What would one expect if one installs a Nichols flywheel on a 620?

Revs rise and fall more quickly, engine feels livelier IMHO.

A lighter than stock flywheel improves engine response and acceleration. On the heavy crank big bores like the 900, 1000 and 1100DS motors a light flywheel really livens up engine response. I would think a 620 had pretty light engine internals to begin with. The overall mass of the engine internals contributes to the engines character on a scale of heavy, smooth, slow and progressive at one extreme Vs light, snatchy and explosive at another. My Evo 1100 is a motor at one extreme with almost everything in the crankcases that spins being lightened at the factory. Some find the Evo1100 motor wonderfully alive while others find it annoying. My buddies ST2  on the other hand with its heavy crank and fat flywheel is buttery smooth, sedate and civilized. I havent played with a 620 bar regular servicing, but others will be able to advise.
For further info use the search on light flywheels.

I have a Nichols in my 695.  My experience was more pep and immediacy.  More subtle than I was expecting if I remember correctly.  No complaints and I'd do it again.  Do be very careful to install correctly.  I eventually added a different throttle plate cam profile and quick turn throttle tube and all those things together worked quite nicely for me.  I ride mainly twisties/canyons/coastal mountains and no city/commuting.

BK

I ran a nichols flywheel on my old M800. All the 620, 800, 900 internals had really heavy 4lb flywheels.

Advantages: You get less wheel lockup on rapid downshifts, the lightened flywheel seems to somewhat mimic a slipper clutch but to a lesser extent.

Revs climb faster and power delivery feels more instantaneous

Disadvantages:

This is a personal opinion but I felt like the bike had too much engine braking with the lightened flywheel.

I'm an aggressive rider but I'm pretty gentle with the clutch. My S2R 800 clutch was still going strong after 47k (ish) miles on the original clutch pack

Conversely, my older M800 with the nichols flywheel upgrade started slipping at 18k miles. I'm not sure if this had to do with the more rev happy motor but I will state it as something to look out for.

I don't think it had much effect on the clutch, as my 800 clutch pack never got changed in 60, and as far as I know, wasn't changed prior to my ownership for  the 20k it ahd already done.

Feels great on a 620 with a quick turn throttle, amazing on the 800.

I like the aggressive engine braking, however it takes some getting used to.

Ducati wet clutches (not including APTC) can last a long time.  My old 750 has 80+k miles on the original clutch.  Dry clutches, not so long.

Why is it that some folks opt to have their stock flywheels machined down to a specific weight, rather than just purchase a Nichols which is lighter?

Some folks feel Nichols is too light.

The bike becomes more lurchy during on/off throttle when you have a lighter flywheel. Conversly it helps allow the bike to rev quicker and frees up the bikes existing power to be put down to the wheels since less there's less inertia holding the motor back.

Essentially, the momentum carried by the heavier flywheel allows for a better transition and a smoother motor response.

The Nichols flywheel weighs next to nothing where as the stock weighs around 4 lbs. A lot of people seek to shave down the existing to obtain a middle ground between the two. Not too snatchy, not too slow to rev up.

My old M900 had its stock flywheel machined down from 1900gms to 900gms. A nice middle ground. My buddies 900 Supersport has a DP/Yoyodyne flywheel closer to 500-600gms which he says is too light. I on the other hand like the lighter flywheel on his bike, so personal preference comes into it. The very light internals in my Hyper Evo motor are great in the canyons but annoying at times when cruising highways. I plan on a two up, touring or adventure bike and I will leave the big ol' flywheel stock on that one.

Quote from: koko64 on February 14, 2017, 01:09:32 PM
My old M900 had its stock flywheel machined down from 1900gms to 900gms. A nice middle ground. My buddies 900 Supersport has a DP/Yoyodyne flywheel closer to 500-600gms which he says is too light. I on the other hand like the lighter flywheel on his bike, so personal preference comes into it. The very light internals in my Hyper Evo motor are great in the canyons but annoying at times when cruising highways. I plan on a two up, touring or adventure bike and I will leave the big ol' flywheel stock on that one.

Why would it be annoying while cruising on the Highways ?

The Evo engine's internals are generally so light, it's like trying to trot on a quarter horse that wants to gallop away. It feels best either accelerating or decelerating through the canyons and I love it!  I have kept stock high gearing with 6th as an over drive that loads it up on the highway to counteract this tendency so it only does 3500 rpm at 60 mph. The bike has also been carefully tuned to smooth things out at cruise. Remember that the factory lightened the Evo's primary gears, timing gears, crank, alternator and flywheel like a race motor. Some of my buddies on sports tourers hate it, but they're pussies.
I think the 620 has pretty light internals as is, so the effect would not be as dramatic as on a 900 or 1000DS.

I love the Yoyodyne 1.5 lb flywheel on my M900. The oem flywheel was 4 lbs. As said above, the bike does not like to troll along at traffic speeds as much with it, it wants to go all the time, full open throttle. Seems to spin up and down a tad quicker, making it racier.

My M900 flywheel was 2 pounds which was pretty sweet. I also went for the lightest clutch parts I could find dropping nearly 2 kg (just under 4 pounds) all in an attempt to improve response.