 |
Bikespares Tech Help Article 1 KTM 400/520 EXC/SX Valve Clearances. Checking the valve clearances on your KTM is a very important part of the maintenance schedule, don’t do it often enougth & at a minimum the bike wont run to its full potential, at worst case severe engine damage can result. How often should you do it? Good question, a lot can depend on how the bike is ridden, i.e. gentle trail riding low rpm type use will most likely have less effect on the clearances than say Thumper nats type racing where the engine sees full rpm constantly. To start with I would recommend checking it at around 15hrs of use a couple of times until you get an idea of how much the clearances are changing by, For racing I would check the clearances after every meeting to keep the engine running at its peak. There is probably several different ways of going about checking the clearances; this is my preferred way of going about this job.
1: Remove the seat, fuel tank, L/H radiator & the crankcase vent hose off the back of the carburetor. Make sure there is no loose dirt etc on the frame above the tappets, blow this area off with compressed air if available or wash the bike with the tank removed, the last thing you want is dirt inside your engine. 2: remove the tappet covers, being careful not to drop the little copper washers into the engine! 3: Remove the crankshaft TDC setting bolt from the front of the crankcases, you may have to remove your bashplate to access this, it is located on the R/H front of the main engine crankcase, it is an 8mm threaded Allen head bolt with a thick copper washer. If you look at the bolt you will see that it has the end tapered to a point, remove the copper washer from the bolt, Now with the bike on a stand & the rear wheel elevated put the bike in 4th or 5th gear, now by pulling on the rear wheel in normal rotation direction slowly turn the engine over, watch the intake valve tappets carefully, when you see the intake valves opening you are getting close to TDC compression which is where you need the engine positioned to set the valve clearances, the next thing you will need is a small torch to look inside the crankshaft setting hole, turn the motor over until the intake valves close again & look for a notch cut in the crankshaft, when this notch lines up with the hole, screw in the Allen head bolt finger tight (with the thick copper washer removed) the engine should now be set at exactly TDC on the compression stroke.
Verify it is in the correct place by feeling the valve rocker arms, you should be able to move all 4 slightly.
4:You are now ready to check the valve clearances (the engine must be cool to check the clearances correctly.) the recommended clearance on the KTM is Intake & Exhaust .12mm, you should be able to insert a .10mm feeler gauge, but not a .15mm feeler gauge. To make the job easier a very long thin plain blade screwdriver should be used to adjust the tappets, as the exhaust valve on the R/H side is a little bit difficult to get at. To get the clearances within range quickly, on the exhaust valves loosen the 10mm locknut, turn the tappet adjuster screw in until it just starts to tighten up, then back off 1/4 of a turn, tighten the locknut (preferably with a small torque wrench to 12nm) & then check the clearance with a feeler gauge. Follow the same procedure on the intake valve but set them at 3/16 out. 5:Remove the crank setting bolt, refit the thick copper washer & refit to engine. 6:Refit tappet covers radiator etc, add a 50% coolant mix to cooling system using a good quality concentrate, 7: Start the engine & make sure everything sounds fine, run the engine long enough to bleed the cooling system. 8: Have a beer & congratulate yourself on a job well done!
|
| © Copyright 2007. bikespares.com.au |