PROTECT
YOUR CRANK!!
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Tightening
(or loosening) Clutch & Driver Nuts the Right Way
By
John Copeland
One
of the most critical elements of 2-Cycle engine performance is proper
crankshaft alignment. If you do your own engine work you know how much
time it takes to get the run-out within acceptable limits (usually .0002
at the most). And if you have an engine builder do your crank work, you
know that it's not an inexpensive service. Just a little bit of crank
mis-alignment can really kill top-end performance, and can lead to
crankshaft breakage. Yet, for all that, too many karters get their
engines ready to go and then promptly screw up all that hard crank
alignment work when they tighten up the nut that holds the clutch or the
driver on.
The
problem is, once the engine is together, there is precious little to
hold onto to tighten or loosen the nut on the driver or clutch. That
starter nut on the other end of the crank is a tempting thing to use to
hold the crank while you tighten or loosen the nut. DON'T DO IT! For
those of you who don't know, the crankshaft is actually a 3 piece
assembly. The crank pin that carries the bottom rod bearing is pressed
between the two halves of the crank that stick out each side of the
crankcase. Even though it's a very tight fit, holding the crank by one
end and twisting on the other end is very likely to ruin the alignment
of the two halves.
OK,
so then how do you get that nut on tight enough when you mount the
clutch or driver? Conversely, if you need to get that little stinker off
when you need to? The answer is to hold the crank by the end that you're
working on. How you do this depends on whether you're using an engine
clutch or an axle clutch. In either case, all you'll need will be tools
you already have in your toolbox, plus an odd bit or two.
For
you axle clutchers, you need a pair of channelock pliers and either a 6
inch piece of old drive belt, or an old piece of chain the same length,
depending on whether you're belt or chain driven. Just wrap the piece of
belt or chain around the driver to protect it, and grab on with the
channelocks. Be sure to set the pliers to the right grip range so you
can get a solid grip, and so the plier's grip tightens as you apply
pressure on the nut. Otherwise you won't be able to a good enough grip
to get the nut on or off.
Too
many engine clutch users seem determined to tighten or loosen the clutch
nut with the clutch cover installed. Sorry, the only way to do this job
properly is with the cover off. Every clutch manufacturer also offers a
clutch wrench to hold the clutch "guts" solidly while you
tighten or loosen the clutch nut. In a pinch, you can hold the clutch
with your trusty channelocks, if you have a pair big enough. Just be
sure to wrap something around the clutch where you're going to hold it,
so you don't chew up the springs or weight levers. Overall, it's really
best to invest the $10 to $15 for a clutch wrench and take the worry out
of screwing up your high dollar clutch.
One
final word: It's always a good idea to use a torque wrench to tighten
the nut on the crank. Particularly on the Yamaha KT100SE engine, the
notoriously soft crankshaft is relatively easy to bend out on the end.
I've even seen more than one heavy-handed karter snap the threaded end
off a Yamaha crank by tightening the nut too hard. If the keyway is in
good shape, and the taper on the crank is smooth, and if the clutch or
driver is lapped onto the crank (always a good idea), and with the
proper key, correctly fitted, the specified torque of 22 ft/lbs is more
than adequate to hold things in place. If any of the conditions above
are not correctly prepared, it is highly likely that the clutch or
driver will come loose, regardless of how tight you tighten the nut.
So
there you have it. With tools you probably already have, and just a
little extra care, you can safeguard that expensive crank rebuild, and
probably enjoy a little better performance too. Take your time and do it
right, it's worth it. See you next month.
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