Cr250 Rebuild

[mladewig]

Hello All

I am about to jump in and replace the piston and rings etc on my CR250. It will be the first time for me on this bike but I have done some rebuilds before on my CR125. I was just wondering if anyone has and specific pointers for me on what to look out for while I have the engine semi unassembeld. Any pointers or comments will be appreciated..

 

[joh9356]

Just be careful taking the cylinder off.

When you do this, patience is a virtue. If it's stuck just slowly work at it, NEVER force it, you'll create more problems than you're trying to fix. Us a soft dead-blow hammer and gently tap it up, adding penetrant if needed. If it takes a few hours, it takes a few hours. If it comes off immediately, you're blessed.

No matter how frustrated you get, leve the flat head screwdriver or prybar in the toolbox, avoid prying on anything at all costs!

 

[cook_04]

Time

Just be careful, I just replaced the top end on my cr 250. It took about 4 hours. so it does take time.

 

[Dragmeistr]

The top end on your bike should be fairly easy as far as top ends go. You do not have to remove the reed cage which is a plus(unless you are replacing reeds as well). The less you mess with your RC valve cables when you take them off, the less adjusting you have to do when you put it back together. Above and beyond that, nothing real special to worry about.

 

[Faded]

Very good tips so far, especially the one about prying. That's a good way to ruin a cylinder/cases.

The exhaust valve shaft doesn't like to come out very easily if there's any sign of deposits/build-up. After removeing the 6mm cap screw and the shaft retainer the exhaust valve shaft (along with the seal) will come out but might require some force. Pull it straight out. A new seal should be provided in your gasket kit.

The exhaust valves should come out realatively easy if you excersise patience (push in and twist a little, then remove through the port). To put them back in I've found it easier to do it with the cylinder upside down. If you're still running the stock reed cage check your reeds, the lower left side petals like to take a beating. Replace them if they're chipped, frayed, cracked and/or don't sit tight against the cage.

Now would be a good time to go through and clean the carb to get it ready for the season. Check the float level and verify that it's set a @ 15mm (for '01-'03 CR250s). This is a maintenance item that should be checked just like everything else.

Any other questions just ask, good luck. :cool:

 

[mladewig]

Cool, thanks for the tips..

Another question - What is the best way to set / check the power valves? I had to replace the cable recently and I am not sure if they are set correctly.

Another one - Here in South Africa we have to order the parts individualy, what would I need:

Top + Bottom Gasket
Small end bearing + circlips
Piston + Rings (Really)

Anything else??

 

[Rcannon]

I would add this. Keep the area clean. Watrch for dirt around the coil and under the gastank.

Paint remover applied with a Q-tip makes quick work of the gasket residue on the cases. This lets you avoid scraping with a razor blade.

After rebuilding my bike 4 times I now have the total time under two hours. Have your manual open to the correct page listing torque values when you put the bike back together.

 

[Revver]

This is going to sound stupid, and I must admit that it happened to me. When you remove the cylinder pay attention to how many dowel pins there are. When I was trying to put my cylinder back on the cases of my '01 cr250, I assumed there were supposed to be four dowel pins and that the previous owner of the bike had done a rebuild and idiotically only re-used two pins. I was wrong, the bike really only used two pins. Imagine how frustrated I got trying to get the cylinder holes to slide over dowel pins that were too big for the opening because they weren't supposed to go there. :bang: :bang: :bang:

 

[Revver]

Oh and you've gotten good advice about the cylinder. Mine was really stubborn but with enough taps of a mallet, and elbow grease, it eventually came loose. Take the time to treat corrosion and apply anti-sieze grease to parts before reassembling.

 

[Faded]

Another question - What is the best way to set / check the power valves?

The first thing to do is to set the right cable. Rotate the RC valve clockwise until it stops. Adjust the right side cable until you have a measurement of 12mm from the top of the RC valve "butterfly" to the bottom of the cable adjuster (as seen in photo - ignore the 13.8 markings).

See Photo Here.

After that, rotate the RC valve counter clockwise until it stops. Now, tighten up the left side cable until it's tight, but not taunt. Generally, if there is enough play that you can gently push it to the left (with light/moderate pressure) and touch the cylinder casting, it's not tight enough. Once everything is set, you're done.

Another one - Here in South Africa we have to order the parts individualy...Anything else??

Reed cage gasket, exhaust valve shaft seal, piston pin, exhaust manifold gasket...

 

[mladewig]

Thanks for the input...

Another quickie, I wanted to use a genuine honda piston and rings etc etc but due to the high price I have to look at another make.

Wiseco or Pro-X ??

I would imagine that the Wiseco would be just as good as a Honda original part..

 

[joh9356]

I would imagine that the Wiseco would be just as good as a Honda original part..

Better, much better. Remember that your bike is mass manufactured and the manufacturer doesn't have time to mic every little thing, so they go with mass quantity every so often on the pistons and cylinders. They stamp the pistons and cylinders and they go together in batches from the manufacturer. The assemblers just match the codes.

Wiseco goes in increments with the understanding that the rebuilder knows what they are doing in miking the cylinder walls for the correct width, therefore purchasing the correct piston.

 

[Gazza2005au]

did you know Pro-X pistons are designed to not melt! i chose these for my jetski over OEM and Wisco heres a tip when putting the new piston on make sure the arrow on the top of the piston is facing the exhaust post and if u look very close at both rings u will see tinny letters these must face up on the piston it will save u time if u look other wise there is a chance u can put them on upside down untill u find out they wont seat into th piston propperly also another tip once u have the head off (piston still attached) cover the main ball (bottom end) with a rag incase one of the sir clips fall into the motor it will save a little time finding it and it will also stop any old base gasket falling down into the motor

 

[Joe_148]

ya like someone else said, you'll also need a wrist pin, exhaust flange o ring, and a new gasket for the exhaust valve cover.

also, I used the stock honda piston and the arrow on those is supposed to face the INTAKE side, so you better double check whichever one you buy because some are different which is kind of stupid..

 

[Gazza2005au]

ive never heard of the arrow pointing towards the intake :|

 

[mladewig]

Ok, so I finaly got a Wossner Piston Kit. All that I can say is that the piston looks awesome. In fact I dont want to hide it away inside my bike! Ha Ha Just kidding.

My CR requires an 'A' piston, now does anyone know how I can check to see if I got the correct size? I never trust the guys at the bike shop and rather double check before I stick it in.

The ring size is Ø 66.34 mm , how can I make sure it is correct? Is there a way of measuring the barrel to see what size is needed?

 

[mladewig]

How safe is it to use the small end bearing again in the new piston?

 

[nickyd]

depends. you might NEVER have an issue....however, when I put a new top end I do the bearing too....its like putting the chocolate in the milk and then never stirring it....mmmmmn, chocolate milk...