Re: Balance [Re: Jerry Roy] #711917
10/18/17 5:36 pm
10/18/17 5:36 pm
Joined: Nov 2011
Posts: 4,642
U.S.
Magnetoman Offline

BritBike Forum member
Magnetoman  Offline

BritBike Forum member

Joined: Nov 2011
Posts: 4,642
U.S.
Originally Posted by Jerry Roy
Did Phil say what balance factor he used? The manual says 58% on a DB34, if I remember correctly.
I have a new Phil Pearson DBD crank and piston on the shelf so it would be straightforward to determine the balance factor. However, I'm not volunteering to take the time to do that because I don't need to know the answer, and I strongly suspect the result would be 58% anyway.

I'll be going through the identical process shortly on my Ariel rebuild where I will first need to determine the balance factor the factory used in 1928 so that I can balance the crank using a modern piston of a different weight. I describe the information needed to do this at this post and this one.


Moderated by  Alan_nc 


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