SXF Valve Adjustment from KTMTalk SXF
Valve Adjustment 250SXF
On this engine several procedures are going to be different than the RFS,
checking is simpler, changing is more complex than the RFS but the
object is, this is a “Race Engine”, designed to withstand higher RPM
than the RFS is.
Part of what makes this bike so fast is a "leverage ratio" that the
Finger Follower allows. All this does make it more complex but that is
how it is going to be in "Race Engine" that will spin 13,000 RPM. Some
helpful Pics are available at
http://ktmtalk.com/index.php?showtopic=144710
The factory specs (cold engine) are:
Intake .10mm to .20mm (converts for us that think in inches to .004” to
.008”), and
Exhaust .12.mm to .22. (converts to .0048” to .0084”. lets call it 5 to
a loose 8).
Tools, In addition to common shop tools you are going to need;
1: Feeler gauges in several thicknesses above and below the spec! While
bent ones are preferred, as there is a bit more room than the RFS I
don’t see the need for the skinny MP ones that are so favored on the RFS
engine.
2: When we get to changing shims we are going to need a long skinny
magnet.
3: When we get to selecting shims you should have a micrometer.
CHECKING THE VALVE CLEARANCE:
Remove fuel tank, clean any debris around the valve cover.
Remove the 4 bolts that attach the valve cover and slide cover out to
the right (it is tapered to make it easier to go right).
Intakes (rear pair)
1: To check intakes, rotate the engine until the Intake (rear) cam lobe
is near straight up.
2: Under the cam lobe there is an arm (“finger follower”) that makes up
the space between the lobe and the valve.
3: The point you need to measure is between the cam lobe and the finger
follower.
4: Select your feeler gauge, the pre-bent ones from Motion Pro are the
favored ones for the RFS crowd but not needed here, generic flat ones
from your tools store are fine and we want a "set" or at minimum several
sizes from the thinnest available up to say .010” as for this design we
need to find out what the clearance is! And then keep records!
5: So starting with the left rear, check with various gauges until you
establish what gauge fits with some drag.
6: Lets use for example it was .004” so we are going to start a record
of LI (Left Intake) = .004”. Next repeat on RI or RR and lets say it was
a 5 so we record RI = .005”
Exhaust (front pair)
To check exhaust, rotate the engine until the Exhaust (front) cam lobe
is near straight up.
Repeat 1-6!
So when complete we have a record something like
Bike new, 5 hours use. Or bike purchased used time unknown.
LI = .003”.
RI = .005”.
LE = .006”.
RE = .007”.
I want you to save that record permanently! Now if those where the
numbers your bike has you are within spec and no need for any
adjustments. However when we do need to make changes we want to record
all shim changes! The reason is we want to keep track of how much each
valve has stretched and or seceded into the valve seat from new! In time
we will learn more about when the valves need to be “cycled out” to
catch them before they fail and damage the engine.
An example would be when you have changed the shim on a valve more than
say .005” then its failure is eminent so change it now while it’s a
cheap repair.
This is a bit like a Top Fuel Drag car throwing away a $3,000 crankshaft
at 12 runs because at 15 they are at high risk of breakage and likely to
do $50,000 in damage not to mention danger.
In our case its more like $100 valve and $2,500 damage & pushing out of
the woods. Still running a valve that has stretched/seceded into the
seat to a point approaching failure is not cost effective.
Intake, As spec is .004 to .008”
LI = .003” so we need to reduce the shim by .001”
RI = .005” OK.
Exhaust, As spec is .005 to .008”+
LE = .005” OK
RE = .005” so we need to increase the shim by .001”.
What I want you to do is AS YOU CHANGE SHIMS maintain a record something
like this.
3 hours 25 hours 40 hours total
LI = --.001”, --.002”, --.003”, .006”! As long as we are running TI (I
am guessing that .005” will be a safe operating range) so now its time
to cycle out NOW!!!!!
ADJUSTING THE VALVE CLEARANCE: I recommend that you have the KTM Shop
Manuel in hand before diving in here!
The concept is we have to change shims that are in the center of the
valve spring retainer. Shims are available from KTM from 1.72mm to 2.6mm
in .04 mm graduations. Establish how much we need to change each and
write it down, then:
1: Turn the engine to top dead center, piston up, both cams lobes near
up! Check that the two crank gears have punch marks on their left side
facing each other and perfectly a lined with the mating surface of the
caps that retain the cams!!!
Install the top dead center lock down bolt in the bottom of the case so
it is engaged into a notch in the crank.
2: Remove the cam chain pensioner (Right Front corner of the head).
3: Remove the two bolts that hold down the black chain guide that is
above the chain, set the guide aside.
4: Remove the remaining bolts holding the cam bearing caps, set them and
the bearing caps aside
5: lift the rear cam and allow it to roll forward within the cam chain
as you lift, once it has come forward the chain is loose and you can
slide both cams out of the chain. Set them aside;
Go to valve;
LI measure the existing shim locate and replace with one .001” thinner
(or whatever was needed)
RI was OK so leave it alone
Repeat until all adjustments are complete
Note, if you need a shim say .001” thinner and do not have that shim you
can lap the shim on a piece of fine sandpaper, check with a “mic” to
determine when you have removed that .001”. If there is a number etched
into the shim to state its thickness we may as well do that side of the
shim as the number is now wrong (you may hate yourself for having done
this next time around).
Reinstall cam without chain, roll so lobe is up and re check clearance,
repeat if necessary.
When satisfied reassemble, the punch marks on the cam gear must point at
each other and match the mating surface of the bearing caps! The torque
specs for the bolts holding the cams in place is 18NM.
INSTALLING THE TIMING CHAIN TENSIONER! Direct from KTM's shop manual!
Note: IF YOU DO NOT FOLLOW THESE INSTRUCTIONS THE CHAIN WILL NOT BE
TENSIONED CORRECTLY AND WILL SKIP, RESULTING IN ENGINE DAMAGE!!
The timing chain tensioner operated with spring force and with oil
pressure. A stop system is used to ensure the right amount of chain
tension in the starting phase, even if the oil pressure is insufficient.
The stop system prevents the piston on the timing chain tensioner from
being retracted. In a dismounted state, the piston on the timing chain
tensioner extends completely.
Fully depress the spring tensioner. This will require some effort since
the oil must be squeezed out. If the timing chain tensioner is released
it will extend completely again; it may not be mounted in this state,
since the locking mechanism will not function.
Press down on the timing chain tensioner to ensure smooth operation.
To prepare the timing chain tensioner for installation, place 2 washers
or similar spacers with a thickness 2 to 2.5mm (two nickels, one each
side of the tensioner in between is perfect) next to the piston of the
timing chain tensioner. This will ensure that the piston can not be
completely retracted when the piston is pressed down. If you release the
piston, the stop system will lock, the piston will protrude approx 3mm
and stay in this position – this position is mandatory for refitting!
If you press the timing chain tensioner again and it extends no more
than half way (preventing it from extending completely), the stop system
will “lock” and the timing chain tensioner can go no longer be pressed
together – this position is necessary to ensure that the timing chain is
adequately tensioned, even if the oil pressure is low.
Slip the hydraulic tensioner into its hole the telescoping end first,
install the plug with its sealing ting and tighten to 25NM.
Then with a substantial screwdriver enter it into the RF corner of the
head, straight down just forward of the cam chain, get the tip of the
screwdriver on the front side of the black tensioner bar and force it
back against the chain to “relieve” the previously “locked” tensioner so
it can hold the chain tension firm until oil pressure takes over!
Caution
If the chain tensioner is not “relieved” after assembly as described
above, the timing chain will skip when the engine is started resulting
in valve damage.
When you are complete the TDC lock down bolt is removed, its washer
re-installed and the bolt should be tightened to 20NM.
edit: following info is from KTM520
TIMING CHAIN ADJUSTER INSTALLATION PROCEDURE
This procedure details the steps required to correctly install the
tensioner once the valves have been re-shimmed and the cams have been
reinstalled. I am assuming that the washer has been removed from the
crank stop bolt and the engine is locked at TDC. When the tensioner was
removed from the cylinder head, it should have fully extended. Note the
o-ring that was on the tensioner and save for reinstallation.
1. Place the tensioner and copper washer from the crank stop bolt on a
flat hard surface as shown in figure A.
2. Compress the tensioner until the outer half comes in contact with the
copper washer as shown in figure A. It requires a decent amount of force
to compress the tensioner, as it is full of oil. The trapped oil will
exhaust at the joint between the inner and outer half of the tensioner.
The tensioner should stay compressed once compressive force is removed.
3. Install the o-ring on the tensioner and lubricate the assembly with
motor oil.
4. Carefully install the tensioner into the cylinder head.
5. Place the copper washer onto the tensioner retaining bolt, thread the
bolt into the cylinder head, and torque the bolt.
6. Using a large flat blade screwdriver, placing the blade end up
against the chain close to where the tensioner contacts the chain guide.
Rest the shaft of the screwdriver against the tab that protrudes from
the upper cam bridge (this is the tab that the right side valve cover
bolt threads into). Refer to figure B. Gently pry against the chain just
enough to compress the adjuster. Slowly release pressure from the
screwdriver and the adjuster will extend to the correct position.
7. Remove the crank stop bolt and reinstall the copper washer. Install
the valve cover.
8. Install the seat and tank, and go ride.
Note: when the bike is started for the first time after this procedure,
the timing chain will make some noise for a couple of seconds until oil
pressure builds in the tensioner. Make sure to let the bike idle until
this noise goes away |
