C[omp]ute

From: andrew cooke <andrew@...>

Date: Tue, 6 Nov 2018 11:49:06 -0300

Lower priced mountain biks often come with forks that contain a coil
spring (rather than an "air spring").  These tend to not get a lot of
love on the intenet.  That's partly justified - an air fork is much
more adjustable and has better damping.  But the spring forks do have
some advantages too.  Most of all, they're very low maintenance - most
people don't touch them once they've bought them.

Despite that, a little care can help keep your fork working well and
extend its life.  I just serviced mine and I thought I'd make a few
notes here ot help others.

First, I am not 100% sure what my fork is.  I removed the stickers
years ago.  I think it may be a Suntour XCM (26").  Whatever, the
general principles below should apply to pretty much and budget fork.

There are two things you can do.  The simplest (and most important) is
to remove the lowers.  More complicated is to open up the "insides"
too.


Removing Lowers

First, remove the two bolts holding the front brake (I'm assuming
disc) so that it's no longer connected to the fork.  Also remove the
clip or zip tie or tape that holds the hose to the fork.  Then you can
ignore the brake (until the end, when we need to put it back on).

(Don't press the brake lever with the caliper loose - you can push the
hydraulic pistons out).

Turn the bike upside down, so it's sitting on the bars (or put it in a
stand if you have one I guess) and remove the wheel.  Have a look at
the bottoms of the forks.  On mine each has a 10mm nut.  Remove the
nuts and see if the you can slide the lowers off.  Don't use violence
- just pull them up with your hands while keeping the bike on the
floor with your foot.

Possibly they won't come off.  This is because the rods inside the
fork tend to stick in the ends of the lowers.  We can loosen them by
pushing the threads that the nuts were fastened on back "into" the
lowers.

To do this, take a piece of wood, lay it on top of the threaded rod,
and strike with a hammer.  You may need a few attempts (change the
position of the wood since the rods makes a hole!) before the threaded
rods moves noticeably.  Once both sides are loose, you should be able
to pull the lowers off, no problem.

With the lowers off, clean the exposed stanchions and the inside of
the lowers (eg with a stick and cloth - if the cloth gets stuck
inside, blow it out from the other end).

The stanchions are steel, so can rust.  This is why it's worth
servicing them - we want them to stay smooth and clean.  So rub some
grease on them (I use random car grease - nothing fancy).

To reassemble, first put some more grease on the insides of the seals.
Then slide the lowers back on the stanchions.  Push them down and the
rods will re-appear out of the ends.  Replace and tighten the nuts
(fairly tight - you don't want these coming undone...).

Finally, replace the wheel and re-attach the brakes (once the caliper
is in place, apply the brakes and then tighten the bolts - that will
help tighten the bolts with the calipers in the right position to
avoid rubbing).


Looking Inside

If you want to look "inside" the fork, first remove the lowers (as
above).

Next, use an appropriate tool from Suntour to unscrew the two caps on
the "top" of the fork (one on each side).  This is easier to do with
the bike lying on its side (or upright in a stand).

I'd really enourage buying the right tool.  Mine is just a plastic
wrench (looks like a big bottle opener or measuring spoon).  You can
get the caps off without it, but getting the spring side back on is
tricky (because the spring is compressed) and without the tool you're
more likely to cross-thread the cap.

If you have a lockout you may need to move the lockout knob before
removing the cap.  Mine just levers off (carefully insert a flat
screwdriver underneath and lift).

It's interesting to see what's inside, but there's not much to do
except clean and grease.  I removed an elastomer damper from "inside"
my spring so that the forks had a little more travel, but I'm not sure
I noticed much difference.  On the other side, my fork has a damper,
but it's a sealed unit with nothing to adjust.

(BTW I couldn't remove the "foot" on the spring side because the
bottom-out damper held it in place.)

Assembly is the reverse process.  Be careful replacing the cap on the
spring side as it's easy to cross-thread.  My caps are plastic so I
didn't tighten them crazy-tight.


I hope that helps.  With a little care you can keep these babies
rust-free and they'll last forever.

Andrew