250 f-up top end install

Finally got piston for my 1985 yz250 took cylinder to machine shop it measured 68.34 mom standard is 68mm so ordered standard wiseco piston piston was boocoo easy to install but had massive trouble getting cylinder over it finally was able to get piston to go in where I could bolt cylinder down snugly I hand cranked the kicker and the piston got stuck at top of stroke I tried taking off cylinder but at top of stroke cylinder wouldn't go over bolt I ended up smack I g piston down with my rubber mallet I took off piston tried putting it through cylinder on the floor it kept getting stuck 7/8 to top of cylinder
 
Should I measure down to first ring and get it honed .001 bigger or should I have kicked the kicker instead of just pushing it by hand slowly.......son of a bitch I need get a break sometime
 
Finally got piston for the 250 had taken to machine shop cylinder bore was 68.34 standard is 68mm so got standard 68mm 0piston from. Wiseco piston was way easy to install but had lot of trouble getting cylinder on piston till finally it went on bout halfway but was able to bolt cylinder down snugly I hand cranked kicker and piston got stuck at top I had to beat piston down with rubber mallet till it got to halfway and it moved smooth I took off cylinder and piston tried putting it in on floor it kept getting stuck 3/4 way up cylinder should I have top of cylinder honed down to where first ring gets stuck?son of a bitch

Obviously you have clearance issues, you need a bore gauge and check to make sure bore is uniform from top to bottom of cylinder. If not the cylinder needs to be re done, if I understand you correctly You had the cylinder bored by a shop. In that case take the cylinder and piston to them and say here, you make it fit.
 

SRAD97750

Moderator
Staff member
Just a few questions.
What was the ring end gap?
What was the piston to cylinder clearance? Where did you take these measurements?
Did you check the deck height to crown of TDC before installing the head?
What are you using for assembly lube?
-BIG DAN:thumb:
 
I would take the rings off and see if the piston goes through on its own. if it does I would put the ring in the top of the cylinder and square it up. then I would measure the end gap and work it down the bore, observing as you go to see if the ring ends ever meet.

For me the right lube is no lube in most cases for the cylinder. Oil the bearings, but my pistons go in dry, especially if it is an old bore. (If i do use oil, it is either atf or the oil I am going to mix.) I clean the cylinder in hot water and soap regardless of how I am going assemble it. If I decide to oil it, I apply just enough to wet it down and then use a piece of those rolled paper shop towels to remove everything the towel will remove.It works to aid the ring seating. Lots of us are convinced that your cylinder does not need 20-200 times the amount of oil it is ever going to see again just to start up. over oiling contributes to glazing.

Anyway, I would check it myself to see if there was something else going on before I took the cylinder back.
 
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Took back to machine shop they honed cylinder little bit more 68.35 everything went together perfectly don't get me wrong was bit tough getting cylinder over piston then had little weeper leak of coolant on head cover but figured when ran it
 
Hardest part was getting the aftermarket gas tank on bolts were a bitch getting too is first dirt bike I ever took apart engine was frustrating knuckle busting pissing me offing having to take shit back apart cause can't get another part on'ing but pretty proud of result Thanx again for all Ur guys input
 

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One thing having a dirtbike for long will teach you is how to work on them. Another thing that I have learned is that a manual and reading it before I do something pays dividends. A few truths reveal themselves along the way: Sad to say that gaskets don't fix themselves, they may however start routing the leak to a place not so visible. if it is into the intake, combustion, or transfer area leaks are quite harmful.
 
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