hi as the title says I just came around to an old Honda 4trx 300
It was not running so I took it to a mechanic and got it running he changed the piston, (by the way he ripped me off he charged me for a new piston kit, and cilinder cut, but let me continue)
So he got it running, but the engine made a lot of noise a loud clonck noise, I asked him what was wrong, but he said he needed to opened the bike and check to see what was wrong but I was not pleased at the fact that he did not know.
So I took it upon myself to investigate and found out that it was the stretched timing chain.
I opened the bike to find out that the piston was a used piston, the cilinder was not cut nor honed, some of the threads were stripped.

I changed the chain and one way bearing, but I was not able to get it running so I took it to another mechanic, he got it running but still I hear noises not as loud nor the same, but now I’m worried that the bike might break down on me.

So all of that to ask you if I’m going to rebuild the engine, what are the most common parts that need servicing, replacing or maintained?

Please help, also what is it cheaper to buy another engine or to repair my engine.
I will try to post a vid showing the engine noises.