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Dynamic balance ?

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Dynamic balance ?

Posted by marcus_bloomfield at July 28. 2017

Any advise on balancing a model 7, is it worth going for dynamic balancing? I was told it works well, but now been advised not too !!!

Re: Dynamic balance ?

Posted by John Shorter at July 29. 2017

Why bother?  The model 7/88 engine ran quite smoothly, as standard.   Why waste money "improving" a machine, that will never be faster than a modern 250?, and, may well shorten it´s life.

Re: Dynamic balance ?

Posted by marcus_bloomfield at July 29. 2017

Just looking to make the bike smoother, obviously not going to win the TT, how do you reckon it might shorten its life?

 

Regards Marcus

Re: Dynamic balance ?

Posted by anna jeannette Dixon at July 29. 2017

Hello crankshaft balancing is best done by  Steve Manely  Middleton engineers or SEP engineering . at the cost of around £130 pound notes  but having said this is really up to you at the end of the day  The Norton Owners Club members can only speak from their own experiences and there for only guide you  and cannot be made accountable  from any endeavor you may encounter  has it your decision in the end    yours  anna j      happy riding 

Re: Dynamic balance ?

Posted by John Shorter at July 29. 2017

I did not mean balancing, itself, would shorten engine life, but many people try to boost the performance of old engines, in some cases well above what was intended.  The natural tendency is to ride faster, which increases wear, and tear, on components operating above their designed limits.  Unless you are into classic racing (which a model 7, or even an 88, were not designed for), spending an extra 130 pounds will make very little difference.  That said, what do you know of the engine´s history, and general condition?  I see you are enquiring about new pistons, so, is a complete rebuild required?  If so, it is doubtful if you will find pistons the exact weight of the originals.   Since a rebuild will (hopefully) a one off exercise, it would be worth taking the pistons, crank, and con-rods, to be balanced together.

Re: Dynamic balance ?

Posted by marcus_bloomfield at July 29. 2017

Previously John Shorter wrote:

I did not mean balancing, itself, would shorten engine life, but many people try to boost the performance of old engines, in some cases well above what was intended.  The natural tendency is to ride faster, which increases wear, and tear, on components operating above their designed limits.  Unless you are into classic racing (which a model 7, or even an 88, were not designed for), spending an extra 130 pounds will make very little difference.  That said, what do you know of the engine´s history, and general condition?  I see you are enquiring about new pistons, so, is a complete rebuild required?  If so, it is doubtful if you will find pistons the exact weight of the originals.   Since a rebuild will (hopefully) a one off exercise, it would be worth taking the pistons, crank, and con-rods, to be balanced together.

Yes, total rebuild, so while I am at it I may as well have it balanced, just about every thing else is being done, thanks for the input.

Re: Dynamic balance ?

Posted by marcus_bloomfield at July 29. 2017

Previously anna jeannette Dixon wrote:

Hello crankshaft balancing is best done by  Steve Manely  Middleton engineers or SEP engineering . at the cost of around £130 pound notes  but having said this is really up to you at the end of the day  The Norton Owners Club members can only speak from their own experiences and there for only guide you  and cannot be made accountable  from any endeavor you may encounter  has it your decision in the end    yours  anna j      happy riding

Thanks for that, was lookin at basset down, its near my daughter so good excuse for a visit,

Re: Dynamic balance ?

Posted by richard_cornish at August 01. 2017

Ni Marcus,

   Just thought I should add a few points. A parallel 360 degree twin is much the same as a single with regard to balance but with the added complication that one cylinder is sucking and squeezing while the other is banging and blowing. Modern designs utilise a secondary balance shaft to help damp the vibration but it will never be the complete answer and of course with a Model 7 you've got no chance. Nortons used a balance factor of somewhere in the region of 50% for most of their touring bikes, but if you read the road tests of the day they very often mention a period of vibration around 55 mph. Dynamic balancing is an elaborate version of having  your car wheels balanced and that gives you the opportunity of making the smoothest period of vibration happen at the speed you use the most, i.e. your cruising speed. What you will probably find is if you have the best balance at say 60mph the bike might be rough at 30 mph. You will probably find the bike will  be smoother than it is now, but don't think this is a cure all process. If you do decide to go for this decide what speed range you most ride at and work out what engine revs that equates to in top gear and ask the balancer if it will be possible.

Regards, Richard.

Re: Dynamic balance ?

Posted by marcus_bloomfield at August 01. 2017

Previously richard_cornish wrote:

Ni Marcus,

Just thought I should add a few points. A parallel 360 degree twin is much the same as a single with regard to balance but with the added complication that one cylinder is sucking and squeezing while the other is banging and blowing. Modern designs utilise a secondary balance shaft to help damp the vibration but it will never be the complete answer and of course with a Model 7 you've got no chance. Nortons used a balance factor of somewhere in the region of 50% for most of their touring bikes, but if you read the road tests of the day they very often mention a period of vibration around 55 mph. Dynamic balancing is an elaborate version of having  your car wheels balanced and that gives you the opportunity of making the smoothest period of vibration happen at the speed you use the most, i.e. your cruising speed. What you will probably find is if you have the best balance at say 60mph the bike might be rough at 30 mph. You will probably find the bike will  be smoother than it is now, but don't think this is a cure all process. If you do decide to go for this decide what speed range you most ride at and work out what engine revs that equates to in top gear and ask the balancer if it will be possible.

Regards, Richard.

Hi Richard,

Thanks for the info, I will think it over some more, while your there, any idea if iron head and alloy head have the same pistons? I have alloy head 54, can only find good iron head pistons,

Marcus

Re: Dynamic balance ?

Posted by anna jeannette Dixon at August 01. 2017
Previously marcus_bloomfield wrote:

Previously richard_cornish wrote:

Ni Marcus,

Just thought I should add a few points. A parallel 360 degree twin is much the same as a single with regard to balance but with the added complication that one cylinder is sucking and squeezing while the other is banging and blowing. Modern designs utilise a secondary balance shaft to help damp the vibration but it will never be the complete answer and of course with a Model 7 you've got no chance. Nortons used a balance factor of somewhere in the region of 50% for most of their touring bikes, but if you read the road tests of the day they very often mention a period of vibration around 55 mph. Dynamic balancing is an elaborate version of having  your car wheels balanced and that gives you the opportunity of making the smoothest period of vibration happen at the speed you use the most, i.e. your cruising speed. What you will probably find is if you have the best balance at say 60mph the bike might be rough at 30 mph. You will probably find the bike will  be smoother than it is now, but don't think this is a cure all process. If you do decide to go for this decide what speed range you most ride at and work out what engine revs that equates to in top gear and ask the balancer if it will be possible.

Regards, Richard.

Hi Richard,

Thanks for the info, I will think it over some more, while your there, any idea if iron head and alloy head have the same pistons? I have alloy head 54, can only find good iron head pistons,

Marcus

 Hello in answer to your query  its NO they are NOT the same compress ratio, the iron heads were 6.5.1  and alloy heads were 7.5.1 and piston designs were both different  has the very early piston had a split the piston shirts  and strengthen bosses where the gudgeon pin fits the model 88 of 1954 has a high piston crown and has drill holes around the oil ring and no split shirt  and are lighter  and in 1954 there were 9.1 pistons has an optional extra  for a cafe racer or racing  the choice was yours  but now with GPM Piston and JP pistons only readily available the GPM are the heavier of the two sets  and you must have the barrel bored to the pistons dimension  and use the GMP piston rings  you cannot mix up the piston rings with Hepiloite  or BHB Or wellworthy or Hap Jones or Novo -covo  has the radiuses are different and ring end gaps should no more than 8 thou,  and piston to bore clearance no less the 3 thou  and you must have a good cross hatch in the bore.   now have fun            yours anna j  

Re: Dynamic balance ?

Posted by marcus_bloomfield at August 01. 2017

Previously anna jeannette Dixon wrote:

Previously marcus_bloomfield wrote:

Previously richard_cornish wrote:

Ni Marcus,

Just thought I should add a few points. A parallel 360 degree twin is much the same as a single with regard to balance but with the added complication that one cylinder is sucking and squeezing while the other is banging and blowing. Modern designs utilise a secondary balance shaft to help damp the vibration but it will never be the complete answer and of course with a Model 7 you've got no chance. Nortons used a balance factor of somewhere in the region of 50% for most of their touring bikes, but if you read the road tests of the day they very often mention a period of vibration around 55 mph. Dynamic balancing is an elaborate version of having  your car wheels balanced and that gives you the opportunity of making the smoothest period of vibration happen at the speed you use the most, i.e. your cruising speed. What you will probably find is if you have the best balance at say 60mph the bike might be rough at 30 mph. You will probably find the bike will  be smoother than it is now, but don't think this is a cure all process. If you do decide to go for this decide what speed range you most ride at and work out what engine revs that equates to in top gear and ask the balancer if it will be possible.

Regards, Richard.

Hi Richard,

Thanks for the info, I will think it over some more, while your there, any idea if iron head and alloy head have the same pistons? I have alloy head 54, can only find good iron head pistons,

Marcus

Hello in answer to your query  its NO they are NOT the same compress ratio, the iron heads were 6.5.1  and alloy heads were 7.5.1 and piston designs were both different  has the very early piston had a split the piston shirts  and strengthen bosses where the gudgeon pin fits the model 88 of 1954 has a high piston crown and has drill holes around the oil ring and no split shirt  and are lighter  and in 1954 there were 9.1 pistons has an optional extra  for a cafe racer or racing  the choice was yours  but now with GPM Piston and JP pistons only readily available the GPM are the heavier of the two sets  and you must have the barrel bored to the pistons dimension  and use the GMP piston rings  you cannot mix up the piston rings with Hepiloite  or BHB Or wellworthy or Hap Jones or Novo -covo  has the radiuses are different and ring end gaps should no more than 8 thou,  and piston to bore clearance no less the 3 thou  and you must have a good cross hatch in the bore.   now have fun            yours anna j

 

 

Sooooooooo, 88 pistons then? must be the same engine basically, with the alloy head, norvil do some nice ones

Re: Dynamic balance ?

Posted by richard_cornish at August 01. 2017

Hi again Marcus,

   Thanks to Anna for the info. As she stated piston weights will vary from one manufacturer to another nowadays and even the originals will vary with over-sizes but within a small tolerance. Also, as Anna said the later pistons will be heavier if they are high compression. If you do go for dynamic balancing this won't be a problem as the balancing machine works out the adjustments. If you statically balance the crank and have the original pistons and some digital kitchen scales you can make the calculation with a pocket calculator to keep the status quo, but if you want to modify the balance, it's a guessing game. As a rule of thumb the faster you ride, the heavier you need the counter balance on the flywheel (effectively making the pistons lighter) from the standard balance factor.

Regards, Richard.

Re: Dynamic balance ?

Posted by marcus_bloomfield at August 01. 2017

Previously richard_cornish wrote:

Hi again Marcus,

Thanks to Anna for the info. As she stated piston weights will vary from one manufacturer to another nowadays and even the originals will vary with over-sizes but within a small tolerance. Also, as Anna said the later pistons will be heavier if they are high compression. If you do go for dynamic balancing this won't be a problem as the balancing machine works out the adjustments. If you statically balance the crank and have the original pistons and some digital kitchen scales you can make the calculation with a pocket calculator to keep the status quo, but if you want to modify the balance, it's a guessing game. As a rule of thumb the faster you ride, the heavier you need the counter balance on the flywheel (effectively making the pistons lighter) from the standard balance factor.

Regards, Richard.

Hi Richard,

Thanks again, I have not got the original pistons, I am guessing I can use 88 pistons, as its the same head and bottom end? probably norvil 88 type.

 

Regards Marcus

Re: Dynamic balance ?

Posted by Barry Carson at August 01. 2017

Re: Dynamic balance ?

Posted by michael_sullivan at August 02. 2017

Barry:  That piston shown is indicated to be Left Hand, I think.  The only right hand one I saw was for a +.030 bore.

Re: Dynamic balance ?

Posted by Barry Carson at August 02. 2017

sorry about that Michael i just saw it said twin so assumed that would be for two pistons of the size required.

Barry

Re: Dynamic balance ?

Posted by les_howard at August 03. 2017

I agree with John Shorter. The model 7 with it's low performance is relatively smooth as standard particularly if you have the cast iron head as this "ton" weight acts as a "mass damper" so heavy it naturally resists high frequency vibration.

In one of the monthly mags (classic Guide I think) Ian Legg rebuilt an iron headed M7 and had the crankshaft dynamically balanced. The photo showed it had the treatment and I was amazed how many huge holes had been drilled in it making it look like Swiss cheese. As I like to keep things as they were historically, that was far too much of a corruption to accept.

 

Les

Attachments

Re: Dynamic balance ?

Posted by marcus_bloomfield at August 04. 2017

Previously les_howard wrote:

I agree with John Shorter. The model 7 with it's low performance is relatively smooth as standard particularly if you have the cast iron head as this "ton" weight acts as a "mass damper" so heavy it naturally resists high frequency vibration.

In one of the monthly mags (classic Guide I think) Ian Legg rebuilt an iron headed M7 and had the crankshaft dynamically balanced. The photo showed it had the treatment and I was amazed how many huge holes had been drilled in it making it look like Swiss cheese. As I like to keep things as they were historically, that was far too much of a corruption to accept.

 

Les

Alloy head mate, new pistons, and no idea of the rods history, so its going to get balanced I think.

 

Marcus

Re: Dynamic balance ?

Posted by anna jeannette Dixon at August 04. 2017
Previously les_howard wrote:

I agree with John Shorter. The model 7 with it's low performance is relatively smooth as standard particularly if you have the cast iron head as this "ton" weight acts as a "mass damper" so heavy it naturally resists high frequency vibration.

In one of the monthly mags (classic Guide I think) Ian Legg rebuilt an iron headed M7 and had the crankshaft dynamically balanced. The photo showed it had the treatment and I was amazed how many huge holes had been drilled in it making it look like Swiss cheese. As I like to keep things as they were historically, that was far too much of a corruption to accept.

 

Les

 Hello LES this Cheese looks more like jasburg  Dutch cheese to me  it lovely  have fun  yours anna j 
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