Fiat TC flywheel weight

dkermode · Post by **dkermode** » November 20th, 2006, 4:32 am

Hello Guy,

Are there any concerns, regarding engine longevity, with using a 8-9 pound aluminum flywheel on a Fiat 2l road car?

It has been indicated by some that the crankshaft and crankshaft bearings may take a pounding with such a light flywheel.

Thanks kindly.

Doug Kermode

Post by **Guy Croft** » November 20th, 2006, 10:26 am

Hi Doug

yes there are concerns as far as I'm concerned regarding an aluminium flywheel especially of the same diameter as original.

Aluminium is a fatigue prone material, like titanium and some other non ferrous metals and alloys. This means it will fracture if the life cycle is exceeded. The life cycle is a function of the number of cycles of applied stress and the stress level and data is available in the form of Sn curves to predict failure.

For example:
One application of the clutch, which puts a bending load on the fw normal to the crank axis - is one cycle; the applied load is readily computed from the clutch clamping force. The bigger the fw diameter the higher the bending stress. Another example is the shear load applied to the fw at the bolt region by the crankshaft torque. Of course this is very hard to compute because the torque and thus shear load fluctuates constantly. Moreover a shear stress is also applied every time you start the engine.

The computations are made more complicated by stress concentration factors which in effect, make the applied stress higher than it appears to be.

Now call me over-cautious, but I am often asked about aluminium flywheels and I always give the same answer. The thing is fairly and spinning at very high speed.What you are doing if you fit one is taking a flying leap into the unknown. Yes they used to use them on F1 engines but they were, say, 5" diameter and weighed nothing at all and were crack tested after every race. Crack testing will tell you, of course, if it has failed, not when it will fail..

Cast iron and steel fw do not fatique and are cannot possibly (in my exp, I have never had one split) be subjected to stress in excess of the endurance strength of the material up to say, cast - 7500 on the 2 liter, way higher with steel. Yes I have run CI ones higher, dowelled but what the absolute limit is I don't know. Certainly excellent balancing is imperative. When a CI fw bursts, it goes off like a grenade.

I am not in favour of running the cast item much higher really, one must consider the internal shear load in the cast material itself - the centrifugal force is huge, and it's only cast material, which is quite weak in shear.

One must also consider the effect of thermal expansion on the ring gear - aluminium has nearly twice the rate of ferrous materials. The hoop stress this places on the ring gear - especially in racing with very frequent and rapid gear changes, high clutch clamp force and all that heat, may cause the ring gear to crack.

And one must also consider the effect of embedding at the bolt region. Embedding is a well-known effect with aluminium. If the fw bolts work loose under this phenomenon, well, they are going to shear.

My advice is do not use an aluminium flywheel. Not unless you do the calculations and life it and check it frequently, or proven life calculations and test data are offered to you by the manufacturer. Which they will never be. It might look nice now, but if it does burst you could find yourself in terrible trouble.

Denise Burchette has just posted some very interesting observations by the way, regarding very light flywheel assemblies, see:

http://guy-croft.com/viewtopic.php?t=559

GC

Post by **Guy Croft** » November 23rd, 2006, 12:29 pm

New article in GC V/W re fw overhaul, lightening and balancing see:

http://guy-croft.com/viewtopic.php?p=2723#2723

GC

pastaroni34 · Post by **pastaroni34** » November 23rd, 2006, 3:40 pm

I also have a little library of technical info I can provide in regards to the subject. It gives fairly accurate estimates for weights and inertial moments. Again, as Guy said, there are many different flywheels but the basic design is similar. See the link below:

http://www.millersmule.com/File%20Libra ... arison.pdf

P.S. The aluminum design has been modified for additional strength, I do not recommend copying it.. I made this sheet a year or so ago, much has changed since then.

-Jason

sumplug · Post by **sumplug** » November 23rd, 2006, 4:46 pm

On the Fiat/Lancia 8v TC engine, is it true the Lancia Delta HF 1600 had the lightest flywheel?

Andy.

Post by **Guy Croft** » November 23rd, 2006, 4:59 pm

Andy, I think the carb version, yes. As for the Delta Turbo 1600 ie. I cannot recall; also I think the 130TC had a factory pre-lightened one. Nicely executed too, beautifully done.

Photos anyone?

Gc

Piero · Post by **Piero** » November 25th, 2006, 5:04 pm

Hope this is helpfull.
The weights of the three flywheels I have are as follows.
131 (from a super mirafiori, 2l) 18lbs 8oz.
Beta Volumex 16lbs 6oz.
130 Strada Abarth 12lbs 8oz
All are standard weights, (to the best of my knowledge).