Seperating fact from myth:
"Do lightweight
flywheels come loose? Do the bolts back out? I've read some
things on message boards about this, what is the truth?"
While there are a few cases discussed on various message boards about
lightweight flywheel crank bolts backing out, the simple truth is this:
lightweight
flywheels do not cause the problem, there are always other factors that
result in the issue. This issue also occurs with OE
flywheels.
Why loose crank bolts? What happened? Three simple causes that are the
most common:
1)
Failure to apply loc-tite during
installation. The crank bolts
should be secured with red loc-tite (which we provide with all kits).
Some techs skip this. Or, if there's a mess of oil on the crank bolt
holes, the loc-tite won't stick. You can't glue something to oil.
The
fact is that even the best BMW techs make mistakes, and sometimes it's
convenient to blame the part rather than the work.
2)
Removal of the crank pulley for
performance. The crank pulley (not
to be confused with accessory pulleys) is a tuned damper that keeps the
crankshaft from getting all sorts of deformations from second-order
harmonics. When this happens, to quote one of the BMW Motorsport race
engineers we've consulted with, the crank shaft "will shake like a wet
dog and throw off the flywheel, piston rod bolts, and bearings."
Lessons learned from high-end racing. The M5x family of engines (which
covers all M50, M52, M54, S50, S52, S54) develop a fairly violent
harmonic around 7K rpm, +/- a few hundred depending on specific
configuration... track use with the motor in this range for extended
periods, are where this perfect storm happens and damage results.
3)
Certain race cams exacerbate this
harmonic issue. With everything
else done right, living at around 7400rpm with those specific cams does
very bad things. One manufacturer that was particularly bad about that
has since revised their design to fix that problem, and has an
otherwise stellar reputation (and to be clear, of all the major brands,
all that I know of have corrected this situation and no new product
from them has that issue).
While we
used to see many instances of the
loose crank bolt problem due to these cams a few years ago, the number
has significantly dropped since that cam manufacturer changed their
design.
Despite the few voices on the internet who like to brand-bash instead
of understanding the physics and mechanics behind products and
failures, this product has proven to be a solid and reliable performer
with less-than-average failure rates. With over 15 years of offering
the M5 clutch conversion flywheel design, we have a ton of data
reinforcing this information.
BOTTOM LINE:
Issues with crank bolts coming loose, with close forensic analysis,
always turn out to be caused by something other than the flywheel
itself. When installed correctly and with proper understanding of
what other engine modifications should not be done, the UUC Stage 2 /
M5 clutch conversion flywheel is every bit as reliable as a standard OE
flywheel.