I need help please. My son's Recon 250 has a rattle which appears to be in the top end. I first suspected a wrist pin based on my experience years ago working on 2 cycle engines. So I pulled the head and cylinder. I used my micrometer and found the pin was within specs with very little wear. I went ahead and put in a new pin, new piston and rings. (I did not mic the cylinder, but I did not feel any ridge) Put it back together and still rattles. Read on this forum about possible timing chain issue. I took crankcase apart and immediately found the centrifugal clutch had fallen apart. Okay, thought that was the cause, replace it, put back together, and still rattle. So, took apart again, replaced timing chain, guide, and oil pump chain and checked tolerances on cam. Still rattle!
I'm perplexed...any ideas? Thanks!

 

Some times the sound is not where you think its from. I though I had a top end rattle and it turned out to be a loose recoil pull core mechanism from the bottom.

Does it still run ok?

 

Thank you for your response! Yes, it runs great. I also read on this forum about the pull starter. I checked that out and it is not the problem. Do you know if it could be the head? BTW - I have checked valve lash and adjusted several times.
Thanks again!

 

I have had a rocker shaft badly worn on a 350 and several loose valve seats, also on 350s.

 

Thank you Merryman for your response. I'm hoping at this point that may be the problem. (Guides) I am taking it in this week to an ATV mechanic and let him listen. I took a video to him last Friday and he thinks it is the upper rod (wrist pin) bearing. I will let everyone know how it turns out.

Thanks again!

 

Found the problem! After much more thought, I decided to tear into the top end again. I compared the original piston with the new one. I didn't notice this before, but the original piston has recessed areas to allow valve clearance. I put the old one back in, with new rings, and the tapping noise is gone. It runs great now. So, what started as a rattle, was actually the clutch. But through my process of elimination, I created a new problem. The new piston is genuine Honda. Although I am not faulting the dealer (they have been great), I am still going to let them know about it. Thanks all for your help!

 

So you're saying that the piston and valves were hitting each other?? And it didn't bend the valves??

 

Yes, we really lucked out on that!

 

Check your valve adgustment