How to - Four-Stroke Top End Rebuild (Part 2) Video
How to - Four-Stroke Top End Rebuild (Part 2)
This is part two of our KTM four stroke top end piston and ring replacement. In our last video, during dis-assembly we discovered we needed a new sleeve, and we sent it off to LA Sleeve. They were able to get it back to us good as new.
We're going to install a Wiseco piston, and the first thing we're going to do is check our ring end-gap. Throw a little oil in there, and then you install the ring and push it down with the piston so it's down a bit into the cylinder. And then on this particular machine it should measure 13000ths. This measurement is critical, because as your engine heats up and your rings heat up, you want to make sure there's room for them to expand so they don't ruin the cylinder.
Now we're moving on to the oil scraper rings. This is a spring separator. You want to make sure that the end doesn't overlap on that. The smaller thin rings actually sit on top of the ring expander. It holds them out. This is where most of the mistakes are made when installing rings on four strokes, so take care to make sure it looks very similar to this.
Now we're moving onto the upper ring. It goes on fairly simple. On a circlips, you want to make sure that you install these by twisting and compressing, not by bending. I like to seat the one side, make sure it clips in there solid. Going to oil up the piston again. Get our pin started, set it on the rod and push it the rest of the way through. Use some paper towel to make sure I don't drop the ring down in the motor.
Once again, we're putting this in by rotating it instead of bending it and compressing it. Here I've got, putting the base gasket on, and once again the cylinder goes on. Take your time; feed your cam chain, your cam guides up through.
Now we're just resting the cylinder under its own weight on the piston. I'm using my fingers to actually compress the rings very carefully. Push them through the tapered edge of the cylinder. Take your time with this step.
Now we've got the piston in. We're sliding our cam chains, tighten them up. Here's our head that we've FACTIONMX reconditioned. They cut the valve seat, and bead blasted it so it looks good as new. We've also replaced our valves. Please refer to our valve replacement video for those instructions.
Now we've just put our two locating dowels in, and we're going to set our head gasket on top of the cylinder. Notice the piston is at top dead center, and it's going to make it a lot easier to find top dead center on the crank here in a minute.
Now we're setting the head on, pulling our cam chain through. Line it up and then our head-bolts with washers, going to tighten those down and for this motor, it's 30 to 35 foot pounds. All ways refer to your service manual for these important specifications. There are the three bolts that go in from the underside that need to be reinstalled.
Now we're going to find top dead center on the crank, so you remove this Allen bolt, the lock down bolt. Remove the copper washer off of it and re- install the bolt. The bolt has a tapered edge on it, so it makes finding the notch in the crank a little easier. What I'm doing is I'm just rotating the engine back and forth and actually feeling for the notch.
Once you get top dead center we can move on to the cam for lubing up the lobes and we're setting the cam in with the lobes generally down for right now. There's a collar on the end by the water pump that needs to go into a grove. These alignment marks need to be horizontal with the top of the head.
Putting our cam chain on, taking our wires that we've had holding it, put them out. We're using our new master link we got from KTM. We're putting it on, we're going to use our chain riveting tool to swedge the ends of the cam chain. We've also put paper towels back in so once again we don't drop anything down on the bottom. This tool makes it pretty slick, makes it so it's a secure master link.
Now we're going to ready the valve cover and put a little silicone, a little sealant on there carefully. You don't want to get too much, you want to make sure it's evenly coated on both sides, both surfaces. We're going to slide the valve cover on, pull up the lifters a little bit, make sure there's no binding. This should all sit flush. We're going to install the bolts, and they are at eight foot pounds, is what this machine calls for.
Now we're on the cam chain adjuster and we've removed the bolt and the spring so we can reset the adjuster. We'll mount it on the cylinder and tighten it down. Then we'll give the adjuster a head start, release it, and then we'll put the spring and the tension bolt in. This holds your cam chain tight, it's automatic.
Now we're on to the water pump cover. As you can see we're using a new gasket from our Tusk top-end gasket kit. Put those on, once again about 8 foot pounds. Now we're going to adjust our valves. We're going to back off our adjusters, and on this model, it's calling for between 4 and 5000ths. We need our feeler gauge. You want to just slide it underneath just so there's slight resistance.
You have your screw driver actually on your tappet and hold it in place while you tighten it with a wrench. Move to the other side, and put your tappet cover back on. Now our valves are adjusted we can release the lock down bolt by putting our washer back in. Now we're re-installing our oil supply line. Make sure and get the copper washer underneath, and on top.
Tighten those both down. Put our ignition cover back on. Tighten it down, connect it. We're going to install our carburetor. Make sure it engages in both the intake boots, tighten them down. Here we're re-assembling our decompression lever, checking our play in the cable. We don't want it too tight. Here we're tightening our spark plug. Putting our cap on, now we're putting our throttle cables on.
Feeding them through the cam. We're checking our cable play, tightening everything down. Put the cover on it, crank case breather hose, shifter, head pipe and our shock, silencer, radiators and our radiator hoses. Slide the tank and seat on, we're adding fluids here. We need to make sure and remove this air purge bolt. This allows both radiators to fill up evenly. Tighten the bolt back down, add the engine oil, and you're ready to ride. Make sure to refer to your service manual for proper braking procedure.