1986 CR 250 - Top end / Water pump concerns

I picked up a 1986 CR 250 awhile back in generally good condition but not running. The PO said the radiator plugged up and it got hot and cooked the piston. The piston was toast; a chunk cracked off the side of it, above the ring, on the exhaust port side. 


The bike went on the back burner for quite some time and recently I have begun to work on it. 


I sent the top end off to be redone. It had been previously sleeved ( :thumbsdn: ) so I had a fresh sleeve installed and bored to stock. They also cleaned the powervalves and everything else I guess.


The top right bolt on the right side power valve cover won't torque down and spins freely, not sure if it was like that before the work was done, but I will need to fix that. 


I purchased and am in the process of installing a wiseco piston and gasket kit for the bike right now. There was no lateral crank play in the bottom end and no vertical play in the rod against the crank. Ring end gap checked out fine with a .008 gauge. I put the rings in the cylinder, pressed them down with the piston to get them even and used the feeler gauge pushed from the center of the cylinder to the wall of the cylinder  in the gap. It fit and didn't seem to be a problem. The max spec (I think it is .012? I don't have my manual with me right this second) did not fit but I don't see that as a problem obviously.


So right now I have the gaskets installed into the top end, bolts are torqued with one exception, and I should be installing the piston over the weekend when I have the time. 


The next step after that concerns me. I don't know for sure if the radiators are clogged, I don't know how to test them. I don't know what the PO knew or if it was even the truth. The water pump cover didn't look seriously corroded, wasn't missing any chunks, but everything in the coolant system (which has been dry for awhile) does have a white powdery film. 


I was leaning towards buying some ebay radiators + silicon hoses for ~$135 shipped so I have a part I know is "good" and will work. I do not know if I can clean the radiators myself and I really don't want to have them cleaned if the money that will cost would be in the same ball park as new radiators. 


I also don't know what kind of coolant to run in the future to prevent corrosion and breaking the bike.


This is my first time doing a top end and I am comfortable with being able to do a lot of work myself. This is the farthest I have ever been into an engine but I have experience working on things from my motorcycles ATV and snowmobiles. I also have an xr100 that I have done some small work on, but that was just involving flywheel/stator/electrics stuff.


A lot of people told me to quit this, and probably will continue to tell me to quit, but the bike ran before and I see no reason that it can't run again. I just want to make sure I do it right the first time because I don't want to sink much more money into it.

Unplugging the radiators is easy. Buy a gallon of 20% acid Vinegar from Lowes or Home Depot. Don't use regular vinegar because it won't be strong enough.


Remove the radiators and all hoses from the bike. Connect the hoses to the radiators and stick the assembly in the sink. Fill the radiators with the vinegar and allow it to soak for a day. Come back 24 hours later and dump the old vinegar out and repeat the process for another day. Come back and dump the old vinegar and flush the radiators with water, then fill the sink with water and submerge the rads several times to get all traces of the vinegar out. The rads should be clear at that point.


The right case cover is magnesium and they usually rot through over time. The best fix is a '89-'91 right case cover as they are made of aluminum. Honda still sells the '91 cover but their stock is becoming depleted so act fast if you want to get your hands on a new one.

Edited by CamP

haha everything makes a lot more sense now thanks. Thats not really a simple or cheap option, wouldn't there be a coolant that would not react to the magnesium? What was Honda's recommendation in 1986?





For example http://www.amazon.com/Bel-Ray-Moto-Chill-Racing-Coolant/dp/B0045LCFGM and http://www.amazon.com/Maxima-82964-Coolanol-Performance-Coolant/dp/B0012TROMU both claim corrosion protection and life extension for magnesium


Would those be safe to run?

Edited by rifkin

Did you check the condition of your side cover/water pump?  If it corroded enough to plug your radiators and over heat the motor, it's probably if poor condition.  It can be rebuilt if you feel like putting the effort into it.   


Evans waterless coolant is a good option.



Here's some pics of an '84 CR250 cover I'm working on....









Just checked mine out briefly, I can see some pitting around the perimeter edge of the propeller on/under the gasket surface. I don't know if that makes sense but it is basically where your large pit is at the 6 o'clock but 1/5th the size and closer to the bolt hole to the left at the 8 o'clock. Also another pitted spot at the 11 o'clock. Nothing showing anywhere else however. I really really do not want to take that whole crankcase cover off, is it possible to just remove the propeller and then use some jb weld on the pitted areas? I have some JB weld steel stik that worked well enough for a similar repair to the crankcase and cover on the flywheel/stator area of my XR100.


With this Evans coolant: will this eliminate the magnesium corrosion? Is this a coolant I can run and be worry free?


Here is a terrible cell phone pic i just took a few minutes ago



A side cover gasket costs about $7. Take it apart and do the job right.

As CamP mentioned, parts are cheap for it......you can get the gaskets, seals and bearing to rebuild the water pump for $30-40.   Prep, rebuild and seal it now, and you won't have to worry about it again. Pay particular attention to the two water passages, they tend to corrode the worst back there.  The cover I'm working on was almost corroded thru in a couple spots.


Evans coolant is what I would use, especially if you do nothing with the water pump.......but I don't recommend that route.  

Had to take the side cover off on mine. Tried JB weld...found that titanium epoxy from auto parts store worked best. 5 minute cure rate. Gotta clean those passages out and make sure it's not leaking into tranny. G.

Quick question: does anyone know what size hex bolt holds the brake lever on? Nothing I have in any of my hex sets is big enough and the brake is in the way of removing the cover. 

8mm or if you have sae hex, 5/16 will probably work

Just bringing this thread back real quick.


I finally finished my bike, BjfX8TYl.jpg 





Thanks for the help, I wouldn't have been able to do it without it. :)

Looks very nice!

I wish I had true before pictures because the bike was a mess. This was the first time I attempted anything like this, though i realize at the heart of it, it is still a simple top end rebuild. I took the bike apart 350 miles and a years time away from home. When I finally was able to get it back to my garage, it had spent a winter outside under a tarp and I had forgotten how I had even got it apart. I never thought I would get it running and it makes me quite happy to have succeeded.

glad you brought another one back to life.

now reroute your brake hose correctly and have fun.

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