Crankshaft balancing

[Pisobiker]

Hi all,

Will need to rebalance the crankshaft+flywheel+beltpulley assembly soon.
Main reasons are:

1) I'm using the 95.5mm stroke crank with the ABY-ADU type twin mass flywheel;
2) I'll be using different from OEM conrods and pistons thus changing both the rotating and alternating masses.

Anybody knows how to compute bobweight masses for the IL5 ?

Thanks

Marco

P.S. Contrary to my expectations, the AAT (Tdi) flywheel is lighter than the ABY-ADU one of around 2 Kg !!

[porkkis]

Yes. Bigend mass (inc bearings) + half of the small end mass + half of complete piston mass with rings and pin.

[Pisobiker]

Thanks for the answer, Porkkis.

can you also give me some info on how numerically (but even only form a quality stand point could be good enaugh) this percentage on the alternating mass is obtained?
I was reading a tech book on U.S. V8s and V6s and I think I understood bobweight was "total rotating + 50% of reciprocating" for the V8 and "+46% of reciprocating" for the V6.
Without knowing how this calculation is supposed to come from there is very little to argue with!

Marco

[S2central.net]

Yikes - yeah where does that 50% come from - this stuff scares me... Volvo couldn't get this right when they specc'd their I5 engines - they had to goto Audi for such mechanical expertise.

Only very few people know how to lighten and balance an I5 crank properly. Sadly I don't have any experience of any, but I do know someone in the UK (from a UR-quattro forum) that raves about the prowess of his engine builder in this department. He is secretive about his name for some reason, but I'll see if I can get a phone number !


Cheers,

Paul

[SteveH]

My crank is at the balancers at the moment. As Paul mentioned, there are only a few individuals in the UK that can do this. Phil from Bassett Down balancing is the man for the job

Bassett Down Balancing
Unit 19 Lower Bassett Down Workshops
Basset Down
Wroughton
Swindon
Wiltshire
SN4 9QP
Tel: 01793 812331

[Lee]

I did this numerical evaluation of engine balancing masses during my studies. Haven't done it since so I need to dig out my lecture notes for a reminder. It is quite straightforward although I never did it for an odd cylider number..we did I4 I6 V8 etc but no I5!! Actually it doesn't matter on the cylinder quantity as the calculation principles are the same (number of throws and crank configuration is essential (I5 is a 5 plane crank so that's easy). I6 doesn't actually need any counterbalance on the crank since it is perfectly balanced system as is with the correct crank configuration!

My notes are in my parents loft so I will look through the dynamics books I have in work for a refresher (can't be arsed to work it out from first principles now).

I use Schenk in Banbury to balance stuff at work. They make balancing machines from desktop units that balance dentist drill turbines (600,000rpm!!) through to hardware to balance power station turbines. They also make most of the automated production line balancers as used by the majority of car manufacturers. I use a facility at their factory. The have never done a crank though as a one off and the practicalities of balancing a crank with rods is a highly specialist task. Steve, any chance of a photo of the equipment being used to balance your crank? I spoke to Schenk about balancing an engine and they were quite cagey about it and they certainly can't do it in house (A crank on its own is more straight forward but you are trying to achieve the appropriate counterbalance mass too)!! Not easy.

Lee

[Pisobiker]

Lee, if you could shed some light on this I would appreciate. I'm absolutely not doubting of Porkkis nubers. It's just me and my need of digging into things. If I don't fully understend the theory behind them and have the chance of getting some numbers through it I just don't feel right.....


Marco

[Lee]

Hi Marco, I'll need to dig it out. My notes were brilliant because our lecturer in dynamics was one of the best teachers in the Engineering department of my Uni (probably explains why dynamics was my strong point at the time!).

I am up to my ****** at work so it will take time for me to refresh from the dynamics books and I will probably have to go from first principals anyway (F=m.a, F=M.r.w^2 etc).

Off topic here, but, Marco, can you check my brake sums in the custom brackets thread as it has been a long and tiring day!! Since you like quantifying stuff it might 'float your boat'.

Lee

[Audi Parts Guru]

What I remember from my learning days is that in an I-5 engine the primary and secondary forces cancell each other out. Unfortunately thats all I can remember :wacked:

[Lee]

That's the I6 mate otherwise Audi wouldn't have fitted a dual mass flywheel [ABY] and a harmonic damper to our engines. These add to production costs so they didn't do it for fun!! Some engines have balancer shafts to cancel out the forces but Audi never did that to the I5.