Ktm 525 Valve Clearance
Ktm 525 Valve Clearance
I do 1/6th of a turn on my 05 525 EXC per DJH at KTMTalk.com, or from one hex corner to the next. This equates to about to .005 inches or .12 mm. Following is the entire text. A little long, but a great resource.
KTM RFS (or ANY 4 cycle) engine
Top Dead Center: Commonly referred to, as TDC is the point where the piston is up.
Power stroke: On a 4 cycle the engine produces power every other time the piston is up, while the piston and crank are in the same position (TDC)
every turn the cam turns of crank speed so the cam is in its position to
adjust, both cam lobes facing down every other turn! Thus you cannot just
put the piston at TDC and adjust, the odds are 50/50 that the cam is in the
Overlap stroke: The other turn where the piston reaches TDC is called the
overlap stoke, the valves are each open very slightly, approximately 1mm
with the exhaust closing and the intake opening. Not the place to adjust the
Clearance: To allow the valve to fully seat and transfer the heat it
accumulated when open, and to allow for heat expansion when hot, the
camshafts lifting pattern and valve train are designed to operate with
clearance lash or gap between the valve train and the valve. Too much
clearance and the cam and cam followers are prone to wear out. Too little
clearance and it can burn a valve, or if you are luck, just not start at all
so get it right. KTM has a service bulletin recommending that we ignore the
prior specs and set the valves at .12mm which in inches translates pretty
closely to .005.
Rotation: Note that the engine rotates the same direction as the wheels and
that when we rotate the engine we are fighting the valve springs, the
easiest way is to put the transmission in top gear, this gives the wheel max
leverage against the engine, conversely to how 1st gear gives the engine max
leverage against the wheel. Then we rotate the engine by the rear tire. If
you want to avoid pulling the spark plug out you can, just hold the manual
compression release while turning the engine.
Getting to it: First remove the seat & tank, from there I have done it
radiators on, and hated every minute of it, I have done radiators off, it is
more labor but maybe less maddening? (On ’03 try setting the radiators aside
without disconnecting the hoses) Unless the bike is spotless I like to take
a can of Brake Clean and someone elses toothbrush, spray & scrub the valve
covers and the area around it, then spray the area around the spark plug
with the brake clean to flush out that area. If you have compressed air a
good blast would help clean debris out of this area but watch you eyes!
Then remove the valve covers and if you are going to the spark plug but if
you do it my way there is no need on the plug.
Now we must locate the heal of the cam where the valve lash is to be
Common way: The common way it to find TDC on the Firing stroke. The
problem with this is too many folks end up on the Overlap stroke. This
causes endless confusion, people putting straws down plug holes and endless
other tricks that still often leave them on the wrong TDC.
My way: With this method you do not need to remove the spark plug, magneto
cover, skid plate or the TDC bolt in the bottom of the crankcase or the
Intake valves; Transmission in top gear, rear wheel off the ground, if you
have a helper one can watch the valves and hold the manual compression
release while the other rotates the engine with the rear wheel. Rotate the
engine gently with the wheel to locate the point where the exhaust valve
starts to open then rotate very gently until the exhaust valves are 1/2 way
open! Minor frustration, we are now fighting against the valve spring which
wants to roll the engine back, so to stop it you either have to have a
helper hold the rear brake or, as this gets pretty boring so;
Option 1; Take a tie down, hook one end to the brake pedal, wrap in under
the bike and up the left side to something like the top of the frame behind
the engine. Now just tighten the strap so the brake can keep the engine from
Option 2; Put a bar thru the spoke of the rear wheel adjacent to the swing
arm to stop the wheel.
At this point the Intakes are on Center of the Heal of the Cam. Proceed to
Exhaust valves; As above, except, locate the point where the intake valves
have opened and are 1/2 way closed (engine rotating forward). As the intake
is closing the engine will want roll forward PAST the way point and the
lash in the transmission and chain will make it so you can not stop the
engine, so let it go just past, then roll the wheel backwards and secure it
with the brake or bar again. Now proceed to adjust the Exhausts.
ALWAYS! ALL 4 STROKE ENGINES: With the engine rotating its correct direction
the exhaust is adjusted when the intake is closing and the intake is
adjusted when the exhaust is opening!
If you are a feeler gauge kinda guy; As the clearance is so small and you
can not get a straight approach with the feeler gauge dont be surprised if
you can not get it in. I like to loosen the jam nut (10mm box wrench) and
loosen the (one at a time) adjuster a couple of turns, slip the gauge in,
turn the adjuster down lightly against it, then tighten the jamb nut. In
doing so often the adjuster will creep tighter slightly and cause the
clearance to close up. What you need to do as you tighten the jamb nut is do
kind of an isometric exercise where you are holding the adjuster against
rotation with equal and opposite force of the rotation of the jamb nut!
This may take several practice attempts. As soon as you have tightened the
jamb nut, do not pull the feeler gauge out, just try to slide it around in
the gap! When you have it right it should slide with some, but minimal drag
or resistance, no drag and it is too loose, heavy drag and it is too tight,
may even be holding the valve open? Take a little time, you will have to
redo a few times at first but once you pull the gauge out you may not be
able to get it back in so get it right first! Oh, and by the way, the jamb
nuts need to be tight!
If you are a 1/6th turn kinda guy; I think it was the Husaberg guys that
came up with the theory that fraction of a turn will do! The Bergs have a
different thread pitch, I think they use 1/5th of a turn? My first reaction
was that is crude, then I tried it a few times, now do it every time. That
is based on a turn equates to .75mm (on the KTM tread) and.75 div by 6 =
.125mm and .12mm is spec so for all practical purposes 1/6 turn is right on!
Loosen the jam nut (10mm box wrench) and very lightly tighten (one at a
time) the adjuster till it contacts the valve, note where the screw slot is
aimed, turn the jamb nut to a corner of the hex aliens with the slot, make a
small scratch in the cover gasket surface in line with the next hex point
left (hex being 1/6th turn to the next point). Then turn the slot to that
point, then tighten the jamb nut. In doing so often the adjuster will creep
tighter slightly and cause the adjuster to tighten up. What you need to do
as you tighten the jamb nut is do kind of an isometric exercise where you
are holding the adjuster against rotation with equal and opposite force of
the rotation of the jamb nut! This may take several practice attempts. As
soon as you have tightened the jamb nut just double check that it did not
creep, the slot aimed at the mark we made 1/6 turn left of contact and move
on the next valve.
The jamb nuts need to be tight and there are a couple of ways to deal with
1: Get out the torque wrench, check the factory spec and torque it down.
Problem is with that is your locked into using a socket so you wont have
the screw driver resisting movement of the adjuster, if the torque was close
it should be OK. If it turned the nut much it may creep the adjuster around
and changed your clearance setting. Thus what you have to do is be very
close by hand before putting the torque wrench on it.
2: Perfect way, fabricate a crows foot type box wrench so you can use the
torque wrench and the screwdriver simultaneously. In doing so there is a
leverage factor that needs to be computed to arrive at a different (lower)
torque spec and you probably need four hands to do it.
3: My way again. Put a nut and bolt together in a vice and torque to the
spec, put the undoubtedly shorter box wrench on it to get a feel for how
tight that is. Repeat a few times and feel how tight that torque feels. Then
set the torque wrench aside and do it by hand.
Now that we are done lets just double check our work, remove the bar from
the rear wheel and rotate the engine forward to the checking points, hold it
there with the rear brake momentarily and confirm a small amount of lash.
Re-assemble dont forget, add coolant, return the toothbrush to its owner,