Vibration genetics dynmamics

From Doug Mcquire in Oregon on how simply complex a Commando's nature can be... speaking to another list, so nothing personal here...

You guys are missing a major point in engine vibration, Namely, the engine.

Engine balance issues almost always come down to manufacturing flaws. Of course the design is the primary cause with the vertical twin, but all in all, BSAs, Norton and Triumphs all are really pretty similar.

It comes down to how well each one was put together. Early BSAs i suspect had the best quality control, followed closely by Triumph, with Norton a VERY distant 3rd.

A Norton, regardless of C-do or earlier all have many flaws and faults, but in my experience, and i live a very short distance from Kenny Dreer, as well as some other very knowledgeable Norton builders and Tuners such as Sir Eddy, Mike Ferrell, DJ, Dick Slusher and others who have even more experience than I do all comes down to if you want to solve the majority of your vibration problems then carefully blueprint the internals, and balancing solves the rest.

I have a GREAT dynamic balancing shop i use, every Norton crank i have had done was WAY off in balance, a huge amount of rocking couple, as well as casting variations.

Once corrected people cannot believe the difference. I have seen some commandos that would shake your teeth out even with the Iso's.. problem solved with the dynamic balance.

When Eddy started the LSR project i gave him a number of Commando cranks. On one he found the throws had been off, mismachined. 20 or 30 thou difference from one side to the other (email him and ask the specific number)... do you think that might effect the vibration a bit?

We found another crank where it had never been apart from the factory, but we learned why it probably was parked and taken apart,,, or at least why i think so,,

the factory lock tabs were still in place, but once prised away, we found the bolts for the crank assy/flywheel were only finger tight. Again, any guess's on if that would effect vibration?

Ive also found piston and pin combos where they varied by 7 grams from one side to the other, any speculation?? any ??

Eddy says a very common issue is machining tolerances and dimensions related to the cylinder to the case and the crank, running crooked parts might have something to do here with vibration...

Another friend,,, who has owned many Nortons over the years including some he bought new off the dealer floors speculated on how some were better than others, some were perfect and needed almost nothing in Maintenance,,, others were constant problems. The ongoing issue again and again is how well it was put together, some bikes were midmorning wednesday bikes, some were beer thirty bikes.

Nortons are usually great bikes, but many of their problems could have been avoided if they had built them properly in the first place instead of expecting the owners to accept these problems or sort them themselves.

plenty of anecdotes from Nortons own staff about the garbage they knowingly shipped out the door.

Harley learned this the hard way too in the AMF years,, and how recommitting to quality brought them back into the success they grew too.. An antiquated design, but improved to asian bike reliability over the years, No mystery how HD ended up with so many people riding their bikes... something its a shame Norton didnt do. Imagine where we would be today if they had.

Interesting response by RohanB ...



Royal Enfield Interceptors were all dynamically balanced from new.
While this apparently smoothed them out, they still vibrated. Although test reports said they were vastly better than previously.

What wasn't fully appreciated at the time was how important frame reasonance was in taming vibrations. These days, any Engineering student can buy a computer 101 vibration analysis simulation kit for a few bucks, plug in all the numbers and see which bits are the problem.
The Yamaha XS2 was the first bike to benefit from this ??

Stiffening - or lightening - various bits can move the vibration around - or shift it up and down the scale.

Some of Nortons previous heavy frames had problems with frame cracking, where Matchless /AJS lighter looking frames had almost no frame breaking problems at all. And had a notably smoother ride, with very similar engines.

Or you can go for the HarleyD or Goldwing school of vibration dampening - make it so heavy the vibrations get lost !

P.S. Improving combustion chamber dynamics also seriously influence vibration output - these EFI systems have tamed down some rough diamonds to be real smoothies.

Opethiselps.

Most interesting. I've put off the assembly of my 850 motor for this very reason; getting it DYNAMICALLY balanced. And, I've had all the pieces ready to go for awhile now; but just couldn't bring myself to assemble without having this done. I've considered "House of Balance" in Maryland, any other recommendations out there ??? BTW, great post Steve !!!

Very good post. I learned several things.

For the average guy with an average stock (ish) Norton, what is the cost for dynamic balancing, not counting the teardown/buildup?

About $300 if nothing found wrong, just fine tune of static and dynamic balance.
I used Lindskogs and also Geoff Collins, but only on Ms Peel as I want to keep all the factory warts on Trixie for true baseline to remind me what rest of Cdo world endures as normal. Internals balanced and rear rod + helpers seem to eliminate all but the turbofan smooth shove on ass as sense of bike underneath. Uncanny.

As far as balancing con rods and pistons, how do you accomplish that? Mine were out and I was happily grinding away on the heaver side steel con rod lower end, but was really unsure of what I was doing and stopped before I got too far. I was out of balance there by maybe less than a half oz. What and where do you grind to remove material to make balance and what is acceptable?

Dave
69S

Mmm ... those are my questions too Dave. I like to take apart and assemble everything on the Norton, but I'm in the dark about the machine work/balancing stuff. :? Perhaps learn more from posts on this forum ... and also pick the experts brains at the rally next week.