Uh Oh, Piston hit head. Confused.

[freerida123]

Alright I just got a 1992 CR 250 for very cheap. The powervalve was broke so I popped the cyl. off and noticed the piston has or is hitting the head a little. It is a hot rods crank and rod with a wiseco std size piston.

The rod maybe has just a tick of up and down play in it but I'm not sure if that happened from the contact? The side to side play is quite a bit in my opinion. It measures .85mm between the thrust washer and the rod. Am I measuring that in the correct place or is it supposed to be between the washer and the crank half? Im not sure if the head has been milled down but thats what I suspect is the biggest problem. The piston looks very new (besides the circle indentation going around the top) so i'm not sure if the head was milled at the time the top end was done and the previous owner milled too much off and then decided to sell it.
Also I was thinking maybe It has a 97 - 01 head. I believe it would cause problems seeing as the 97 - 01 has a flat top piston and the 92 - 96 has a domed. Is there an easy way to tell what year it is? If anyone has any ideas I would appreciate hearing them as I would like to get all the parts ordered in one shot. Hope we can figure this out. Thanks alot in advance. -Craig

 

[mtk]

If the rod has up & down play in it, the crank is toast and needs rebuilt. There should be NO vertical play in the connecting rod. Your bottom end bearings are shot, which is allowing the piston to come up and hit the head.

I think you just discovered why you got the bike so cheaply; the entire engine needs rebuilt.

 

[youngr51]

If all parts a fubar'd replace correctly and forget all about the money wasted on the bike. Just fix correctly and call it a day.

 

[freerida123]

Im not worried about the money. I got the bike for $400. so a few hundred in parts will be no problem. I would just like to find the cause of the problem. It's hard for me to believe that the lower rod bearing is the culprit. The up and down is so minimal. Sometimes I think I feel it moving and other times I don't, but when I pull up and hit it with my hand it makes a metallic sound so I know it is moving. Any insight is helpful. Thanks

 

[Jasle]

if you have ANY movement up and down in the rod bearing you need to replace the crank or have it rebuilt. then from their we can check your squish clearance. its possible that someone set it up too tight by shaving the cylinder or did not use a base gasket. search squish on this site for directtions. just keep in mind with a toasted crank they results are not valid only ballpark.

 

[IndyMX]

Im not worried about the money. I got the bike for $400. so a few hundred in parts will be no problem. I would just like to find the cause of the problem. It's hard for me to believe that the lower rod bearing is the culprit. The up and down is so minimal. Sometimes I think I feel it moving and other times I don't, but when I pull up and hit it with my hand it makes a metallic sound so I know it is moving. Any insight is helpful. Thanks

ANY up and down is over the limit.. There should be NO up and down movement, none at all. So when you say it's minimal, you really mean, you don't want to replace the parts, you want someone to justify to you that a little movement is ok. Well, no one on here with any brains is going to tell you that, cause it would be a complete lie.

It's toast, replace it. That's pretty much all the insight you need.

 

[lestat357]

anytime you buy a used mx bike its probably gonna need more than what you think it needs parts are cheap but they add up fast get a manual read it then decide if you think you can do the work yourself if not take it to a pro

 

[freerida123]

Thanks for the replies. I am not worried or trying to avoid buying parts. When I say the movement is minimal it means the movement is minimal and i'm looking for another cause. I'm planning on buying a new crank assembly, main bearing and seals, piston kit, and gasket kit. The work will be done by me and I am very familiar with engines. I'm an ASE certified mechanic for gas and diesel. I guess I'll get the new crank and piston and see what happens. Is there an easy way to tell if I have the 97-01 head or not really? Thanks -Craig

 

[Jasle]

put the new crank in. assemble without a base gasket and measure your SQUISH. The distance from the piston to head... This will tell you, and us, if your setup is close to correct. I don't know your specific reccomended squish but i'm thinking its .050" or more. So if it were .050 you'd expect the gap without gasket to be about .035 because the gasket is about .020 and it will compress...
I'd suspect someone just slapped the topend together without measuring and had conflict. i've seen that many times. What compounds your issue is the bad rod brg.
someone esle can chime in with your actual spec as i only work on smaller bore bikes typically.

 

[Eric Gorr]

The spark plug is off-set bon an angle on the 1992-96

 

[freerida123]

Thanks for the info. I guess I have the 97 - 01 head. The head is different like Eric said. The plug is on a little angle and not recessed on the 92 - 96 heads. The one I have has no angle and is recessed in the head a little. So i have found the problems. Bad rod bearing and wrong head. Thanks guys.

 

[whenfoxforks-ruled]

You can get a complete engine kit for around 300 dollars. A new head should be had for around 100 dollars. If you are wanting, send the jug and new head to Eric, mo power everywhere and a bigger piston. If they do not offer a complete crank, Eric is about the only guy I would trust to press it, when he is not using it on ktm swingarm bolts!