Need info for lightened Flywheel

[naboula01]

Hi everyone. i was just asking myself : what if i lightened the flywheel of my 126Bis ?
I talked to a couple of people and they told me that the Flywheel on the 126bis had vivration system ( )
So my question is what would happen if i lighten only my Flywheel? Or should i change also the crank etc(like i saw on another post) ? Is it a good idea? Anyone ever tried?

[Rusty's Uncle]

OK my theory on this , having recently dismantled a Bis engine, is that the standard balance on a Bis engine is achieved by the relationship between the flywheel and the crankshaft pulley. Pete tried just lightening the flywheel and ended up with bad vibration. I think that the lightening would need to be matched on the pulley which would be a bit of a pro job to get it right 

[Pete126]

Hi Nab, I was that man The bis flywheel weighs somewhere around 13/14KG and we managed to trim just short of 4.75KG off the back, What i didn't know at the time is that the bis crankshaft is balanced from the front pulley to the flywheel, I installed the lightened flywheel a week before the big Retro Rides Gathering, When i started the car up after fitting it i could feel the vibration on tickover but it was too late to to put the old one back, even though it was out of balance you can feel the difference especially the acceleration 0 to 50 MPH, also the engine revved up quicker.
Needless to say the following weekend on the motorway going down to the show the excessive vibration broke the alternator bracket then the bottom bolt and finally the alternator dropped off and came to rest between the engine, back-panel and radiator.
So yes you can lighten the flywheel but you need someone with the knowledge and equipment to balance the crankshaft/front pulley/and flywheel which are reciprocal forces But then you have to take into account the weight and linear/horizontal forces of the pistons and connecting rods on the Bis Engine.

The aircooled are easier to set up    

[naboula01]

 
i won't touch the Flywheel anymore... 
Thanks for the info, so you're telling me if i lighten the flywheel i'll  get a better performans, but on the other hand this will broke my engine due to bad vibrations... Hummmmm...
I got to think about it... Thanks again for the info, you might have saved the life of my 126Bis 
I might lighten it later, after i've calculated al the crankshaft/piston/flywheel linear/horizontal thing...
And by the way, how much would you advice me to lightening it for a good acceleration, without losing much inertia? Like a flywheel weighting 5Kg or more like 9Kg?

[Rusty's Uncle]

You got me thinking about this one because I am going to try a Bis crank in an air cooled engine because I can see no reason why it should not be OK . So why not fit air cooled parts to a Bis. If you had the Bis crankshaft pulley machined to remove the "out of balance" bob weight so it was totaly symetrical and would not require the appliance of science. Then you could use a lighter air cooled flywheel "MAYBE" 
Who dares wins as they say and I can't remember the figures but (I did post them here somewhere) a standard fiat 500 flywheel will be considerably lighter 

[Pete126]

Get cracking Dave If it works that way round then there is no reason why the bis engine can't be run with air-cooled front pulley and lighter flywheel

The only thing that worries me is that I have been told that balancing is different on a horizontal engine to a vertical engine, if you remember Damon500 was after a bis flywheel for his Giardiniera

by the way, how much would you advice me to lightening it for a good acceleration, without losing much inertia? Like a flywheel weighting 5Kg or more like 9Kg?

To be honest Nab, The only thing say is that by taking 5KG off the flywheel it made a noticeable difference
to the acceleration and engine felt allot livelier

[Allan]

I would imagine the first thing to do is to check the balance of the standard crank with front pulley and flywheel attached. Not having ever done this I can't say what the result is. But if the complete assembly is not perfectly balanced like a 4 cylinder unit would be then you got big problems because some kind of allowance has been made for the two pistons and rods flopping up and down together. Let us know how you get on Dave.
Regards
Allan

[Rusty's Uncle]

Pete the air cooled standard pulley will not align with the alternator pulley which is why I said to modify ithe original. Also I think that you may have got your units mixed up as you may have been talking pounds not Kgs. The standard 126 flywheel weighs in at just over 7 kgs and the 500 is about 1.8 kgs lighter. Rain & hail stopped play on my car today so I finished stripping a 126 air cooled engine back to a very dirty "blank canvas" crankcase. So do not worry Allan I will keep you all up to speed 

[Pete126]

Also I think that you may have got your units mixed up as you may have been talking pounds not Kgs. The standard 126 flywheel weighs in at just over 7 kgs and the 500 is about 1.8 kgs lighter

You could be Wright Dave I'll weigh it tomorrow

[bis13]

it must have rained hard as he rang me!!