Trials bike flywheel weight

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camman - 03/06/09 at 7:32pm

I made a flywheel weigh on the lathe for a trials bike. It turned out fairly well but the combined weight is 7 lbs. (flywheel and weight). I was shooting for 6 lbs (this is the weight of the Ron Liddle/Jay Lael flywheel weight). But before I return to the lathe to shave off another pound, I am hoping someone in Hodaka land has been down this road before and could answer the question; what is the ideal weight? Will one extra pound be disastrous? Any help is greatly appreciated.

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hodakaronwa - 03/07/09 at 9:39am

Gosh! You would have to try your flywheel yourself and tell the rest of us. None of this flywheel stuff is a perfect science and it all has to be time tested and rider "seat of the pants" performance has to be pretty much up to rider preference. Some guys are using no additional weight and doing just fine with it. As far as I can see there is nothing wrong with your weight if it works and does what you need to be done.
HEY! if it works for you we will all be using more weight. Jay has experienced a crankshaft twisting with one of his bikes so they welded it. You must have used brass? I started with 1" steel plate. Thinking about aluminum? for my own. Every change finds a weakness......

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camman - 03/07/09 at 11:23am

I used mild steel round stock and it's 1.25" thick. I attempted to copy the Hodaka-Parts.com version. I can't afford $250 to buy one, have access to a lathe and like the challenge of building stuff.

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hodakaronwa - 03/08/09 at 9:38am

Cool stuff and you did good I am sure. Building the flywheels isn't that difficult but it is time consuming.
This is all experimental stuff and I will be interested in hearing how it works out for you.
I am a bit of a Tim The Tool Man myself and have a hard time leaving things as they come. Sometimes it works out and sometimes it flops.
Another thought is to add additional weight to the clutch side. With the hybrid wombat/93 rat motors you have the option of the very early all steel clutch which is even heavier than the 5 plate 97 model clutch. But how much weight is enough?

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R Duttry - 03/08/09 at 11:05am

Hey Guys! This is some interesting stuff, Keep the R&D info coming. In the early 70's we were taking the flywheel completely off for the battery ignition engines, this allowed it to wind-up quicker. The draw back was, when the battery died, so did the bike. Not good in the middle of a race.
Roger

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Bullfrog - 03/08/09 at 1:16pm

Camman:
I can't tell you the "all up" weight of the flywheel setup on my Bullfrog, but I can report the weight of the individual added weights.
The weight added to the magneto side is essentially a thick steel disk which weighs 3 pounds 3 ounces.
The weight added to the clutch side is a considerably more complicated part which replaces the alloy clutch cover. It has 7 spring pockets machined on the inside face and 7 pockets where the screws come through to allow access to the ends of the screws for the safety wire. It weighs 1 pound 15 ounces. It was machined from steel - if made from brass it would weigh about 2 pounds 2 ounces.
I have a simplified design for the clutch weight which would come in at about 1 lb 13 oz in steel and 2 lbs in brass.
Shoot me an e-mail (or private message using this chat group which includes your direct e-mail address) and I'll send you a drawing of the simplified clutch weight.
For 125cc Hodaka trials engines I am of the belief that all the weight you can add will be almost enough. I have ridden my trialer with the magneto side flywheel weight removed . . . and I think power delivery is too abrupt without it . . . but I am a "full bore VINTAGE rider" and WANT a "tractor" engine. More skilled and modern-type riders would likely want quicker throttle response.
HOWEVER, I have not yet ridden a 100cc Hodaka engined trialer which could loft the front end immediately on command - they always seem to require a couple of seconds of "advance notice" that the front end should be lofted. So for the hunnerts it is EASY to over-do the addition of flywheel weight. (NOTE: This is a statement of my opinion - not a statement of scientific fact.)

Ed
PS: For the flat trackers, removing the flywheel meant that all the energy from the piston was used to immediately accelerate the crankshaft, clutch, gears, chain and rear wheel - without "using up" any energy to accelerate the significant mass of the magneto flywheel.

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BATMAN - 03/09/09 at 8:55am

I hope this helps, The flywheel weight on my trials bike is 5lb. 10.2 oz it is on a wombat motor with magic porting from Rich Gagnon, and it works very well. My gearing isn't dialed in yet but Im working on it. Looking for a 70 or 72 rear sprocket as this is a test mule bike and a work in progress. The flywheel weight you build should be tested, it sounds like your going the right direction. These Hodaka trials bikes are really competitive and fun like you wouldn't believe I ride mine in the back yard almost daily and it is quieter than the neighbors weedeater so there are no complaints. Best of both worlds, yes Im hooked on trials.....Leo

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swcaudill - 03/09/09 at 9:38am

Last year I made a couple of Ace 100 flywheel weights. One weighs in at 2.6 oz. There is a picture it at Hodaka owners group under SCaudill project.
The second one is on Rick Motts famous Spyder trials bike.
Sterling

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