Heavy flywheel equals more torque? (2014)

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Well spotted that rod length mm typo...

Interestingly, the rod length in the early dommie 500 and 600cc engines was precisely 6".
And that for a stroke of only 72.6 mm, for the 500cc.

I'd imagine that the reason for going shorter rods in the bigger engines was
to keep the overall height of the engine down ??
 
Time Warp said:
Sorry about that,I got the conrod length from here.
.
Click to expand...

From which we can conclude that the factory worked in inches,
and someone did the mm conversions later. ?
 
It looks that way or there was a typo with the 2 (129) and 4 (149) only.

Ducati twins of the same era had 145 mm conrods with a 74.4mm stroke giving a very healthy ratio of 1.94.
Perhaps the conrod ratio was another factor with the Combat due to high rpms with high angularity.

Edit.
I went and took a photo.
Triumph unit 500 / Norton Commando / Triumph 650 conrods.

Heavy flywheel equals more torque? (2014)
 
For a long time I tried desperately to get more torque from my 63mm stroke 500cc Triumph motor. It used 650 rods, and 650 barrels which I had already shortened 12mm. Faced with making new barrels so I could fit shorter rods, I eventually gave up and sold the bike back to the friend who had originally made it many years earlier. That's when I built the Seeley 850 and learned that road racing did not really have to cause stress and anxiety. That Triton taught me how to avoid crashing, it was a thrill a minute.
 
Will Triumph 650 rods fit into a commando engine - (big end size) ? It might be an opportunity to use modified 73mm Honda Fireblade pistons in a 750 commando. They cost $100 complete with rings, gudgeons etc. they are extremely light and Teflon coated with very skinny rings. I think it might be possible to shorten the barrels a bit without running into trouble. (the height from gudgeon pin centre to crown is much smaller than with a standard Norton piston).
 
If you put a heavier flywheel in, it won't match the factory Isolastics, and you'll be bitching about the increased vibration levels. The factory isolastics were designed fot the engine being made in 1967. There was absoltely NO vibration that could be sensed by the rider above idle RPM. That's what made the Commando such a breakthrough compared to its competitors.

Maybe, as the engines were further developed, the original concept of the Isolastics got lost, possibly because the guys that designed the original Isolasticss had left the company as it declined. That's probably why modern owners complain about vibration - what was good for the early 750 motor was never re-optimised for the Combat or the 850.

Where's Bob Trigg when you need his expertise?
 
Sorry Frank, but your statement "design" ,,i personaly dont see a grand "design" ..more a panic button, Knee jirk reaction ...If the Designers where that good...why did they produce a "widow maker" frame that snapped within weeks of ownership [and they where advised it would]...and a Combat engine that exploded ! not to mention all the other issues...this GRAND DESIGN had? Design no, development? no! After all Rubber isolation was not new, in industry many, many machine parts where Rubber mounted...didnt take a Expert designer to apply those [rubber mounts] to a motorcycle.

Designer's at norton in the panic room... did it go like this " OK lad's we have a good Brand name , but the market is changing, our competing machines ie honda,kawasaki are producing a smooth four cylinder machine's ,and our customers are seeing double with our 40 year old design!" "any suggestions?
The designer who had just seen a maintenance worker on a old lathe replacing the rubber mounts ...came up with the answer....you guessed it.

I have worked in engineering 40 years ,and the common rule applied...if you cant cure it...then isolate it! thats the British way...the Japanese way if you carn't cure it...re-design it! Sorry to be busting your bubble..but facts are facts, history as shown .
 
acotrel said:
Will Triumph 650 rods fit into a commando engine - (big end size) ? It might be an opportunity to use modified 73mm Honda Fireblade pistons in a 750 commando. They cost $100 complete with rings, gudgeons etc. they are extremely light and Teflon coated with very skinny rings. I think it might be possible to shorten the barrels a bit without running into trouble. (the height from gudgeon pin centre to crown is much smaller than with a standard Norton piston).
Click to expand...
If I recall correctly, the Norton big end journal is bigger, and has a bigger hole in the middle of the journal. So Triumph rods won't fit, and if you grind the crank down to suite it is dangerously thin. I've seen it done, it broke.
Anyway, Norton rods are stronger, it wouldn't be much of an 'upgrade' to fit weaker rods to a weaker turned down crank methinks.
 
I'm in Franks camp about the uncanny disappearing act possible with isolastic Commando and not give up handling neither. Where did Bob Trigg end up? I would like to know more about him. I think it was more the bean counters that interfered with stem geometry and adjustable isolastics from the start than the clever designers called in to save Norton in their stop gap to get something modern in the works.

http://www.trailtech.net/stators-flywhe ... -flywheels


QUESTION EIGHT: CAN A HEAVY FLYWHEEL MAKE A BIKE FASTER?

Yes. But only if the engine characteristics are too snappy, powerful or explosive for the rider's style or track's terrain. A bike with an engine that's too explosive will accelerate quicker with a heavier flywheel weight.

Why? Because the weight smoothes and broadens the transfer of power to the ground. The power is delivered more consistently and in more of a conservative manner. The bike is more hooked up off the line and less volatile on the course. QUESTION NINE: CAN A HEAVIER FLYWHEEL CHANGE A BIKE'S HANDLING?

You bet. Toning down the abruptness of the power delivery makes the chassis less susceptible to sudden bursts of acceleration, excess wheelspin and engine stalling. Adding flywheel weight will make a bike feel less twitchy. If the tires stay hooked up, with less bounce or spin, the bike is easier to control.
http://www.thumperfaq.com/mxa_flywheel.htm
 
From Steve's link :
'The weight and size of the engine's flywheel determine how easy a motorcycle is to ride. And, flywheel weight plays a role in acceleration, throttle control, suspension action, braking and cornering.'

Before a factory's engineers can choose the proper flywheel, they have to consider seven factors:
1.Overall engine weight: Lighter is always better.
2.AC current: The size of the flywheel must be large enough to house the magnets that are used to produce engine spark. But, at the same time, small enough to make room for the stator windings without creating a bulky engine case.
3.Engine acceleration: An engine builds speed quicker with a light flywheel and slower with a heavy flywheel.
4.Inertia: A heavier flywheel carries speed further, but is also harder to slow down than a light one.
5.Flywheel effect: Every rotating component in the engine and chassis creates its own spinning force (clutch basket, gears, chain, wheels, and how the crank counterbalances piston weight and stroke). The manufacturer needs to pick a flywheel weight that best accommodates all the independent gyroscopic forces inside the motorcycle.
6.Angular momentum: Believe it or not, too much flywheel weight will make a bike hard to move around or corner.
7.Intended use: The power characteristics and riding styles used on a 60, 80, 125, 250, 300, 500 and 4stroke all require different flywheel mass.
 
frankdamp said:
If you put a heavier flywheel in, it won't match the factory Isolastics, and you'll be bitching about the increased vibration levels. The factory isolastics were designed fot the engine being made in 1967. There was absoltely NO vibration that could be sensed by the rider above idle RPM. That's what made the Commando such a breakthrough compared to its competitors.

Maybe, as the engines were further developed, the original concept of the Isolastics got lost, possibly because the guys that designed the original Isolasticss had left the company as it declined. That's probably why modern owners complain about vibration - what was good for the early 750 motor was never re-optimised for the Combat or the 850.

Where's Bob Trigg when you need his expertise?
Click to expand...

The vibration is not just a function of different engine weight but different vibration frequency's produced by the engines at certain rpm especially 850 compared to 750. When the engine frequency matches the iso rubber natural frequency vibration is transmitted. I think most vibration problems are caused by the iso thrust faces out of parallel to each other - typical bodge is to adjust iso's much wider than recommended but then the handling suffers.
 
Tri 750 T140 rods are alledgedly A70 rods ( 750 Lightning BSA ) shorter than T120 / 650 rods . for what its worth . :?
 
The arguement about long stroke and better low-rpm torque torque is a wives' tale.The only grain of truth to it is that a long stroke engine requires more cam duration at the same rpm.If you halve the stroke and don't change cam duration,the engine will be happy at twice the rpm (provided all other things are optimised to suit that rpm).That's no secret,and I can find reference to this that was printed 90 years ago.

You're still only going to get about 70 ft-lbs of torque from a 1000 cc engine,but within reason you can have that torque at any rpm you like.The maximum valve size you can fit in a small bore can be a limitation at high rpm on a long stroke engine.

Flywheel inertia does more than just give you a slow stable idle speed.If you haven't got enough flywheel inertia and/or camshaft/camwheel inertia it can play havoc with valvegear acceleration.That can lose you a big heap of power and torque.In one instance,Jerry Branch dyno-tested an engine (1/4 of a Chevy engine) that was expected to make 100+ bhp and it didn't make better than 35 bhp because the crank didn't have enough inertia.You'll find it mentioned here in motty's quote,about 1/4 way down the page http://www.gixxer.com/forums/archive/index.php/t-61151.html
Engine speed and torque aren't constant throughout the cycle.Most of the useful work is done between TDC and 45 degrees ATDC on the firing stroke.Even with a reasonably heavy flywheel in a twin cylinder engine running at 6000 rpm,that can be enough to instantaneously change rotational speed by 5%.It doesn't sound like much,but it happens quickly with severe acceleration.It happens when one intake valve should be opening at a constant speed and when one exhaust valve should be gently closing on its seat.
In the case quoted,increased crank inertia would have improved torque and power by about 200% increase.

Jack Wilson knew this when he built the engine for Johnny Allen's speed attempt in 1956.The crank weighed 50% more than a standard crank.
A light crank is good when you're accelerating in the low gears,but not so good after that.
 
Very good point about valve time control I'd over looked so thanx for bringing me more up to speed.
Flywheels also must be thought of in relation to the piston jerk down mass so JSM's kit should make a 5 lb lighter flywheel feel like better than normal on a Commando, I hope.
 
hobot said:
Very good point about valve time control I'd over looked so thanx for bringing me more up to speed.
Flywheels also must be thought of in relation to the piston jerk down mass so JSM's kit should make a 5 lb lighter flywheel feel like better than normal on a Commando, I hope.
Click to expand...

I can't afford Jim's rods and pistons at present, when I can I will buy them. My crank is currently balanced to 72%, I won't be changing it for the lighter pistons. The balance factor change from the new components will be in the right direction for higher speed work. If you are worried about a bit more vibration when doodling around town, then it might be an issue. I suggest that even with Jim's bits, the reciprocating mass in the commando is quite high and it takes the heavy flywheel to get smooth power delivery. My feeling is that the lightened flywheels I've seen on this forum look excellent, however once you've made the billet crank, correcting it's weight if the performance is not realized can be expensive. It would be interesting to hear what Steve Maney and Herb Becker have to say about lightened flywheels. I found Dave Nourish's comments very interesting. With my own bike, the only problem I've found with the heavy flywheel has been with downshifts using the standard gearbox. I'm extremely sensitive to bikes that are awkward to ride and have bad engine set-ups - my Seeley 850 is great with it's almost standard engine, and CR box. I will say one other thing - in our local historic races the guys are using 1100cc CB750 Hondas which give them the big blast in a straight line. Eventually I will again be able to afford to race them. I've installed the six speed TTI box, and knowing what I had when I was using the old 4 speed CR box - I will beat them.
 
I'm way more concerned with off road low traction climbing hook up and instant break frees of rear that just as fast stop and re-hook for better drag spring into a sharp trouble spot. Peel's crank some how ended up about 25 lb so on the heavy side but does have big holes to put in plugs to move BF form low 60's into 90's%. Me and motorcycles can only take so much smoothness on or off road then suddendly its skipping sliding, tripping down &/or tank slapping so I shift styles to a more ballistic method that still allows control would sliding drifting, which I abhore for a number of reasons, but a controlled crash input in the middle of these events can cut them short to get on with the power hook up fun. I want digital traction easy break free and fast predicable spin stoppage so suspect my herky jerky style will like a lighter flywheel, yet with the Drouin on and spiking torque I may be glad Peel flywheel is on the heavy side but narrower than factory so maybe more like ballerina pulling in arm? Running up to most bikes max out cornering conditon is just first stage finished for Peel with 2-3 more stages to fire up beyond anything than can only stick to rails. My home is surrounded by potential Mt climbs that challenge my go getter 4wd pickup to have to charge them of spin out in place. Yet Ms Peel could out climb it on the loosest steep situations by hooking up better power to wt ratio planting. Road-track play will be less demanding as feels like always a safety net to stop out of control events in time.
 
Finally the bikes back on the road! Halle-fuckin'-lujah. Going well, just done 60 miles revving to 5,000, first kick starting, good tick-over and no oil leaks. I'm pretty sure acceleration from a standing start and also roll-on is quicker (lighter Steve Maney flywheel fitted). Only down side is driving through congested town traffic when she seems happier one gear lower than before but this is not a problem and I'll quickly adjust. Leaving for the Britti Ralli week on Friday so I'd be happy if I can get 700 - 800 miles on the clock before then. :D :D
 
Last Monday [yesterday] i watched Duncans Manx out pull the G50 of Mike Edwards from a standing start, but exiting corners the G50 had the edge...and watching the G50's taco on Mikes you tube blog, the G as quicker responce above 7000 ...Duncan recons the manx as the heavest flywheels which give it that extra whoomp from a stand still.
 
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