Flywheel lightening

[bike grim]

Is there anyone on here that offers flywheel lightening. I have a couple of SIL flywheels that are 2.5 kg and wanted them taken down to closer to 2kg as per the AF medium weight. Would also like the rivets welding.

Thanks

Gareth

[Knowledge]

A good question G. A grown up will be along shortly to give you the name of a dealer who can do this.

I have lightened a big-fin flywheel myself for the 283 engine and I got the weight down from 2.8Kg to 2083g.

During the process, it was necessary to remove all the holes that had been drilled to balance the flywheel. I've got an idea on how to re-balance it, using a static (not rotating) lathe as a mandrel, and I will let you know how I get on after next weekend.

Good luck.

[burnside]

Chris Sadd at CS Engineering in Norwich did one for me a couple of years ago

[holty]

I have lightened my own flywheel on my lathe using the crank taper off an old sil crank in the chuck and a rotating centre in the tailstock, mine is for my 290 rotax that's liquid cooled so I lost all the fins as well, I think I got to 1.8 kg, but I am very interested how to re balance as I removed all the material that has balance holes drilled in it, can you please let me know how you get on,
Thanks in advance,
Holty

[Wee Mark]

Hello Chaps, Readspeed offer this service I understand............
Cheers
Mark

[carlos fandango]

Live centers in a lathe wont work to rebalance ....too much resistance with them .......i used knife edges and a mandrel......or use a dynamic balancer

[Knowledge]

I like the look of that CF.

Do you balance the flywheel on the knife edge and just allow the flywheel to roll until the weight is at the bottom? I guess you mark the bottom, drill a few holes to remove mass, and then try again.

Is that a special mandrel you have made?

[carlos fandango]

Yes its a mandril i made ....it was to lighten a motaplat flywheel ....but also works with the gp taper .

Heaviest part should go to the bottom, i give it a little nudge and see where it rests, put a mark at the bottom , then repeat a few times, if all the marks are in the same area then thats where to take some material from .

[holty]

That's a good little jig you have made there, I think I will be able to machine my mandrel to copy your idea, many thanks for posting the pic, I checked my flywheel and I reduced it to 1.6 kg

[Knowledge]

Carlos,

Thanks for the reply.

So the mandrill is just a piece of machined steel, not a modified section cut from an old crank.

I guess the flywheel does not need to be secured to the mandrill with a nut, and need only be tight on the taper.

Each end of the mandrill, where it rests on the knife edge, would need to be the same diameter, I assume.

Finally, does the knife edge need to be a "knife-edge"? Your picture seems to show two lengths of 3mm wide steel strip, but not a knife edge as such (not a criticism, just an observation)

[carlos fandango]

They are knife edged , look closer at the ends

They are actually wood planer knives (blades) . The knife edge gives minimum contact with the mandril.

Heres a pic of the mandrill i turned , the taper will take Li and GP tapers

[holty]

thanks for the pics carlos, finally balanced my flywheel last light, firstly i turned my flywheel piece of crankshaft down slightly at the end so it was the same diameter as the flywheel nut so it would sit on the jig level, i then cut a piece of straight timber into two lumps and cut 2 slots for my steel rules, i then leveled them in both directions using a spirit level, mounted the flywheel on the mandrel, fitted the nut wrong way round so the round part was on the outside, and sat the flywheel on the steel rules to see how balanced it was. it took a lot of drilling to get it to balance perfectly which makes me very happy as it wouldnt have done my engine or bearings or crank much good, as it is now it should keep the engine smooth as its going to be, and best of all it cost me nothing, heres some pics,
holty

[Knowledge]

Good work Holty.

Reversing the flywheel nut is the missing piece of the jigsaw for me. I now see how I can do it, once I have found a second steel rule.

[Knowledge]

Ahhh, no. Hang on. My flywheel still has fins on it.

I will have to build a Carlos Fandango style mandrill after all. Damn, I thought I had saved myself an hour there.

[holty]

just weld a bit of tube onto a fly wheel nut, then turn it down on your lathe to true it up, will be quicker than making a mandrel ?

[Knowledge]

Yes, you are right. Thanks for thinking outside the box, so I don't have to.

[carlos fandango]

Good stuff holty

Although one word of warning .......i have found using old crank tapers , that the threaded end can be bent slightly , i suppose from using flywheel pullers ...or worse ! ....also the nuts arnt always drilled central .

Easy enough to check if you have the tools ....but worth considering

[Knowledge]

I have machined a mandrill and created a chassis to hold two steel rulers (a la Holty) and I have it sitting on the hearth under the TV, as this is the most level thing in world-of-knowledge.

The heavy spot has been identified and I will get to work on balancing it tomorrow, meanwhile ....

Would the mandrill be more sensitive if the diameter of the mandrill (where it rests on the straight edge) was bigger or smaller? Mine is about 17mm diameter.

[carlos fandango]

I'd guess smaller diameter would be better ....2 reasons

1. less contact area .....ok very little difference ...but a difference nevertheless .

2. ...not sure how to explain this ??....... the greater the distance from the outside of the flywheel to the center line, the more sensitive it would be, to being out of balance . Imagine if the flywheel was twice the size ( diameter ) i think the it would turn more freely . as opposed, to if it was a solid cylinder on the knife edges ? does that make sense ? its the leverage effect of the
heavier weighted spot/area .

Just my thoughts .....i cant back it up with anything lol

Russ

[holty]

your 17mm diameter will be fine, its roughly the size of the flywheel nut, and i was very surprised how sensitive it was when sat on my jig, it would roll back and forth until it settled with the heavy side lower most, i then drilled holes until it balanced, i drilled some on the inside and some on the outside to help with the overall balance.