Commando Crankshaft Porn

Stayed up reading on crank and shaft critical speeds and all the influences on that but didn't post here as very very long and equation filled drudgery to get the plain language basics. So Twiddle and Tweedledum are both right and wrong as what matters most is simply how far from a support a flywheel disc mass is located to judge its whippoorwill effect on crank and the longer this is the slower lower the critical speed occurs when harmonic forces of cyclic spring back and trust magnify greatly. A flwheel mass between 2 supports is inherently more stable that one hung out cantilevered, unless of course it tight up to a robust bearing.

What might help the most 360 twins is a dual mass damper with friction or viscous meterial in between. So a massive ring cushioned around the basic crank shaft dia may allow more rpm before the jump rope bowing suddenly occurs.

There are examples of no flywheel engine that run on pure combustion power but would suck in traffic as more on/off engine response. Aircraft prefer these.



I'm a bit steam traction engine studied so assume center flywheels in 360' twins was mostly for being a compact sightly cheap way to package rather than most extreme tolerance to rpm. On the other hand having stiffening plate/flywheel cheeks on either side of rod throw to spread the center mass also tames sling distortion.

Oh yeah on Ms Peel her flywheel is about1/2" smaller OD so bit like ballerina pulling in arms. Nitrided all over the solid welds in case that helps.

Yes, good example of a four cylinder crankshaft; probably flat four if it is aircraft. Note the crank throws are 180 degrees apart between the main journals.

Still looking for an example of a parallel twin 360 crank w/o center main that does not have a central mass flywheel. Would even be interested to see if there's an equivalent instance of this in a multi cylinder engine.

Do I hear crickets?

Now , these young puppies , I dont know , it wasnt like this when . . . . :lol: :shock: :wink:
Reputed 9.000 from the Austin 7 . Then theres the Eddie Dow 10.000 Goldstar , and other mythical creatures . :?
This is the modern Pheonix crank , the original was more like a piece of twisted Number Eight Wire .

Matt Spencer said:

Now , these young puppies , I dont know , it wasnt like this when . . . . :lol: :shock: :wink:
Reputed 9.000 from the Austin 7 . Then theres the Eddie Dow 10.000 Goldstar , and other mythical creatures . :?
This is the modern Pheonix crank , the original was more like a piece of twisted Number Eight Wire .

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Whoa! The holy grail. Good find.

I think they call this a plane crank where all the throws are in one plane. Counter weighting is in balance

Close but no cigar :lol:

You basically have two 180 degree cranks married together ; not quite the same.

In my mis spent youth a did a lot of wrenching on AH Sprites. 1,098 seems to ring a bell but I just cannot recall whether they used a center main; I am pretty sure they did.

Let's see who can roust up a parallel twin 360 crank w/o a center bearing and no center flywheel mass.

I am starting to see a pattern here where no credible one exists.

Hmm, wonder why?

Dances with Shrapnel said:

In my mis spent youth a did a lot of wrenching on AH Sprites. 1,098 seems to ring a bell but I just cannot recall whether they used a center main; I am pretty sure they did.

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I think Sprites had the Austin/BMC A Series engine as did Morris 1000s and Minis: it had three main bearings.

Dances with Shrapnel said:

Let's see who can roust up a parallel twin 360 crank w/o a center bearing and no center flywheel mass.
I am starting to see a pattern here where no credible one exists.
Hmm, wonder why?

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I like your idea that the center flywheel mass acts as a damper, but I'd take more convincing that the flywheel was put there for that reason. Wouldn't it be the case with an air cooled parallel twin that you have to have a certain separation between the cylinders? and if you weren't going to use that space for a center bearing you may as well put the flywheel there?

Young TURNERs design was concieved to appear as a single , to calm those who considered unnesesary bits as something extra to go wrong .a " Twin Single " in fact . Hopwood ? We'd better ask Him .

ggryder said:

Dances with Shrapnel said:

In my mis spent youth a did a lot of wrenching on AH Sprites. 1,098 seems to ring a bell but I just cannot recall whether they used a center main; I am pretty sure they did.

Click to expand...

I think Sprites had the Austin/BMC A Series engine as did Morris 1000s and Minis: it had three main bearings.

Dances with Shrapnel said:

Let's see who can roust up a parallel twin 360 crank w/o a center bearing and no center flywheel mass.
I am starting to see a pattern here where no credible one exists.
Hmm, wonder why?

Click to expand...

I like your idea that the center flywheel mass acts as a damper, but I'd take more convincing that the flywheel was put there for that reason. Wouldn't it be the case with an air cooled parallel twin that you have to have a certain separation between the cylinders? and if you weren't going to use that space for a center bearing you may as well put the flywheel there?

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Fair enough statement. As the records and people are gone who designed and built these engines. We are left with intuition and logic to work it out. I am not sure if there is really any difference between an air cooled and water cooled parallel twin with respect to space between two adjacent rod journals. It would be governed by bore diameter in that the bore centerlines are a little more than a bore diameter apart (unless you decide to put a cam chain there).

Maybe the question is why didn't the Brits put a center bearing in there. I am speculating here but maybe there may have been some design philosophy with regards to a vertical split case being better than a horizontal split case. Staying with a vertical split case makes a center bearing difficult and lubrication a little more complex. I read where Matchless had a twin with a center bearing and presumably a vertical split case.

So if there were design philosophies that favored a vertical split case this more or less precluded a central bearing so you are left with a dampening mass. My hunch at this time is that the mass is a proxy for a middle bearing in this particular instance.

This gets back to another posting where the question was posed (off list) about Nitriding crankshafts. Was Nitriding introduced as a surface wear durability enhancement and was then recognized for its ability to enhance the flexural durability, was it the other way around or was it both. A similar thread is the patent on the Norton twin cylinder head. Speculation on my part but I suspect the driving inspiration was to spread the exhaust ports further away from each other to allow more cooling fins yet this did wonderful things with respect to the intake valve/port geometry which makes Norton heads flow very good. Was this dumb luck or insight to all that was happening with the new design.

But back to the center mass issue. I think I have been cautious to state that "they got it right", out of inspiration and insight or shear dumb luck I do not know. My hunch is they knew what they were doing due to the apparent abscence of any significant crankshafts that are parallel twin 360 w/o a center bearing and without a center mass/flywheel.

I do see your point that maybe it was a matter of convenience but I suggest there are industrial and non motorcycle applications (parallel twin 360 crank w/o a center main) where space is not a constraint and a flywheel could be placed on the outside (and no center dampening mass) yet I cannot think of an instance where this was done.

As for the Healeys, I recall there was also a 948cc and a 1275cc. When you mentioned the sprite engine had middle main I had a flash back to the days peering down into the bottom end and seeing the two chambers. Neat stuff.

' As We All Know ' :lol: The manufacturers existing tooling and machineary were a dictum in their design development.And three bearings have more drag than two , when two are more than adequate .
It wasnt untill the tuned 60 HP 650s that the Ball Bearing load capebility / durability came into question, and two ball races were still less drag than two rollers , so worth maybe half a horsepower, at least.
Also inhibited rate of acceleration rotationally less .So if ou were after speed , they were still adequate , you just changed them out more frequently .

As an aside , Dunstalls heavy duty deep track Eight Ball H.Duty ball races were were the increased ridgidity / alignment causein crank breakages first came to light.Not entirely a sucess .
It wasnt untill the Barreled Roller Hoffman ' roller ' ( Barreled roller and track ) were utilised that the whip could again occur without something gnashing .

The flywheel has a lot of work to do , being a counterweight as well as a inertial dampner . The sums for its natural rotational displacement would be quite interesting .
This is what computors are for . PROVIDED the correct parameters and figures are utilised by the programmer .

The sums for the force through the big ends being seperately calculated . the Primary Forces being combustion when the rod is approximately tangental to the throw ,
and the reorganiseation of the pisto travel at the ends of the strokes .Hopefully .Piston ring drag being opposite disposition to piston inertia . Quite simple really . :lol:



L.J.K. Setright .

http://www.goodreads.com/author/list/60 ... K_Setright

:shock:

One data point to add to our ponder
Single-cylinder engines require both a larger flywheel and a heavier-duty gearbox


T16 engine but with 270' throws with looks like a center bearing, hm










For stress loads graphic of 360' twin and other degrees twins
http://www.xs650.org.au/smoothness.htm

Ain't read it yet, posted cause may not find again and must shut down this 'puter.
http://www.xs650.de/tips/rephase-e.htm

hobot said:

One data point to add to our ponder
Single-cylinder engines require both a larger flywheel and a heavier-duty gearbox


T16 engine but with 270' throws with looks like a center bearing, hm

For stress loads graphic of 360' twin and other degrees twins
http://www.xs650.org.au/smoothness.htm

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All of the above have central bearings so a big "not applicable" but interesting.

To me this quest is getting interesting but I am easily entertained by odd stuff.

Granted the lack of a center bearing in our beloved Norton twins has been belittled by some yet in my opinion it looks like w/o a center bearing it is beneficial do something (ex. mass above and beyond a porkchop for balance).

So this is the grand inquisition, the gauntlet has been thrown down: Let's see who can roust up a parallel twin 360 crank w/o a center bearing and no center flywheel mass.

Thanks for noting what I couldn't tell well -these Not-Nortons have middle bearings.

Ok John, let me see if I get your point, that there is some performance/ endurance advantage in an unsupported central flywheel in 360' twins and hunting excpetions to that rule. I've hunted w/o success, bfd, so won't put a bet against your statement being true, yet have not found a reason beyond compactness for a center lump. I also can't find enough info to refute your claim the center mass ring helps stablize the weird going ons in 360's vertical-ish twins.

Look ma, No Wrist Pin!
[video]http://www.youtube.com/watch?v=0H0stoFw3DY&feature=related[/video]

hobot said:

Thanks for noting what I couldn't tell well -these Not-Nortons have middle bearings.

Ok John, let me see if I get your point, that there is some performance/ endurance advantage in an unsupported central flywheel in 360' twins and hunting excpetions to that rule. I've hunted w/o success,

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I am beginning to believe that for manufacturing and generic use and as a general good design practice, the center mass and flywheel also acts as a proxy for a center bearing on a parallel twin 360 configuration. As someone else has suggested, putting all this mass to one end of a Norton twin engine would be a disaster. I can honestly say I have not seen a significant manufacture in that configuration without a center mass. In the beginning of this topic you see all sorts of "porkchop only" crankshafts. Clearly this reduces an engines rotational mass as well as a bikes translational mass. I am not saying it is a wrong direction as it is the direction for the application and in racing there are sacrifices. I have a lightweight one piece that is excatly that configuration.

If you want to reduce a Norton twins vibration, add mass to the engine. Where does it make the most sense to add the mass, in the center of the crankshaft; for a Norton twin at least. The whole point is this practice seems to be more or less universal for a parallel twin 360 w/o center bearing.

That is why I was soliciting your help but it looks like you reached the end of the internet.

John, and naysayer, wish you'd leave the data base you're working form so rest of us can catch up. How does center mass subsitute in some way for a fixed bearing support? I can see the extra stiffness of big thick heavy disc in middle of a crank but also see it as detrimental at some rpm from piston jerk down deflection taking it into shaft critical speed. But do note, shaft critical speed is only over a certain zone of rpm/harmonics and some cranks can be rev'd beyond that upseting zone safer than staying in the positive feeback zone.

In the really olden days 360' twins were called "Straight Two's". Here, see if you can pick out the main feature the English companies got sold on, besides cosmetics of course, which may be the main reason we're 1st addicted to Cdo's.

* A parallel twin is cheaper to make, having only one cylinder block and one cylinder head.
* Both cylinders can have the exhaust pipe exiting at the front, in the cool air stream.
* Siting of ancillaries (air-filter, carburetters, ignition etc.) is simpler.
* This simpler layout can potentially make maintenance access easier.
* The parallel twin is both lighter and shorter, allowing a lighter frame and shorter wheelbase.

*The BMW F800 parallel twin motorcycle is a 360° design. Inherent vibration in the BMW F800 means its engine is limited to 9,000 rpm. BMW reduced the vibration using a third "vestigial" connecting rod to act as a counterbalance.

http://en.wikipedia.org/wiki/Straight-two_engine

hobot said:

http://en.wikipedia.org/wiki/Straight-two_engine

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From the above reference: "A modern development is the 270° crank, which imitates the sound and feel of a 90° V-twin. A 270° engine requires a balance shaft to reduce vibration"

OK, modern in terms of the pre industrial revolution? Requires a balance shaft? Sounds like this was written by someone from Generation Z. This is why I take what I read on the internet with a grain of salt.

The balance of the article seemed ok; at least they showed a Norton as an example.

As for explanations for how the center mass dampens; re read all my blatherings above. The main concept is the mass really does not want to translate up, down, forward or aft because of its mass. Even without a central mass there are harmonics, nodes and anti nodes the crankshaft will (hopefully) transition through unscathed, both torsional and flexure. Think simple, think the bar weight scenario.

Fresh Crank Porn

All work shown is by Herb Becker, Norton engine builder extraordinaire and all around good guy. This engine configuration was a collaboration between Herb Becker and myself; Herb did the work and I provided encouragement and cubic meters of money.

The crank


The crank, view #2


Top view of cases with crank and middle bearing carrier


Side view of crank, middle bearing carrier and PTO crankcase halve.


Rods, cranks and center main bearing carrier. Herb makes the rods and they have not given a hint of trouble on any of the engines he has built for me.


13.5:1 compression ratio, around 74mm bore


And this is how we make the oil go into the center bearing to feed both rods.


Needless to say this is a very angry motor with a 59.6mm stroke. Best dyno pull we did was 64 rear wheel HP. RPM was 10,700; it has seen past 11,000 rpm. Herb said he did most of the metal removal and shaping of the crankshaft on the Bridgeport vertical mill in his shop.

I don't recommend anybody doing this as it is really pushing beyond the limits of pushrod technology.

The engine goes in a Colin Seeley Mk2 with a TTIndustries magnesium cased six speed. The bike weighs 265 lbs wet. We've since toned this motor down a bit for obvious reasons. Won a few races with it , did well in a few races and blew up in the rest. :cry:

Needless to say this engine has been one interesting journey and a real credit to Herb Becker.

Ah Ha .

Is that to transfer the flex from the crankshaft directly to the cases for vibration .

NOW , Have you seen a Sunbeam S7 - S8 Crankshaft . It appears to meet youre criteria . :wink:

Well John you and Herb have done jumped over the ole Norton fence w/o center flywheel for a 3rd bearing support. If I mathed right your screamer has 1 hp for just under 5 lb of bike. Glad to see a restored faith in Al rods, made for it of course. I'm suitably impressed with slack jaw awe of course. Blew it up too, way to Go Go!

In my defense on the last article I only quoted the likely manufacture's reasons for unsupported center flywheel, but note your Vtwin catch.

Matt Spencer said:

Ah Ha .

Is that to transfer the flex from the crankshaft directly to the cases for vibration .

NOW , Have you seen a Sunbeam S7 - S8 Crankshaft . It appears to meet youre criteria . :wink:

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If you are referring to the 500cc crank I just exposed , well not exactly since it is a 180 degree crank. I know, I know, you got excited and started typing before you really looked :lol:

From my point of view, the only reason there is a middle bearing is to get oil to flow equally to both rod journals. We have seen rod bearing starvation in the LH side when trying to feed from the timing chest on a 180 degree crank. The Norton oil pump on this motor was upped by 50% and the scavenge was upped by 100%. I really don't know how Dave Nourish does it with his 180 degree cranks or maybe we were doing something drastically wrong. Either way, without a center bearing I would be giving a hard look at getting some mass there.

This crankshaft is flywheight but it idled just fine with Mikuni carbs.

It runs like a hyperkinetic swiss watch and has a nice whirring sound as the cam is all gear driven.

I'll do a search for the Sunbeam S7-S8 crankshaft; if you have a few pictures handy to either post or PM me and email.