Alright so I picked up a 1978 Yamaha 250e for free. When it was kick started, you could hear a faint hiss. I took the engine off the bike and removed the piston, which was cracked. (pic related) I installed the new one. Moar to come\/
There is a difference in the top ring on the piston. The new one has a receded top for the piston to fit into. The old one does not.
Also, the old piston is scored to fuck. The walls of the cylinder have minor scoring(pic related). Does it need honing? Can I use this new piston?
>>998313
Old piston
Check the fitting of the new piston against the walls of the cylinder. Depending on the mileage of the bike, they tend to wear into each other, which means the walls may not completely seal against the piston ring. If its a snug fit, go with a small amount of honing. From >>998315
it doesn't seem too bad. Then again, I have only rebuilt a couple bikes and haven't done much in terms of honing the cylinder.
>>998324
Anon thank you. This is my first and I'm learning. Do you think I can still use the piston if they are different?
>>998327
Wait, the piston came from a completely different engine(different model)? Check head clearance and make sure the valves aren't running into the piston head. Very first thing you do is check fitment. If it doesn't even fit in the sleeve, then obviously the piston running into the valves on its upstroke isn't going to be an issue. Take a side by side picture of both pistons and post them. Another concern could be that the piston geometry can be different. Some pistons are oval instead of circular.
>>998328
I'm sorry, what I meant was the only difference is the top piston ring. I bought the new one as a direct replacement. It's supposed to fit this exact model.
>>998315
that cylinder looks like garbage. Doesn't look like honing would be sufficient to get a seal. Looks like it needs to be bored out to fit an oversized piston
>>998315
This folks is what happens with improper oil. No air filter. And when all your gaskets leak letting in sand particles... That cylinder is fucked. But good news. A decent dirtbike shop or even machine shop can press out that cylinder sleeve and press in a new one. (what id do instead of going over sized.) those sleeves are friction fit believe it or not.
>>998372
I'm pretty sure the whole rotating assembly on that motor is roached. A new piston and cylinder sleeve still leaves a lot of bearing surfaces. No point in putting it back together if it just coughs up a rod a few hundred miles later.
>>998434
If he orders a new sleeve its 43 dollars. For a whole head with an okay sleeve its 134 dollars with unknown fuckery. If he just buys a new sleeve he can buy an oem piston head and rings and not have to worry about the fuckery of getting matching parts. This is DIY not LSEDIFY. also I just took a look at bikebandit hes got two crank case bearings that look to be pretty easy to remove. As long as his bike really is a DT250e. Its a two stroke single. Parts should be pretty much had anywhere. And who knows maybe his crank case bearings aren't fucked.. Wouldnt know until he looks.
>>998434
Its clearly a 2 stroke and it looks like its been run without oil so this is highly plausible. Check all the bearings in the bottom end too.
