Motorcycle 2 Stroke Top End Rebuild – Piston Replacement

Motorcycle 2 Stroke Top End Rebuild – Piston Replacement


Hi I’m Eric with Rocky Mountain ATV/MC.com
and today I’m going to show you how to rebuild a two stroke top end. We’re gonna need an
owners 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, the 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 up we want to take the top
motor mount headstay off, the spark plug. it helps remove the compression so the piston
will go up and down pretty easy. Some radiator hoses, always like to have an extra rag there
in case there’s 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’s two little
dowels on the sides 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 the power valve cover off now. Inside
there we have our linkage and on Yamaha’s 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’s a spacer behind there also. Next up
we’re going to loosen our cylinder bolts, some of there are hard to get to. A lot of
times you can get to them with an end wrench though. We need to move the carburetor up
out of the way. It’s kinda nice just to lay it over the top and then 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, kinda 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 wristpin clip out. Grab
a socket, suitable size and push that wristpin out. When you pull that out make sure you’re
being careful not to drop anything. There’s your wristpin bearing. Now is a great time
to refer to your service manual for wear tolerances and parts inspection for assembly. As we begin
installation the first thing we need to do is check our ring end gap. And to do that
we are going to install a ring in the cylinder and measure with a feeler gauge the gap. Wiseco
recommends .0013 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 by on one end get it in the groove and then use your thumb to kind
of spread the ring very carefully without scratching the top of the piston, and slide
the ring all the way in. Now pay special attention to that centering pin, make sure you have
that ring centered on there 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’s normally an arrow or a marking on top of the piston. Wiseco’s normally have
the arrow marking the exhaust but always refer to your piston manufacturers instructions.
We’re going to go ahead and put that on and then we are going to slide the wristpin in,
make sure everything lines up nice. And then next we’re going to go ahead and install the
circlip on the other side. Make sure that rag is still in the bottom so if you do 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 held
the rings slide in a little 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, and 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’s 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 criss cross pattern so there’s no warpage.
It’s always good to have your piston all the way to the top so there’s no way you can drop
anything down. We have our o-rings installed, we’re gonna drop our cylinder head on. We
put on our bolts and once again there’s our copper washers. And then we’re going to put
our cylinder bolts on and tighten them in a criss cross 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 it’s 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’s a little gasket down at the bottom, you need 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’ve filled it with antifreeze. Now it’s time to put the tank on, seat, subframe. Go
ahead and refer to your owners manual for proper break in procedure and let’s go ride!

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