balance factors for crank and lower end-Fulvia 1.3

[bryan dugdale]

Hi,i am tying to find the data[balance factors] required for the dynamic balancing of a crank/flywheel assembly. I have tried several respected sources of information, but drawn a blank. Are there factory or racing team specs still available? many thanks, Bryan

[ncundy]

I asked about this about a year ago but drew a blank as well. I couldn't find a specialist who would admit to knowing. Vibration Free will balance them but do not use the balance factor method. I believe Martin Cliffe (Omicron) may know, but I doubt he will tell you as it seems to be a closely guarded secret

If however you do have any luck please let me know !

Regards
Neil

[Geoff]

One possibility is that some leg work in Italy (Turin) will find balancing shops with this information. But I've never seen it either.

[lancialulu]

Try Paul Leclerqe

var1016.blogspot.com

Tim

[bryan dugdale]

Thanks for the replies; i will try the leads suggested and let everyone know the outcome, Bryan

[VAR1016]

Hello.

I had my engine balanced by Serdi at Uxbridge. They did a lot of research on this and told me that the factor is 50% I expect Neil can tell us what this means.

I recall that the original Autocar article about the Fulvia said that the engine was balanced on a "Gisholt Harmonic Balancer". Old Harry Manning always said that the whole thing was a compromise because of the crank.

I feel that the essential thing is to keep the original flywheel: original engines are always smoother - I once drove a 1600 that felt like a 1200 - I couldn't believe it. Mine's like a bear's backside (to take a leaf from David Scott-Moncrieff).

I say this because I believe that the asymmetry of the crank has to be compensated somehow.

Of course reduction of weight is a good thing (as anywhere on a Fulvia). I was told that modern conrods would be both stronger and about 35% lighter than the originals (1600). I just couldn't afford them.

Paul

[ncundy]

The balance factor is the % of reciprocating weight (little end+ piston + rings + gudgen pin) that is added to the rotating weight (big end + allowence for a little oil) to create a bob weight that is bolted around the rod journals before dynamic balancing.

I have a table of the different balance factors for common V engines at home, but I cannot remember all of them. I think a 60 deg V6 is 60%.

I think the crank issue you mention is because the crank is vertically offset. I tried to calculate it from first principles. I could do it for V6 and V8 (but I found reference materials for these calculations in several text books), but nothing for a system which has a vertical offset - and thats where I caught a cold !!

I have spoken to many people about this now - the common theme being that it doesn't make much diference but I also believe that many have had engines rebuilt, lightened, balanced using maybe approximate calculations, that whilst good enough is exactly that, people forget just how good they can be. Your comment that you once drove a 1600 that was as smooth as a 1200 gives me confidence that there is a right way of doing it.

I have no idea if 50% is correct, but as it is the first figure I have ever seen quoted I shall do a bit of chasing - don't hold your breath !

And good to see you are still up and at it Paul, your posts always take us a step foward.

[bryan dugdale]

Neil and Paul, thank you both; very useful information, which is helping me to build on my limited, non-technical ,level of understanding. On the point you made Paul, about keeping the original flywheel, when i was lightening the original on a lathe, it fell into two parts. My mate who was operating the lathe had heard a rumour about the two-piece aspect, was very suprised when the outer section flew past his left ear. I have a new single part flywheel, which obviously needs careful balancing before use, so any futher advice from you both would be very well received. Thank you again,and best regards, Bryan

[ncundy]

Yes , they are two piece. I know someone who lightened his and it exploded on the road - luckily at low speed with no lasting damage. Whilst it's not obvious from looking at it, the Technical Data book has a section drawing in it that shows the construction.

I'm not sure about swapping flywheels but bow to Pauls greater experience. The fly wheel can be balanced separetly from the crank/rods/piston assembly so theoreticaly it should make no difference. Unless they were originally balanced together as an assembly.

Did you get anywhere with the balance factors?

[bryan dugdale]

No luck with the balance factor, although i do have one more avenue to explore, i will let you know if i get a result. I think the seperation of the components looks like the most likely outcome. I have some new pistons as well, which are 65 G lighter than the OE, so some careful attention will need to be given in that respect. Its slightly suprising that the balance factor isnt commonly known? Bryan