smooth 65% balance factor and best sealer

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jseng1

jseng1

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I just reduced my balance factor from 72% wet (78% dry) down to 65% wet (72% dry) and its definitely smoother at all RPMs. All balance factors should refer to "wet" specs so you can relate to solid cranks etc. So I'm going on record as recommending a 65% wet BF for Nortons - both solid frames as well as isolastic. I have not yet measured the vibration to see if it shakes one direction more than another. I reduced the BF because it was shaking horizontally more than vertically with the 72% wet BF (too high). If I get more scientific representation later then I'll post it.

I ride a solid frame but the 65% BF also applies to isolostic frames. Remember that the swingarm, pipes, engine cradle, rear wheel, carbs - all that heavy stuff is connected to the motor and there really isn't much BF requirement difference between isolastic frames and solid frames - even though there are different opinions.

Also - using string on copper head gaskets is not necessary. Yamabond or Permatex Motoseal #29132 (or "the right stuff" by permatex) smeared thinly on upper & lower surfaces around the pushrod tunnels and oil return hole seems to be leak proof. Loctite #518 works OK on the crank case split but it won't hold at the bottom of the cylinder flange because its worms its way out under the vertical vibration.
 
Yes - with lightweight JS pistons. The lightweight pistons change a stock Commando BF from 52% up to 65% and everyone I hear from says the ride is MUCH smoother with the lightweight JS pistons and 65% BF.

No amount of balancing perfection for a Norton will solve the problem of severe vibration with stock or heavier pistons. Its either bad or worse.
 
Jim, my all stock mk 3 is smooth as glass above 3 k, the mirrors at 70 mph on the freeway are as still as in a new car. It does shake a little from idle to 3 k however, although I don't spend much time in that range. Would lightweight components make much of a difference to the low speed operation?


Glen
 
worntorn said:
Jim, my all stock mk 3 is smooth as glass above 3 k, the mirrors at 70 mph on the freeway are as still as in a new car. It does shake a little from idle to 3 k however, although I don't spend much time in that range. Would lightweight components make much of a difference to the low speed operation?


Glen
Click to expand...

I ride a feattherbed so Personally I cannot say but one customer with lightweigh JS pistons said his Commando was much smoother and that there was "no vibration at all" up to 3500 RPM".


The paragraph below is from the bottom of my balance web page in the tech section at:

http://www.jsmotorsport.com/technical_balance.asp

"If you just lighten the pistons and don't change the flywheel counter weight of a Commando crank, the balance factor goes up and the motor runs smoother because - the higher balance factor reduces the up & down shaking of the pistons (reciprocating weight), but the fore & aft shaking (rotating weight) stays the same because the lighter pistons do not affect the fore/aft counterweight shaking forces when the flywheel counterweight is at 90 and 270 degrees (half way through the stroke). So the fore & aft shaking stays the same but the up & down shaking is significantly reduced and this is why you don't have to rebalance a Commando crank for lightweight pistons - it will always run smoother and with less stress with lighter pistons. As noted earlier, the Norton production racers used a 62% balance factor. You can re-balance your Commando crank at 54% for the lighter pistons but in my opinon, a wet balance factor of around 65% is an excellent choice for Commandos and that is what you get by just installing the lighter pistons. Note that a wet balance factor of 65% equals a dry balance factor of 72%."

The above would be true the more you lightened the pistons up to the point where your BF became 100% - but you could never achieve that and anyway, you should rebalance before you get thet high.

The only way I know of to determine the ideal BF is covered in an earlier post at:

balance-factor-scratch-test-tool-t15134.html?hilit=BALANCE%20FACTOR%20SCRATCH%20TEST%20TOOL
 
Interesting finding Jim. Your light psitons/rod shot Peel BF into 90's% as I guessed to start with 77% on prior Cosworth lightened pistons. I felt guilty asking Ken Canaga to bore through nitride flywheel to bring BF down into upper factor range.
Peel had extra cushions in rear and bevealed ones in front that definitely lower the disapearance threshold in lower 2000 range. My pure factory Trixie isolastes nicely before 3000 rpm and gone before 3500 rpm hwy cruise. Ken left threads in flywheel so can fine tune to Peels structures with most attention to how it harmonizes with tire sounds rather than smooth ride sense.

I"m confused a bit - thot the oil mass in crank raises dry BF a handful of points not lowers it. 750's dry 52% BF become like 63% wet, I think.
 
Hi Jim BF of 63% achieved by using a std crank, -0.010" grind on the big ends to clean them up, your rods, +0.040" pistons and pins Stuck to the 0.090" radii
Trying to upload chart but IMG codes wont copy at present from photo bucket
Regards Mike
smooth 65% balance factor and best sealer
 
jseng1
Interesting post,
Just a small point ,i read some where that at 7000 rpm there is no oil in the crank, ie zero pressure due the the central forces flinging out the oil from the crank,quicker than the pump can replace it? so if this is correct the crank balance must change fron "wet" to "dry at high RPM?
 
hm, do cranks sling out more oil than refilled? My Combat's & others may show no oil pressure at 7000+ but they sure as heck flow enough oil through to wet sump and supply the rod ends from spin sling. Its entirely possible d/t some fault not to flow enough oil to fill crank but its not d/t a factory short coming to flow a sufficient supply to keep crank full or the rods would seize or at least wear out a whole lot faster than they do in practice. There are examples and I had one of them of Cdos that were made to often reach 9 grand yet oil pump still factory issue.
 
Rechecked history of calc's for wet vs dry BF to find 52 dry becomes 63 wet. Lighter pistons or heavier oil filled crank both raise BF not lower it. If so then Jim's figures are reversed typo or logic error and better smoothness gotten in mid 70's% zone, as our motion witness marked implied to aim for.
 
There was a typo but it was in the old 750 manual. They finally fixed it for the MkIII manual.

" Lighter pistons or heavier oil filled crank both raise BF not lower it." Lighter pistons, yes. Oil filled crackshaft, no. IIRC.
 
Jim's lighter pistons shoot BF way up I found out by extra expense crank mass change, so got that factoid ingrained.
We add mass to the crank to raise BF, so should the extra oil mass inside vs dry BF.
The typo I was referring to is Jim's initial post logic not the manual we known is full of typo's and errors.

Bob your report of smoother with extra rear cushions was very informative to me as I changed so many things in past Peel I don't know what all was making such a nice and transforming improvement in her that my reports are not believed but is sole reason i'm spending an extra decade and 10's of $1000's more to take more advantage of the smooth secure crazy making transformation. While yoose guys are discussing BF for comfort, disappearing Ms Peel is designed to experiment with the BF power pulses on tire edge traction. At this point of my knowledge I'm still thinking mid 70's Wet BF is way to go. Hope by then to have a means to measure vibration at the handle bars or other mounts then pass it around to see the scope of sets ups. Do realize I do not compare Peel sensations and handling to old clunker Cdo's or even elite vintage racers, nope I'm into showing up over loaded Goldwing buzzers and over powered elite corner cripples, at least up to Peel blown big block hp limits. i could not imagine such a result either so don't expect anyone else too w/o full proof.
 
hobot said:
We add mass to the crank to raise BF, so should the extra oil mass inside vs dry BF.
Click to expand...

So if a Commando crankshaft is balanced at 52% dry which way do you (or anyone else) think the effective balance factor will be when the journals fill with oil? :oops:

Looks like jseng1 is stating the direction of the wet to dry difference correctly.
 
From Phil Irving, "Tuning for Speed" regarding Balance Factor:

"There are in fact so many considerations involved that it is impossible to quote one figure as being the ideal, since it varies with every type of engine, and even for the same engine in different or differently-equipped frames."

Regarding an appropriate balance factor and Phil Irvings nice summary above, a Commado is different from a Featherbed; a cast iron barreled Commando is different from an alloy barreled Commando; a light weight Featherbed is different from a street ladened Featherbed; a verical Atlas is different from a Featherbed with converta plates and an inclined motor; lighter rods and pistons are different from heavier rods and pistons. A Commando in a steel cradle is different from a Commando in an alloy cradle. The list goes on.

It has to do with so many things including the distribution of the masses, engine speed & harmonics, how the masses are connected (example: solid versus Isolastic).

This is not to diminish what jseng1 reported as his experiencee with the change at the start of this thread but it is specific to his application and can certainly be used as guidance for others. I would like to hear from more with Commandos and the conversion. We do know that less reciprocating mass is a winner no matter how you look at it and in my opinion, you really cannot go wrong.

I posted a nice summary about three quarters of the way down the thread below; bullets 1, 2 & 3.

http://www.accessnorton.com/balance-factor-scratch-test-tool-t15134.html
 
I read that Phil Erving , wrote that Vincent owners who complained about vibes ,found that the Re-Alignment of the crank corrected matters,
Is it correct that commando cranks are not even paired ,that webs and flywheels are randomly assembled from a "couple of bins" ? If that is the case then some mis-alignment may be present,with the vibes transmitted from such mis-alignment?

just how where the cranks made, engineering wise the whole assembly should be dowl fitted and all the diameters ground...keeping all these parts to gether?
Please correct me if this is not the case?
The flywheel face's dont look "super finnished" any small degree of taper will mis- aligned the whole assembly.
When Tony Maughan was alive he showed me how the Vincent crank assembly was put together, errors where kept to a minimum 1/2 a thou !
Remarks very welcome please.
 
Dances with Shrapnel said:
So if a Commando crankshaft is balanced at 52% dry which way do you (or anyone else) think the effective balance factor will be when the journals fill with oil? :oops:
Click to expand...
The balance factor will go down. The screwed up numbers in some of the 750 manuals were a topic of discussion on BI around 15 years ago. Kinda like the switched oil lines in one of the diagrams of the same vintage.
 
A dry BF on a stock Cmdo crank is about 7% higher than the same crank measured wet. So a 52% wet Cmdo crank would be about 59% dry. This changes with solid cranks that don't have an oil sludge trap.

Oil cannot sling and empty out of a cmdo crank because the oil holes are on the side - not top & bottom. The sludge trap is always 1/2 full.

I don't believe all the talk about different frames needing different BFs. Just imagine a naked engine and what BF it would need. The crank wants to be balanced against the reciprocating forces of the pistons. 100% is best for the vertical piston motion but then the counterweight throws the motor fore & aft when the pistons are 1/2 way up. So a compromise is made and in my opinion its best around 65% wet (maybe less but I haven't made accurate tests below 65%).

Different frames can have a vibration problem at a certain RPM and I have seen this happen when motor mounts break - but the vibes stay about the same throughout the RPM range. But adding or subtracting weight will only change the intensity of the vibration. The heavier the frame and flywheel the more it will dampen out the vibes and make the motor FEEL smoother. Someone will have to prove to me with tests (not just math) that lighter bikes need different BFs.
 
Would be good to get feed back from a few on say Commandos who went with the lighter rods and pistons and brought the balance factor down to the factory correct 52% dry. Just saying it would be nice to see a few more opinions on this.

As for math, just about anybody can build a suspension bridge so I see what you are saying - right? And who is Phil Irving anyway? Furthermore, the math says the Norton should vibrate less with lighter pistons and rods so I for one would not be too quick to throw the baby out with the bath water.

Today you can numerically model vibration of systems with computers but in the past it was trial & error with some measurement and some seat of the pants. Right now we are talking about the latter. Even with the best of math and engineering there is testing. In other words, trust but verify so I do understand where you are coming from.

In the big scheme of things the Norton twin survived well in most applications with balance factors from 52% dry to beyond 80% dry so it really comes down to points 1 & 2 of my post reference above which have to do with 1.) not breaking the frame and 2.) comfortable at some nominal rpm range.

Again, if one can simply bolt on the lighter JSEngineering rods and pistons without a rebalance and have a successful outcome then this is very good.

My questions are: is there a wealth of experiences out there to support that and can it be smoother in a Commando if you rebalance to the factory tested and recommended 52% dry?

I know when we did dyno pulls with the 1,007cc using JSEngineering pistons and rods (at 75% BF) it exhibited surprisingly little vibration through to 7,000 rpm and it spun up quick - all good stuff.
 
who "was" Phil Irving OBE Vincent designer,Velocette and Brabham.....Aussie Engineer with a "bit" of Know how!
Dances with Shrapnel said:
Would be good to get feed back from a few on say Commandos who went with the lighter rods and pistons and brought the balance factor down to the factory correct 52% dry. Just saying it would be nice to see a few more opinions on this.

As for math, just about anybody can build a suspension bridge so I see what you are saying - right? And who is Phil Irving anyway? Furthermore, the math says the Norton should vibrate less with lighter pistons and rods so I for one would not be too quick to throw the baby out with the bath water.

Today you can numerically model vibration of systems with computers but in the past it was trial & error with some measurement and some seat of the pants. Right now we are talking about the latter. Even with the best of math and engineering there is testing. In other words, trust but verify so I do understand where you are coming from.

In the big scheme of things the Norton twin survived well in most applications with balance factors from 52% dry to beyond 80% dry so it really comes down to points 1 & 2 of my post reference above which have to do with 1.) not breaking the frame and 2.) comfortable at some nominal rpm range.

Again, if one can simply bolt on the lighter JSEngineering rods and pistons without a rebalance and have a successful outcome then this is very good.

My questions are: is there a wealth of experiences out there to support that and can it be smoother in a Commando if you rebalance to the factory tested and recommended 52% dry?

I know when we did dyno pulls with the 1,007cc using JSEngineering pistons and rods (at 75% BF) it exhibited surprisingly little vibration through to 7,000 rpm and it spun up quick - all good stuff.
Click to expand...
 
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