How To - Rebuild A Two Stroke Top End Video

How To - Rebuild A Two Stroke Top End

Our informative video will walk you through how to rebuild a two stroke top end in a short amount of time. Watch our industry expert as he replaces pistons and rings. Rocky Mountain ATV/MC is your online information source for several online videos that provide step-by-step instructions. Trust us to have the answers and instructions you need – every time.


Hi, I'm Eric with the and today I'm going to show you how to rebuild a two stroke top end.

We're going to need an owner's manual, some common hand tools, a Tusk top end gasket set, Wiseco piston, and some contact cleaner. We're going to start with the tank off, the subframe removed, and antifreeze drained, and it's always really important to start with a spotlessly clean bike. You want to make sure you don't have any dirt or anything that can fall down into the top end.

We're going to start by taking off the pipe and we're going to use our Tusk spring puller to remove the springs. Go ahead and pull the pipe off. Next step we want to take the top motor mount head stay off, spark plug, helps remove the compression so the piston will go up and down pretty easy. The radiator hoses. Always like to have a little extra rag there in case there is any coolant left in the lines. We're going to go ahead and remove the head now.

As you pull that off some models are going to have O rings, others are going to have a gasket. This model has O rings. Make sure and get those out. There are two little dowels on the side that help center the head, make sure and pull those out so we don't drop them down into the cylinder. We're going to pull a power valve cover off now. Inside there we have our linkage and on Yamahas it has a little groove right there that you place a holding tool in so when you loosen the linkage bolt it doesn't damage the power valve assembly. Go ahead and pull that off. There is a spacer behind there also.

Next up we're going to loosen our cylinder bolts. Some of them are hard to get to. A lot of times you can get to them with an end wrench, though. You need to move the carburetor up out of the way. It's kind of nice to just lay it over the top, you don't have to undo the cables and everything. Just get it out of your way.

On this model we need to move that CDI box out of the way but on other models it might be necessary to move the radiators or anything else that might be in your way. it might be necessary to tap the side of the cylinder with a mallet to loosen it up from the base gasket. Go ahead and pull the cylinder off. Kind of pull the piston down out of the way and then move it out of the way. Now we're going to go ahead and put a rag in the bottom end and pull our wrist pin clip out. Grab a socket of suitable size and push that wrist pin out. When you pull that out, make sure you're being careful not to drop anything. There's your wrist pin bearing.

Now is a great time to refer to your service manual for where tolerance is and parts inspection for assembly. As we begin installation the first thing we need to do is check our ring end gap. To do that we're going to install a ring in the cylinder and measure, with a feller gauge, the gap. Wiseco recommends 13/1000ths of an inch. Always refer to your piston or ring instructions to get the correct gap. If it is too small you can take a small file and file away a little bit of the ring and open up the gap a little bit.

Next, we're going to install the ring on the piston and you start on one end, get it in the groove, then you use your thumb to spread the ring very carefully without scratching the top of the piston. Then slide the ring all the way in. Now pay special attention to that centering pin. Make sure you have that ring centered on there for when you install the cylinder. Next up is our circlip. You want to make sure and twist that on not bend it. If you bend it, it won't stay in place and it will fall out. Now we're going to go ahead and use a little raw premix and lubricate the rod and the bearing.

Now, when we put the piston on you need to pay special attention. There is normally an arrow or a marking on top of the piston. Wisecos normally have the arrow marking the exhaust but always refer to your piston manufacturer's instructions. You're going to go ahead put that on and we're going to slide the wrist pin in. Make sure everything lines up nice.

Then next we're going to go ahead and install the circlip on the other side. Make sure that rage is still on the bottom so if you drop the circlip it doesn't fall in the bottom end. Now we're going to install our centering dowels and our base gasket. Make sure the surfaces are clean so you have a good sealing surface. There again, you can see the sealing surface on the cylinder. We're going to use a little bit more raw premix on the bottom, on that beveled edge of our cylinder to help the rings slide in a bit better. Now we need to compress the rings as we slide that beveled edge on. Make sure that the rings are centered on the centering pin. You can feel them kind of slide down and into place.

Make sure and take some time right here, get everything lined up. Now is a great time to make sure the piston goes up and down nice and easy. There are no snags; you can feel that it's installed correctly.

Now we're going to go ahead and put on our base cylinder bolts in a crisscross pattern so there's no warpage. It's always good to have your piston all the way at the top so there's no way you can drop anything down. We have our O rings installed. We're going to drop our cylinder head on. We put on our bolts and once again there's our copper washers. Then we're going to put our cylinder bolts on and tighten them in a crisscross pattern once again so there's no warpage. Always refer to your service manual for torque specifications.

Now we're going to reassemble our power valve exactly how we took it off. There's a spacer, the link, make sure that goes on its groove correctly. We're going to put our holding tool in so we don't damage the power valve when we tighten the bolt.

Next we're going to put the cover on. There is a little gasket down at the bottom; you want to make sure it's lined up correctly. Install our bolts.

Next up we want to make sure we've got our spark plug, our radiator hoses, our cylinder head stay. We're going to put our pipe back on with our Tusk spring puller.

As you can see we have our CDI box back installed, spark plug cap, carburetor, we filled it with antifreeze, and now it's time to put the tank on, seat, subframe. Go ahead and refer to your owner's manual for proper breaking procedure and let's go ride.