Author Topic: Dynamic balancing  (Read 375 times)

Online JHG1958

  • Moving Up
  • **
  • Join Date: Sep 2019
  • Posts: 13
  • Karma: 1
Dynamic balancing
« on: 19.10. 2019 18:57 »
I am down to the crankshaft looking at new big ends.  I was wondering if anyone though it was worth dynamically balancing the crankshaft. SRM think it is a must but they would wouldn’t they. 

Now I have gone to all the trouble of stripping it down. I would like to do all the jobs I can.

John

Online Bsareg

  • Valued Contributor
  • ****
  • Join Date: Mar 2016
  • Posts: 250
  • Karma: 2
Re: Dynamic balancing
« Reply #1 on: 19.10. 2019 19:35 »
Had the RGS balanced, holes everywhere, done by an old chap lived down by Wrotham Hill, Kent. Can't remember his name but famous for balancing and I think either he or his brother also did mags. He asked what did I use the bike for (speed wise) and balanced to that rev range. Really smooth engine now.
C11,B40,B44 Victor,A10,RGS,M21,Rocket3,REBSA

Online Bsareg

  • Valued Contributor
  • ****
  • Join Date: Mar 2016
  • Posts: 250
  • Karma: 2
Re: Dynamic balancing
« Reply #2 on: 19.10. 2019 20:09 »
Just remembered the old boys name Fred Cooper. That "old boy" was probably younger that I am now......
C11,B40,B44 Victor,A10,RGS,M21,Rocket3,REBSA

Online muskrat

  • Global Moderator
  • Wise & Enlightened
  • **
  • Join Date: Jul 2009
  • Posts: 7979
  • Karma: 106
  • Lake Conjola NSW Oz
    • Shoalhaven Classic Motorcycle Club Inc
Re: Dynamic balancing
« Reply #3 on: 19.10. 2019 20:50 »
G'day John.
The short answer is yes.
I have only balanced my shafts static myself and get good results.
 Anyone that has it dynamically balanced will tell you it's worth it giving a much smoother ride.
Cheers
'51 A7 plunger, '57 A7SS now A10CR, '76 XT500, '77 AG175 '83 CB1100F, '81 CB900F project.
Australia
Muskys Plunger A7

Offline Servodyne

  • Moving Up
  • **
  • Join Date: Feb 2018
  • Posts: 24
  • Karma: 0
Re: Dynamic balancing
« Reply #4 on: 19.10. 2019 21:35 »
I took a chance with my A10 Spitfire and didn't get it balanced during a rebuild and now find it vibrates a bit, over 60mph.
I put an A10 crank in my A70 and got it dynamically balanced by SRM.
It's very smooth and just hums up to 70mph and beyond, so yes get it balanced.
1957 BSA A10 Spitfire
1971 BSA A65 Firebird
1971 BSA A70 Lightning
1975 Norton Commando

Online groily

  • Wise & Enlightened
  • *
  • Join Date: Jul 2007
  • Posts: 1045
  • Karma: 17
    • www.brightsparkmagnetos.com
Re: Dynamic balancing
« Reply #5 on: 20.10. 2019 16:59 »
+1 for dynamic balancing - does make a difference.
Not sure where you are, but T&L Engineering in Beds have done good jobs for me in the past using state-of-the-art kit - and I'm sure SRM - and other people recommended - would also be great.
Bill

Online Dave c

  • Moving Up
  • **
  • Join Date: May 2018
  • Posts: 35
  • Karma: 0
Re: Dynamic balancing
« Reply #6 on: 20.10. 2019 18:32 »
Re:how much does balancing cost?

Online Sluggo

  • Serial Hoarder, or Eccentric Collector depending on viewpoint
  • Resident Legend
  • *****
  • Join Date: Jun 2017
  • Posts: 616
  • Karma: 11
Re: Dynamic balancing
« Reply #7 on: 27.10. 2019 22:55 »
Re:how much does balancing cost?

+1 x 1000 for dynamic balancing, record ALL your measurements and weights so if you end up replacing parts later you can keep in the specs.

As to cost, thats situational for many reasons.   One is the skill of the balancing person, as its a bit of a science and black art.  Secondly is what kind of issues they have to deal with.

It might be easy to balance but some can be really challenging even by a expert.  Also,, depends on the job itself. a FULL WIDTH Flywheel is easiest as there is material to remove to balance, but cut down flywheels are more challenging.  In some cases the area to remove weight does not exist so the only alternative is add Mallory metal to even it up.

Im in the US but my old crank guy, Dan Halls 5 point automotive would charge $150 to $250 for the balancing alone.   However my main guy, EV Lewis,, was typically $75 to 150 unless he had to add Mallory metal or other problems.  If you included them he also would do timing gears, trans main and lay shafts, clutch baskets and Alternator rotors and often CHEAP!  $10 each item.

But 100% worth it. Every  penny.  Ive worked in manufacturing, My wife does as well.  Everything has a tolerance, and "Close enough is good enough" is the mantra for most everything.  British factories back in their day had a low margin of profit and many were struggling to stay afloat, so many items were built to a cost.  Thats not an insult,, but simply reality and any company worldwide had that issue.
Remember that any advice received on a free internet forum is generally worth about 1/2 of what you paid for it.
We overcharge every 3rd customer to pass the savings onto you.
You can have High Quality, Low price, and fast turnaround. Pick any 2, Never all 3 at the same time.

Offline Rocket Racer

  • Wise & Enlightened
  • *
  • Join Date: Jun 2009
  • Posts: 1377
  • Karma: 16
  • A kiwi with a racing A10 rig
    • NZ Classic Sidecar Racing
Re: Dynamic balancing
« Reply #8 on: 28.10. 2019 05:00 »
on top of the previous responses the original balance factor was based on the slower speeds on b roads so on faster modern roads  a differing balance factor is preferable. Also as engines gain oversize pistons and heavier rods the balance factor is altered the wrong way.
If your engine has modern rods and oversize pistons it will be much happier balanced
A good rider periodically checks all nuts and bolts with a spanner to see that they are tight - Instruction Manual for BSA B series, p46, para 2.
New Zealand

Online groily

  • Wise & Enlightened
  • *
  • Join Date: Jul 2007
  • Posts: 1045
  • Karma: 17
    • www.brightsparkmagnetos.com
Re: Dynamic balancing
« Reply #9 on: 28.10. 2019 07:02 »
Might have posted this before, but here's the info sheet that came with a crank balanced at T&L. It was for an AMC twin, with the centre bearing, so might have been more complicated than one of ours here, not sure. Cost about £140 from memory.
From memory again, most A10s were done to about 55%? This one was done to just over 60%. The higher the % the further up the rev range you push the sweetest spot, if I understand it correctly. So a racing motor might be as high as 70%, fast road machines in the 60s, tourers nearer the 55% mark. But IKBA - I just enjoy the benefit of the results!
Bill

Online groily

  • Wise & Enlightened
  • *
  • Join Date: Jul 2007
  • Posts: 1045
  • Karma: 17
    • www.brightsparkmagnetos.com
Re: Dynamic balancing
« Reply #10 on: 28.10. 2019 07:04 »
and here's the first sheet
Bill