Balancing Atlas crank

If it were me, I'd ask Mr. Hemmings.

About to become the proud owner of a 68 Atlas that needs finishing. Friends say, no matter what MAY have been done to the engine, strip it and send crank off for balancing otherwise an Atlas will shake your fillings out.

Question is, where to send it and how much might it cost?

If it were me I wouldn't take any notice unless said friends each had an Atlas that has been radically improved by said balancing. I bet they've just read about it in one of the glossy mags; and the journalists by and large repeat the same stories for decades. Saves doing real research.

Even then, after spending all that cash, owners who have changed the balance factor would say it was a good idea, wouldn't they?

The laws of physics cannot be changed: if a parallel twin is balanced up and down then it vibrates backwards and forwards - and vice versa. If it's balanced in between then it vibrates a bit less but in both directions. A big one will vibrate more that a little one. Hence the Commando...if Norton could have improved it 'simply' by changing the balance factor then that's what they would have done...

You could always buy a BMW instead. Just a thought.

Well said David. My Altas-engined 99 vibrates but my fillings are safe and I can ride it all day and still feel my fingers. Just get it up and running and ride it. If you want to feel real vibration, forget to put the head steady on, as I did as an 18 year old who had bought a dismantled 99. Cor it was bad - shook the speedo to bits and the plates off the battery!

Previously andrew_orr wrote:

About to become the proud owner of a 68 Atlas that needs finishing. Friends say, no matter what MAY have been done to the engine, strip it and send crank off for balancing otherwise an Atlas will shake your fillings out.

Question is, where to send it and how much might it cost?

Any thoughts?

Andy

Get the crankshaft balanced as thecrankshafts that were balanced at AMC Plumstead or the Norton Matchless division was 1 in 10. I know this as an American dealer friend of mine when he visited Plumstead with Joe Berliner watched the guy balancing the Norton twin crankshafts. One he did perfectly with the weights on, and the other 9 as per the one he had just done. I have 12 Atlas engined bikes, and the ones that have had their crankshafts rebalanced run much better. Get the crankshaft dynamicaly balanced and not statically. Royal Enfield alway dynamicaly balanced their twin crankshafts.

Ride it first - you may find that you got one of the nicely balanced ones...

hi i think that this is a bit of good advice !!! as i the first time i rode my 65 atlas that i restore i was shocked at the vibration and it has a tooth over standard gearing to keep the rev's down and was running itin,so the next thing is a crank rebalance.

Previously anthony_curzon wrote:

Previously andrew_orr wrote:

About to become the proud owner of a 68 Atlas that needs finishing. Friends say, no matter what MAY have been done to the engine, strip it and send crank off for balancing otherwise an Atlas will shake your fillings out.

Question is, where to send it and how much might it cost?

Any thoughts?

Andy

Get the crankshaft balanced as thecrankshafts that were balanced at AMC Plumstead or the Norton Matchless division was 1 in 10. I know this as an American dealer friend of mine when he visited Plumstead with Joe Berliner watched the guy balancing the Norton twin crankshafts. One he did perfectly with the weights on, and the other 9 as per the one he had just done. I have 12 Atlas engined bikes, and the ones that have had their crankshafts rebalanced run much better. Get the crankshaft dynamicaly balanced and not statically. Royal Enfield alway dynamicaly balanced their twin crankshafts.

Previously david_cooper wrote:

If it were me I wouldn't take any notice unless said friends each had an Atlas that has been radically improved by said balancing. I bet they've just read about it in one of the glossy mags; and the journalists by and large repeat the same stories for decades. Saves doing real research.

Even then, after spending all that cash, owners who have changed the balance factor would say it was a good idea, wouldn't they?

The laws of physics cannot be changed: if a parallel twin is balanced up and down then it vibrates backwards and forwards - and vice versa. If it's balanced in between then it vibrates a bit less but in both directions. A big one will vibrate more that a little one. Hence the Commando...if Norton could have improved it 'simply' by changing the balance factor then that's what they would have done...

You could always buy a BMW instead. Just a thought.

Not sure what to make of this last jibe. As it happens I have Beemer, oh and a Commando and a Dominator. I ride both nor tons regularly. My original question was about where to get a good job done if I do have the crank balanced.I think I will get it up and running and ride it first. However, my friends who advised getting crank done all have Norton twins,including one Atlas.

Sorry - I apologise - I didn't mean to be rude. I just wonder what magic the balancing experts exert.I read that Basset Down are often mentioned favourably

http://www.bassetdownbalancing.co.uk/bike_services/balancing/bike_twin_cylinder.html

But they can alter the balance factor which will shift the excitation direction and the owner will certainly notice the difference. Anthony has vastly more experience than I in suchresults and it sounds as if you do also.I wonder if the bestbalance factors are public knowledge?

Dynamic balancing will control the rocking couples but surely in a parallel twin they must be very small compared with the primary and secondary effects? But without balance shafts the parallel twin will always be out of balance in one direction or another. The opposed piston BMW styletwin can be in perfect balance - but even thenunless the con rods are forked (like Harleys)the rocking couple will still remain - causing oscillating rotary direction vibration forces around the vertical axis.

Likewise 90 degree cranks like the new Norton are better but still cannot be perfect until the angle opens to 180 degrees (Boxer) - at 90 degrees roughly half the inertia forces remain. Hence the need for balance shafts.

Has anyone bothered to try fitting external balance shafts maybe in the old dynamo location in front of the original Norton twin? One might waste a lot of money and effort on such an experiment...

On a production line where all components are mass produced using the same methods it seems quite possible that 'properly' balancing one in ten is acceptable. It will pick up the time when something has gone wrong - and the previous ten could be re-visited. But since the precisely best balance factor isn't precisely known it is a bit of waste of effort to get it precise on every single one. It's common on production lines to test samples of the product rather than every item manufactured.