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1989 CR250 rebuild help. Need to know what to replace/service.

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I bought this bike used, and instead of immediately rebuilding it, I just rode it. Finally decided to check it out, and these are some of the pics of the top end. How do the cylinder and piston look? This is the first top end I do, and am confident in my mechanical skills, just not confident in what is considered "working". The piston and the head seem to have some marks from debris, but the cylinder looks smooth.

If I do a top end rebuild, can I get away with just a piston/rings, or is the cylinder in need of a bore/honing? Not quite sure when it comes to this. I'll show the rest of the cylinder and the bottom end as soon as I can get the cylinder off. That thing is crazy stuck... I have the service manual PDF as well. These pics are preliminary of the whole tear down.  

Also, I noticed the gasket for the head didn't have the full hole open on some for be ports where coolant passes through. Is that normal? I have a pic that shows the actual holes on the head and the cut outs in the gasket.

(You'll see some coolant still in the cylinder, is that supposed to stay? I tried draining it through the release screw)

Thanks for any help! Hope to continue to participate in this forum. Clueless when it comes to classifying the integrity of components, just know how to replace.

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REPLACE THE PISTON. It looks like there are pieces of the piston missing that gouged the head. The cylinder doesn't look too great either. Run your fingernail along the cylinder wall. If you can feel anything with you fingernail, I think you are supposed to have it replated. (Someone who is more familiar with this can correct me) Also, while you have it apart, check the tolerances on the crank.

 

 

 

 

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Yea ill check the crank out. As for the cylinder wall, from the top side I don't feel much with my nail. But "much" is relative to what i have to compare I guess lol. 

Any ideas on how to get the cylinder unstuck? I was going to try heating it tomorrow. 

As for the head, would that be reused if I replaced the piston?

Edited by Alberto Gamez

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5 minutes ago, Alberto Gamez said:

Yea ill check the crank out. As for the cylinder wall, from the top side I don't feel much with my nail. But "much" is relative to what i have to compare I guess lol. 

Any ideas on how to get the cylinder unstuck? I was going to try heating it tomorrow. 

As for the head, would that be reused if I replaced the piston?

Try rubber mallet lightly tap back and forth . Pull up, back and forth while tapping.  :thumbsup:

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Since it is apart you should measure the cylinder for out of roundness and taper. A service manual will give you specs to go by and if it has exceeded the service limit. That will mostly tell you if the cylinder needs to be bored or not. Regardless if you plan on putting only rings and a piston in it you will need to get the cylinder honed.

 

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8 minutes ago, Motox367 said:

Try rubber mallet lightly tap back and forth . Pull up, back and forth while tapping.  :thumbsup:

Been trying the mallet, but not the pulling at the same time. Thanks

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Hope it works for ya. Either stuck on dowls or someone used gasket maker on base gasket.  Seen that few times 

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That cylinder looks like it has an iron liner in it. Pluses and minuses to that.  It can be bored cheaper than replating.   That has had some debris from somewhere.   Could be stuff from a previous failed piston or it could be new damage,  like your big end bearing is shedding metal.  I would want to know that before it goes back together.   I had an 88.   Great rigs for their day.  

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18 minutes ago, ossagp said:

That cylinder looks like it has an iron liner in it. Pluses and minuses to that.  It can be bored cheaper than replating.   That has had some debris from somewhere.   Could be stuff from a previous failed piston or it could be new damage,  like your big end bearing is shedding metal.  I would want to know that before it goes back together.   I had an 88.   Great rigs for their day.  

I'll update this thread tomorrow or Saturday once I can take off the cylinder and see the bottom end.  Thank you guys for your input.

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You are welcome for mine.   some fishing with a magnet might tell you  more about what could be floating around in the crank case if you can't see anything.  (Stick a strong magnet onto the crank.  carefully rotate the crankshaft while the case slides the magnet along,  as long as it doesnt lose contact with the crankshaft the magnet should pick up stuff under it.  Rubbing bearing grease on it,  like a stripe and inch wide and turning it slowly is another way.)

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Alright guys, I took off the cylinder and the results were scary. It appears part of my piston is missing at the bottom. I figured do an oil change to see if there's any in the crankcase, but I'm not sure if shards in the crank would make it to the tranny. 

Anyways, I noticed it was really grimy on the bottom of the case before I took the drain screw off. Upon further inspection, I noticed my case was cracked under the exhaust port as well. What a bummer. 

Well, at least the connecting rod doesn't have any vertical play ?. Also, I can't get the oil screw off easily cuz it's an allen key type.  

I'm surprised it still ran, and started second or third kick when cold. So, advice on how to proceed? Splitting the case seems to require special tools from what I've gathered. My game plan is as follows:

 1. Check for metal shards in oil and I'm crank with magnet

2. If none are found, JB weld case and put a new piston in her with a hone. And a new head? That one is dinged up.

As you can see from my plan, I'm on a budget. I'd just like this bike to last until summer, and if I'm extremely lucky, through a few rides in the next few years. I'm leaving to college and won't be able to ride much, but my plan is to buy a new bike as soon as I graduate. Priorities, am I right ?.

But any advice is helpful. If it seems like it's the right thing, I may do a full rebuild if some advice. Sorry for the long and late reply!

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I'm still waiting on a gauge to measure the bore of the cylinder and see if it's in spec. No one has it in my town. So idk if I'll order one or just hone it. Piston came in. 

Here's the head.

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If it were me I would sand the mating surface flat with some fine sandpaper on a good flat surface like some granite or a table saw and run it!

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The head is gouged a ton, but it'll be fine. Just make sure the gasket surface is smooth and put it together.

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If I can't find a bore gauge, and just hone it, I'd just lose some compression if it's a bit out of spec right? It ran on one ring and 3/4s of a piston before I decided to take it apart lol

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It's possible it will run. Just not very good if it's out of spec. And if there's too much slop, you would probably find yourself doing this again very soon. Personally I wouldn't run it without checking it first. If you have a feeler gauge you can put a piston ring in the cylinder and measure the gap. Measure top middle and bottom and see how much difference there is

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It's possible it will run. Just not very good if it's out of spec. And if there's too much slop, you would probably find yourself doing this again very soon. Personally I wouldn't run it without checking it first. If you have a feeler gauge you can put a piston ring in the cylinder and measure the gap. Measure top middle and bottom and see how much difference there is

You should gap your rings regardless, but also check the bore. If it's too far out of spec, you'll get piston slap and break another piston.

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