Adjusting YZF's valves
YZ250f/400/426, WR250f/400/426 Valve Adjustment Procedure:
- Remove seat, tank and shrouds
- Remove breather hoses from top of engine cap.
- Remove the spark plug.
- Remove the top engine mount brackets (12mm, 14mm and hex wrench needed)
- Remove the two engine cap screws (hex wrench needed).
- Remove the engine cap taking care not to damage the gasket.
- Remove the two timing caps from the left side of the engine crankcase (standard screwdriver)
- Using a 14mm socket, align the timing mark ("I" not the "H") with the marks on the cover for the compression stroke (cam lobes should be facing away from each other). The marks on the cams should also match up to the top of the engine per WR or YZ timing.
- Using a feeler gauge, you should be able to check all your valve clearance numbers.
- Start with the manual specs and shove the feeler gauge under the cam lobes. If it won't go under, go down until it does. If it goes in to easy, go up. I beleive there should be a slight resistance when checking the correct clearance but it should slide under the lobe.
- Compare your numbers with the manual's specs. If they are not in specification, then you will need to change out your shims.
- Make sure you keep track of which clearance measurement goes with each valve as you will have to match them up with shim numbers if you need to adjust them. That is all you need to do to check your clearance. Now if you have to actually adjust your valves, then you need to keep reading.
Adjusting your valves:
- Remove the chain tensioner on the back of the engine (8mm and 10mm)
- It is a good idea to stuff some rags anywhere in the engine openings to help prevent dropping something down there. You should have an extend magnet handy just in case you do drop something.
- Working in a criss cross pattern, remove the cam cap bolts (8mm, 4 on exhaust, 5 on intake).
- Carefully, carefully, carefully lift off your cam caps. There is a halm moon retainer at the front of each cam. If you have one, use the extend magnet to grab it as you lift. Otherwise, be very aware of it. Also, there should be two guiding dowels on the bottom of each cam. Mine were frozen in the caps themselves. But if they are not, they could also drop out and down the engine.
- Your cams should just lift up and forward. Carefully remove them from the chain. Do not let your chain drop down the engine. If you can, zip tie it or rubber band it so that it won't fall. Reason being is that it can come off the shaft down at the bottom of the engine.
- Remove the compression release from the front of the engine. Take note of how the spring is setup for when you put it back on. Once the bolts are removed, it will slide out.
- At this point, it is a good idea to have paper and pen ready to mark where the valve lift covers come out and go back in as well as keeping track of your shim numbers. You want to make sure you get the covers back in the same spots you took them out.
- Carefully lift out the valve lifter covers. The shims are underneath these covers. Mine were stuck to the inside top of the covers with oil. But they are very small and could drop out and into the engine.
- Once they are all out, match the shim number with your earlier clearance markings. Using the table in the manual, calculate what shims you need to install. It is easy to follow.
- At this point, you will have to wait until you can get new shims from the dealer. Some carry them, some have to order them. Cover up your engine so no dirt gets in there.
- Once your new shims arrive, carefully install them on top of the correct valves pressing them into their fittings
with the NUMBERS FACING UP.
Note: On reassembly always put assembly lube on both sides of the adjusting shims and the buckets. Also
coat the CAMs with assembly lube.
- Put the valve lifter covers back into there original spots. Once fitted, you should be able to rotate them in their spots.
- Install the compression release setup at the front of the engine. Make sure you have the proper 5mm free play upon the lever after you do this.
- Install the cams making sure the timing marks on the cams are matched up to the engine top correctly per WR or YZ timing. The cam lobes should be facing away from each other when done. This may take some pushing and pullin on the chain, make sure you do not dislodge it from the bottom shaft. Also make sure your timing mark in the crankcasecover has not moved.
- Carefully install the cam retainers and cam caps. I found it easier to put the retainer on the cam first then putting the cam cap on. This may take a little time to find the exact position the cam is supposed to be in, but the cap won't fit on unless the cam is in the exact spot. Remember the guiding dowels on the bottom of the retainers.
- Working in a criss cross pattern, install the cam cap bolts and tighten down to 10 Nms.
- Before installing the chain tensioner, take a small standard screwdriver and put it in the end of the tensioner. With your finger on the push rod, twist the tensioner until it locks.
- Install the tensioner. Take the screwdriver and slowly release rod until it stops. Do not force it once it stops. Make sure it did release and put the end bolt on.
- Using the 14mm socket, turn over the engine a couple of times and re-allign the timing marks.
- Re-check your valve clearance measurements. If they are still out of specs, redo the whole adjustment process.
- Install the timing mark caps on the left side of the crankcase.
- Install the engine cap making sure not to damage the gasket.
- Install the engine cap bolts and tighten them down.
- Install the top engine mount brackets, torque to specs.
- Install the breather hoses.