Stuck piston

NH1984z50r

New Member
Getting ready to remove a rusted in piston, on my 86 z50. I was going cut out a round piece of wood that would match the top of the piston and hit it, to see if I can get it to free up. I've been letting it sit in M.M oil and then PB. With the cam chain unhooked and the tranny in neutral. How bad can I hurt the crank and tranny. Should I free it and try to work the cylinder off. Not really worried about hurting the piston it looks beyond repair.
 

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I'd try a piece of wood like you said, and tap it with a hammer to see if it would break loose. It looks like it struck about half way down so as soon as it moves it should be free. If the piston is a Bottom of the stroke I would'nt rap it much as not to hurt the needle bearings in the rod. If that were the case I'd pull the studs split the cases and take the crank and piston and cyl out as a whole. Then you could put PB or marvel on the back side too. or very worse case take a cutoff wheel split the cyl. and remove everthing from there. Hope this helps.
 

motodevo

Active Member
had the same problem with a ct70. I first soaked it with penetrating oil for a few days, then tapped the piston gently down the bore with the handle of a rubber mallet until i could move it up and down by turning the flywheel back and forth. If you undo the bolt at the bottom of the cylinder you should be able to slowly pull the cylinder off as the rust is actually the cylinder, the piston technically shouldnt rust.
 

NH1984z50r

New Member
Thanks

I freed it up this morning. After everything moved around good. Pulled the cylinder and piston off the crankshaft. After looking at everything I going classic restore instead off a big bore kit. Bore the cylinder over .025 and replace the piston. The head is rusted up just around the valve heads. I should be able to clean that up. Replace or rework the valves. Add air and fuel and I'll be in business. Thanks for your input and info.
 

Art

Member
Many years ago a friend had a similar situation with a Z50.
Brazed a short 1/8" pipe nipple inside a spark plug bottom, then a grease fitting to the pipe nipple.
Bolted the head back on, used pressure from the grease gun to break the piston loose.
 

fatcaaat

Well-Known Member
.25????

You better take it in to have them look first. If you have a frozen piston, chances are you may need to go to .50 or .75 depending on condition because scoring may not come out at the first overbore.

You can ususally find brand new, take off honda cylinders from the crf50 crowd when you look for them on the cheap.
 

NH1984z50r

New Member
Damn

I was hoping .025 would be enough. If I go bigger will I have trouble with the stock exhaust? The carb is shot. Will a replacement stock carb be enough fuel? Just move the clip down on the needle right? The air box it also cracked up so I'm going to repalce that too.
Thanks
 

Art

Member
My orange 77 sat for years outside with the carburetor and intake dangling from the throttle cable. I was able to break it free after a month of soaking and rocking the bike in gear. I was sure It would need to be bored 2nd oversize so I ordered .5mm oversize. Cylinder was pitted severely.

The machinist told me the 1st oversize (.25mm) would have been plenty.
 

NH1984z50r

New Member
Brought my cylinder and head down to my local bike shop. The guy there has a 86 z50r. (Mine is an 84 not 86 as listed above.) He said .025 should be plenty and to replace the valves. I should be starting to put it back together at the end off next week.
Thanks for you help.
Also I'm jealous of you guys in cal. Seems like there are more old hondas to be had out there. If a bike gets left outside in the Northeast, it dies.
 
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