I'm getting ready to replace the top end on my 2001 honda cr250. I'll be using a weisco piston and want to know if I need to drill exhaust bridge lubrication holes. Does the 2001 have a vertical exhaust bridge? Also, what is the best way to drill holes in your piston. :yikes: Thanks everybody.
To drill or not to drill?
- Thread starter Revver
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If the old piston has the holes then you need to drill them. A hand drill is good enough. They don't have to be that accurate so long as they are blocked by the exhaust bridge. There are instructions with the Weisco piston on how to put them in.
It doesn't have a vertical exhaust bridge, and does not need holes drilled in the piston.
You probably already know this, but I'll mention it just in case this is your first top end job on this motor: When you install the piston, be careful of twisting the cylinder. It is really easy on those engines to knock the rings out of their groove on the piston, causing them to get hung up on the intake port on the cylinder. I did that a few years ago, and accidentally destroyed a brand new Wiseco piston. I mention that because I learned that the hard way, and wanted to make sure that doesn't happen to you.
Also, be sure to get the fork on the power valve to line up with its connector on the bottom end. If you don't, the PV wont work. Twisting the cylinder and not getting the power valve actuator lined up seem to be the two most common problems when doing a top end on those motors.
Anyway, I digress, as that wasn't your question. No drilling is needed. Good luck.
You probably already know this, but I'll mention it just in case this is your first top end job on this motor: When you install the piston, be careful of twisting the cylinder. It is really easy on those engines to knock the rings out of their groove on the piston, causing them to get hung up on the intake port on the cylinder. I did that a few years ago, and accidentally destroyed a brand new Wiseco piston. I mention that because I learned that the hard way, and wanted to make sure that doesn't happen to you.
Also, be sure to get the fork on the power valve to line up with its connector on the bottom end. If you don't, the PV wont work. Twisting the cylinder and not getting the power valve actuator lined up seem to be the two most common problems when doing a top end on those motors.
Anyway, I digress, as that wasn't your question. No drilling is needed. Good luck.
It can be tough to get the piston in the cylinder and compressing the rings. A trick for installing the cylinder is to put one c-clip in the piston and put it in the cylinder first. Have the wrist pin hole so you can see it and place the cylinder/piston assy on the motor. Line the rod up with the wrist pin hole and slide in the wrist pin. Then install the second clip and your set to go. It save a lot of hassles with getting the piston in the cylinder without having a ring catch in a port.
RM Guy's suggestion would work well. I never did it that way, I'd just compress the rings by hand and slip the cylinder over the piston when the piston was already attached to the connecting rod, but his way would probably be easier.
Once you get the motor re-assembled, take off the round powervalve cover on the left side of the engine. You'll see a shaft that has a line cut into it. If the powervalve is installed properly, that line will move when you rev the engine. Nonetheless, if it isn't installed properly, you'll definitely notice the loss of power either on the top or bottom end.
I used Wisecos in my CR and was very happy with them. Just be sure to warm your bike up thoroughly, particularly for the first few times, because the piston is forged. Inadequate warmup with forged pistons can result in a seizure.
These are fun engines to work on. I hope your project goes smoothly. Once you've done it once, the next top end job is really easy.
Mike
Once you get the motor re-assembled, take off the round powervalve cover on the left side of the engine. You'll see a shaft that has a line cut into it. If the powervalve is installed properly, that line will move when you rev the engine. Nonetheless, if it isn't installed properly, you'll definitely notice the loss of power either on the top or bottom end.
I used Wisecos in my CR and was very happy with them. Just be sure to warm your bike up thoroughly, particularly for the first few times, because the piston is forged. Inadequate warmup with forged pistons can result in a seizure.
These are fun engines to work on. I hope your project goes smoothly. Once you've done it once, the next top end job is really easy.
Mike
I forgot to mention, stuff a rag in the crank to keep stuff from falling in--like c-clips :ohmy:
