lightening flywheels

[Anorak_ian]

Hi guys, I have a few questions about lightening flywheels.

1) Does lightening a flywheel increase vibrations (balanced)?
2) What power increase can be expected (have been told 1 to 1.5 horsepower)?
3) Has anyone lightened the flywheel or just cut off the fins?
4) What weight was removed?
5) My flywheel is 11.1kg and I'm thinking of making a new 8kg (or less) mild steel job. Your input on this please.


My engine Ruggerini rd211 954cc twin 23hp.

Ian

[alexanderfoti]

I have removed 2kg of cooling fins from my flywheel and statically balanced it afterwards.

A lightened flywheel shouldn't increase vibrations if it's balanced.

I think the power gains are very low, less than a hp. It will make the engine rev more freely. The gains come from removing the fins as they take engine power to turn.

A good idea to modify a seperate one to see what the differences are. A higher idle most likely.

[alexanderfoti]

Just read it's a twin as well, if you kickstart it and the firing pulses are very far away it might make it harder.

[Anorak_ian]

I have removed 2kg of cooling fins from my flywheel and statically balanced it afterwards.
A lightened flywheel shouldn't increase vibrations if it's balanced.

That's what I thought, but I had to ask, as on my bike there's always a knock on effect somewhere.

I think the power gains are very low, less than a hp.

My engine being a twin, I think the gains may be greater maybe, hopefully.

[alexanderfoti]

The gains would be had at acceleration, rather than top speed.

As it decreases the mass that the engine needs to spin. This is a good article on it:

http://www.uucmotorwerks.com/flywheel/h ... _works.htm

[Anorak_ian]

Yes I understand it's only acceleration, top speed is governed by the amount of fuel and ignition timing.
Nice to loose a few pounds anywhere on the bike, all adds to the mpg.
I could loose a few pounds myself, no chance of that with Christmas coming up

[alexanderfoti]

Yes I understand it's only acceleration, top speed is governed by the amount of fuel and ignition timing.
Nice to loose a few pounds anywhere on the bike, all adds to the mpg.
I could loose a few pounds myself, no chance of that with Christmas coming up

Indeed! Tell me about it, I cant wait for all the Christmas food...... hmmmm

[tappy]

Another thought on swapping flywheels etc.
I had resolved to just get the bike done by keeping the original flywheel and alternator. Then I decided to check the engine CoG (Hatz 2G40). It's about 25mm to the flywheel side of the cylinder pair. By the time the starter motor, gearbox etc are on, I'm thinking the bike is going to be right-side heavy.
Thinking about how to get weight over to the left hand side, I could put my Harley alternator outboard of the primary drive (a la Enfield).
This would then free me up to put what ever flywheel I liked on the right hand side. Both these effects would reduce the "right side heavy" problem.
At this stage in the game I think I can do either.
SOOO, all those Ruggerini / Lombardini / Hatz twin owners: How much does your bike prefer to fall on its right hand side?

[henneberg]

I have let the MD151 go about 1 cm left to the primary drive side of the cylinder pair.

The gravity center line of the engine is approx. 3 cm right to the cylinders center.

The Primary drive with chain cases and clutch adds up a sufficient counterweight, allthough its just a qualified guess

At the time being, the exhaust is at the right side ( flywheel side ) but the complete bike is in good balance.

[mark_in_manchester]

I used a Ural flywheel on a Daihatsu engine - replacement weighed at least 30% less, and with much less mass at the rim, where it creates the most rotational inertia. Who knows how the Japanese thought old ladies were going to dump the clutch on their Charades - even with the light flywheel the bike ticks over fine and pulls off frighteningly when the clutch cable breaks (yes, twice). So long as it ticks over, you're fine.

[Anorak_ian]

SOOO, all those Ruggerini / Lombardini / Hatz twin owners: How much does your bike prefer to fall on its right hand side?

My engine is 3cm over to the left (as you sit on the bike). Measured from the gap between the cylinders and the frame back bone. Right from the start of my build I moved the engine left and right until the balance was spot on. So what have I done now? Put a dirty great Harley battery on the left hand side, Doh.

I recommend to anyone who is building a stationary engine bike, to reduce the size of the flywheel and so move the engine over to the right to facilitate the ease of fitting / aligning the primary. This has been a friggin nightmare, the only way I could do it was with clutch belt running on the outer edge of the clutch drum. It would have been impossible with a chain primary.

[sbrumby]

When I was building bikes I thought about the weight problem, and it never is a problem. If you think about it, if the bike was perfectly balanced and you were riding it normally everything is fine. If you then shift your weight on the saddle to one side in my case you would be shifting 80kg but this does not affect the bike or the ride.

[alexanderfoti]

That's what I had on my build, the engine wasn't central to the frame but it didn't affect the balance at all when riding.

[tappy]

Yeah, I'm inclined to agree. But on the other hand the ballast I'd need to compensate and bring the CoG central would be about 10Kg in the left hand pannier - and I know that on my SV I can feel the difference if I've got such a large load asymmetry.
But that's on a bike with much sharper geometry and much higher CoG than the bike I'm building, so I shall take what you guys say and not worry about it

[alexanderfoti]

True, I suspect as it's a spinning mass in our cases that it's not so obvious when the bike is moving.

[Anorak_ian]

When I was building bikes I thought about the weight problem, and it never is a problem. If you think about it, if the bike was perfectly balanced and you were riding it normally everything is fine. If you then shift your weight on the saddle to one side in my case you would be shifting 80kg but this does not affect the bike or the ride.

Do you mean when cornering or when a bum cheek falls asleep?
Try sitting your left bum cheek on the right of the saddle, and turn left in to a junction, I think you would notice it. I would.

The mind compensates un consciously for minor shifts in weight on the bike through our hands on the bars, but a load of weight over a period of time could become a problem. First you'll feel it more to one side of the bike, it will nag at your mind, gnawing at your brain like a mother in law, then you'll try to find the perfect balance and in finding it then flop the bike to it's up wright position, knowing it's all wrong you'll develop a nervous tick to to you right eye, your head will start to twitch, you go home and kiss the dog and kick the wife out, use the laundry basket as a toilet, and wake in the morning in the spare bed room with the mother in law. It's just not worth it!
Thank goodness were only talking 2kg per 3cm and not a hippo in one pannier, or even worse my wife.

I have fitted a 7.5kg battery to the left hand side of the bike and I really haven't noticed any difference to the bikes balance but this is close in to the frame, if it were heavier or out as far as the flywheel then I'd have to phone a shrink.

The centrifugal force of the fly wheel will help balance the bike at high revs, and also the centrifugal force of the wheels at high speed? Something to do with gyroscopic stuff in it?

[tappy]

He he he, I have no dog , no mother in law and no wife .
But I'm clearly still mad

[alexanderfoti]

Did you end up lightening the flywheel?

I have a spare one floating about that I might take the machiners for them to remove 50% of its mass.

[Stuart]

I'd like to get some removed from my Daihatsu flywheel to make it more throttle responsive - but how much?

[mark_in_manchester]

Read upthread, Stuart. I can weigh a Ural flywheel for you if you want...rim is only about 3mm thick, so loads of mass could come off the outside of the Daihatsu flywheel which is substantial. Less can come off if you want to retain the starter ring, I guess. If you bollocks it up I have a spare you can have for postage, since I think I'm sticking with Russian flywheel and a kickstart.

[Anorak_ian]

Did you end up lightening the flywheel?

I have a spare one floating about that I might take the machiners for them to remove 50% of its mass.

I haven't done anything with mine as yet, it's something I want to get done, but it's not on the top of my list of priorities at the moment. Too much going on elsewhere.

[Mahesh]

1) vibrations only occur only when the flywheel is not balanced or the engine isn't rigidly bolted on to the frame and also lightening may increase vibrations but shouldn't be much noticeable if done correctly.
2)by lightening a flywheel you will be experiencing higher low end torque and will loose top end torque...in a sense you will rev faster but will loose top speed...as the flywheel will stores less energy at higher rpm...
3)never cut off any fins...you don't want to mess with the cooling of the engine instead cut from the back side of the flywheel preferably on a lathe. given if its a liquid cooled engine get rid of those fins at once.as they are not needed and account for extra baggage weight
4)what weight can be reduced depends on the engines and user satisfaction. i suggest you reduce 1kg at first and if not satisfied keep testing with 500gms or 250gms reductions at a time finding a sweet spot is worth the trouble...

[klondikekid]

I know this thread is old but, I thought i'd throw in my results with lightening my flywheel, My original Kubota D950 flywheel was 30 lbs. i seem to remember, I had a local machine shop remove 10lbs from the outboard face, I don't notice any more than usual vibration, and yes it does rev up quicker, would I do it again? yes. would I take off more? yes, if I had a spare handy in case too much was taken off.

[UAofE]

Also if you have a recoil (pull) start engine, starting will require a lot more effort.

[gearhead1951]

check out "Panic's" dissertation on flywheels at www.victorylibrary.com !

[coachgeo]

check out "Panic's" dissertation on flywheels at http://www.victorylibrary.com !

Is this what your referring too? http://victorylibrary.com/tech/inertia-c.htm

[sbrumby]

Thanks Coach for finding the article, very informative, I am not sure I can understand it all, but with a quick read through it might have different implications for people with gear boxes as to those with CVT.

[gearhead1951]

Thanks Coach for finding the article, very informative, I am not sure I can understand it all, but with a quick read through it might have different implications for people with gear boxes as to those with CVT.

Yep , That's the one !

I've found the victory library to be as useful to a custom bike builder for engine problems as www.choppercompendium.com is for all else !