1986 cr250 Top End Help

Ok... My dad has an 86 cr250 in great need of a new piston and rings (the piston is missing a chunk...). It still ran great until recently when I think the rings finally died (there is like zero compression). I think the bottom end is still ok (it kicks fine and very smoothly). My dad has like no money to get the jug re-honed, etc., but he really wants to get it running. So...can we just pick up a new piston/rings/wristpin/etc and throw it in there and hope for the best? Assuming the bottem end isn't full of crap how risky is this? I know this is obviously not ideal, but it is either this or sell the bike broken... Thanks guys! :worthy:

If the cylinder is plated, you can usually just toss a new piston in. Sleeved cylinders may require a hone or even a bore.

Ok... My dad has an 86 cr250 in great need of a new piston and rings (the piston is missing a chunk...). It still ran great until recently when I think the rings finally died (there is like zero compression). I think the bottom end is still ok (it kicks fine and very smoothly). My dad has like no money to get the jug re-honed, etc., but he really wants to get it running. So...can we just pick up a new piston/rings/wristpin/etc and throw it in there and hope for the best? Assuming the bottem end isn't full of crap how risky is this? I know this is obviously not ideal, but it is either this or sell the bike broken... Thanks guys! :worthy:

What did the cylinder look like? What is the history of it? Do you know? Find out what the bore size is stock and measure it, or take it to a dealer and have them Mic it for you. It all depends on what the Cylinder looks like. If it is cast, which I am pretty sure an 86 is, then you can find someone to bore it fairly cheap. It may just need skim cut or honed. Just take the cylinder to a good dealrship and ask their advice.

That's SK's $.02 worth

"carry on"

First the proper way would be to have the cylinder replated and put a new piston and ring set in. I know riding on a budget is hard to do so you make compromises. you are riding an 86 so I see you are on a budget. What I would do in your situation is to take the cylinder off the bike and clean it up really good. If you can find someone with a beed hone that could just run it in and out a few times to break the glaze on the cylinder that would be good. Maybe you could rent one...You can power with a standard hand drill. I would then clean it again and put it back togeather with new piston and rings...That should get you running assuming the bottom end is good. You could just throw a new piston and ring in there with no other prep but the rings may not break in properly.

You might get away with it...If that is all the money you can come up with go for it....It isnt running now so what do you have to lose? good luck

86 should be plated.

Thanks for all the help guys! Not sure about the cylinder yet, it's my dads bike so I haven't been able to get over there and pull the cylinder yet. But from what I saw when we pulled the head it looked to be in decent shape if I remember right. Hoping to check it out this weekend though and I'll post what I find with some pics. :worthy: Appreciate all the help!

i was thinking about it last night. You said you have a missing chunk out of your piston...It would probably be a good idea to locate that chunk if it is floating around your bottom end.

i was thinking about it last night. You said you have a missing chunk out of your piston...It would probably be a good idea to locate that chunk if it is floating around your bottom end.

Good point... no point to fixing the top end only to blow the bottom...

86 should be plated.

1986 cr125s were DEFINATELY not plated stock

i dont think 250s were but im not sure.

check around.

now, my ghetto motor work is as follows:

you can do a totally ghetto top end job on this thing if you are SURE of the piston size (you could bore these steel cylinders -if its not plated quite a bit) so you need to know how big you piston is, replace it with the same.

Ghetto says, you need to take the motor out of the frame, rinse the bottom end out with a lot of premix or kerosene if you dont want to esplode in a ball of fire. reason being you got small bits of metal and crap floating around down there because you have metal missing from piston. after you get it clean, reassemble

more ghetto. get some 6oo grit sand paper and try to crosshatch the cylinder walls by hand.

put it together.

finally, because this is ghetto. Your mileage may vary. it may run great for a long time or the lower end may grenade due to the metal bits down there grinding for who knows how long.

if we are going ghetto I would recomend using steel whool on the cylinder before you use sand paper. I agree clean the bottom end.

Use red scotch brite and try to replicate the crosshatches. Red scotch brite works the best.

if we are going ghetto I would recomend using steel whool on the cylinder before you use sand paper. I agree clean the bottom end.

Master Bator sez, to be truly ghetto, you rub with whatever you have on hand.:worthy:

When you say rinse out the bottom end, do you mean like pour a bucket of kerosene in there and swish it around and then dump it out? And won't kerosene destroy the gaskets and crap? I got a crapload of steel wool around so I'll prob just try that first. I'm kinda curious to see what kind of shape this thing is in on the inside...

When you say rinse out the bottom end, do you mean like pour a bucket of kerosene in there and swish it around and then dump it out? And won't kerosene destroy the gaskets and crap? I got a crapload of steel wool around so I'll prob just try that first. I'm kinda curious to see what kind of shape this thing is in on the inside...

kerosene wont hurt anything. you could use gas, but thats very dangerous.

properly, you should split teh cases but were talking way ghetto. you definately need to clean out the bottom end. use kerosene (thats pretty much just wd 40 ya know). it wont hurt anything more than whats already been happening.

use a lot and get it clean. pour it on your neighbors lawn:banana:

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