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crank balancing
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dienelt1
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September 13, 2021 - 5:33 pm
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 Hi all,

 Like riding my B175 , but on longer runs vibrations spoil the enjoyment,  so looked into what could be  the cause.

 Followed the instructions on the you tube clip" crank balancing made easy"

,and discovered the factor was 90% instead of 60%, the counter weights seem to be to heavy needing a heavier hung weight.

after pipping the flywheels ,the heavy side (practising on an old crank) got it to just over 60% , truing a crank is a lot of

 fun to, quite easy when  you get the hang of it ,using a dial gauge a run out of a thou or less can be achieved.

 like to hear any views on this subject.

     Diene.

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Doug B.
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September 13, 2021 - 9:21 pm
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Am I the only one who understands very little of this . ? 🤔 Obviously cranks have to be balanced but it's the percentages that are bamboozling me !

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GlenAnderson
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September 14, 2021 - 5:20 am
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I’m considering balancing my crank. I’ll check out the video. 👍

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BASIL
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September 14, 2021 - 8:54 pm
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Mike Foster the Bantam club tech rep is very good at this.

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Ringting
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September 14, 2021 - 11:04 pm
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Hi Diene.

Yes, my D14 vibrates a lot more since fitting a Rex Caunt con rod kit. Comes in about 45 and stays right up till max at a bit over 60. It's on my to-do list to re balance it (and refit some side plates). Rex's kit is a lot lighter than the original so I wouldn't be surprised if mine is a similar amount out.

Hi Doug.

The reason for not using 100% balance factor is that the balance weight on the crank is moving around in a circle but it's trying to balance out a piston, rings, gudgeon pin and part of the con rod that are moving up and down. A balance factor of 100% (the same as piston etc) would almost cancel out the weight of the piston moving up and down and stop the engine from vibrating up and down but it would create its own out of balance forces when half way between TDC and BDC and make the engine vibrate fore and aft. The percentage is a compromise between the 2 extremes.

Alan.

D1, D14/4, Guzzi LeMans, Guzzi V35, Triumph Trident 900, Maserati 160 t4. Mk1 Mini Traveller, Berkeley T60.

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cocorico
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September 15, 2021 - 7:43 am
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Now you have unbalanced this crank. I need to go and lie down in a darkened room for a bit... tip-my-hatrofl

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dienelt1
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September 15, 2021 - 11:15 am
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Ringting said
Hi Diene.

Yes, my D14 vibrates a lot more since fitting a Rex Caunt con rod kit. Comes in about 45 and stays right up till max at a bit over 60. It's on my to-do list to re balance it (and refit some side plates). Rex's kit is a lot lighter than the original so I wouldn't be surprised if mine is a similar amount out.

Hi Doug.

The reason for not using 100% balance factor is that the balance weight on the crank is moving around in a circle but it's trying to balance out a piston, rings, gudgeon pin and part of the con rod that are moving up and down. A balance factor of 100% (the same as piston etc) would almost cancel out the weight of the piston moving up and down and stop the engine from vibrating up and down but it would create its own out of balance forces when half way between TDC and BDC and make the engine vibrate fore and aft. The percentage is a compromise between the 2 extremes.

Alan.  

 I have a spare crank to practise on , so if it goes pear shaped all is not lost ,just hope the chap in the u tube clip has got it right!

  same con rod kit as yours , could be that the counter weights are to heavy , or the run out is at fault that accounts for your vibration.

   I'm going to lighten the counter weigh end of my crank , to get a balance factor of 60%" hopefully" a turbine smooth engine will result!

   Had a d14 in my youth flat out all the time ,so fast could beat any home produced 250s much to the owners embarrassment .

  can't remember bone tingling vibes ,or more than likely didn't notice . any improvement with my endeavourers  expect further rubbish!

 

     Diene.

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Number6
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September 18, 2021 - 4:51 pm
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Slight deviation, but I am reminded of my Triumph T140V (and later, the 'E') – 750 parallel twin – I'm sure the factory did their best but the bikes were often criticised for too much vibration (so maybe an example of why it may not be a good idea to go larger than 500cc for a single or parallel twin – unless you start introducing balancer shafts or suchlike).

It could be amusing, at tickover, to watch the engine rotating in circles while the whole bike gently bounced up and down on its mainstand, which in turn would slowly creep backwards because it was on a slight slope, on the footpath in my front garden. laugh

Mike H --

Murphy's 4th law of motion states that any small object that is accidentally dropped will immediately hide itself under a larger object.

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Doug B.
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September 19, 2021 - 8:48 pm
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I took a ride around on one that vibrated so much it affected my eyesight ! Compare that to my same vintage Kawasaki z750 twin which was very smooth .

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Number6
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September 20, 2021 - 5:48 pm
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Yep – my point tho (maybe not made clear enough) was the circular motion, due to less than 100% counter-balance of the pistons + conrods weights – for the reasons explained earlier laugh

Mike H --

Murphy's 4th law of motion states that any small object that is accidentally dropped will immediately hide itself under a larger object.

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