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Urgent technical note: Fiat/Lancia TC cast-iron Flywheels

Posted: April 1st, 2009, 9:28 am
by Guy Croft
With immediate effect a new regime is in place at GCRE (that you would be wise to copy) and that is the non-destructive (NDT) crack testing of OE flywheels in every case. Part of the reason for an abnormal incidence of cracks around the central region on items I have examined lately is age, the material is just 'weaker' than it used to be.

Primary reasons for cracking:

1. Severe imbalance of fw or assy
2. Embedding of fw bolts into fw and subsequent loss of preload
3. Incorrect torque setting (over/under) on fw bolts - easily upset by incorrect lubrication regime.
4. 'Swashing' of fw friction face. This can be balanced out - but it puts an fluctuating and very adverse axial load across the radius of the fw every time the clutch is engaged. It can be caused by a poor quality regrind of the item or bent crank/flange out of true.
5. Cracks inherent in fw - precision grind and crack test is advisable on each rebuild.

Cracks in the friction face are not uncommon and usually disappear after grinding.

GC

Re: Urgent technical note: Fiat/Lancia TC cast-iron Flywheels

Posted: April 8th, 2009, 1:02 pm
by Guy Croft
I just want to add, given some of the comments flying around the net about this post. It seems that every time I publish something there is a smart-alec out there how knows better and has to say so without delay.

1) I don't do aero engines and I don't operate under a CAA regime so I don't have to certificate my NDT. Thus I don't feel compelled to charge £120 an hour and I don't have to keep copious records.
2) I have NDT'd more engine parts than most will in their lifetime (in F1) and figure I have a sporting chance of discerning what is and what is not a crack.
3) Lightening a cast iron flywheel in the right places (ie: well outboard of the centre bolting region) makes the thing safer, not more likely to fail. Because there is less inertia and less load on the holding region. Of course if your go too thin and leave sharp corners everywhere you are asking for trouble. FWIW I have never seen a cast-iron FW exhibit cracks in the friction face area (apart from small heat cracks), only in the central region.

I remark on the lightening aspect because I have run cast-iron fw at unbelieveable speeds and never had a GC prepped one fail in 20 years and don't want people put off lightening simply because I publish an article about cracks.

GC