The Saga Begins: January 2000
Up until KTM re-embraced linkage rear suspension a couple years
ago, anyone who owned a 1998 and newer KTM had the PDS
damping system, which is pretty cool because there's no shock
linkage to maintain. One slight problem, though: the bearing in the
lower shock mount is a teflon coated heim-type bearing (sometimes
referred to as spherical-type). The heim isn't the problem; actually it
is necessary to handle the slight side-to-side movement that would
destroy a conventional bearing in no time. The KTM engineers
decided to use a bearing with a "maintenance-free" teflon coated
race. In theory, good choice. In reality, bad choice. Because of the
various movements of the swingarm, the seals can't keep out all the
dirt and water from contaminating the teflon coating (the seals
actually move around a bit). Normally you would smear a bunch of
grease in the heim and around the seals, but that's bad, because the
grease breaks down the teflon coating. So you're kinda darned if you
do, darned if you don't grease the thing. Without any servicing at all
(as with mine the first year I owned my KTM), the teflon breaks down
after 60 or 70 hours of use and play develops in the swingarm. I
found this out by putting the bike on a stand and lifting up and down
on the swingarm. The end of the swingarm had about 1/4 inch of
movement before engaging the suspension.
What's the solution?
Prolonging the life is about all you can hope for. In the early days of
PDS, a KTM dealer was about the only option for find a replacement,
and back then KTM's parts were expensive. The first time I replaced
the bearing, seals and spacers in January 2000, I think I paid about
$100. That was tough to swallow, so I began wrapping the lower
shock mount with an old inner tube (see below). The goal was to
keep as much water, dirt, and mud from contaminating the heim's
teflon coating. Also, I would regularly pull out the seals and smear a
light layer of waterproof grease around the edges. My second heim
bearing lasted about 100 hours, so these precautions added 30-40
hours to its useful life.
Over time, PDS-equipped KTM's were all over the trails and tracks, so
an after-market gradually developed for the heim bearing. In
response, KTM actually started reducing their OEM prices for the
bearing kit. Companies like Enduro Engineering now sell the heim kit
for about $30, which is a lot more reasonable than it used to be.
One thing I would recommend is buying a heim bearing tool. I used to
drive the bearing in and out of the swingarm with a socket and
sledgehammer, but many years ago I bought a special tool from a
now-defunct company called eRider. This tool greatly reduced the risk
of driving the bearing cockeyed and putting grooves in the housing.
Motion Pro makes a nice tool, but if you're careful, the socket and
sledgehammer method still works.
Heim Removal & Installation
1. Remove the swingarm. Not completely necessary, but you need to
grease the swingarm bearings anyway. Don't forget - gotta take off
the chain guide, too.
2. Pop out the bushings using a drift or other long metal object. Work
at them from within, attacking them from the opposite sides. After a
year of corrosion, they may need some persuasion.
3. Pop out the seals around the heim bearing using a flat blade
4. Use a socket or heim bearing tool to drive out the bad heim.
Pound on it like hell, and use some heat around the housing if it won't
budge. Be careful not to get the bearing mis-aligned on the way out
or it will dig into the soft aluminum housing. If this happens, a Dremel
tool or file can be used to smooth off any rough spots. The heim can
be removed from either side.
5. Line up the new bearing and start tapping it gently until you know
it's going in straight. A night in the freezer (the bearing, not you)
helps with installation. If you're using a socket as a driver, make sure
it is only contacting the outer race and not the round thingie that
swivels inside (you DON'T want to ruin your new bearing, trust me).
Then pound like hell until it's centered in the housing.
6. Tap in the new seals (don't even think about trying to re-use the
old ones). A little dab of grease around the seal lips is a good idea.
7. Put in the new bushings.
8. Re-assemble the swingarm and shock.
|Here's how I used to try extending the life of my heim bearing. There
are some aftermarket alternatives to this now. The life of the heim will
depend on your riding conditions. If you like to play in the mud, plan
on a shorter life.